12/03/08 FCST: IA/IL/MO/WI/MI

[Bill Schintler]

A fast moving winter storm will bring as much as four inches of snow starting Wednesday morning. Snowfall will taper down to flurries by late afternoon however winds will increase out of the northwest with gusts in excess of 30 mph, resulting in blowing and drifting of the snow. Travel conditions will be treacherous during the evening commute. Looking ahead, a clipper system will bring some minor accumulations on Saturday. Below are specific area forecasts for eastern IA locations:

Cedar Rapids (Eastern IA Airport):
Snow will start at 8:00 AM with a total accumulation of 3.8 inches.

Iowa City:
Snow will start at 9:00 AM with a total accumulation of 3.2 inches.

Northern Linn Co. (Paris and Coggon):
Snow will start at 7:30 AM with a total accumulation of 4.3 inches.

Marengo:
Snow will start at 8:00 AM with a total accumulation of 3.9 inches.

Discussion:
This is a complicated FCST due to subtleties in the phasing of two branches of the jet as well as the possibility of banding of the snowfall. Currently, the Upper Midwest is in a split stream flow with the northern wave overspreading the southern Hudson Bay while an upstream wave is amplifying over the Pacific NW and into the northern Rockies. At the SFC, a CF of Arctic origin will dive SE and sweep through all of ERN IA by 12Z. Post-frontal snowfall will develop in a zone of strong SFC-H7 frontogenetical forcing beneath an increasingly amplified H5 L/WV. Large scale assent will be enhanced beneath the right entrance region of a 130kt H3 streak. An H85 wave will develop over NRN OK and travel NE along the front during the day. This degree of lifting suggests banded structures and possibly even some convective snow, with locally enhanced higher rates. The storm motion will be progressive; however, there exist the possibility for a few hours of 1-2 inch/hour of snowfall rates within banded structures. I’ve gone with a snow to water ratio of 12:1, with the possibility for higher ratios verifying. The latest models (WRF, GFS, SREF) are advertising increased dendritic growth and higher snowfall amounts with the post-frontal precipitation.

The other feature of this system will be gusty northwest winds as the SFC-H85 gradients tighten. Temperatures will fall during the day Wednesday as strong CAA overspreads the area.

- bill
3:32 PM CST, 12/02/08

 

[Scott Weberpal]

Add Wisconsin to the discussion? Current indications look like 3-6" from central to southern parts of the state. Not confident we'll hit the higher end, but a broad swath of 3-5" across the southern half of the state looks likely.

 

[Joel Wright]

The most reliable model (GFS) has shifted the heaviest snowband north quite a bit since last night's runs. Looks like the heaviest snow may end up falling from central IA up into central WI. NAM is further south, but already trending north and will eventually catch up to what the GFS is suggesting. Kind of anxious to see what the 00z has in store. I'm hoping the GFS shifts the band further south, but I highly doubt that'll happen. If anything it may continue to nudge it northward.

Wherever that band sets up folks can expect to see a quick 4-5"+ followed by some strong winds.

 

[Brandon Sullivan]

Just from browsing quick through the 00z NAM, it appeared to break precip out a lil later around 00z when it really got going.. Also pulled it back south a bit.. From OTM to DBQ Line..

I added WI to the thread.

 

[Joel Wright]

Well, the 00z models failed to add confidence to me. Surprised to see such differences between the NAM and the GFS this close to the event. The NAM insists on a fairly intense band of snow setting up from eastern IA into southern WI tomorrow afternoon. The GFS maintains a much broader and less intense area of snowfall, and is also placed further to the north than the NAM.

The new Canadian models actually trends toward agreeing with the NAM, surprisingly. Usually in a situation like this I'd side with the GFS, but the Canadian model is usually pretty good within 48hrs. Hmm.

Up until the 12z run, the GFS showed pretty much what the latest NAM/Canadian/UKMET model now show. Don't know why it backed off on a weaker/further north solution. Is it "seeing" something the other models aren't?

I guess if I was actually making a forecast I'd have to comprimise between the models (something I hate doing) and go with a blend. I do think the GFS may be underestimating the amount of snow in the heaviest band, but it may well be right with the placement of the heavier snow.

 

[Chris Fitzgerald]

I also looked at the 00z Nam and the strength of the cold front seems rather strong compared to what the GFS is showing. The NAM seems to be wanting to sag the system south. I'd expect some sort of product issued in the future for the farther south counties that are bordering the current Winter Weather Advisory.

 

[Mike Kovalchick]

Might as well mention Michigan in this thread where the brunt of the storm will be felt with the added lake effect component. NNW, NW, W, & SW wind locations will all see action with this setup.

Per NWS,

"TOTAL SNOWFALL AMOUNTS FROM WEDNESDAY MORNING THROUGH FRIDAY MORNING WILL RANGE FROM ONE TO TWO FEET IN SOME AREAS WITHIN THE WARNING AREA...PRIMARILY NORTH OF M-72."


I plan on heading up North Friday for some fun in the snow after this storm wanes and before the next storm moves in Saturday. I think some decent drifting action could setup Saturday afternoon with the expected winds, cold temps and very deep snow pack.

 

[Joel Wright]

Man, these models are driving me nuts! LOL. Well, now it's clear the NAM was wrong last night, as was the Canadian (and 12z UKMET). GFS picked up on a more progressive, less dynamic solution before the rest of them. Should have known not to trust the NAM, but since a few other models actually agreed with it, and looking at how dynamic this system coming in looked to be it was hard to ignore it.

So now it looks like the more conservative QPF the GFS spit out is the real deal. Looks like just a broad swath of 1-3" from much of IA into northern IL and much of WI. The storm will get it's act together in time though, along with increasing gulf moisture will give folks east towards the lakes more snow. Plus as Mike mentioned there'll be the lake-effect component as well.

These little systems are hell to forecast, but man is it fun!

 

[Joel Wright]

Ended up with about 3" here. Just enough to allow for a few very cold nights for this time of the season.

 

[Chris Fitzgerald]

We ended up with around 1 inch here. NAM was pretty on with the snowfall totals for our area. The heavy snow lasted about an hour, which was shorter than models were showing.

 

[Scott Weberpal]

Ended up with 3" here around Whitewater. Some areas north of here received up to around 5".