Sunday, November 18, 2012

November 27-29 Potential Winter Storm

There is potential arising for a major storm system to hit the Midwest, Plains, Ohio Valley and Northeast. Let's look at how this could all go down.

This is hour 228 of the 12z GFS, valid on the 27th of November. There is precipitation falling across the nation, with rain and thunderstorms hitting the Ohio Valley, Northeast and Midwest, while a snowstorm rages in the Plains. This comes from a 989mb storm system- quite strong for a system on land. At this point, the storm has not yet pulled out of the mountains and has not reached its full potential. Despite this, it is clear that this system will cause troubles as it is producing major precipitation across a wide swath of the nation.

Moving ahead 12 hours to the morning of November 28th, we now see this system has emerged from the mountains and is now located in the Upper Midwest. The storm's pressure rests at 988mb, ever so slightly weaker than what it was in the mountains. The GFS model now indicates the storm system has developed a strong cold front, as the frigid air wrapping around to the western side of the system would indicate. Thanks to this front, heavy precipitation has emerged ahead of the frontal boundary, with heavy rains down both sides of Lake Michigan into Arkansas, and as far east as the Michigan/Canada border. Because of the cold air now wrapping around the system, a larger portion of the Plains looks to be under threat from a snowstorm. Blizzard conditions appear to be in the cards for Minnesota and the Dakotas, the three states closest to the low pressure system yet still north of the blue rain/snow line.

Fast forward another 12 hours and we find this system has intensified quite a bit. The system is now down to 978mb, a whole 10mb lower than the morning of November 28th (the second image of this post). This strong storm system is now into south central Canada, where it is battering the region with blizzard conditions. Due to the intense cold air wrap-around from the cold front, the blue rain/snow line has now caught up with the heavy precipitation, meaning that states like Iowa, Wisconsin, Illinois and Missouri would be seeing snowflakes fly- possibly at an accumulating rate. To the east of the rain/snow line, what could be a linear thunderstorm formation is now progressing east, and hitting Indiana, Ohio, Kentucky and Tennessee with its wrath. As is the situation in the aforementioned Midwest states, these heavy storms would likely switch to snow, more likely in the northern states. Still under snowstorm conditions is Minnesota, which, should this forecast verify, would emerge with several inches of snow under its belt.

Another 12 hours later and we are on the morning of November 29th. The strong storm system has now moved off to the northeast, well off into Canada. Blizzard conditions have now ceased in the Upper Midwest and lower Midwest states, but now the Ohio Valley is north of the blue rain/snow line. Judging by the amount of precipitation accumulated in this forecast, some accumulation could be found, especially in Ohio and western Pennsylvania. Cold air would follow this strong storm system, which has now strengthened further to 965mb- another 10mb dropped in a 12 hour period. Heavy rain could be ongoing in New England before the cold front races through.

I know what you're thinking: "Why should I get excited over a forecast over 10 days away? It'll never happen- the model is too far out!" But there is substantial evidence that this isn't just another 'fantasy forecast' (a forecast that looks great but doesn't happen).

This was the observed surface map for November 13th, just 5 days ago. This surface map is for the northern Pacific and Bering Strait. As you can see, there is a very strong storm system swirling around in the waters just off the end of the Aleutian Islands on this date.

Why is this significant? There has been a connection found between strong Gulf of Alaska (GOA) storm systems, and a strong storm system hitting the Lower 48 around 17-21 days later. If we take November 13 and apply that 2.5-3 week gap, we find that this strong storm system would hit...

...between November 30 and December 4. It just so happens that the storm system forecasted above falls in this timeframe.

Is this a coincidence? I doubt it. While the GFS may be over-exaggerating some aspects of the storm (i.e. strength, precipitation, air temperature), I have a feeling that the GFS is catching on to this Bering Sea Rule, as it's called.

I can't say I am willing to pinpoint the exact track and effects of this storm system because the models are all over the place. One cannot figure all those factors out just by seeing a strong GOA system, either- all you can determine is that a strong storm system will be around the Lower 48 roughly 17-21 days later.



Anonymous said...

If this does happen how much snow would south central minnesota get, just a rough estimate?
Thanks Amy

Anonymous said...

Come to the accuweather forums to find out...that is where all this information comes from anyway.

Anonymous said...

Hey Andrew, Rock on brother. You do a great job. Haters will always hate. Whats the chance of getting snow in ohio this coming up storm? Thanks Justin.