Thursday, December 27, 2012

January 3-6 Potential Winter Storm

It looks like the potential is arising for a winter storm to hit the Midwest and Ohio Valley at the end of the first week of January. This possibility is being shown by the two major models (ECMWF and GFS) which we will review right now.

The above image is the ECMWF's 500mb height forecast for the evening of January 4th. Depressions in these isobars (lines of constant pressure) signify low pressure systems, while arcing formations depict high pressure systems. The ECMWF shows the storm system in the southern Midwest at this time. Typically, this would be a good snow maker for many in these two regions. However, the jet stream is aligned in something called a split flow pattern.

The split flow pattern involves high pressure stationed in the Pacific Northwest, leading to a literal split in the jet stream, and thus two branches of energy form: what I call the Southern Jet stream and the Northern Jet Stream. In this ECMWF Forecast, the Northern jet stream is stationed in Canada, and is shown by several isobars very close together. The Southern jet stream goes through Baja California, Mexico and the Southeast in a situation that could easily provoke severe weather. This split flow pattern keeps the cold too far north for these types of systems to access.

The GFS forecast for this storm system has the system further north, into the Midwest at this point. The GFS later brings the system down south into Kentucky like the ECMWF, but there are still big timing differences. The ECMWF and GFS do seem to be in good agreement as far as showing a common track, but the key thing is timing. It may just be 24 hours between the two forecasts, but that 24 hours can and will dramatically alter forecasts for this system, as demonstrated by these two models.

I think the ECMWF's forecast is more realistic. I find the split flow regime more likely at this point in time after a temporary Rex Block gives way.



armando said...

first of all can you make a post for this weekend? Some models like the canadian has that storm blowing up. Second would the 3-6 storm affect the northeast at all? Would these merge or just be a little far apart? Thanks

Anonymous said...

Andrew just a minor correction. I'm sure that you just mistyped. Those lines in the pictures are called contour lines, not isobars. Isobars align equal pressures at the surface, while contour lines unite equal heights of a set pressure level.

Andrew said...

Armando: I'm kind of strapped for time, I can try to fit it in tomorrow.

Anonymous: My bad- thanks for the correction!

Simon said...

Andrew, love your blog (even if I'm thousands of miles away in the UK!).

Just to say fwiw Bastardi agrees with you:
Joe Bastardi ‏@BigJoeBastardi Major stratwarm getting ready to start precursor to major US cold outbreaks. Plenty of winter this year

Anonymous said...

Andrew, do you know if any of the models are showing this storm affecting Iowa?

Anonymous said...

how about affecting kansas??
a few days ago models were showing the new years day storm possibly hitting kansas what happened to it?
kansas probably like iowa wants the moisture we need the snow and lots of it
so there any hopes of this hitting kansas then helpin iowa before the east gets more

mike paulocsak said...

Hey anonymous above me! Why do you have to put a comment on here like that.This is a site to talk about weather.This is not a porn site.Another words,if you cannot talk about weather leave!Ohh,I forgot,don't hide behind anonymous use your real name!!!!!

Anonymous said...

Mike at 6:22 pm thank you so much for outing the childish behavior, ladies ( and yes I was raised as one) do read this blog.
Andrew, keep up the great work you do for us.

mike paulocsak said...

Hello Andrew.No worries buddy.I know that was not you.When I first saw that comment I thought,man that is a sick thing to say on a weather site.I don't know what is wrong with some people today.I really think some are in need of serious mental help.Anyways PLEASE do not let this stop you from doing what you like doing.Bringing us very useful info. on the weather.Looking out for the next big snowstorm!