Finally!! A legit Winter Storm!

Our first winter storm of the season is taking aim on northern IL and the Chicagoland area and will arrive late Weds Night bring at first rain to the area before a changeover to heavy snow accumulating possibly several inches along with lots of wind! A strong storm system made it's wave onshore this evening in CA as is now slowly moving eastward towards the four corners region.

As seen here on a WV loop

http://weather.rap.ucar.edu/satellite/displaySat.php?region=EVV&itype=wv&size=large&endDate=20111020&endTime=-1&duration=12

This is progged by the models to continue moving eastward across the Rockies inducing pressures to fall on the lee side of the Rocky Mtns leading to cyclogenesis of our storm at the sfc. Now that the southern stream wave is onshore the models will get a better handle on the track now given it's now in the upper air raob network. The track of the sfc low has been bouncing around the last few days. As seen below, as well as the upper level system moving over the four corners region

 

And now the wave crossing the four corners region valid 12z tomorrow morning off the 0z GFS

 



Now as the sfc low gets its act going the low level baroclinic zone begins to tighten and now only will the sfc low ride along this but a tigher gradient leads to quicker and stronger intensification of the sfc low.

As the sfc low begins to moving ENE out of OK it will begin pulling up gulf moisture due to a strong LLJ and really nice feed of good theta-e air up over the warm front and into the cold air as precip blossoms in the cold sector. So 24hrs from now we should have a good area of snow falling across KS/NE and into parts of IA.

 

 

 

Now as the sfc low continues northeast, rain and possibly some embedded thunderstorms will make their way into northern IL during the overnight hours and into the morning as it will be too warm for snow production. Heavy snow and a blizzard will be taking place in parts of IA and WI by Thursday morning where it will be cold enough for snow as well as strong low level winds in the CCB creating blizzard conditions. Also looks like there will be some enhanced banding and even possible thundersnow.

 

 

Now is the fun part of this event, atleast for us in northern IL. Some models are hinting at second deformation zone developing in northern IL during the afternoon and evening hours on Thursday and the sfc low rapidly deepens near and just to our east. The pressure gradient really tightens creating strong winds along with heavy snow falling across the area. Now these next few images are pretty impressive. You have 60kt winds in the 925mb layer, that is beyond rare to get in the CCB of a winter storm, unless its the GHD blizzard! Then you go up just a tad and you have 75kts! And with any possible convection (thundersnow) it's not going to be hard to mix those minds down to the sfc. The 0z GFS is progging very impressive UVV's (lift) during the afternoon Thursday across the area. Not a given that we'll see thundersnow but it's something to watch.

 

 

top left image valid 18z Thursday and other two valid 0z Thursday night.

 

Now for totals....this is the tricky part....a lot of variables like time of changover, track of the sfc low, is amount of CAA underdone or overdone, dry-slot etc. I'm sticking with 2-4" right now, more up near the IL/WI and less down near/south of I-80. Any shift in the storm track will have big implications on those current totals.

 

 

 

Matt