Heat moves in tomorrow, increases in intensity all week

The heat wave is here.

So far, the NAM remains a bit cooler than the GFS regarding what we're going to see, but the last two model runs still show pockets of 90° temperatures showing up in various regions throughout the state. Couple this with dewpoints in the 70s, potentially exceeding 75° in some places, and you have heat indexes that should exceed 100°F for several days straight.  Let's add in the bonus that night time lows may be in the 70s.

Yeah, somehow I doubt I'll be sleeping well this week.

Expect no relief at all until Monday of next week, when temperatures once again become fall like, and that will likely be the true beginning of our fall weather pattern.  Until then, spend all the time you can at the beach.  There will be a chance of thunderstorms Tuesday and Wednesday afternoon as a very weak disturbance moves in from our west. Chances of severe weather are about as slim as Lloyd Christmas getting with Mary Swanson, however - there's just no wind to work with.

Humidity rising faster than temperature - Dense fog tonight in Thumb, Tri-Cities and SE Michigan

With nearly 100% humidity levels and temperatures not yet rising to exceed the dewpoints, a thick layer of fog has developed across most of southeast lower Michigan.  To that end, NWS Detroit/Pontiac has issued a Dense Fog Advisory, in effect until 9AM tomorrow:

URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1113 PM EDT SUN AUG 30 2015


MIZ047>049-053>055-060>063-311300-
/O.NEW.KDTX.FG.Y.0003.150831T0313Z-150831T1300Z/
MIDLAND-BAY-HURON-SAGINAW-TUSCOLA-SANILAC-SHIAWASSEE-GENESEE-
LAPEER-ST. CLAIR-
INCLUDING THE CITIES OF...MIDLAND...BAY CITY...BAD AXE...
SAGINAW...CARO...SANDUSKY...OWOSSO...FLINT...LAPEER...PORT HURON
1113 PM EDT SUN AUG 30 2015

...DENSE FOG ADVISORY IN EFFECT UNTIL 9 AM EDT MONDAY...

THE NATIONAL WEATHER SERVICE IN DETROIT/PONTIAC HAS ISSUED A
DENSE FOG ADVISORY...WHICH IS IN EFFECT UNTIL 9 AM EDT MONDAY.

HAZARDOUS WEATHER...

 * VISIBILITY HAS FALLEN TO 1/4 MILE OR LESS ACROSS MUCH OF THE
   AREA.

 * DENSE FOG WILL CONTINUE TO DEVELOP INTO EARLY MONDAY MORNING.


IMPACTS...

 * MOTORISTS WILL EXPERIENCE DECREASED VISIBILITY.

 * THE MORNING COMMUTE MAY BE ADVERSELY AFFECTED.


PRECAUTIONARY/PREPAREDNESS ACTIONS...

 * A DENSE FOG ADVISORY MEANS VISIBILITIES WILL FREQUENTLY BE
REDUCED TO LESS THAN ONE QUARTER MILE. IF DRIVING...SLOW DOWN...
USE YOUR HEADLIGHTS...AND LEAVE PLENTY OF DISTANCE AHEAD OF YOU.

The last super foggy night I drove through was back in April, and I had to go all the way to Midland from Pigeon.  I sympathize with anyone who has to deal with this on the road tonight, and advise patience.

Weak disturbance to target the region on Saturday; thunderstorms likely

The dreary, cloudy weather and the low pressure system that has caused it (along with my sinus headaches) should be moving out of the region tonight.  With it, some sunshine should make itself known tomorrow and rise again Friday morning.  However, the weekend weather doesn't look particularly great. 

The latest NAM model is forecasting that a relatively weak upper level disturbance will amplify a bit before moving into the Great Lakes region Friday night into Saturday.   An associated surface low will likely peter out as it moves northeast into our area.  With it will likely come a bit of instability, and widespread rain and thunder throughout the state Saturday, perhaps intensifying a bit during peak heating time.

Widespread stormy weather is predicted by the latest NAM run to be ongoing throughout the day Saturday.  Conditions might clear up a bit in SE Michigan to ignite some stronger storms over the thumb, but I'd not put any money on seeing anything more than a few rumbles of thunder along with perhaps some gusty wind with the rain.

The NAM does suggest some curved wind profiles which favors rotation, but considering what occurred the last couple of times a storm system like this has come from the south, I'd not put much stock in any severe weather this weekend.  Both the 08/19 and 08/23 systems were much stronger, and the conditions looked a lot more favorable, yet we were left with less-than-anticipated yield; to expect more out of this one would be to bet on the tortoise over the Bugatti.  To quote a certain Lord of the Rings character, though, mother nature has been very tricksy for the last few weeks, so I guess anything's possible.  For now the models seem to indicate that ongoing rain and thunder will move into the area Friday night and continue throughout the day Saturday.  This should serve as the punctuation mark to what has been a rather dismal, dreary week.  

Rain may continue Sunday, as the system is currently forecast to stall overhead.  Everything should be out of the way by Monday, though, in preparation for a potential late summer heat wave to take root.  More on that later.

Friday and Saturday may be cooler than I thought

Not to alarm anyone with the title - it's just that we'll likely be looking at low mid 70s rather than 80°.

All in all, not that much of a bad thing considering how comfortable it will be... and how much of   reminder of our latitude the last couple of days have been.

This morning's GFS run indicates stark temperature context between this week and next

Meteorological fall may begin September the 1st, but apparently nobody explained that to the GFS. Here's what it has to say about temperatures around the country next week:

Those dark reds in the Great Lakes region indicates temperatures that exceed 90 degrees.  As the GFS tends to be a bit on the conservative side when it comes to predicting heat, I'd say there's a fairly decent chance of us seeing those temperatures.  I suppose we're lucky we're not in the Great Plains, where temperatures may skyrocket to over 110°F.

The best news of all about this, though it's not entirely a sure thing yet, is that the GFS is seeing dewpoints rise only into the mid 60s.  That would make this somewhat of a dry heat, without the crippling humidity we've experienced with our 90 degree days so far this summer.  All in all, it would make for at least one more good trip to the beach without making it too difficult to breathe.

The remainder of August looks to be very dry. Is our fall weather pattern taking root?

Now that today's round of thunderstorms is over, the mid-to-long range models are in fair agreement that Michigan will see a very dry, cool, pleasant, early-fall-like week ahead, with highs in the 70s and lows in the 50s (possibly even the 40s in some areas).  Don't kiss summer goodbye just yet, as we'll probably see 80° again by Friday.  More thunderstorms also appear likely early to mid next week, too, signaling that our summer pattern of stormy weather hasn't quite ended.

The SPC's day 2 and 3 outlook are reminiscent of our typical fall pattern in Michigan.  The jet stream is starting to dip south, leaving us devoid of the dynamics which create thunderstorms.

One thing that I do want to point out though is that the absence of rain this week could be quite telling in regards to what we should expect for the fall and possibly early winter months.  Think about how much rain we've received this summer in Michigan.  It's been quite a bit.  Now, subtract thunderstorm activity from the equation.

It would be near zero.

Very few days of stratiform precipitation have occurred in Michigan this year, let alone this summer. Spring was uncharacteristically dry, and even stoked fears of a possible drought in some circles. Day after day of thunderstorm activity put a literal damper on those fears, but when the stormy summer pattern goes bye-bye and the jet stream starts sinking to the south, we may wind up not seeing much in the way of precipitation at all.  For winter fans like me, this could be heartbreaking.

I'm not going to write off snow just yet.  We're still a long way from winter's doorstep and I plan to enjoy the last weeks of our stormy summer and our fall, first.  Even devoid of snow, the super-strong El Niño giving us a mild winter would be a nice change after two years of hell's 9th Circle enveloping Michigan.

Severe threat just about over

Update: A brief tornado warning for radar indicated rotation was issued for Oakland county in the remaining slight risk area just after I made this post, however it was quickly cancelled. There are no reports of any tornadoes touching down as of this hour.

Short of a small slight-risk area remaining in extreme SE Michigan, the likelihood of any severe thunderstorms is pretty much nil.

Today's severe weather potential looks to have been even more deceptive than Wednesday's; there just wasn't enough energy to sustain updrafts.  Storms actually formed in two phases - one right behind the other.  The first round of storms fizzled out and tempered the atmosphere before the second phase, which looked like it had the potential to be more intense, could get going.

With today over, we're going to begin an extended dry period, with very little chance of rain currently apparent over the next week.  More on that in the next post.

Several storms headed toward Lansing taking on Supercell characteristics

Note the shape of these storms and the fact that they're all looking like they're starting to develop a bit of rotation.  Nothing severe warned on yet, let alone tornado warned, but I'd be a bit concerned if I was in the area SW of Lansing.  Be on guard if you're there.

These "notches" indicate intensifying thunderstorms.

These storms are heading in the direction of Lansing.

Possible rotation, tornado SW of Hastings MI in Barry County

This one has me somewhat alarmed.  Not only is there an indication of rotation, but also what appears to be a hook echo on radar with a possible debris ball.

Hook/pendant with the area of rotation

The Correlation Coefficient is a dual polarization product in Doppler Radar which checks to see how reflectivity in a given area "correlates" with its surroundings by hitting it with beams at two different angles.  This "spike" angled out from the direction of the radar tower may mean that the beam hit something solid, like debris.

The "specific differential phase" is another dual polarization product which attempts to see rain only and ignore frozen precipitation or solid objects.  Those black dots surrounding the circled area may indicate such objects.

This could indicate the presence of a damaging tornado.  If anyone is in the area seek shelter until the storm has passed.  If you safely spot any damage, report it to the NWS Grand Rapids' Facebook Page.

SPC updates categorical outlook to pretty much match mine, issues MCD for Central/SE lower Michigan

SPC has updated their categorical outlook to include a slight risk for central and SE lower Michigan, which pretty much matches what I posted for mine last night.  This includes a risk for an isolated tornado or two.

They've also issued a mesoscale discussion which indicates a 40% chance of a severe thunderstorm watch being issued within the next hour.  Updates as they come.

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

A fairly decent squall line may plow through Mid Michigan, SE Michigan Sunday afternoon

I'm going to go out on a limb and say that our chances for severe weather in Michigan Sunday are a bit better than they were on Wednesday.

Jet core wind speeds and tilt of upper level disturbance as forecast by the NAM's 8PM run

18,000 ft wind speeds as forcast by the NAM's 8PM run

First and foremost, we're going to be dealing with another negatively tilted upper level disturbance pushing into our area.  The NAM in particular is forecasting this one to be quite a bit stronger than the disturbance which affected us Wednesday, with a negative tilt already in place prior to the system affecting our area. This is in stark contrast to the forecast the name was giving us for the Wednesday event, where it never quite predicted to be as robust as the GFS did, and when the system only took on a negative tilt after it began to affect us.  This time around, the NAM is predicting a much stronger cold front and upper level wind pattern, as shown above.  Hodographs are looking a bit curved/kinked on this one, too, meaning there could be enough shear to produce some severe weather and possibly even supercell thunderstorms.  Right now, the winds aren't looking particularly fast, though, so it's still quite questionable.  The timing of this thing currently looks really good to produce severe weather.  The cold front should be coming through in the late afternoon/overnight, driving storms during peak heating time. 

Simulated radar as forecast by the NAM4KM's 8PM run.

The result of all of this may be what the NAM4KM model is predicting - the formation of a strong squall line over western Michigan tomorrow at around 2PM EDT, intensifying as it moves eastward across central and SE Michigan.  This is the best evidence so far of problems, as a single round of storms has a better chance of producing severe weather than two, as the fuel tank will only have one straw in it.  Wednesday included widely scattered storms popping up in different locations throughout the afternoon, which served to drain some of the energy available for storms that formed later in the day, in a more favorable environment than what was there initially.

The biggest factor is going to be how much instability develops over Michigan. Enough instability should exist for severe weather, but right now it's still looking fairly modest.  If more instability develops than what is currently forecast, we may wind up with an even bigger severe risk.  Mid level lapse rates are, like Wednesday, currently predicted to be modest. This could be offset by enough surface heating tomorrow causing SBCAPE to climb to extremes. The chances of this happening isn't particularly great, but with enough of a warm sunny day, it is possible.

On a scale of 1-10, with June 22nd being a 6, August 2nd being an 8 and Wednesday being a 2, I'd say this sits at about 3 or 4 right now.  It could go in either direction depending on what the observations look like in the morning. The risk of hazards associated with the storms primarily favors damaging winds, as lapse rates look to be too modest to support large hail, though I'd not rule out a tornado or two with the curved wind profiles and negatively tilted cold front.  The line also looks as though it could be semi-discrete, which could wind up making the tornado threat greater than zero.

Severe storms looking more likely Sunday afternoon

I'm currently out of town right now so a long post will have to wait, however it would appear that severe weather conditions are looking more likely tomorrow in Michigan.

   ...LOWER MI TO THE MID-SOUTH...
   HAVE EXPANDED MARGINAL RISK PROBABILITIES TO THE NW ACROSS LOWER MI
   AND NRN IND FROM PRIOR D2 OUTLOOK. PORTIONS OF LOWER MI AND NRN
   IND/NWRN OH APPEAR MOST LIKELY TO BE UPGRADED TO SLIGHT RISK IN D1
   OUTLOOKS.

I will post more updates on the situation when I return home.

Isolated severe storms expected Sunday

While there isn't enough instability forecast to warrant a slight risk, there should be enough in some areas for one or two storms to cross the severe threshold this Sunday.  I'm expecting nearly a direct repeat of this past Wednesday in terms of what we see, as the setup is looking very similar, even if the storm system is a bit further north this time around.

My current thinking (along with the models) is that the Thumb Area might see the most out of this once again, as the lakes have been enhancing thunderstorm growth quite a bit this month.

Quiet, cool pattern settling in for the next few days - thunder to return Sunday

No thunderstorms are forecast for the next several days, as high pressure and cooler temperatures are forecast to build into the region.  This will push lows down into the 50s and possibly even the 40s in some areas, with highs only in the mid 70s.  Temperatures should again reach 80° by Wednesday.

Our next shot at thunderstorms appears to be Sunday, August 23rd, as yet another powerful upper level trough takes root to our west, and a strong surface low is forecast to develop to our north.  The GFS is predicting yet another negatively tilted monster, which would again suggest severe weather potential, however the instability forecast is meager over the region at best, leading me to believe that a system even less potent than yesterday's will have a tough time brewing any.

   ...DISCUSSION...
   MODELS AGREE DOMINANT UPPER RIDGE IS EXPECTED TO BUILD NORTH ACROSS
   THE ROCKIES INTO THE EARLY PART OF NEXT WEEK AS NRN PLAINS
   SHORT-WAVE TROUGH EJECTS EWD ACROSS THE GREAT LAKES.  WHILE THIS
   FEATURE WILL LIKELY ENHANCE SEVERE THREAT DURING THE DAY3 PERIOD IT
   APPEARS AIR MASS DURING THE DAY4-5 TIME FRAME WILL BE SIGNIFICANTLY
   LESS BUOYANT DOWNSTREAM ACROSS THE GREAT LAKES/OH VALLEY REGION. 
   BEYOND DAY5 SIGNIFICANT DIFFERENCES DEVELOP BETWEEN THE GFS AND
   ECMWF AND PREDICTABILITY DECREASES MARKEDLY.

The NAM looks as though it might be a bit more robust with moisture and associated instability, though just like last time it predicts that the surface low won't be quite as strong as what the GFS is putting out.  The next few model runs should shed more light on the situation.

Storm activity over - no true severe threat manifested

Today's storms are essentially over.

While there remains a swath of rain over much of lower MI, the cold front now sits over the middle of the state, and all the forcing for ascent far to the east.  

The severe threat never really manifested.  Outside of the Thumb Area and Lapeer County, there were no severe thunderstorm warnings were even issued to my knowledge, though there were some reports of downed trees in Genesee and Livingston Counties which did not fall under any active warnings.  One brief tornado warning was issued for Oscoda County after strong rotation was seen on radar, but no touchdowns were reported.  Total number of severe reports were 5 (all wind damage).

So what caused this situation to go bust?  Well, it was a couple of the things that I mentioned in previous posts:

• Overall lack of instability - This was a big one, if not the big one.  Instability levels never quite got high enough to fuel big thunder without other factors compensating, which they didn't.  This was in part due to yesterday's convection over Illinois causing a warming of the low to mid levels of the atmosphere over lower Michigan.

• A weakening of the storm system, causing the predicted negative tilt to vanish and a decrease in overall wind shear/horsepower potential, or the system not quite manifesting in the manner as is currently being predicted - This.  That upper level disturbance and surface low never, ever got to the point that the GFS said they would. While the trough was strong, it wasn't quite negatively tilted.  It actually was slightly positively tilted:

The surface low - and associated winds - were even more disappointing:

As a result, the cold front and low level wind speed were just not up to snuff, and together couldn't drive big storms on a day like today when instability was marginal. 

The funny part is that nearly everything else went *right* for this to get off the ground.  The day was warm and sunny in most places, and the surface was definitely ripe for thunderstorms.  A moderate southeast wind was blowing at the surface.  Early day convection was basically non-existent. It *felt* like it could blow up, which fooled a lot of people like myself, and even some of the pros.  The fact remains, however, that the action doesn't take place at the surface, but around 5,000 feet in the air.  If that area isn't unstable enough, and there aren't enough other factors to compensate, it won't matter how hot the surface gets.  The exception of this was a narrow corridor from right around I-69 into the Thumb, where a bit more mid-level instability existed.

Now that everything's said and done, high pressure is going to build into the state.  Once the remainder of the rain moves out of the area by mid-morning, we're going to be dry and cool for at least a couple of days.  

Severe Thunderstorm Warning remains in effect, but threat quickly ending

A Severe Thunderstorm Warning remains in effect for northern/eastern Huron County, but the severe threat never really manifested outside of the Thumb.

There is one storm near Alma, heading for Midland, that shows signs of some broad rotation, but as of now it doesn't appear to be much cause for concern.  My thinking is that the events of the day are drawing to an anticlimactic close.

Severe Thunderstorm Warning for east/northeastern Huron County and most of northern Sanilac County

New severe thunderstorm warning just issued.  Dangerous, intensifying line of storms heading toward Kinde, Port Austin, Bad Axe, Ubly, Minden City, and may just scrape Deckerville.

Storm heading for Mayville and Kingston looking very nasty

This severe-warned storm is heading north at 40MPH may plow north through the entire Thumb and wind up affecting Huron County, too.  The northern Thumb should consider itself under a watch.  Not a nice looking storm.

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 500 PM EDT
FOR NORTHWESTERN LAPEER AND SOUTHEASTERN TUSCOLA COUNTIES...

AT 425 PM EDT...A SEVERE THUNDERSTORM WAS LOCATED NEAR CLIFFORD...OR
NEAR MAYVILLE...MOVING NORTHEAST AT 40 MPH.

HAZARD...60 MPH WIND GUSTS.

SOURCE...RADAR INDICATED.

IMPACT...EXPECT DAMAGE TO ROOFS...SIDING AND TREES.

THIS SEVERE STORM WILL BE NEAR...
  CLIFFORD AROUND 430 PM EDT.
  KINGSTON AROUND 440 PM EDT.

OTHER LOCATIONS IMPACTED BY THIS SEVERE THUNDERSTORM INCLUDE EAST
DAYTON...WILMOT...FOSTORIA...SILVERWOOD AND DEFORD.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

FOR YOUR PROTECTION MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A
BUILDING.

TORRENTIAL RAINFALL IS OCCURRING WITH THIS STORM...AND MAY LEAD TO
FLASH FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED ROADWAYS.

MCDs issued for upper and lower MI

Two mesoscale discussions were just released by the SPC indicate a 40% chance of either a severe thunderstorm or tornado watch being issued within the next 1-2 hours.

   PROBABILITY OF WATCH ISSUANCE...40 PERCENT

See MCD 1718 and MCD 1719 for further details.

NAM4KM 8AM run suggesting two rounds of potentially severe thunderstorms for eastern MI

It looks like two distinct rounds of severe thunderstorms are possible this afternoon and overnight, specifically for the eastern U.P., north eastern lower Michigan, south eastern lower Michigan and especially the Thumb area.  Round 1 should begin at around 4PM and end around 9PM, and round 2 should begin around 11PM into the overnight, ending around 4AM.

The Thumb may once again bare the brunt of the storms if this model forecast is to be believed.  The 2PM NAM4KM run will shed more light on this situation.

Models back off from tornado risk, some severe storm risk still present

Quite a difference in the model predictions this morning.  Very little tornado risk appears to remain across Michigan, so it looks as though we're going to be spared a potentially high-end event.

From the SPC:

   ...LOWER AND UPPER MI TODAY...
   PRIOR CONVECTION AND UNFAVORABLE TRAJECTORIES HAVE REDUCED MIDLEVEL
   LAPSE RATES TO THE NE OF THE SRN PLAINS.  STILL...SOME CLOUD BREAKS
   ARE PROBABLE ACROSS LOWER MI BY AFTERNOON...AND POTENTIALLY ACROSS
   WRN UPPER MI BENEATH THE MIDLEVEL DRY SLOT.  RICHER MOISTURE
   /BOUNDARY LAYER DEWPOINTS IN THE UPPER 60S/ AND AFTERNOON SURFACE
   TEMPERATURES AOA 80F WILL CONTRIBUTE TO MODERATE BUOYANCY /MLCAPE
   1000-1500 J PER KG...WITH NAM SOUNDINGS LIKELY TOO UNSTABLE AS A
   RESULT OF THE SHALLOW CONVECTIVE SCHEME/.  WIND PROFILES WILL NOT BE
   PARTICULARLY STRONG OVER LOWER MI...BUT ORGANIZED MULTICELLS/LINE
   SEGMENTS ALONG AND AHEAD OF THE FRONT COULD PRODUCE A FEW DAMAGING
   GUSTS THIS AFTERNOON.  DEEP-LAYER VERTICAL SHEAR WILL BE STRONGER
   OVER UPPER MI IN PROXIMITY TO THE MIDLEVEL JET...WHERE PROFILES WILL
   BE SUFFICIENT FOR LOW-TOPPED SUPERCELLS.  STILL...THE DEGREE OF
   DESTABILIZATION IS IN QUESTION THIS FAR NW AND THE WINDOW OF
   OPPORTUNITY IS NARROW...SO WILL MAINTAIN LOW DAMAGING WIND
   PROBABILITIES. 

A slight risk remains for severe wind this afternoon, but for the most part, today's severe weather risk has gone way down once again.

Tornado risk tomorrow potentially higher than any time yet this year

I've been reading a lot of posts from people who are scared, and I want to begin by addressing those people. I make posts like this not to incite panic but to keep people ahead of the game on what's going on.  I do not want them to become a source of anxiety for anyone.  Please remember that your chances of being hurt in a severe weather event is low, especially if you take precautionary/preparedness actions in lieu of a severe weather risk. A little fear is a good thing, but it is probably more dangerous to one's health to be driven to an anxiety attack over this type of situation.  Above all else, I engage in this hobby because I love storms, and snow, and rain, and sunshine, and everything that makes this state as naturally beautiful as it is.  At the same time, I want to inform and educate those who are interested in what makes the atmosphere tick, and learn more myself at the same time.  If I ever feel like I'm doing more harm than good, expect this page to disappear overnight.

Posts like this one in particular are not meant to alarm anyone to the point of panic, but to help people prepare.  There is no reason to fear even the worst severe weather event any more than taking a drive down I-75, provided that you keep a plan of action on what to do if things go wrong.

Now, let's get to the outlook.

Latest model guidance is suggesting that the vigorous upper level disturbance to our west and associated negatively tilted surface low will push a cold front through Michigan tomorrow afternoon or evening.  This cold front will be robust and cause occlusion within the warm sector, meaning upward forcing will be very, very high, and updrafts should be robust.  Depending on the timing, moderate to extreme instability may be in place in some parts of Michigan when this occurs.

The general NWS consensus as of right now is hinging on around 1000-2000j/kg of CAPE, which is about par for the course for the average severe weather event.  NWS DTX is suggesting less - perhaps 500-1000j/kg - in place over SE Michigan.  The NAM4KM model, however, suggests that a great deal more - up to 3000j/kg - may be in place in some areas.  If that kind of instability manages to combine with the types of winds that are forecast to be in place in the upper atmosphere tomorrow, we could be looking at a much higher end event.  The deepening low is also causing low-level and surface winds to pick up, which adds an entirely different (rotational) dynamic to storms that may form.

Earlier in the week I talked about things that could make this go boom or bust.  I'm going to add to/refresh that list now, and talk about simple, non-technical things to watch for tomorrow that would indicate signs of big trouble:

• A bright, sunny mid day - How much instability is in place and where is going to be the key to just how big storms will grow tomorrow.  Needless to say, if it's bright and sunny in the late morning and early afternoon, it's going to contribute to this factor quite a it.  This is especially true in SE Michigan where instability is currently forecast to be low.  SE Michigan and the Thumb area tend to be where the storms "move to" on these types of days, and the instability factor will likely determine whether they dissipate or intensify as they enter these areas

• Moderate to strong surface winds - Pay close attention to which way the wind is blowing tomorrow and at what speed.  If a strong southeast wind begins to develop, this is a sign of bad things to come.

• Lack of early day convection - This one can have big potential to put a squash on things but also has big potential to be deceiving.  The more rain that cools things off in the morning, the less robust thunderstorms should be in the afternoon.  However, just because it rains in your area doesn't mean you won't see severe weather.  It may cause it to be -less- severe than it otherwise could be, but June 22nd should be enough of a lesson that early day rain/storms do not always kill off the risk.

MODEL GUIDANCE

The last few model runs are painting a picture that sits somewhere between concerning and grim. The NAM4KM model is far and away the most nasty looking right now, while the Rapid Refresh and its high-resolution counterpart aren't predicting quite as ugly conditions, at least initially; their forecast are still cause for concern, but the NAM4KM just takes things to a different level.

I've talked about the supercell composite index enough times that most people probably realize what it means by now - the darker the red, the better the conditions are for supercell thunderstorms to develop.  While those colors are foreboding, that isn't what has me most concerned.  Take a look at this loop:

This is the model's forecast for "1 hour maximum updraft helicity".  Let's discuss what that means. The updraft is the key to a severe thunderstorm.  The stronger the updraft, the longer the thunderstorm lives, and the more severe it becomes.  The other side to this coin is that an updraft that rotates can connect with wind shear on the ground, and spawn a tornado.  This parameter essentially forecasts just how much potential to rotate an updraft has in a one hour time frame; it literally predicts rotating updrafts, and can be a great indicator of tornado risk.  Wherever you see colors in that image, the model is predicting the presence of a rotating updraft.  The stronger the color, the more powerful the rotation, and the better the likelihood of a tornado.

Needless to say, those markings concern me a lot, especially when you take into consideration how accurate this model has been over the summer. The colors don't necessary indicate strong or violent tornadoes being possible yet, but they do indicate a fairly robust general tornado risk.

Tomorrow is likely going to be an active afternoon/evening.  I don't know just how severe an event we're looking at just yet.  Right now, it's sitting on the fence between Jekyll and Hyde.  The key is to be warning aware tomorrow.  Watches will likely also be issued, which should provide some indication of how intense storms that form will be.  Don't allow a day like tomorrow to paralyze you. So far, the chance of this plunging into the high end of the spectrum remains modest.  Simply stay forecast aware, keep your TVs and radios on, and turn an eye to the sky every now and then.

SPC updates day 2 outlook - Severe weather back on

No sooner had I made the adjustment to that post and the thunderstorm outlook that the SPC punched out an update:

   ...THERE IS A SLGT RISK OF SVR TSTMS WEDNESDAY AFTERNOON AND EVENING
   ACROSS MUCH OF MICHIGAN...

   ...MICHIGAN...
   A BAND OF MID/UPPER FORCING FOR ASCENT ASSOCIATED WITH AN IMPULSE
   PIVOTING AROUND THE MID-LEVEL CYCLONE APPEARS LIKELY TO SHIFT
   NORTHEAST OF THE REGION EARLY IN THE DAY.  IN ITS WAKE...GUIDANCE IS
   SUGGESTIVE THAT BREAKS IN CLOUD COVER MAY ALLOW FOR SUFFICIENT
   BOUNDARY LAYER HEATING TO ALLOW FOR THE DEVELOPMENT OF MODEST CAPE
   /ON THE ORDER OF 1000-2000 J PER KG/.  AT THE SAME TIME...SOUTHERLY
   850 MB FLOW IN THE WARM SECTOR OF THE CYCLONE MAY REMAIN AS STRONG
   AS 30-40 KT.  THIS ENVIRONMENT MAY BE CONDUCIVE TO AT LEAST WIDELY
   SCATTERED VIGOROUS CONVECTIVE DEVELOPMENT...PERHAPS INCLUDING
   SUPERCELLS...AS EARLY AS MIDDAY.  THEREAFTER...INCREASING DEEP LAYER
   SHEAR ASSOCIATED WITH A GRADUAL STRENGTHENING OF MID/UPPER
   FLOW...AND AN INCREASE IN FORCING FOR ASCENT...IN RESPONSE TO
   ANOTHER IMPULSE PIVOTING AROUND THE MID-LEVEL LOW...MAY ENHANCE
   STORM COVERAGE AND INTENSITY THROUGH THE REMAINDER OF THE AFTERNOON.
    POTENTIALLY DAMAGING WIND GUSTS...MARGINALLY SEVERE HAIL AND
   PERHAPS A COUPLE OF TORNADOES MAY ACCOMPANY THE STRONGEST STORMS
   BEFORE THE THREAT DIMINISHES WEDNESDAY EVENING.

Could get ugly.  Will detail more when I get back home and have more time to post.

(BE ADVISED - SITUATION MAY CHANGE) Some good news from the SPC

UPDATE: This post will likely be recanted if the latest NAM4KM model run is to be believed.  If the same forecast shows up in the next run, we may wind up with nasty weather after all.

Quick post before I leave for Ann Arbor - the SPC has decreased their categorical outlook down to Marginal for the day as they believe convective overturn will cause a huge decrease in instability.

As of right now I agree with them, as the models do.  The only exception may actually be a pocket of the U.P.  More as it comes in.

Storm with very heavy rain moving through Mulliken

Be advised - a storm with some exceptionally heavy rains is currently moving through Mulliken in Eaton County, to the west of Lansing.  If you happen to be driving through this area be on the look out for flooded roadways.

SPC releases updated day 1 outlook that includes marginal risk for northeastern lower MI

Text of the outlook:

   EAST OF THE HIGH PLAINS...SEVERE WEATHER POTENTIAL APPEARS RATHER
   LOW...LARGELY DUE TO THE LACK OF SUFFICIENTLY STEEP MID-LEVEL LAPSE
   RATES...LARGE-SCALE FORCING FOR UPWARD VERTICAL MOTION... VERTICAL
   SHEAR...OR SOME COMBINATION THEREOF.  ONE EXCEPTION MAY BE ALONG A
   FRONTAL ZONE EXTENDING FROM PARTS OF NORTHERN LOWER MICHIGAN INTO
   NORTHERN MISSOURI...WHERE IT DOES NOT APPEAR OUT OF THE QUESTION
   THAT INCREASING STORM DEVELOPMENT COULD CONSOLIDATE AND BE
   ACCOMPANIED BY SOME RISK FOR POTENTIALLY DAMAGING WIND GUSTS.

Some of the models (specifically the HRRR) do indicate the potential for semi-discrete cells to pop up this afternoon and evening.  There are a few cells currently on radar and a few significant weather advisories issued for the southwestern quadrant of the state regarding >40mph gusts.  The thumb area looks to have the most instability in the state right now, but it should be removed from any impulses (provided nothing moves in from the north) and this instability should wane by the time any storms reach the area.

For now, I'd say the risk of severe weather in the state today remains very low.

No news... good news?

SPC current day 3 convective outlook maintains a slight risk over lower Michigan

The GFS and NAM continue their dispute as to whether or not the surface low on Wednesday is going to speed up and deepen into a negatively tilted monster.  The Storm Prediction Center puts it perfectly:

   A COMPLEX FORECAST SCENARIO PERSISTS ACROSS THE GREAT LAKES/MIDWEST
   REGION DAY 3 /WED. AUG. 19/...WITH THE COMBINATION OF
   LIKELY-TO-BE-WIDESPREAD ONGOING CONVECTION AT THE START OF THE
   PERIOD ALONG WITH MODEL DIFFERENCES WITH RESPECT TO STRENGTH AND
   SPEED OF THE SURFACE LOW/FRONTAL SYSTEM.  THE GFS REMAINS
   SIGNIFICANTLY STRONGER/DEEPER WITH ITS SURFACE LOW /OVER THE WRN
   UPPER GREAT LAKES REGION/...AND FASTER WITH ITS TRAILING FRONTAL
   PROGRESSION ACROSS THE MIDWEST/OH VALLEY STATES.  MEANWHILE...THE
   NAM DEPICTS A MUCH SLOWER FRONT...TRAILING SWD FROM A MUCH WEAKER
   LOW.

There you have it.  Clear as mud.  We likely won't know just what we're going to be looking at until the shorter term models like the NAM4KM, RAP, and HRRR get closer to crunch time.  I'll be traveling Wednesday but I'll attempt to post updates via mobile if anything significant does look like it's going to happen.

NAM predicting not-quite-as-strong surface low

The last couple of NAM model runs are now able to see into Wednesday afternoon.  While it is still mostly in agreement with the GFS regarding the upper level disturbance taking on a negative tilt, it doesn't have the surface low deepening anywhere near to the point that the GFS does:

Surface low forecast by the NAM's 2AM run for Wednesday afternoon

Surface low forecast by the NAM's 2AM run for Wednesday afternoon

Upper level disturbance forecast by the NAM's 2AM run for Wednesday afternoon

This is good news if you're looking to avoid a day like November 17th 2013.  Without the deepening surface low, you're not going to get that super-strong low level jet which is the key ingredient to large tornado outbreaks.  

I'm still somewhat concerned and am not going to exhale too much until a few more model runs come in and show a similar forecast.  It is a little strange that the GFS is showing this deepening quite a bit more than the NAM is, and that is still cause for concern.  However, as of right now this doesn't look like a high-end event.  With dynamics like this, though, that can rapidly change.  

What a negatively tilted storm system is and what it does for severe weather outbreaks

I promised to make this post to help explain why this coming Wednesday has me so concerned, and after today I hope that all my readers will be able to understand just what dynamics go into "cooking" major severe weather events, and why the words "negative tilt" should immediately make the hair on the back of your neck stand up.

The atmosphere is a little bit like a giant pot of water, only the water happens to be in gas form. Now, the atmosphere consists of many different gasses, from hydrogen to oxygen to nitrogen to ozone, but water vapor is the dynamic gas that makes weather as we know it happen.  Every cloud in the sky contains water in some form or another, and it is the thermodynamic reactions of water changing from gas to liquid to solid that is responsible for virtually every weather phenomenon we're familiar with, from a rain shower to a thunderstorm to a blizzard.  Every thunderstorm is like a sea of boiling water vapor, with heat needed to initially make the pot boil.

That being said, nowhere in the atmosphere does the temperature reach a steady 212°F.  Quite the opposite; most of the upper troposphere (where all the action occurs) is below freezing.  What needs to happen to get clouds is that warm moist air from the surface has to rise into surrounding air that is cooler. As the air cools, it condenses, and dense pockets of water vapor form clouds, while water that gets cold enough to become liquid or solid form both clouds and precipitation.  The cooler the air that surrounds a lifted parcel, the further it can rise freely.  The quicker it condenses depends on how moist it is.  If the air is sufficiently moist, water vapor can begin condensing at a very high temperature, even above 70°.  This is the dewpoint that you hear me talk about so much.  Once a parcel of air hits the dewpoint, it begins to cool more slowly than when it was dry.  This allows it to rise further in the atmosphere, provided that the surrounding air it rises into is cooler.  This is what I mean when I refer to atmospheric instability - surrounding air that the parcel rises into is cooler. Warm air rises, cold air sinks.  If warm air beneath cold air, you get this unstable environment.

Now, you can have plenty of instability, but you may not have any action whatsoever.  Imagine a pot of boiling water.  Keeping a lid on the pot (cap) can be an effective way to keep it from boiling over. As long as the temperature within the pot doesn't rise high enough to overcome the cap, you won't have an issue.  Even if it does, you may only get a small simmer-over provided you get to the pot in time and turn the temperature down.  However, imagine the havoc that would be created by pouring a bucket of cold water into that boiling pot of water on your stove. You're going to almost certainly turn your kitchen into a flooded mess. This is what happens when you add a cold front to the mix of a warm, unstable environment.  The strength of the cold front can have a huge impact on how much water boils over; if the cold front is weak, you may only be pouring a cup or so of cold water into your boiling pot, or be pouring it slowly enough that it won't cause too much havoc.  

A positively tilted storm system, and associated cold/warm fronts.

This is what you get with positive and negatively tilted storm systems.  A positively tilted storm system usually consists of a low pressure center that isn't quite up to snuff.  It takes a fair amount of warm moist air ahead of this type of system to make severe weather occur.  That isn't to say it doesn't occur; quite the contrary, most severe weather events are driven by positive to neutrally tilted storm systems, and their associated cold fronts.  Even in the complete absence of a proper cold front, severe weather can occur if that pot is boiling like an angry demon and just a drop of cold water gets tossed in.  This is exactly what happened yesterday; there was a great deal of warm unstable air in the lower atmosphere, and lake breezes caused some very severe storms to pop up.  They weren't widespread, but they dropped some severe hail, produced damaging winds, and possibly even a tornadic waterspout over the Saginaw Bay if radar was to be believed.  Extreme instability helped fuel the August 2nd event, too, as a moderately strong cold front descended from the north.  A cold front doesn't need to be on the extreme side to produce severe weather in that kind of an environment.

A negatively tilted storm system and associated cold/warm fronts.

If, however, the cold front is very strong, then it's the equivalent of taking that entire bucket and dumping it into the pot on the stove; even a pot that's only JUST coming to a boil will react violently. This is what happens when a low pressure system deepens to maturity, sometimes rapidly enough to be characterized as something known as bombogenesis, which is a relatively rare drop in pressure of 24 millibars over 24 hours. Even if it doesn't quite reach this criteria, explosive cyclonic deepening can push severe weather to extreme heights.  You may have heard me talk about this before, as it was something I feared might happen back on June 22nd.  It didn't quite turn out that way, yet the state of Michigan still saw quite a few tornadoes, one of which was strong.  Now imagine if it had turned out that way.  

When a storm takes on a negative tilt, one of the things that happens is that the cold front picks up like gangbusters and literally begins to pass the warm front near the center of the low.  This is known as occlusion, and it helps to create very strong forcing for ascent, or lift, in front of the cold front, as it's wedged violently under the warm moist air ahead of it. In this type of environment, instability can be marginal, yet storms can still take off like rockets and drop violent tornadoes if moisture content is high enough.  This is exactly what happened back on November the 17th of 2013.  Very little atmospheric instability - 700-1000j/kg of MLCAPE in some places - was present ahead of the cold front.  Normally, this would make for a "general thunder" day at best, or just a typical rainy fall day. However, the system which was moving this air was a very powerful winter-style storm, and when winter storms happen on warm days, bad things tend to occur to their south and east.  Those "bad things" can be characterized by 136 tornadoes across six states, and 429 instances of wind damage, at least 19 of which were caused by hurricane force winds which exceeded 75mph.  Pretty crazy, even for a Great Lakes November Gale.

November 17th 2013 300mb jet core as forecast by the NAM for roughly 1PM EST on that day

August 19th 2015 300mb jet core as forecast by the GFS for roughly 2PM EDT this Wednesday

Many if not most of the violent tornado outbreaks that have occurred in this country have happened due to negatively tilted troughs.  November 17th was but one, and it's the one I tend to refer to the most as it was recent and in our neck of the woods.  I do think there are lots of parallels between what the models are forecasting right now and that event.  I don't think that it's quite there yet.  A lot of other factors will need to become illuminated before anyone will be able to say that this event will be anything close to as extreme as that day was.  With that in mind, if conditions do line up, it could wind up being worse.  August is typically a much warmer month for the Great Lakes than November.

Things that could wind up making this go bust include, but are not limited to:

• Early day or previous day leftover convection sucking up energy before and/or tempering the atmosphere before the cold front arrives

• Overall lack of instability

• Timing of the cold front's arrival not coinciding with enough instability to generate storms

• A weakening of the storm system, causing the predicted negative tilt to vanish and a decrease in overall wind shear/horsepower potential, or the system not quite manifesting in the manner as is currently being predicted

Things that could make this go boom include, but are not limited to:

• A strong low level jet developing and sucking up ample moisture and warm air and drawing it into the Great Lakes

• Timing of the cold front's arrival coinciding with ample instability or - God forbid - peak heating

• Strengthening of the storm system into an even more powerful monster than what's currently benig predicted to form

I'm not going to lie.  As of right now, this looks pretty bad.  Michigan in particular may wind up receiving a bit more out of this than we did back in 2013, where the focus was Illinois and Indiana. The reason being is that the main jet streak is forecast to be a bit further north this time around. Upper level disturbance aside, the center of the surface low is also forecast to be further north, which is most concerning to me.  The 12z GFS run puts it right in the "sweet spot" - roughly the same position that the surface low was in during the July 2nd 1997 Southeast Michigan Tornado Outbreak.

I'm anxiously anticipating getting data from the mid range and short term models on this for a clearer picture.  Any categorical risk upgrades will be posted as they're made.  For now, I'm maintaining the SPC's "slight risk" assessment.