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

[V. Gensini]

Vince,

completely understand the model disagreements and poor sampling. I am however impressed with the overall consistency of GFS.

As far as what you say - sit back and let the storm get on shore - what fun is that? I personally enjoy keeping up with the models and forecasting even 3-4 days away. That's the fun of it, Vince Remember, no one's proclaiming anything at this point, just analyzing the data we have and explaining what we see.

I agree 100%!! I was referring to the DVN HWO & AFD Should of made myself clear. Making forecasts on here is one thing, but issuing something like that in a HWO is a different story!

 

[Mike Hollingshead]

http://www.rap.ucar.edu/weather/model/eta84hr_850_wnd.gif

http://www.rap.ucar.edu/weather/model/gfs084hr_850_wnd.gif


Now there's some model agreement! lol Nam is apparently 12+ hours slower.

http://www.rap.ucar.edu/weather/model/eta84hr_500_wnd.gif

http://www.rap.ucar.edu/weather/model/displayMod.php?var=gfs_500_wnd&hours=hr072hr084



Meanwhile, what the hell is that off the west coast? Wish Nebraska got things like that. http://www.rap.ucar.edu/weather/model/gfs120hr_sfc_mslp.gif

 

[Jason McKittrick]

I am excited about the potential for the first major winter storm of the season here in Omaha. As I have been watching the models over the last few days I have identified, what I believe, are important characteristics of this weekends setup.

1. There is a very impressive cold airmass in place accross the northern plains. Highs in parts of ND failed to get out of the single digits today and highs here in Omaha were about 10 degrees cooler than the 24 model forecasts indicated.

2. The Gulf of Mexico is very, very closed right now. There are northerly winds as far south as the Bay of Campici with dewpoints in the 50's over the GoM and near 40 in south Texas. A lot of modification has to occur before good moisture return can be realized.

3. Cut offs definitely tend to take there sweet time ejecting and the GFS has a northerly bias.

4. Most importantly as has already been pointed out these systems are over the Pacific and are poorly sampled. The current model forecasts, while they have been quite consistant they could change dramatically once the energy is sampled which probably won't be until Friday afternoon.

I think that we will probably see some decent accumulating snows across parts of NE and IA however at this point it does not look like a 12+ inch event for anyone, to me, I do however see some serouis ice storm potential.

 

[Michael O'Keeffe]

I think Jason may be right the CPC hazards assessment was issued yesterday and they outlined E Nebraska, most of Iowa, and S Wisconsin/N Illinois under Heavy Snow on Dec 1. While most of Kansas, MO, C IL/IN/OH all the way to W New York could see freezing rain on Dec 1-2.

 

[Brandon Sullivan]

Wow.. I think this system will have a very sharp rain/snow/frz line, and I think that line is going to be very hard to pin down. This does look like a good icing event. I will be interested to see HPC's thoughts tommorow night. Personally, I dont think local gov't/highway dept is ready at all, so this ought to be interesting..

 

[rdale]

I think Jason may be right the CPC hazards assessment was issued yesterday and they outlined E Nebraska, most of Iowa, and S Wisconsin/N Illinois under Heavy Snow on Dec 1. While most of Kansas, MO, C IL/IN/OH all the way to W New York could see freezing rain on Dec 1-2.

Remember that the CPC synopsis is just a general outlook, there's very little "real forecasting" going into that product.

 

[Jeff Miller]

Latest information...

GFS...

GFS continuing heavy QPF over the Central Plains and essentially the same path but a slightly more northern component. This model takes the rain/snow/mix line farther north, and almost has even KSUX in an all rain pattern as warmer air works in according to the model. It also takes the heavier snows farther north into Minnesota and Wisconsin, leaving Minneapolis with close to a foot of snow - thus also leaving cities such as Davenport and Des Moines in the warm sector with just rainfall. ECMWF also in agreement with general path of storm so we have some continuity here with GFS/ECMWF. UKMET just coming onboard with the storm at the 72. Latest total snowfall potential:

NAM...

NAM Model is producing really different results. It is coming in slower and with a farther south solution...much farther south on the 84. NAM is hedging towards a freezing rain/sleet event for areas such as Kansas City and Columbia, MO and Topeka, KS. NAM throws a monkeywrench in the consistency of model runs reducing the certainty of the northern scenarios for sure - but I am discounting for now.

For the time being, due to model discrepencies as expected at this timing, I'm not expecting a lot of change in the forecast with this run with GFS a little farther north with a warmer solution and ETA way south with a colder solution north and a significant ice storm KS/MO... perhaps by tonight things will be a little clearer on exact path/strength/precip type.

The big concencus is the storm itself is looking extremely likely, and the questions are as always on path and precip type/strength.

.

 

[Jeff Miller]

NEW INFORMATION including WFO Early Evening Forecast Reasonings:

According to Hastings NE WFO AFD, the Hastings office is considering issuing a Winter Storm Watch as early as tonight for the FRI-SAT period for snow, freezing rain and sleet accumulations. I'm awaiting to see what the other WFOs will think about that - in my mind, it's a little premature due to the possibility of stronger warm air intrusion than currently indicated.

Omaha is very specific. Specific for NE/IA area according to Omaha reasoning: (This reasoning is for NEBRASKA)

1. Blend of GFS ensemble and SREF mean for forecasting.
2. Confidence is very high, According to Omaha that surface air will remain subfreezing with lack of sunshine and the depth of the airmass Friday Night through Sunday.
3. Strong isentropic lift/Warm air advection should be strong enough to advect over surface based arctic airmass by, at the latest, Saturday afternoon.
4. Convective Slantwise Instability or just Upright Instability will exist along and south of I-80 Sat afternoon and evening with heavy precipitation likely, 1" of liquid precipitation is possible.
5. Two possible scenarios for the winter Precip:
I. Significant icing event if an elevated warm layer exists. This appears to be a threat along and south of I-80 with signigicant snowfall possible north of I-80.
II. Snow in the north and also to the southern counties if NE if warm elevated layer stops short of Beatrice, NE, however heavy snow concerns are if the highest instability doesn't match the highest area of dendretic growth - and also sleet and non-dendretic snowflakes hampering accumulation potential.
6. Winds will be a problem as well with surface gusts of 20-25 MPH.
7. Final analysis is
[FONT=lucida sans typewriter, lucida console, courier]

MUCH OF THE FORECAST
AREA SHOULD SEE A VERY MESSY MIX OF SNOW/SLEET/FREEZING RAIN
COMBINED WITH GUSTY WINDS... OR VERY HEAVY SNOWS COMBINED WITH GUSTY
WINDS.

[/FONT]

 

[Jayson Prentice]

The Des Moines NWS office mentioned how they may begin to put out watches on Thursday night if the run to run consistency can stay good for the next 36 hours or so... Des Moines's currently thinking that their CWA will encounter all modes of the storm, mainly snow north, sleet/frz rain and rain across the central/southern zones.

I took a look via BUFKIT today at the GFS runs from last night and this morning, some fluctuation in how much of a warm air intrusion we will get. But, for here in central Iowa it continues to look like this may be a nice event of snow/frz rain and possibly rain to finish it out?

 

[Mike Hollingshead]

http://weather.cod.edu/forecast/GFS/gfsUS_850_thetae_78.gif

http://weather.cod.edu/forecast/GFS/gfsUS_2_temp_78.gif

Someone's going to get icy, especially with a sort of morning timing going for things too.

http://weather.cod.edu/forecast/GFS/gfsUS_2_temp_60.gif

That air ending the day on Friday, then being rapidly overrun above the sfc front into Saturday morning...fun times. Guessing the sfc warming surging north Saturday is a little overdone. The cold loves to win these battles. Give it a morning go with heavy precip and clouds all day, sure ain't going to do the sfc front any favors in surging north like it wants.

That's really one of the most important factors to a big ice event. Getting the front to stay in one position for a long duration of time. Otherwise each area only gets some of each form. It's when one area gets locked into the freezing rain zone forever things get crazy. That's what happened with last years major ice event in NE and KS. The sfc freezing line did not budge for 2 days, so the same areas kept getting the same precip type. That probably won't happen like that this time, unless the system wants to evolve a bit slower like the nam seems to want. I bet with the cold that will be in place and the system wanting to at least fight it back north, I would guess there'd be a strong tendancy for that wannabe warmfront to stay stationary.

Sort of sucks hoping for a major ice storm when you know it could cause you to be without power for weeks.

 

[Jeff Miller]

Jayson,

I agree with you on the snow/frz rain to rain transition in Central Iowa. I also looked at Davenport's reasoning and they are also thinking of a wintery mix to rain scenario with mainly snow in the northern counties of Iowa. Regardless, I think its fairly certain the rain snow line will set up somewhere from central Nebraska through Central Iowa - with a plethora of winter weather along the transition zones. The question will be how long the shallow cold air will hang on to keep rain freezing or just plain rain in those zones.

 

[Mike Hollingshead]

The Des Moines NWS office mentioned how they may begin to put out watches on Thursday night if the run to run consistency can stay good for the next 36 hours or so... Des Moines's currently thinking that their CWA will encounter all modes of the storm, mainly snow north, sleet/frz rain and rain across the central/southern zones.

I took a look via BUFKIT today at the GFS runs from last night and this morning, some fluctuation in how much of a warm air intrusion we will get. But, for here in central Iowa it continues to look like this may be a nice event of snow/frz rain and possibly rain to finish it out?

Yeah if one looks at the gfs for exactly what it says, it sure wants to change things to rain. My problem with that is, it seems like a rare thing in these parts. Along the ocean, yeah, but here in the plains it seems things rarely change back to rain. I guess they do from time to time though.

Edit: Looks like the 18z gfs is liking you Jeff. http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/namer/gfs/18/images/gfs_p60_084m.gif

This 18z snowfall total out 96 hours should be interesting when it updates(whenever the link ends in 18z not 6z like right now) http://wxcaster4.com/gfs/CONUS2_GFS0P5_SFC_ACCUM-SNOW_96HR.gif Guessing it'll show 12+ over Mr Miller's house, lol. (yeah silly prog's I know, but I'm bored)

 

[rdale]

NEW INFORMATION including WFO Early Evening Forecast Reasonings:

According to Hastings NE WFO AFD, the Hastings office is considering issuing a Winter Storm Watch as early as tonight for the FRI-SAT period for snow, freezing rain and sleet accumulations. I'm awaiting to see what the other WFOs will think about that - in my mind, it's a little premature due to the possibility of stronger warm air intrusion than currently indicated.

Very premature and against NWS regulations... You need at LEAST a 50% chance of meeting warning criteria, and they can only be issued to 48 hours. I struggle believing they'd put 50% odds on the accums, and if my math is correct, Saturday is > 48 hours away :>

 

[Rhyuan Janssen]

Jaysen, I seriously hope we don't wind up with rain at the end, that would bum me out incredibly. IMO I would say we'd wind up with snow at the end due to cold air behind it, but one is never certain.

Rdale, are you serious about the 48 hours thing? Because someone needs to let the NWS office in DSM know because they have issued as far out as 72 hours before.


Sioux Falls seems to think warm front might reach Highway 20 or beyond to the Iowa great lakes, which would not make me happy since I live on 20 just about. However they are trending towards NAM which keeps more cold air in place than GFS and according to La Crosse NAM handles shallow air masses better than GFS does.

At any rate I think someone is headed for a big snow and/or ice event in Iowa

 

[Jeff Miller]

Rhyuan, Welcome to Stormtrack!

In answer to your question, directed at Rdale, I took the liberty of looking up the NWS Directives. This was issued in 2001, so Im not sure if there are any changes...

6.2 Winter Storm Watches. Winter storm watches shall be issued when
conditions are favorable for hazardous winter weather conditions, as defined
in section 4, to develop over part or all of the forecast area, but the
occurrence is still uncertain. Winter storm watches should be issued for the
second, third, or occasionally fourth forecast periods, when the forecaster’s
confidence is 30 percent or greater of a hazardous winter weather event
meeting or exceeding local warning criteria. Watches shall be updated
whenever there is a change in the timing, areal extent, or expected
conditions.
Watches shall be issued via the WSW product category and subsequently
headlined in all appropriate state, zone, and local forecast products. The (Z)
form of the UGC shall be used as described in WSOM Chapter C-63. The MND shall
be "URGENT - WINTER WEATHER MESSAGE."

Therefore, a Winter Storm watch can only be issued up to the fourth forecast period, or 48 hours - but with only a 30% criteria chance according to this document.

Rdale, feel free to correct if I am in error.