12/22/07 FCST:IA/IL/MO/IN/WI/MN

[Brandon Sullivan]

A large storm system is forecast to move northeast out of the southern plains on saturday. As it does it will deepen rapidly and dump some moderate amounts of snow over IA/IL/MO/WI.

The latest 0z Models have come in to somewhat better line. Indicating the low to move northeast and move through central and southeast Illinois. Current model QPF values would indicate the heaviest amounts of snow from 6-8 inches falling from Kirksville to Ottumwa to Iowa City line.

Also, model forecast temperatures show bitter cold air being pulled in behind the system, this combined with strong winds of 20-30 MPH and near blizzard conditions could cause dangerous wind chill values to be achieved.

Below are some Key model images. Two of them are Snowfall amount forecast, One is the NAM forecast reflectivity (which matches nice with the heaviest QPF) and the final one is an image with surface wind and temp (to show the cold air)

 

[Joel Wright]

Well, it looks like most of the models are finally getting the jist of what will happen. The majority of the models take the surface low over Arkansas early saturday, and rapidly deepen it as it moves north over Lake Michigan saturday night. All the while pulling in arctic air as it strengthens. It looks to lay a band of moderate to heavy snow down from eastern KS up through eastern IA, and into WI. This exact band may be tweaked a bit as the exact strength of the surface low, and associated upper level phasing features are solidified.

The true winners for the heaviest snow will be somewhere up in northern WI and/or the UP. A full-blown blizzard may be in the offing for you guys.

Further south, the folks that end up in the heaviest snow will see it pile up very quickly once the snow begins (or changes over, depending on your location), but due to the relatively short duration of the event amounts shouldn't get too out of hand. The speed of the storm's movement will definitely have to be watched, as any slowing could very significantly up the amounts. The models have been pretty consistent overall though in keeping the surface low zipping along. At least until it finishes "bombing" over the lakes anyway.

By tonight we should have a pretty good idea of exactly how much will fall in the heaviest band. Right now, the early guess would be a quick 3-6", with isolated higher amounts to the lucky people who can get caught under a nice band for awhile. 3-6" is usually not a big deal, but since it will fall in a rather short time, and with high winds moving in during the twilight of the event, that makes it a bit more interesting. That and the fact that this will happen a few days before Christmas lol.

 

[Brandon Sullivan]

Welp, I have been put under a winter storm watch much to my delight.. But cant say it is much of a surprise. DVN still mentioning blizzard conditions with blizzard warning not out of the question. The exact placement of that heavy snow band will be key in the next few runs.

 

[Brandon Sullivan]

Looking at the Suite of 12z models, am liking the high QPF axis right over me, east of the MS river.. Keeping an eye on the surface obs, seeing how this thing is developing. 12z didn't change much. Slightly stepped up the QPF I believe, but te main track of the low was pretty neutral..

Here it comes!

Would expect some areas to go to warning products this afternoon, some going Winter Storm, some others going Heavy Snow, and even some Blizzard Watches/Warnings not out of the realm of possibility.

Edit: Looking at some NAM precip/snow overlays, they are indicating 1.00 Inches of Precip to fall over my county, but only few inches of snow, so obviously the rain snow transition time will be a huge factor.

 

[Brandon Sullivan]

18z products are out. Not much to add.

 

[Joel Wright]

Sort of looking like the best snowband will set up from southern KS, up through the KC area, up to about Ottumwa IA, to LaCrosse WI, and up to the extreme western tip of the UP. With amounts steadily going up the further north you go in that band.

 

[Brandon Sullivan]

Did you mean southern stream?

QPF is not that much higher, total precip values may have changed, but not any drastic jump for any Fcst Hour. The only exception to this would be in western Illinois, where amounts did rise. However the inch or so of liquid equivalent in Central Illinois will most likely not achieve heavy snow amounts, due to the fact of warmer temperatures, and the strongest UVV doesn't coincide with the SPZ (Snow Production Zone) which is the favored zone for Dendritic Development.

And, yes, people could get over a foot, primarily in WI. Which is evident on multiple model runs, from QPF to snow conversion, only using a 12:1 ratio.

But for at least Central IL, as ILX just said, looks like things will be limited by warm temperatures..

 

[Joel Wright]

Yeah, there's going to be a pretty sharp cutoff from lighter accumulations for the folks stuck in the warmer air on the front side, to the heavy accumulations on the cold side. Actually, even within the band of heaviest accumulations there will likely be large variations in amounts due to the strong banding nature this storm will have. Just for example, Iowa City could get 8" of snow, while Cedar Rapids is brushing off 3".

the 18z models do look a shade slower than the earlier runs, which is why the QPF is a bit higher. Any slowing of a system with this much forcing will have large implications on precip amounts obviously.

For all but maybe extreme western IL, this is looking like mainly a snow-eating rain event, followed by some light accumulations on the back of the storm as it pulls away.

 

[Rhyuan Janssen]

HMM dsm thinking 4-8 for me, which with 40mph winds or higher would be just fantastic... here's to hoping trowal slams me over 8

 

[Brandon Sullivan]

Update to DVN WSW talks about .5 inches of Ice now!! Wow!

Wow. Milwaukee saying watch may no longer be needed. Still waiting on DVN AFD..

 

[Joel Wright]

I sincerely don't see how they're forecasting that much ice for any area, anywhere in the midwest with this thing. I don't know what they're looking at, but all the models I see show a classic rain to snow transition, with maybe just a brief shot of sleet/freezing rain for a short time. With a storm this dynamic, with as much lift and mid-level CAA, I don't see it happening.

There certainly won't be enough cold air in place ahead of this storm for it either. Temps will be above freezing long before the storm arrives. So there's really no chance at cold air being trapped at the surface. Especially with decent surface WAA and southeast winds!

 

[Rhyuan Janssen]

I just saw that DVN said up to .5 ice too!! I think they had some crack laced coffee at lunch or something! I see almost 0 chance of ice as Joel has mentioned...classic rain to snow...DVN will have to eat crow on that!

 

[Joel Wright]

GFS from 18z tends to push the heavier snow just a bit west. Not much overall change though. Des Moines may end up being a pretty decent location to see the heavier snows. Interesting.

If the trend continues though, a line from KC to Des Moines, to Eau Claire WI may be the "big winners".

What's really interesting is this is about what the models all showed originally. Say even a week or so ago.

 

[Rhyuan Janssen]

Well zippie for me since if you draw a line from DSM to EAU you run right over my house LOL...

what is your take on any blizz warnings up here in iowa Joel??

 

[Brandon Lawson]

Are the models slowing the system down a little bit? I was noticing the 500mb jet streak keeps getting pushed back. maybe the system will dig a little further south yet. i am eager to look at the 00z runs tonight.