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WINTER STORM FCST 11/30/07-12/02/07: IA, NE, SD, MN, MI, WI, IL

I am definately liking the forecast for my area now. DSM says this could turn into an 'EXTREME ICE STORM EVENT' for nothern Iowa with pws pushing record values...YEE HAW!!

I hope the hastings forcaster is right and we get even HIGHER winds...will be a distructive ice storm for me I believe.

What I do not understand and maybe someone can explain to me is DSM did not put anyone north of hwy 30 in the Ice storm warning but has Northern Iowa getting almost twice as much ice as the south?? That does not make any sense to me?! Besides that the southern 1/3rd of the state is to raise above freezing!
 
I am definately liking the forecast for my area now. DSM says this could turn into an 'EXTREME ICE STORM EVENT' for nothern Iowa with pws pushing record values...YEE HAW!!

I hope the hastings forcaster is right and we get even HIGHER winds...will be a distructive ice storm for me I believe.

What I do not understand and maybe someone can explain to me is DSM did not put anyone north of hwy 30 in the Ice storm warning but has Northern Iowa getting almost twice as much ice as the south?? That does not make any sense to me?! Besides that the southern 1/3rd of the state is to raise above freezing!

The northern part of Iowa will experience heavy ice accumulations but will also experience significant snowfall accumulations. This justifies the Winter Storm Warning instead of an Ice Storm Warning for that part of the state. The Ice Storm Warning is issued for areas that will receive almost pure ice of sleet or freezing rain forms.
 
I'm guessing the reasoning is more likely due to timing. Just like ne KS and nw KS got an ice storm warning issued earlier today...and now we have been upgraded to it here. It won't be in northern Iowa till later than it will the other areas outlined. Just a guess.
 
Nebraska forecasters have declared a Crap Your Pants alert:

ohcrap.png
 
I suppose LOT is waiting a little longer into the event to decide what to do for the CHI-Metro. NW counties in WSWarn while ILX placed nearly all of the counties north of I 72 in ISWarn. That lake throwing curve balls into the forecast again no doubt. Southeast winds still blowing over "warm" lake waters into the city and north-side might spell all rain or no significant icing.
 
The DVN area has gone with an icestorm warning as well. The real key is the sleet aspect. This thing is going to be almost impossible to forecast until we start seeing some observations late tonight and early tomorrow. Hopefully this thing is loaded with sleet to cutdown on the glazing. Personally, I don't want to lose power.

Looks like the southern half of MN could get a real big snow. Maybe into eastern South Dakota too.
 
Well as a few others have touched on....it appears we are in for a major ice event up here in Northern IA. DMX is calling for up to .7 inches of ice and that is after 3-5 inches going with a more ETA solution. Hoping to not lose power, will try to post some updates on Sat.
 
Looks like extreme N.IL is in for a mixed bag. Typically up here we end up with a mix of all three or all snow. Rarely have seen a significant ICE STORM in RFD. due to being in the slightly colder air. Timing and a couple degrees will mean everything. Mixed frozen precip and a slight glaze sound like the thing here.Down in the Ice storm warning area though I would be worried about losing power..that looks like a wicked ice storm set up.
I'll post on Sat when some significant precip moves in here..
Not too worried here but Good luck to you all in the Ice Storm warned areas..
Interesting to see how this pans out as far as precip type goes.
 
I'm going with the pure snow/mix line staying just south of Minneapolis, and therefore with varying ratios as suggested by the NWS/FAA liquid to snow tables and the Kuchera method, i'm going with 12-16" of snow for the Twin Cities from the 18z NAM and GFS.

Looks like snowfall rates around 2" an hour between 3pm and 6pm on Saturday here.

PS... I posted earlier about not agreeing with what appeared to be a rain/snow line in the Kuchera maps on Earl Barker's site. I still maintain there's something goofy there, but now it appears the line is too far north in my opinion... IE more snow on the southern sides of the snow band than what is depicted, maybe by 30 miles or so... but I'm probably getting picky here, and perhaps detail is lost in image rendering too. So I'll shut up.

Also regarding a post with the significant ice event in Iowa... I would agree that the reason for the winter storm warning is because of the involvement of snow along with the ice... I am guessing 2-4" of snow across northern Iowa in addition to the freezing rain.

Good luck everyone! Put sand bags in your pickups, use 4 wheel drive, ESP and anything else you got. Keep your chase vehicles in one piece for when this crap melts.
 
Damn. Anyone notice the 925mb winds tomorrow? NAM is forecasting 50+kts at 00z in the cornbelt. That's insane. That's only a few thousand feet up. At 850mb winds are over 60kts! There could be some very high wind gusts tomorrow in the midst of some serious glazing. This could make even a somewhat marginal glaze MUCH worse. Definitely going to have to watch that.

The RAP NAM precip model shows quite a wide band of sleet much of the day tomorrow. I'm kind of wondering how accurate that is. That sure seems like a wide band of sleet. Usually sleet is sort of a transitional precip type that doesn't last all that long. (Unless you're positioned in an area where the storm is sort of pivoting around you.) So I'm questioning how much of that band could be just plain freezing rain, or, freezing rain with just a bit of sleet mixed in, in spots. Hmmm.


It's sure going to be cool to watch this thing unfold. In my particular area, looks like snow will begin around 11am. That may whiten the ground a bit before the sleet moves in by early afternoon. Depending on which model you look at, it looks like freezing rain should fall in my immediate area for 3 to as much as 6 hours. What's really interesting is that temps may eventually spike above 40° as midnight approaches. All the while winds will be howling.

I'll try to post some updates in the future NOW thread tomorrow as things unfold. Maybe post a few pics if anything interesting occurs. Hopefully all of us will retain our electricity so we can track this baby as it unfolds tomorrow! :)
 
Winter Storm FCST: Central and Eastern IA

Specific forecasts for eastern and central IA.

All locations in central and east central IA can expect 1" of snow on Saturday, 0.25"-0.5" of ice accumulation on Saturday, and then 1" or less of additional snow on Sunday. The following are forecasts for specific locations:

Ames:
Snow will start at 8:15 AM Saturday, change to sleet at 10 AM, freezing rain at
12:30 PM, (liquid) rain at 4:15 PM, and then back to light snow around noon on Sunday.
Snow will end by Sunday afternoon.

Cedar Rapids:
Snow will start at 10:15 AM Saturday, change to sleet at 11:30 AM, freezing rain at 1 PM, (liquid) rain at 7 PM, and then back to light snow around noon on Sunday. Snow will end by early evening on Sunday.

Iowa City:
Snow will start at 10:00 AM Saturday, change to sleet at 11:15 AM, freezing rain with occasional thunder and lightning at noon, (liquid) rain at 6 PM, and then back to light snow around noon on Sunday. Snow will end by early evening on Sunday.

Marengo:
Snow will start at 9:45 AM Saturday, change to sleet at 11:00 AM, freezing rain with occasional thunder and lightning at 11:45, (liquid) rain at 6 PM, and then back to light snow around noon on Sunday. Snow will end by early evening on Sunday.

Synopsis:
Visible satellite imagery clearly showed a plume of moisture in the form of an ST deck surging N into WRN KS and SERN CO, along with an impressive subtropical plume in the SWRN CONUS. Upstream PW/S were 1 inch per 00Z KOUN and KAMA soundings, and 0.5 inches on KDDC and KTOP, which is well above normal. Looking at guidance; the NAM, which had trended slower and further S then the consensus (GFS, UKMET) on earlier runs, now is in better agreement. Earlier discrepancies were associated with sampling of ULVL energy in the PAC NW and BAJA areas, and with the SFC reflections beneath phasing ULVL energy.

Discussion:
WRN CONUS trough will phase with system in the BAJA area, and move slowly EWD and flatten slightly while a lead 90kt H5 jetlet races from NM towards SERN IA Saturday afternoon. Precipitation will rapidly develop in a region of strong isentropic up glide on 290K-300K SFCS, frontogenetic forcing along the NRN edge of precipitation, and weak elevated CAPE as a 60kt LLJ noses into IL/ ERN IA. Kinimatic forcing increases towards 00Z with the approach H5 streak left-exit region. Given the impressive moisture feed for this system, precipitation amounts may be underdone, especially in areas receiving convection. During the day Sunday, the primary H5 S/WV will race E from CO towards the WRN Great Lakes. Precipitation will be concentrated along a deformation zone axis extending from NWRN IA into WI. The ULVL system should maintain precipitation for a longer period then most MDLS suggest for QPF.

The all important question is the type and timing of winter precipitation that will fall. Prior to the onset of precipitation, a very cold and dry polar airmass will be entrenched over the NERN 2/3rds of IA. Top-down saturation of the atmosphere will take place, with SFC-3km temperatures falling over five degrees F owing to evaporative cooling. Very strong WAA will commence at the nose of a 55kt H925 LLJ, bringing the 0C isotherm to a line bisecting IA from NW to SE by 00Z Sunday. NAM is probably too cool with SFC-3km temperature fields given strength of WAA, and so sided with the GFS for LLVL fields. Another issue will be with gusty winds Saturday afternoon/evening as 60kt LLJ rides just above inversion, and perturbations may provide for momentum transfer to the SFC resulting in gusts in excess of 40 MPH.

- bill
[FONT=&quot]9:23 PM CST, 11/30/07[/FONT]
 
NOTED FROM FSD:

WELL...SOUNDINGS ARE IN AND ONE THING JUMPS OUT RIGHT AWAY. BOTH DDC
AND LBF ARE MUCH DRIER THAN THE 18Z NAM/GFS INIDICATED IN THE
700-550MB LAYER. SO THE QUESTION IS...WILL THIS BE A HELP OR A
HINDERENCE. GENERALLY...LESS MOISTURE IS BAD. IT EITHER MEANS THINGS
WILL BE SLOWER OR PRECIPITATION AMOUNTS WILL BE LESS. BUT...IN THIS
CASE...WITH MUCH OF THE FOCUS FOR PRECIPITATION DEVELOPMENT COMING
IN THE 850-750MB LAYER...THIS COOLER AIR MAY IN TURN AID IN
INCREASING INSTABILITY.

IF THE WARM SECTOR DOES IN FACT COME IN A
COUPLE OF DEGREES COOLER THAN PREVIOUSLY THOUGHT...WE COULD END UP
WITH MOSTLY SLEET...AND QUITE A BIT TO BOOT. MODELS CONSISTENTLY
SPITTING OUT ABOUT THREE QUARTERS OF AN INCH TO AN INCH OF QPF AND
IF EVEN HALF OF THIS IS SLEET...WE ARE LOOKING AT ABOUT 1 TO 2
INCHES OF SLEET.

Pretty significant changes with much drier air than NAM/GFS indicated.

ALL bets are off.
 
Here’s my snowfall forecast map based off of 00z NAM data.
This is storm total snowfall accumulations.

[This is not yet a feature in F5, but coming in future upgrades]

eta00z12012007.png
 
Oz WRF holds onto precip over IL all the way into Sunday Night, surface temps are to be below freezing, so we will likely switch back to snow. The GFS has not moved further south really, but it and the WRF appear to have pulled the highest precip values further north...
 
I'm a bit baffled by the local Minneapolis news casts. They still want to work in ice in the Twin Cities. I must not be as smart as I think I am because I just don't see it. Maybe they are playing it safe because the line will be close.

For Minneapolis from TV stations at 10pm newscast:
WCCO (Paul Douglas) calling for 4-8"
KMSP calling for 8-12"
KSTP (Dave Dahl) calling for about 6-10"
KARE (Sven Sundgaard) calling for 4-8" by 6pm with more after that, so lets say 8"
NWS calling for 10"

I think 12-16" is a fair forecast.

I'm sure I'll be eating crow. Sounds like a lot of snow. I'm going to pull apart some point soundings from GFS and see if I overlooked something there.
 
Well at 30 hours there is a brief period above freezing. Removing the time period above freezing from the equation I'm still calculating out 11-17" of snow from GFS over Minneapolis.

Here's a question for ya...

We've discussed the wet bulb or warmest wet bulb rules... I think Mike Umschied mentioned he prefers to use the environmental temperature... when looking at model data, the models produce precipitation and therefore shouldn't they already be lowering the environmental temperature appropriately, and therefore looking at the wet bulb temperature in model graphics is attempting to reduce the temperature twice?

Or do you still look at the wet bulb of the cooled model air because it's not capturing the actual cloud physics and just the air "around the cloud"

???
 
OAX mentions the DDC/LBF moisture progs (that Jeff noted above) and says:
THERE WERE SOME DISCREPANCIES IN MOISTURE PROGS OVER
THE HIGH PLAINS...ESPECIALLY ABOVE 700MB...WHEN COMPARING 00Z NAM
AND DDC/LBF SOUNDINGS. HOWEVER ABUNDANT MOISTURE WAS DEPICTED ON
UPPER AIR CHARTS AND SATELLITE IMAGERY JUST TO THE WEST OF THESE
AREAS...AND THINK REALITY WILL CATCH UP WITH MODEL FORECASTS IN
THIS REGARD. UPPER TROUGH WAS STILL ROLLING INTO THE SOUTHWESTERN
U.S. WITH 120M HEIGHT FALLS NOTED IN SOUTHERN CALIFORNIA.
IMPRESSIVE TROPICAL MOISTURE PLUME WAS SURGING NORTH AND NORTHEAST
AHEAD OF THIS SYSTEM AS PER WATER VAPOR IMAGERY...AND IS ON TRACK
TO OVERSPREAD EASTERN NEBRASKA LATE TONIGHT. BROAD SCALE ASCENT
WILL BEGIN IN OUR AREA AFTER MIDNIGHT IN DIFFLUENT UPPER
FLOW...INDUCING STRONG CYCLOGENESIS IN THE CENTRAL ROCKIES.
INCREASING SOUTHERLY FLOW WILL PUMP LOW LEVEL MOISTURE NORTH AHEAD
OF THIS SYSTEM...AND STRONG ISENTROPIC UPGLIDE WILL ENSUE LATE
TONIGHT. 00Z NAM IS JUST A TAD SLOWER IN BREAKING OUT
PRECIPITATION OVER THE CWA...

GID has been silent since 5:55 PM CST (probably because they are quite busy puzzling this one out). All I can add is, "that's one heck of a trough coming this way!
 
Here's a question for ya...

We've discussed the wet bulb or warmest wet bulb rules... I think Mike Umschied mentioned he prefers to use the environmental temperature... when looking at model data, the models produce precipitation and therefore shouldn't they already be lowering the environmental temperature appropriately, and therefore looking at the wet bulb temperature in model graphics is attempting to reduce the temperature twice?

Or do you still look at the wet bulb of the cooled model air because it's not capturing the actual cloud physics and just the air "around the cloud"

???

Yes, when the model generates precipitation, it is in effect "wet-bulbing itself", which is one reason why I use just the model temperature once precipitation starts in the model. Wet bulb temperature is most useful for me at the onset of precipitation, in any layer of the atmosphere, prior to saturation, of course -- but once the model produces precipitation and saturates the column, the model has "wet-bulbed" itself, which is why it's really no different, in my eyes as an operational forecaster, to use ordinary T versus Tw when forecasting precipitation type. Each model has its own precipitation parameterization schemes, but in my experience, the NAM does a better job of "wet-bulbing" model Temperature -- the RUC as well, or at least it is most noticeable in these models due to better resolution.

That said, I've noticed the NAM has a really dry bias on occasion, like near the center of an anticyclone in a very shallow near surface layer, such that when it generates precipitation through this layer, it wet-bulbs the temperature too much, b/c the model was too dry in some arbitrary shallow layer. This is the problem with models and trying to resolve the highly varied distribution of water vapor in the atmosphere, so sometimes when a high resolution model shows -20°C dewpoint, for instance, in reality, that particular level might actually be closer to -5°C, and thus the model would forecast too cool of a temperature at onset of precipitation and subsequent wet-bulb effects. I'm basing most of this on my own experience as a high plains winter wx forecaster :)
 
For what it is worth, this storm has been warmer than predicted in New Mexico. Snow levels thus far have stayed pretty much above 10,000 feet (except in the NE plains, where the air is much drier), versus earlier forecasts of more like 8,000. Hope it comes down tomorrow (as it is forecasted to do, but not sure how much this will occur before the precip lightens as the day goes on), as I am out here in hopes of getting in some decent skiing.

I'm not sure I can ever recall seeing such a widespread, persistent precipitation shield in Arizona - this storm has a ton of tropical moisture to work with. I would think that the warmth combined with the abundant tropical moisture would tend to drive the p-type gradients north, as it has raised the snow levels higher than predicted in NM, but time will tell.
 
watching sfc T trends for Nebraska, northern KS

Thought I would throw out a few tidbits as of 6z regarding guidance vs. reality:

Russell KS: Actual T=30 NWS fcst=28 0z MAV fcst=31 0z MET fcst=31
Hastings NE:Actual T=25 NWS fcst=21 0z MAV fcst=27 0z MET fcst=21
Omaha NE: Actual T=25 NWS fcst=24 0z MAV fcst=24 0z MET fcst=21

Not to make too much out of this...but at least at 6z it would seem that in general...reality seems to be trending at least a few degrees warmer than the NWS forecasts...and 4 degrees warmer than the MET fcsts for HSI and OMA. Up until now, I had thought all along that the GFS was way too warm with the sfc T evolution vs. the colder NAM...but now I am starting to wonder if WAA may be kicking in a little better than I expected.

Taking it one step further...I noticed that the 5z GFS LAMP output had a very good handle on the 6z obs. So looking 9 hours ahead...here is a forecast comparison for 15z:

Russell KS: NWS fcst= 38 LAMP fcst= 41 0z MET fcst=38
Hastings: NWS fcst= 22 LAMP fcst= 36 0z MET fcst=29
Omaha: NWS fcst= 28 LAMP fcst= 33 0z MET fcst=31

Hmm...in this case the GFS LAMP fcsts are anywhere from 3 to 14 degrees warmer than NWS...and even the "cold" MET numbers are 3 to 7 degrees warmer at OMA and HSI. So, bottom line here is that at a quick glance...it appears maybe the WAA may surge north quicker this morning than currently reflected in the NWS grids...which could mean a shorter duration ice/sleet event...especially across northern KS and southern NE. Of course, this is a very simplistic analysis...and does not necessarily account for factors such as substantial cooling from wet-bulbing etc. That being said, its gonna be interesting to see just how close (or far off) these warmer guidance numbers play out and any impact this would have on ice accumulations.

Update at 8z: Sometime around 145am CST very light freezing rain kicked in here in Hastings...with a surprisingly decent little glaze already covering my vehicle. Sidewalks are just starting to show that "feel" of getting slick. At any rate...didn't expect this for at least a few more hours so things may be getting underway a little early. I figured this might start off with some sleet first...but so far just light ZR.
 
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From this mornings Desmoines NWS forecast discussion:

COBB OUTPUT SUGGEST ONE HALF TO ONE INCH
AMOUNTS (of ice) ON TOP OF ANY SNOW WHICH COULD BE QUITE CRIPPLING. ON TOP
OF ALL THE PCPN...EXPECT TIGHT GRADIENT TO PRODUCE AS STRONG
SOUTHEAST WIND WITH GUSTS OF UP TO 35 MPH OR SO WHICH WILL AGGRAVATE
THE SITUATION BY DOWNING POWER LINES AND BREAKING TREE BRANCHES.
WILL CONTINUE TO HIT IT HARD WITH QUARTER TO HALF INCH ICING AMOUNTS
IN THE SOUTH AND HALF TO ONE INCH ACRS THE NORTH. THIS MAY RIVAL
THE FEBRUARY ICE STORM AND CERTAINLY MAY BE MORE WIDESPREAD.

The February ice storm was the worst ice storm that I have ever seen so if this statement pans out :eek: we could truly be facing a VERY serious situation in my area. My next door neighbor has a generator so we will go there when our power gets knocked out to stay warm etc. I have warned all of my friends and family about the potential seriousness of this weather dituation so they too are as prepared as they can be.
 
Well it's only 22 degrees here and we have mostly freezing rain with a tad bit of sleet. DVN says this could rival the ice storm of last year and certainly could be more widespread with more power outages and the like...
YAAY for ice!!
 
Yeah, the 12z models are pretty much unanimously agreeing on a short lived, yet fairly impressive icestorm all across IA into IL. The band from just north of SUX, to Ames/Waterloo IA, to about Clinton IA, on towards Sterling IL look to get the most ice accums. Probably about 1/2", with some local higher amounts.

The latest GFS has a bullseye of 1"+ QPF in a six hour time period this afternoon over northeast IA, into southwest WI, and extreme NW IL. That's very intense for just stratiform precip.

The million dollar question is just how fast will the melting temperatures in MO and SW IA make it north to put an end to the icing. The NAM and RUC look way too cool, keeping the freezing line south of I-80 still at late this afternoon. The GFS is probably closer to reality, yet may be just a bit to bullish in bringing the warm air northward, taking the freeze line well into northern IA by late afternoon. Temps there now are still in the upper teens. I think a compromise of those models is the way to go. The GEM looks way too warm as well, yet it is usually very reliable.

In either case, still a substantial icing event to be sure, yet somewhat short lived...
 
I'd like to point interested people to the NSSL WRF. For the most part, it's usually pretty damn accurate in forecasting radar reflectivity... In this case, it pretty much nailed the 16Z-17Z radar output at the 16-17 hour time step; not too shabby if you ask me.

Quite a widespread area appears to be looking at 0.50 inches of QPF, with many areas approaching one inch or more.

http://www.nssl.noaa.gov/wrf/
 
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