December 20-22 Potential Blizzard Event (Updated 12/15)

(Originally posted earlier today) I have upgraded my thinking of this winter event from a 'Significant Storm' to a 'Blizzard' event. I'll now explain why.

This is the ECMWF forecast for Hour 144, a.k.a. the evening of December 20th. We see a very strong storm system in northeast Illinois at this time with a minimum central pressure of 986 millibars- pretty strong for an onshore system. Let me first start off discussion of the model by saying I trust the ECMWF more than other models at the moment, as although all models have been having troubles, the ECMWF has historically outperformed most models in the past. The ECMWF shows a high pressure system in the Southeast, off to the east of Florida.

Moving quickly along, we now visit the ECMWF Ensemble prediction system, or the ECMWF EPS. This forecast is for the same timeframe as above- the evening of December 20th. We see our storm system is on the Michigan/Indiana/Ohio border, with a central minimum pressure of 998 millibars. Considering the ECMWF EPS is composed of 51 separate forecasts, and we are 144 hours away, the strength of this system that is being projected is astounding. It's not that common to see an average of 51 forecasts, 6 days out projecting such a strong storm system. The ECMWF EPS believes the system will be submerged in cold air, as shown in 850mb temperatures (colors). This, combined with tightening of isobars, makes me believe that a blizzard-like solution could evolve in the Upper Midwest and South Canada into Michigan.

The GFS model has not been mentioned, but for those wondering, it is similar to the ECMWF EPS solution above as far as placement of the system goes.

Going back to the ECMWF model, we can see that it is projecting very heavy snow to fall over some Midwestern states. Snow is shown as precipitation north of the dark blue 32 degree line:

ECMWF Precip/Temp forecast for the Morning of Dec. 20

ECMWF Precip/Temp forecast for the evening of Dec. 20

ECMWF Precip/Temp forecast for the morning of Dec. 21

I don't have access to snow depth forecasts from the ECMWF, but if I were to give a rough estimate of snow amounts from the above few images, I would predict the following accumulations for the following locations:

-Northeast IL: 6 inches+
-South WI: 5-8 inches
-Michigan: 5-8 inches+


(Begin updated data) Now, I bring to you the updated 12z model suite and some information you'll find pretty darn interesting.

The ECMWF Ensembles are farther south than their 0z counterparts this morning, as shown in the below images:

As I explained, to have the ensemble system so confident on such a strong storm system this far out is very encouraging to those wanting snow. Now, in this scenario, Wisconsin, Iowa and maybe north Illinois would get the heaviest snow before the system moves off to the east. When that happens, we see a massive cold air dump from the heart of Canada into the Northeast. If this happens, heavy lake effect snow is likely. Not possible, LIKELY. This would be air that doesn't force you to wear a heavy jacket, it chills you to the bone- and then some. The warm Great Lakes will take this and, if such a solution happens, vigorously expel potentially high amounts of lake effect snow. The fact that this is the ECMWF EPS showing this happening is great news for the states I mentioned above for snowfall, because when you have the ECMWF Ensembles on your side, you're looking pretty good as far as probability of a forecast happening goes.

Now onto the interesting part. As I previously stated, the ECMWF is my trusted model at the moment. I will show you why I trust it's 0z solution just below:

These are North America model track errors. Basically, the higher the model is on this chart, the worse it has verified. If we look in the long range, we see there is one blue line that actually goes down in the long range, meaning it gets more accurate as time goes on (not a common sight at all). This blue line is none other than the ECMWF model. The Hour 120 forecast (just about when this storm gets going) is looking very well according to this chart above- all the more reason to trust the ECMWF. If you're looking for the GFS, it's that red line that is too high up to see at hour 96. (For those of you wondering about the 12z models, the GFS is about the same as the red line above, and the ECMWF has not come in yet.)

Forecast Preference: 12z ECMWF EPS / 0z ECMWF
Confidence: 45%

I'll have my first call out tomorrow morning. Until then, updates on this system may be found on the Facebook page at www.facebook.com/TheWeatherCentre

Andrew