This is hour 156 of today's 12z GFS Ensembles. This is the timeframe we are looking at for a potential snowstorm in the East US. As we can see, there are two camps: One that brings all precip north into the Midwest (North Camp) and one that has the most precipitation down south in this page (South Camp). For a simple reference, let's count out how many ensemble are in which camp.
(Out of 12 ensembles)
NORTH CAMP: 8 ensembles (67%)
SOUTH CAMP: 4 ensembles (33%)
Now, of course, many things will change- that was simply for just a glance at it.
Something that makes me think about this storm is checking out the teleconnections.
Here's the PNA forecast.
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| Most Recent PNA Forecasts |
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| Positive PNA Phase |
In a positive phase of the PNA, a ridge sets up over the West US, and the storm track is diverted into the Southwest and then either into the Midwest or Northeast. The forecasts for the PNA in this timeframe (Feb. 2-4) are a strong positive, meaning that the effects of the +PNA will be more pronounced. This is shown in many of the ensembles of the 12z GFS. You can see the +PNA by tracing the red rain/snow line through Canada in the West US then diving back south into the East US.
Something else we can use to check out the storm is the NAO and AO. In the positive phase of the NAO, we see warm temperatures across the East US. The big snowstorms usually fall during a negative NAO. In the ensembles, we have checked and see a -NAO developing on the forecasts. This would bring the biggest snows to the Northeast, theoretically.
The AO is forecast to be negative during this timeframe, which would supply the cold air as well as increase chances for snow for the East US.
But here's where the buck stops for the Northeast's big snow possibility: The MJO.
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| MJO Forecast |
Basically, when the MJO is closest to the edge of the image, the effects of each phase are stronger. Right now, we are in Phase 6. The Green line is the GFS Ensemble forecasts for the MJO, enhanced by individual ensemble forecasts shown in the yellow lines. The current forecast by the GFS Ensembles and other models are to have the MJO go into a strong phase 7 around the time of the storm. Here are the temperature and precipitation effects of a Phase 7 MJO.
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| Temperature Anomaly |
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| Precipitation Anomaly |
The Northeast is typically dry during Phase 7 and phase 6 (in case the MJO ends up in Phase 6 during the storm). That would be a major blow to the forecast, seeing as the MJO would be at a strong level and therefore could deter the AO/PNA/NAO effects. For temperature, Phase 6 and 7 both involve the East US being warmer than usual.
My Thoughts
In my opinion, I think that while some indices are pointing toward a total Northeast Snowstorm, i'm going to have to go with a Midwest/Northeast shared snow event for now. Based on the strong MJO combined with a strong PNA and subsequent -NAO/-AO, it seems likely that the end result will be a shared snowstorm with these two regions. Another thing that enhances my shared snowstorm theory is how the ensembles are more unified with that idea than a pure northeast snowstorm. In this winter where the models are doing poorly, I find much more confidence in a group consensus rather than just one person's idea of a scenario.
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