Saturday, December 17, 2011

December 20 Snow Event Discussion (Morning of December 17)

Confidence: High
Water Vapor imagery of East Pacific. The Dec. 20 system is the dark blue circle of increased
water vapor.
We are watching the system that will soon become the December 20 snowstorm spin offshore Baja California right now. It is a cutoff low, characterized by the distinct circular shape- some of its vapor is being transferred east through the jet stream. You can see this from a blue line stretching eastward from the cutoff low. The cutoff low itself will move onto US soil soon by the line of dark blue to the west of the cutoff low. This is another separate disturbance that will push the original cutoff low eastward, through the Southwest, and eject into the Southern Plains.
The cutoff low you see in the water vapor image above does indicate that this system has quite a bit of energy to work with. After moving into the Southern Plains and giving them at least a fair 4 inches of snow, the system will begin to work northward along a ridge in place.
Measure of Predictability map from NCEP Ensembles.
Darker colors indicate more confidence by NCEP Ensembles that a certain atmospheric
feature will be present.
The NCEP Ensembles are showing two things. The disturbance cut-off low, and the ridge of high pressure. The ridge of high pressure is the orange colors with the arcing isobars in the Southeast. Compared to yesterday, it looks like the ensembles are thinking twice about the extent of the ridge's influence in the Midwest. More influence would push the storm track of this disturbance farther north. We will have to closely monitor how the ensembles continue to handle this.
The second feature we see is the disturbance itself. Unlike previous runs, this run of the ensembles is in ally showing confidence that the storm will be present in a strong manner. Confidence is indeed high, with widespread 80%+ colors in the region of the proposed trough. The disturbance is characterized by the isobars taking a dip southward as seen around Texas in the image above.
Yes, we did show this image at the beginning of the post.
But now it's recap time.
To recap, we expect the disturbance to come out of the Southwest guns blazing, and likely put down a sizable accumulation in the panhandles of Texas and Oklahoma. After that, the storm system will be weakening as it crosses through the Midwest, with accumulations there topping out at 4 inches. The low will then move into the Northeast and likely strengthen as it is near the oceans, just like coastal storms. That said, some sizable accumulations may also fall in the Northeast. The entire time the storm will have to navigate around the ridge of high pressure in the Southeast, and may have some Gulf Air accompanying it to help strengthen and/or add more precipitation to the storm.

15 comments:

Mike Paulocsak said...

Hello Andrew.What are your thoughts on this storm snowfall wise for this storm in my area in Ohio?I'm located in Holmes county.Also just a long shot guess,when do you think the first pretty good storm will be in January?I also want to thank you for answering my questions all the time.I have visited other sites and they never post back to my questions.Keep up the formative and easy to understand winter weather postings.Thanks again!!!!!!!!!

Andrew said...

Ohio certainly has a chance to get some snow from this system. Light accumulations remain on the table. Exactly how much remains to be seen.

Eddie said...

So I see detroit wont get snow

Andrew said...

It might, because our storm track seems to be a little too far south.

Anonymous said...

This is Tom from West Central CT: Hey Andrew, I posted a message on your main wall for the winter forecast, fyi. Could you please recap what your forecasting for my area of the North East? When and how much, ect.?

Andrew said...

If you haven't given a location for a town's personal winter forecast already, you can give it to me here. It will be released on Dec. 23 if you haven't already commented your location earlier.

Anonymous said...

I'm at Bethel, CT

AJ said...

So Chicago area won't get heavy snow?

Anonymous said...

Do you think that the weather balloons will say that this will change and Chicago area get heavy snow?

Andrew said...

To AJ and Anonymous: Since the system is relatively close to making landfall on the US (if it hasn't already), the solution we have now should stick.

Anonymous said...

Right now how much snow should Valparaiso,Indiana get?

Andrew said...

It is too far out to tell. This is an unusually tricky system.

Anonymous said...

Hi, What are your winter storm expectations for Greenbelt, MD ( adjacent to Washington, DC) Thanks for your thoughtful analysis.

Anonymous said...

How much snow do you think will accumulate over northwest Indiana?

Andrew said...

Anonymous #1: There might be some snow for that area.

Anonymous #2: There is a potential to see some flakes fly, but we are not too sure.