Last week I began to watch the forecast put forth by the GFS with increasing interest as what appeared to be a very significant Nor'easter was appearing in a few model runs. The most interesting aspect of the storm is that it had a significantly western track for a Nor'easter, and was showing some flags that it may become what I've come to call a Nor'hook - a cross between a Nor'easter and a Panhandle Hook. All models are now in very close agreement that this is exactly what's going to happen.
These types of storms are exceptionally rare. They begin like a typical Nor'easter - that is, in the deep south, in and around the Gulf Coast. Nor'easters are named as such because they tend to plow up the northeastern-most states that make up New England. They accrete ample moisture from both the Gulf AND the Atlantic coast prior to doing so, which is why they usually pack such a wallop. However, every now and again the Nor'easter either encounters a strong high pressure ridge over the Atlantic, or "bombs out" - that is, rapidly strengthens - usually in conjunction with an amplification of the jet stream and a very powerful upper level disturbance. When either of these things occur, the storm takes on a more northernly track. The result is a Nor'hook - a storm with the power of a Nor'easter and the track/amplitude of a Panhandle Hook, like the storm pictured above. That storm was the January 4th-5th 2014 Winter Storm, which dumped 18" of snow across SE Michigan.
The storm coming next week looks like it could be much more powerful.
First, let's take a look at what the midday GFS run is predicting as far as pressure depth for the center of the storm at 4AM Thursday: an astonishing 978 millibars. That's over 20 millibars deeper than the storm that hit in 2014, and the model doesn't even have it reaching its maturity there; it is forecast to strengthen even further over the subsequent hours, taking on a negative tilt (unsurprisingly, severe weather is expected for the south on Tuesday). It isn't quite forecast to "bomb out", but it's damned close.
A high pressure ridge is forecast to dominate the north Atlantic right around this time, too, which serves as both a block to keep the storm from tracking up the east coast, and helps it spin up a bit tighter. The ridge isn't as far west/south as it was in 2014, but with a storm this strong it doesn't have to be. The predicted track is very similar to the 2014 storm, though, placing the state of Michigan squarely in the cold sector.
The jet stream looks positively pissed off with this one. A coupled jet core winding up to 140-150kts means this thing would be a Bugatti in terms of storms. That is one seriously negatively tilted upper level disturbance, and notice what state is dead center in the middle of it.
So let's get down to business - snowfall rates and accumulation totals. Unsurprisingly, we're looking at a whopper - the ECMWF is predicting snowfall rates of 1½-2 inches per hour over a wide swath of lower Michigan. These would be long duration rates, too. This storm could very well be over our heads for most of Wednesday and wouldn't be gone until Thursday afternoon. This thing is going to be picking up moisture from both the Gulf and potentially off the Atlantic coast, so it's going to have ample fuel to power that 150 knot engine.
That kind of horsepower means winds are going to be a serious factor this time around. 18-23 knots equates to around 20-25mph, which is what the ECMWF is forecasting to be blowing across most of the area. The exception would be the Saginaw Valley and bay shoreline, where winds are forecast to reach 28-35 knots, or 40mph+. Coupled with any significant snowfall, that is blizzard criteria.
Storm total accumulations have varied over the last few GFS runs. This afternoon's has backed off a bit from the midday, but the previous runs also put out totals like the image above, so this could be an outlier.
UPDATE: 00z (Midnight UTC) 02/22/16 run of the GFS produced this:
Coupled with what the ECMWF is putting down, I'd expect a LOT - at least 6" plus. For me to say this right now is different, as normally I wouldn't forecast anything beyond "more than 3 inches" this far into the future, but suffice to say this is a very extraordinary setup. Keep in mind that the above image is a 10:1 ratio, and this will be the factor that makes or breaks this storm. Temperatures are about the only thing in question at this point, and higher temps will mean less snow and a storm that may even start out as rain or sleet. The system could even start out as snow, then change to rain, then change BACK to snow - this is what NWS DTX currently predicts will happen. The zeitgeist of the year has been that each storm that has come up from the south has been defeated by warm temperatures. All eyes are now focused on the thermometer.
One more factor throws a monkey wrench in the snowfall prediction, however, and that is what's unique to Michigan - the Great Lakes, and in this case in particular, Lake Huron. Two weeks ago the Thumb Area experienced an extremely heavy snow event born from a system which was otherwise an ordinary Alberta Clipper, the strongest of which usually tend to drop snow between 3-5" over Michigan. We saw a foot, and it was because of Lake Huron - the lake is extremely warm for this time of year, which means that it enhanced the storm with moisture as it sat spinning, anchored to our east. So now I paint you a scenario - if the lake could do that to an ordinary storm like that one, just imagine what it could do for a monster like this. The storm will be anchored for a few hours as it wraps up and reaches maturity, and it will be in roughly the same location as the storm two weeks ago.
I caution against underestimating the potential of this thing. I STRONGLY ADVISE considering alterations to travel plans beginning Wednesday and to prepare for a potentially life-threatening winter storm which could snow everyone in for several days. This could be a roof-collapser on the order of the storm that hit the east coast earlier this year. I am NOT joking about this.
Again, nothing is for certain yet. As stated above, temperature will make or break this system, and cause it to drop rain for the first half of its cycle and/or become more warm-sector dominated and peter out its available moisture before it could wreak too much havoc. The track could change, and we could see next to nothing. My gut feeling at this point, though, is that we're looking at a potentially historic, dangerous storm crossing lower Michigan this week.
To summarize:
• A very powerful, potentially life-threatening winter storm may make a direct hit on Michigan this Wednesday/Thursday
• This storm has the potential to drop six inches to over a foot of snow across a very widespread area, in combination with strong northernly winds
• Exact nature of the beast is not yet certain, and temperature/freezing line remains yet-to-be-determined, which could make or break this system.
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