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)

http://img524.imageshack.us/img524/7341/wintergfs0p5sfc12hraccuwt5.gifhttp://img339.imageshack.us/img339/6862/wintergfs0p5sfcaccumsnogt1.gif
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/nam/00/images/nam_ref_048s.gifhttp://www.weather.cod.edu/forecast/ETA/GL/etaGL_2_temp_60.gif

[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.

[Bob Johnson]

Its gonna be interested. Forcing will be strong so there will be heavy snowfall rates per hr. Will have to see where that havy bad of snow sets up

btw, we are discussing it to on central weather forums

www.centralwx.com

[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.

[Bob Johnson]

Yes there.

Southern storm is stronger and showing more of a angle instead of due North. Its much stronger across Il and Wisconsin. Look at QPF charts! Someone could get over a foot. Plenty of deep forcing.

[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.

[Rhyuan Janssen]

Hmm..my local weather stations are saying blizzard conditions and they expect blizz warnings... and that models are trending even stronger...will be interesting...

[Jeff Piotrowski]

The new 0Z WRF is much more aggressive with QPF .50-1.25 from END-PNC-EMP-MCI line with winds over 30+. I think parts of NC-OK/SC-NE/KS may need to be upgraded to a Blizzard Warning.:eek:

[Bill Schintler]

A well advertised winter storm will affect the Eastern Iowa area this weekend. Following are forecasts for specific locations followed by a forecast discussion.

Cedar Rapids:
Expect periods of light rain or rain showers Saturday morning. Precipitation will change over to snow at 4:30 PM Saturday afternoon. During the change over, a brief period of freezing rain is likely however little ice accumulation is anticipated. Snowfall will become moderate to heavy for a few hours during the late evening hours. Gusty northwest winds to 35 mph will result in blowing snow. Total snowfall accumulation will be 3.0 inches before the snow ends during the early morning hours on Sunday.

Iowa City:
Expect periods of light rain or rain showers Saturday morning. Precipitation will change over to snow at 4:40 PM Saturday afternoon. During the change over, a brief period of freezing rain is likely however little ice accumulation is anticipated. Snowfall will become moderate to heavy for a few hours during the late evening hours with thunder possible. Gusty northwest winds to 35 mph will result in blowing snow. Total snowfall accumulation will be 3.8 inches before the snow ends during the early morning hours on Sunday.

Quad Cities:
Expect periods of light rain or rain showers Saturday morning. Precipitation will change over to snow at 6:10 PM Saturday afternoon. During the change over, a brief period of freezing rain is likely however little ice accumulation is anticipated. Snowfall will become moderate to heavy for a few hours during the late evening hours with thunder possible. Gusty northwest winds to 35 mph will result in blowing snow. Total snowfall accumulation will be 4.5 inches before the snow ends during the early morning hours on Sunday.

Marengo:
Expect periods of light rain or rain showers Saturday morning. Precipitation will change over to snow at 4:10 PM Saturday afternoon. During the change over, a brief period of freezing rain is likely however little ice accumulation is anticipated. Snowfall will become moderate to heavy for a few hours during the late evening hours. Gusty northwest winds to 40 mph will result in blowing snow. Total snowfall accumulation will be 2.2 inches before the snow ends during the early morning hours on Sunday.

Paris and Coggon (north and northeast Linn CO.):
Expect periods of light rain or rain showers Saturday morning. Precipitation will change over to snow at 4:20 PM Saturday afternoon. During the change over, a brief period of freezing rain is likely however little ice accumulation is anticipated. Snowfall will become moderate to heavy for a few hours during the late evening hours. Gusty northwest winds to 40 mph will result in blowing snow. Total snowfall accumulation will be 3.3 inches before the snow ends during the early morning hours on Sunday.

Synopsis:
WV imagery indicated energy diving S towards AZ along with a developing baroclinic leaf structure over ERN CO into NE. Meanwhile, a NRN-stream disturbance was moving rapidly to the SE towards ERN MT and ND. Over the next 36 hours, the SRN stream trough will become increasingly negatively-tilted while a couple of disturbances eject from the trough base and merge with the NRN stream ULVL system. The main challenge of the FCST lies in the details and timing of this phasing. Weak and disorganized SFC low pressure in the TX panhandle will shift slowly E and then NE towards WRN IL along a developing CF through 00Z Sunday, at which point rapid cyclogenesis will commence. Behind the CF, a surge of very cold air will race to the SE towards IA, with H85 temperatures falling to below -20C while raising concern about wind.

Discussion:
UA analysis and MDL initialization continue to indicate that MDLS are too warm and are underestimating the amount of mid-level CAA that should take place behind the system.
Given the very dynamic nature of this winter storm, elevated convection cannot be ruled out, especially between 04Z and 06Z on Sunday. MDLS have come into agreement with strength, location, and timing of key ULVL features. The latest trends also indicate a stronger SFC low that will track from S to N through NWRN IL while approaching bomb criteria. This increases confidence that ERN IA will see a significant precipitation event with about 70 percent of the QPF in the form of snow. Examining the evolution of the H85 low… Between 00Z, and 12Z, Sunday; the NAM keeps it in the DLH area and then shifts it slowly to the E towards the WRN Great Lakes as a secondary weaker low further S merges with it. The GFS, on the other hand, tends to redevelop a new low center further S along the trough in WRN IL. Other MDLS have solutions between these two extremes. In any event, the strongest forcing is not maximized at any specific location for more then about three hours, and SN will be maximized along a line parallel to and 90 miles NW of the H85 low track which will also be collocated with impressive H85 CAA. Taking a look at PROGGED H5 vorticity, MDL confidence remains low with the all important details as several compact vorticity bulls-eyes rotate through the area. Motion of these features and attendant UVM will be fast along the E side of the H5 trough. This all adds up to a short period of heavy snowfall rates along an axis from DVN NWRD into WI from 01Z-04Z. SN rates should be light for the remainder of the storm duration.

Regarding timing of changeover from RA to SN, the 1000-500mb thickness 540dm line should reach the Mississippi river by 00Z, leading to confidence that all but the very eastern tier of counties in IA should have changed over to SN. Wind should be a major factor, especially after midnight, as H85 temps fall to -20C, resulting in efficient downward momentum transfer of a 40-50kt NWRLY LLJ.

- bill
9:30 PM CST, 12/21/07

[Brandon Sullivan]

It looks like the Oz Models have slowed down the system. Keeping precip over the area (IL/WI) through 6z-12z Sunday. Dont know how to take this, could mean cooler temps would be present during the heaviest precip.. Also, could mean the system will dig further south/east then proggd...

Interesting.. Hopefully morning packages will bring out some Warning Headlines

[Bob Johnson]

I can't argue. I got two 5+ snowstorm so far this winter. 1st one I got 6 inches and the second one I got 8 inches.

[Rocky Rascovich]

Convective snow bursts are occuring around Sumner Co. KS. as of 0900
reports of lightning with these echoes currently. My guess is that heavy snow/sleet with 2"+/hr occuring.

Rocky&family

[Ben Prusia]

Already some freezing rain falling with air temps around 30 degrees here in Gardner. TOP already upgraded some of their CWA to Winter Storm Warning, most likely expect EAX to do the same shortly.

[Mike Umscheid]

man, this does look pretty good for the I-35 corridor in KS... I'm actually in KC this weekend visiting fam for christmas, so I missed out on the mini-blizz back home in Dodge, looks like we may get more snow here in Overland Park than Dodge... looks like the intense deformation zone currently blitzing Wichita will slowly work eastward towards far east-central KS... a lot of warm frontogenetic pcpn now overspreading LWC and portions of KC metro with temps in the 31-32 range... NAM soundings suggest sleet here in Johnson county until about 2pm or so... then wherever that deformation band sets up with the heavy snow... a healthy dosing of 3-6" of wind driven snow :-D

[afischer]

Emporia reported thundersnow on a recent ob. No shortage of forcing with this sytem with intense DPVA, high-level divergence/difluence, 850-700mb frontogenetical forcing, and a developing trowal signature/elevated convective instability via the 12Z NAM and RUC. Moderate rain/sleet just began in a hurry outside my window as I type this.

[Dick McGowan]

Here in Lawrence, thunder every minute or so, with some bright flashes every once in awhile also. There were huge flakes about an hour ago, now it has switched back over to sleet, with some pea-sized or larger pieces, with a pretty strong north wind!

[Ben Prusia]

Moderate sleet continues to fall in the southern parts of Kansas City. Major highways out of the Kansas City area, including I-29 north of Dearborn and I-70 west of Topeka are closed. Whiteout conditions have been reported at numerous locations.

Right now, it appears heaviest snowfall to occur to the N and W of the KC Metro Area.

[Jim Zandonai]

Well most of the action in our region will be west of the MS river. Here the best we can hope for is about 2". But the biggest or most impressive part of this storm for us should be the wind field generated by the strong pressure gradient on Sunday..At least it should be rather impressive that way for us.

[Brandon Sullivan]

welp, DVN certainly wont have to eat crow. I already have .15 inches of ice! Roads are slick, and have reports of power lines down in the county west of me (Carthage,IL)

[Bill Schintler]

Very heavy snow and wind here in Iowa City, IA (11:45 PM) - mostly smaller flakes... Winds are probably gusting 30 mph or more with visibility of a few hundred feet. One lightning discharge noted about 15 minutes ago, the only one I've seen so far for the storm. I made a note that I heard thunder - often when there's a bright flash during an intense winter storm, it's a power line fault and not lightning. Radar trends indicate that the most intense precipitation band will shift east of the area over the next hour or so.

- bill
11:48 pm, 12/22

[Bob Johnson]

30dbz in Iowa City. Looks like heavy snow will start to end within the next 2 hrs as this torm rapidly intenisifies into the UP of Michigan.

[Joel Wright]

Sleet and freezing rain (I'm still shocked this storm had this much ice!) has changed over to snow here in the last half hour. Full blown blizzard conditions at the moment. Winds have REALLY picked up in the last half hour, gusting to about 40mph already. It's only been snowing a short time and the ground has already become whitened again.

Edit: Moline officially reporting thundersnow and 1/4 mile visibility at 1am.

[APritchard]

Never figured I'd have a short range impromptu chase with the system. Severe warnings blanketing eastern Illinois now as a line of heavy showers and thunderstorms is apparently producing 60 mph wind gusts across central Illinois. I drove a quarter mile to the edge of town and parked it at a gas station and let it hit me. About what I'd expect, rain moving sideways. No thunder or anything in this area. Too bad the transition to snow wasn't faster, that would have been fun.

[Joel Wright]

Wow, this is amazing. Temp has dropped from 29 to 24 in the last half hour or so. Visibility is down to I'd say maybe 300 yards, and the snow has accumulated at least an inch in the last half hour. Still no thunder and lightning here yet, but I'm hoping to see some here shortly.

Less than 100 miles to my east in Dekalb it's a balmy 48° with a screaming southeast wind, and a line of low-topped thunderstorms heading north right at them associated with the rapidly deepening surface cyclone! AMAZING!

[Joel Wright]

57mph wind gust just reported from the Clinton IA location at 1:15am. Now pushing 2" here. All of that has fallen in less than an hour...

[Joel Wright]

Nearing 3" now. That is what has fallen in the last 70 minutes. Heaviest bands are beginning to shift north now, so heavy snow about to abruptly shut down. Never saw any lightning or heard thunder. A bit disappointed in that, but DAMN, that was impressive guys.

NIU/Dekalb about to see their temps drop a good 20 degrees over the next hour or so as the surface low passes right over them in the next 15 minutes...

[Derek Weston]

Here in lovely Cedar Rapids Iowa we have experienced near 8 inches or so of new snowfall.

I believe around 8 or 9 CST we experienced thunder and about a half dozen strikes of lightning in near white-out conditions.

A fun evening.

[APritchard]

Temp has dropped from the mid 50's to 33F here in the last hour.

A good amount of wind damage reports coming in from the line of cells that passed through. Reports of telephone and power poles snapped, shingles taken off, and one barn in the middle of a road scattered across eastern Illinois.

[Jim Zandonai]

Here in RFD we had some Moderate rainshowers last evening..and mild 46 degrees before the cold front moved by and the temps dropped like rock.. We got some snow about 1 inch maybe to re-cover the ground.
This A.M winds gusted to 44mph. Looks like EC IA and Quad Cites had more excitement then here and where the warmer air was in SE IL..
An impressive Storm system indeed.

[Mike Peregrine]

St. Joseph got sucker punched again with this one ... 8-10" up there with heavy drifting. One of the two large pile-ups happened on I-29 in St. Joe yesterday with around 30-40 vehicles involved. The heaviest bands set up to the west and north of KC, and if you were in that zone, you're snowed in today. Kansas City keeps getting off the hook -

Edit: Story from St. Joseph Newspress (http://www.sjnp.net/news/2007/dec/23/snow-causes-pileup/)
Preliminary Accumulation Map (http://www.crh.noaa.gov/crnews/display_story.php?wfo=eax&storyid=11225&source=0)

[Nate Gillson]

Man, what a storm! I got like a foot of snow last night. I saw 3 flashes of lightning and heard thunder. The heaviest snow fell from 10:40 PM saturday night to 1:50 AM sunday morning. The wind was also wicked. I'm snowed in big time!

[Danny Neal]

70+ mph knocked the power to my whole neighborhood from severe "thunderstorms" at around 2 AM. The powerpole 15 feet in back of my house blew and broke off....LOL a ton of expletives later I finally bailed and went to my grandmas house.....no telling when power will be restored....the automated response from COM ED says 1-4 days lol.....there goes X-mas at my house!

[afischer]

The heaviest bands set up to the west and north of KC, and if you were in that zone, you're snowed in today. Kansas City keeps getting off the hook -

Yeah, about 2.5" at my house. The dry slot was just a little too strong/progressive, and the deformation snow band weakened rapidly by the time it pivoted fully into Clay/Jackson counties as things rapidly refocused up into eastern Iowa and Wisconsin. Friday's GFS runs actually did quite well with this system, though underestimating the heavy/convective snows from ICT to STJ.

[Bob Johnson]

It was 51 degrees at 1am and now its 15 degrees. It currently has gotten colder. Currently seeing flurries but what a big temp difference from 1am to 11am.

[Joel Wright]

I see an 88mph wind gust was reported in Chicago. http://www.weather.gov/view/prodsByState.php?state=IL&prodtype=public

Simply an amazing, yet very fast moving little storm.

[Mike Pohlen]

I picked up about 2" here. MSP Int'l closed for about 45 minutes today due to the inclement weather, and about 60 flights were canceled. Minneapolis has declared a snow emergency with all of the blowing snow, and I have about a two foot drift up against my garage with absolutely none on my driveway. Makes for easy shoveling.

[Darrin Rasberry]

Superfail for Ames on this one.

We were forecast for tons of snow last weekend. We got a trace of dry snow.

We've been covered in snow since the beginning of December, and haven't had an above-freezing day since the day before this monster stunk up the Midwest. Of course, the day before it was around 42, generously melting all the soft snow into sludge, and when the storm passed, it gave us a miss, putting us into freezing and thus making all the snow-sludge into a huge, encompassing block of ice, not to mention all the black ice all over the roads from the melt drainage the day before. Then came the light dust-dry snow that covered the black ice and blew around in huge, powdery gales my friend said were sometimes called "ghosts" or "wisps." To this Texas boy it looked like a friggin' crack factory exploded.

We've since had another melt and another freeze, but this morning saw a gracious layer of snow added, making things *somewhat* less slippery, especially the walk to the billbox (i.e. mailbox to most other humans).