Friday, December 16, 2011

December 20 Snow Event Discussion (Updated 12/16)

Confidence Level: Medium
System that will eventually become the Dec. 20 storm system.
Defined as the dark blue circle of increased Water Vapor.
The system that will eventually turn in to the December 20th storm for the Midwest and Ohio Valley is currently just offshore Baja California. The system is defined above as the dark blue circle of increased water vapor. The circular shape is similar to that of a cutoff low, which this storm system actually is. A cutoff low basically is disconnected from the jet stream, or cut-off, and can spin around for days in a single area before eventually being nudged somewhere else by a different atmospheric feature (another disturbance, for example).
This cutoff low will be progressing eastward into the US at some point in the next couple days. From that point on, the system should sit by itself, possibly losing some of its strength to the storm-ravaging Rocky Mountains. The cutoff low should be moved eastward by another disturbance sliding southeast-ward from the Pacific Ocean. It can be compared to a 'one leaves, another takes its place' sort of pattern.
This first cutoff low should be nudged far enough eastward to be influenced by the jet stream and be pulled back into the flow. One question is just how strong the second system that will be moving southeast will be. It is possible that a stronger system would move the first low farther east, thus moving the track farther east. We want to find out what the models think will happen, but models are known to not be good with systems in the Pacific due to lack of upper air observation data. So we turn to the ensembles.
Measure of Predictability using NCEP Ensembles for the December 20 period.
Darker colors indicate more confidence in a certain atmospheric event happening.
As the system ejects eastward out of the Southwest, the NCEP ensembles are believing that a strong ridge (high pressure system) will be in place in the Southeast. This would do two things. One, it would stop eastward progression of the disturbance due to the ridge being in the way. Two, the ridge would take the disturbance and pull it northward, moving the disturbance around the ridge. This would ideally take the system through the Midwest and Ohio Valley before entering the Northeast.
Something we are monitoring, however, is how strong the ensembles take this ridge. The ensembles appear to be really pushing this ridge northwestward, farther northwest than previous ensemble predictability images have seen. This increased northwest ridge presence would alter the disturbance's track, presumably taking the storm more northward.
The big concern with this is how the ensembles may not be picking up the system. We can see an area of light orange colors in the Texas region, around where the disturbance is projected to be by models. However, the shade of colors would indicate that 50-70% of the ensembles are predicting this disturbance to be present, with more than 80% predicting that the ridge will be present. We do believe that the disturbance will be in place, but with the ensembles not agreeing, the final solution may be altered due to the disagreement.

9 comments:

AJ said...

Where is the present indication about this storm in Valparaiso Indiana?Where will the heaviest snow be?

Andrew said...

Valparaiso is in an area i am hesitant to issue a forecast for in this storm. It appears that this will be an interesting scenario and may come down to the eleventh hour, so to say, to figure out a forecast for Valparaiso and areas like that.

Mike Paulocsak said...

Hello Andrew.Do you believe that this could possibly bring some snow to northern Ohio or not?The track looks kind of a potential to do so.Also,what are you predicting the temps,to be during this storm?

Mike Paulocsak said...

I forgot to mention in my last post.If the low would move on an more east northeast direction through Arkansas,Tennessee,Kentucky direction it would lay down the heaviest snow 100 miles or so northwest of the storm track.Is this correct if this scenerio would play out?

Andrew said...

Mike: North Ohio is outlined in our graphic as having potential to receive snow.
And yes, that would be correct.

AJ said...

Do you think Valparaiso will get heavy snow out of this storm?

Owen12789 said...

How much snow do you think Springfield Il will get if any?

Andrew said...

AJ: It is too far out to tell.

Owen: Possibly. It depends on the track and amount of warm air and cold air.

Owen12789 said...

When will this forecast be set? What day?