Strongly disagree with SPC's day 3 outlook - Possible repeat of June 22nd this Sunday

Two things have become apparent to me over the past 24 hours regarding this weekend's weather: a) the series of "shortwave troughs" which were expected to affect Michigan this weekend have merged into one massive trough, per the southward movement of the monster low pressure system currently spinning over the Hudson Bay, b) much stronger flow is going to be present over our area than what was originally expected, and this potentially explosive weather - along with the trigger - are going to arrive this Sunday evening in one fell swoop, rather than spaced out into Monday as the thinking was last week.

As I stated in an earlier post, when such patterns are spread out over several days, it usually lessens the chances of widespread severe weather over a given area, mainly because you have multiple straws sucking up the energy.  This is definitely not always the case, as you can get strong enough shortwaves combined with high moisture jets which can drive multi-day severe weather events (as what happened in April of 2011), but it's the exception.  With that in mind, what was originally looking like a decent if somewhat tempered chance of severe thunderstorms across Michigan is now looking like it could very well be an event similar to what occurred on June 22nd of this year.

Simulated radar, 2am NAM run 07/31/15

Looking at the simulated radar from the latest NAM run, we can immediately see that a line of thunderstorms are expected to move through Michigan in the morning to mid-afternoon hours.  Should these storms appear where they're forecast to occur, they may strengthen as they move across the state, as conditions for severe weather - instability/moisture content and strong flow aloft - are expected to improve throughout the day.  These conditions will remain in place into the late afternoon and evening hours, and that's when a second round of thunderstorms should erupt as the cold front plows through.

Supercell composite, 2am NAM run 07/31/15

Significant tornado potential, 2am NAM run 07/31/15

This second round of thunderstorms is what I'm most concerned about.  Wind profiles are quickly arranging in such a way that supercells should be the initial storm mode when they develop, and even after they coagulate into a squall line, they should have adequate power at their disposal to produce significant damaging wind gusts.  With all of this in mind, I've issued a "widespread severe possible" outlook for mid-to southern-lower Michigan for this Sunday evening.

So far, the Storm Prediction Center does not agree with me:

Storm Prediction Center's day 3 severe weather outlook

There are likely a couple of reasons for this, chief among them that the NAM tends to overestimate moisture content in its forecasts on a regular basis: 

The NAM is forecasting dewpoints in the 70s despite forecasting temperatures only reaching 75° in some places.

This leads to much more instability being forecast than what will actually occur.  The second reason is that, as was the case before, the morning storm complex could significantly temper the atmosphere to the point where instability is marginal. 

With that in mind, I still strongly disagree with this day 3 outlook, and believe widespread severe weather is possible.

Despite potential issues with the NAM, the GFS is also forecasting strong severe potential throughout Michigan, as well as late afternoon/evening convective precipitation matching this severe potential.  Wind profiles are forecast to be even stronger by the GFS than the NAM.

My number one reason for this is the wind profile being forecast across the spectrum of models.  Winds aloft are expected to be significantly stronger than what was originally expected for this weekend, as the monster Canadian storm system dips to the south.  Under the influence of this system, wind speeds in the mixed layer may increase to 60 knots in some areas of Michigan (as forecast by the much more conservative GFS), and even the low-level jet may also reach this point.  Winds higher up in the atmosphere at the tops of the thunderstorms will be coming from the northwest, and they may reach 65-70kts (again, according to the GFS).  Both models suggest storm initiation in the late afternoon/evening hours across lower Michigan, and I believe that regardless of how unstable the atmosphere is, the storms should have enough horsepower to pose a significant danger to life and property.

I will be continuing to monitor this situation throughout the day today and tomorrow, too.  The SPC could still be spot on, and we could wind up seeing very little severe weather in our state this weekend.  But my gut won't allow me to believe this based on what these models are saying and what very recent history has shown us.  The setup is a bit different than it was then, and it isn't looking as nearly as scary as it was back then, either, so this could wind up being a paper tiger.  I just won't discount it until I have more model runs and data to analyze.

Update: To be fair, I had yet to read the SPC's day 3 outlook in its entirety before I made this post.  They do specifically mention a potential upgrade in later outlooks, but that the impact of morning thunderstorms makes predictability too low at this time:  

   
   HAVE INTRODUCED A MARGINAL RISK AREA...BUT AN UPGRADE TO HIGHER PROBABILITIES IS
   LIKELY AT SOME POINT IN FUTURE UPDATES ONCE UNCERTAINTY REGARDING
   EVOLUTION OF EARLY THUNDERSTORMS AND THEIR IMPACT ON THE MESOSCALE
   ENVIRONMENT HAS BEEN MITIGATED.

This outlook was likely issued before the 06z (2am) run of the NAM and GFS was complete, so I can't fault them for the want of more data before delineating a higher risk area.  With that in mind, without significant changes to the forecast, I have a suspicion their Sunday outlook will look a bit like mine come tomorrow.