FCST: 12/23/08-12/24/08 MIDWEST/GREAT LAKES

[Joel Wright]

Well, here we go again. Models have latched onto another bout of wintery weather for much of the central CONUS starting later monday night and lasting well into Christmas Eve.

Very strong warm air advection will commence over the midwest later on monday, and should induce widespread snow to develop over much of the midwest by early Tuesday morning. 850mb temps will increase quite a bit by later Tuesday introducing the possibility of sleet and freezing rain for areas south of I-80 in Illinois.

Initially snow to water ratios will be high, but as warmer air just above the surface advects in tuesday they will drop quite a bit. Right now it looks like eastern IA, the northern half of IL, southern WI, and northern IN are in the favorable location to see the heaviest WAA snows. GFS Model indicates a 0.50"+ QPF bullseye over northern/central IL by evening Tuesday. That could fluff up to 4-8" of snow quite easily given higher ratio snows that this event started with. Southern portions of this QPF bullseye will likely have sleet and or freezing rain to contend with though which would cut down on snowfall amounts.

If that weren't enough, a second wave of snows will move northward out of KS and MO very early Christmas Eve as a surface low moves northeast along the baroclinic zone. This doesn't look to be a particularly strong system, but will have the potential to lay another 3-6" layer of snows ontop of the earlier WAA snow.

 

[Robert Dewey]

Definitely a difficult forecast... NAM and GEM are weaker and further southeast, while the GFS has been consistent with a stronger/further NW solution. NAM has been trending that way, very slightly.

Right now, I'm thinking a track and strength in between the NAM and GFS.

 

[Bill Schintler]

Winter storm on Tuesday through Thursday

A winter storm will provide an extended period of winter precipitation starting tonight. On Tuesday, the heaviest snowfall will fall over northern MN where several inches is likely with lighter amounts falling over central and eastern Iowa. On Wednesday afternoon through Thursday, another system will track through central and southern IA while providing several more inches of snowfall with heaviest amounts south of I-80. The following are forecasts for specific locations in Minnesota and eastern Iowa:

Twin Cities, MN:
Snow will start at 12 AM tonight with 3.2 inches accumulation.

St. Cloud, MN:
Snow will start at 12:20 AM tonight with 3.4 inches accumulation.

Duluth, MN:
Snow will start at 2:30 AM tomorrow with 3.4 inches accumulation.

Cedar Rapids (Eastern IA Airport), IA:
Snow will start at 11:10 PM tonight with 4.5 inches accumulation.

North Linn Co. (Paris and Coggon), IA:
Snow will start at 11:00 PM tonight with 4.4 inches accumulation.

Iowa City, IA:
Snow will start at 11:20 PM tonight with 4.4 inches accumulation.

Marengo, IA:
Snow will start at 10:50 PM tonight with 3.7 inches accumulation.

Union, IA:
Snow will start at 9:20 PM tonight with 3.4 inches accumulation.

Synopsis:
The PAC NW trough will continue to amplify while ULVL flow over the upper Midwest transitions to SWLY. The storm will arrive in two parts. First, low pressure will organize over SERN CO with an inverted trough nosing into the Dakotas. A broad zone of isentropic upglide and WAA develops over IA and MN starting early Tuesday over the retreating arctic AMS. Tonight a LLJ will increase to 60 kts while nosing into MN with UVM of -6ub/s noted in the H8/H7 layer. Later in the period, a potent SHRTWV ejects ahead of the WRN trough while providing strong lift over IA on Wednesday.

Discussion – IA:
The ECMWF appears to have initialized best of all models investigated; with less consistent verification noted for the WRF, GFS, and SREF. As has been the case for the last few systems, models are having trouble with snow pack and attendant shallow cold AMS in place. On Wednesday models have problems with non-linear forcing mechanisms. A mix of ECMWF, WRF, GFS, and SREF was used. Application of the Garcia method along 276-286K SFC/S supports a general 1-2 inches snowfall in IA through Tuesday. S/liquid ratios of 14:1 to 16:1 were used. Lift rapidly increases with the approach of the aforementioned SHRTWV late Wednesday through Thursday, with several additional inches of snowfall S of US-30 in ERN IA. Siding with the GFS and ECMWF solutions, more then 6 inches of snowfall are indicated, with higher amounts in SERN IA into NRN IL.

Discussion – MN:
A WAA snow event develops after OOZ with mixing ratios AOA 1.5 G/kg indicated. A zone of strong H7 frontogenesis swings NE through MN between 06 and 12Z.

- bill

3:30 PM CST, 12/22/08

 

[Joel Wright]

So far looks like Chicagoland is getting the most snow. Some sections of Chicago reporting over 5" already. A fairly narrow band of moderate snows set up from north-central to northeast IL and has basically been training there most of the day. North and west of there amounts drop off quite quickly, and south of there precip changes to liquiform. Some of that freezing.

Looks like another wave of snows will evolve out of Kansas and southern Nebraska later tonight. GFS is by far the most bullish in laying down 3-5" with that. NAM is way drier, but it's not a very dependable model anyway. The GFS has been pretty consistent in insisting this second wave of snows will be more formidable. Looking at radar trends, precip is already on the increase out in Kansas.

Picked up a bit over 2" here since early this morning. Have actually had some light freezing rain at times since late afternoon. Should see another 2-3"+ with second wave late tonight and early tomorrow.