December 19-22 Potential Blizzard Event (Updated 5:30 PM)

**This post is dedicated to Charlotte Bacon, age 6, a victim of the Connecticut shootings.**

This is an update to this morning's original blizzard post, which can be found by clicking here.

This update concerns the new models from the 12z suite, and not so much for teleconnections, which were covered in the morning post. Also, I have now established the two 'camps' for the models. The 'North Camp' involves models that take the system into north Illinois at Hour 96, and the South Camp has the system in central/southern Illinois at Hour 96.

We start with the GFS model, known as one of the better forecasting models that is out there today. The GFS is forecasting the storm system to be in north Indiana on the morning of December 20th. The solid blue line is the rain/snow line- any precipitation to the north of this line is theoretically snow, and precipitation to the south is rain. The storm system has a central minimum pressure of 994 millibars, meaning it is fairly strong. The forecast calls for snow to be ongoing in Illinois, Wisconsin and Michigan, with a potential severe weather situation ongoing in Kentucky and Tennessee. I will not make an assumption on if the GFS is right of wrong until I review the other models below. Needless to say, the GFS is in the North Camp.

This is the European's ECMWF model forecast, once again valid for the morning of December 20th. The ECMWF is widely regarded as the best forecasting model used for daily weather forecasting, like this. The model predicts that the storm system will actually be in south Illinois at this time, thus being further south and slower than the GFS. The central minimum pressure is down to 995 millibars, roughly the same strength as the GFS. The ECMWF solution has shifted south from recent forecasts, not a surprising thing to happen in the winter. I am cautiously optimistic with this forecast, as I think the teleconnections fit in nicely here, but models are notorious for shifting south in this time period, only to shift back north later on. The ECMWF is in the South Camp at this time.

This is the forecast from the ECMWF Ensembles, also called the ECMWF EPS. The ECMWF EPS can be thought of 51 separate ECMWF model forecasts, each with slightly different starting parameters. This forecast, once again valid for the morning of December 20th, has the storm system in southern Illinois, actually a tad farther south than the ECMWF model itself. The minimum strength is at 1002 millibars, meaning it is fairly weak. However, there is something slightly more significant. The fact that an average of 51 different forecasts, all originally based off of the best forecasting model known to man, came up with such a solid solution is very supportive at this point for the South Camp.

The current overview of the models is this:

North Camp: GFS, GFS ENS (2 models)
South Camp: ECMWF, ECMWF EPS (2 models)

We now move to the Canadian's GGEM model. It shows the storm system in central Illinois with a central pressure of 1000 millibars. The blue rain/snow line remains in North Illinois, but far enough south for cities like Des Moines, Chicago and Milwaukee to get snow at this point. Considering the GGEM is taking a cold solution to the mentioned cities, I feel like it belongs in the South Camp.

This is the forecast for precipitation, 850mb temperatures and the freezing line from the GGEM Ensembles (GGEM ENS). Although the Canadian model is not the best, ensembles are always better than models. The GGEM ENS believe that a solution not all that different from the ECMWF will evolve, with the storm system taking a path through south Illinois and snow given to the previously mentioned cities. Heavy rain in TN/KY suggests a possible linear storm event could be ongoing. This is indeed a South Camp storm.

Another model overview at this point in time tells us the following:

North Camp: GFS, GFS ENS (2 models)
South Camp: ECMWF, ECMWF EPS, GGEM, GGEM ENS. (4 models)

This is the image of the GFS Ensembles. Yes, I know the ensembles were already listed in the North Camp, this is just for you all to see what it says. The GFS Ensembles (GFS ENS or GEFS) shows a major snow event in much of the Midwest after the storm system blows through. Rain is ongoing in southeast Michigan, and again that linear storm threat appears with the states of Kentucky and Tennessee.

Here's the final total after reviewing some other models:


North Camp: GFS, GFS ENS, JMA NOGAPS ENS,  (4 models)
South Camp: ECMWF, ECMWF EPS, GGEM, GGEM ENS, FIM. (5 models)

Analysis: This is not as difficult as you may think. Despite the input of 9 models and ensembles, only a select few are worth making note of. The GFS/GFS ENS should be watched carefully, as should the ECMWF/ECMWF EPS. The JMA and NOGAPS ENS are worthless; I threw them in there for some diversity. As for the FIM, it has historically verified slightly better than the GFS, so it can be taken note of. I would watch the Canadian model and ensemble set, but not as closely as the American and European sets.

Forecast Preference: ECMWF/ECMWF EPS
Confidence: 60%

Snow amounts, totals and eventual track will need to be determined at later dates, so please do not ask me for snow totals for your city, because I just don't know yet.

Andrew