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

[Jeff Miller]

I'm not certain of the procedure in this new forum for winter storm forecasting. The rules seem to be much more lax since this is not a part of Target Area, but many are used to the format so I will follow that in here for now unless more direction is provided.

The GFS 12Z run and latest Ensembles are both projecting at the least a significant winter weather event for a good part of the Northern Plains and upper midwest this weekend. The model path is subject to great change, and the next 48 hours will be critical to exact path and strength.

Ensembles are painting a greater than 90% Categorical POP for snow - and GFS is now painting on the 12Z run a 993 low over central Kansas.

Ensembles:
http://www.emc.ncep.noaa.gov/gmb/ens/fcsts/ensframe.html

This low is then forecast to rapidly deepen over Central lower Michigan to an impressive 986 low - with a 125kt Jet Stream fueling the storm. Ensembles are also in great agreement with a large storm developing this weekend as well. This storm could have all varieties of severe winter weather with snow, wind, and freezing rain looking quite likely.

We have 3 to 4 days until cyclogenesis - but it's looking better on this run so the official winter storm forecast begins.

http://rap.ucar.edu/weather/model/gfs132hr_sfc_mslp.gif
http://rap.ucar.edu/weather/model/gfs108hr_sfc_prcp.gif
http://rap.ucar.edu/weather/model/gfs108hr_250_wnd.gif



Here is the 108 Precip total snowfall accumulation potential as of latest run:

 

[Mike Hollingshead]

http://rap.ucar.edu/weather/model/gfs102hr_sfc_prcp.gif

http://www.rap.ucar.edu/weather/model/gfs102hr_sfc_ptyp.gif

Could be a fun event if it can slow down some and move slower. I had only looked at RAP's 12 hr interval prog's of 6 hr precip and wasn't thinking much of it till I saw your snow total map. I was like, what the hell. Guess the system likes the 6 hr off intervals...as seen above most comes in that time frame. The rest in the other one.

http://rap.ucar.edu/weather/model/gfs114hr_sfc_prcp.gif

http://www.rap.ucar.edu/weather/model/gfs114hr_sfc_ptyp.gif

Looks like it wants some of that freezing rain to change to rain Saturday evening. It seems often the cold air is thicker than prog'd and it's less likely to change to rain in the central US. But maybe I'm thinking of more inverted trough situations and this more e-w setup may be more likely to warm some as shown.

Too bad it's so many days out, as I like it just how it is for us right now. Looks like later in the period there may be quite the LES event, while at the same time the west coast gets hammered.

Will be fun to see if a severe icing event unfolds around here this weekend(looks like gfs is showing around an inch of that stuff near here).

Edit: Nevermind. I kept thinking red was freezing rain, but it is sleet. An inch of sleet would be the worst case scenario! BORING.

 

[rdale]

I'm much more comfortable with the GFS today than yesterday when it did that funky low-pressure split over eastern TN. That would have been a big ice event, but just looked unrealistic.

ECMWF certainly MUCH colder and stormy for the Great Lakes. GEM has similar low track but warmer.

 

[Dan Robinson]

The GFS is painting quite the arctic air intrusion - subzero temps in Wisconsin by Tuesday morning. Ptypes should easily be all snow with this system by the end of the weekend. Wind fields look great for LES and upslope in PA-WV-OH-NY through Wednesday.

 

[rdale]

The last thing I'd ever believe on GFS is a cold snap at long-ranges... ECMWF offers support, but this is the first run it's done that so I'm still not too excited.

 

[Dan Robinson]

Very true. I don't expect the full brunt of what it's showing, but with such a strong cold signal I have more confidence in at least getting everything frozen by Monday night.

 

[Jeff Miller]

I want to mention some reasoning from DDC. It appears that precipitation type could be a serious concern with this clear down toward the OK border in Kansas with the prospects of freezing precipitation or a downright chaotic wintery mix.

THE COMBINATION OF INCREASED
MOISTURE, COLD SURFACE TEMPERATURES AND WARMER TEMPERATURES ALOFT
COULD CREATE AN ICY SCENARIO ACROSS PORTIONS OF SOUTHWEST KANSAS
THIS WEEKEND. ISENTROPIC LIFT IS IMPRESSIVE WITH 5-7 G/KG SPECIFIC
HUMIDITY VALUES ACROSS THE BULK OF THE FA SATURDAY. 06Z GFS
CONTINUES TO POINT TO THE WARM FRONT LYING ACROSS THE KS/OK BORDER
WHILE THE 12Z GFS IS NOT TAKING THE WARM FRONT WELL INTO NE. THE 00Z
ECMWF LIFTS THE WARM FRONT FURTHER NORTH INTO NE. THIS WILL BE AN
INTERESTING STORM TO KEEP AN EYE ON OVER THE NEXT COUPLE OF DAY.
PRECIP ACROSS SOUTHWEST KANSAS APPEARS LIKE A GOOD BET BUT PRECIP
TYPE IS A HUGE QUESTION AT THIS POINT. ACROSS THE NORTHERN FA,
TEMPERATURES SHOULD BE COLD ENOUGH TO PROVIDE FREEZING RAIN OR SNOW
FOR MUCH OF THE EVENT WHILE ACROSS THE SOUTHERN FA, NEAR THE OK
BORDER, RAIN OR FREEZING RAIN LOOKS LIKE THE DOMINATE PRECIP TYPE.
AREAS IN THE MIDDLE FA COULD BE A MIXED BAG OF RAIN, FREEZING RAIN,
SLEET AND/OR SNOW. FOR NOW, WILL BUMP UP POPS SATURDAY AND CHANGE
PRECIP TYPE TO ACCOUNT FOR COLDER AIR NORTH AND WARMER AIR SOUTH.

Des Moines reasoning in this early point is clarifying the confusion as central Iowa as well could see at least a period of freezing rain and sleet - but is not discounting that it could change to snow earlier should the cold air swing around earlier than anticipated.

Kansas City also brings across a very important point:

ALSO AM NOT CONVINCED OF THE NICE AND CLEAN PHASING THE MODELS
SUGGEST LATE THIS WEEK. FIRST CONCERN IS IF AND WHEN THE UPPER LOW
OFF THE BAJA COAST EJECTS NORTHEAST. THIS FEATURE WILL LIKELY HAVE A
SIGNIFICANT IMPACT ON THE TIMING AND TRACK OF THE SFC LOW THIS
WEEKEND. WITH THE LATEST MODEL GUIDANCE SUGGESTING A MUCH WARMER
SCENARIO FOR THIS WEEKEND...WILL BEGIN TO HEDGE TOWARD THAT DIRECTION AND AWAIT FUTURE GUIDANCE.

And as a note of humor, don't you love it when NWS uses the term "Interesting storm"? That always seems to get my attention!

 

[Brandon Sullivan]

Looks like at this time, big accums may stay north of me. im trying to watch the thermal profiles to see where the frz line is gna be... Dec 1st last year we had 12 inches overnight preceeded by .5 inches of ice.. I think it would be weird but cool to have 2 "December 1sts"

And as a note of humor, don't you love it when NWS uses the term "Interesting storm"? That always seems to get my attention!

I also love this wording too.. From DVN

CONCERN IS COLD AIR WILL BE IN PLACE OF ARCTIC
ORIGIN FOR ICE AS STRONG WAA KICKS IN. INSPECTION OF ANOMALIES SHOWS 2 UPWARDS
TO NEAR 4 SIGMA.../90 TO 99 PERCENT STRENGTH/ OVER FORECAST REGION
WHICH SUPPORTS STRONG TO NEAR RECORD STRENGTH SYSTEM.

 

[Jeff Miller]

Question for those knowledgable with relation to this system:

Is this SIGMA referring to SIGMA Theta or SIGMA the [SIZE=-1]System of Icing Geographic identification in Meteorology? And with that said, how does this point to a record storm.

Davenport states:

[/SIZE]
VOLATILE AND VERY DYNAMIC...A CHANGEABLE PATTERN CAUSING SIGNIFICANT
MODEL ISSUES THROUGH PERIOD. THIS CULMINATES WITH A STRONG TO VERY
STRONG...POTENTIALLY NEAR RECORD WINTER STORM THIS WEEKEND INTO EARLY
NEXT WEEK...

ECMWF IS STRONGEST WITH INTENSE
SYSTEM...GFS...VERY STRONG AND UKMET JUST STRONG. UPDATED HWO FOR
CERTAINTY OF SIGNIFICANT WINTER WEATHER WITH GREATEST RISK NW OF A
SQI TO OTM LINE. CONCERN IS COLD AIR WILL BE IN PLACE OF ARCTIC
ORIGIN FOR ICE AS STRONG WAA KICKS IN. THIS RISK SHOULD BE CLARIFIED
NEXT 24-36 HOURS. HAVE UPPED POPS TO LIKELY TO HIGH CHANCE WITH SNOW
NORTH OF HIGHWAY 30 AND A MIX SOUTH.

For being this early in the system I find it eyebrow-raising for Davenport to use the wording
"Potentially Near Record Winter Storm".

For a city in the Midwest, that's certainly saying a mouthful and a big gamble.

 

[Joel Wright]

Question for those knowledgable with relation to this system:

Is this SIGMA referring to SIGMA Theta or SIGMA the [size=-1]System of Icing Geographic identification in Meteorology? And with that said, how does this point to a record storm.

Davenport states:



For being this early in the system I find it eyebrow-raising for Davenport to use the wording
"Potentially Near Record Winter Storm".

For a city in the Midwest, that's certainly saying a mouthful and a big gamble.

There's a certain forecaster (I won't mention any names) at DVN that notoriously seems to say that a few times each winter. I think he seems to let his excitement for a potential storm system cloud his better judgement sometimes. But, on the other hand, I always like reading his forecasts.

Definitely looks like a very large storm system, with plenty of cold air to work with. Somebody may end up getting a nice snow and or ice this weekend. Maybe one of you guys reading this right now lol. ;-)

 

[Danny Neal]

Skilling here in Chicago seems to be hyping up the storm. He seems to think well get a 1-2-3 punch of snow storm, lake effect snow, then bitter cold. All the models that are provided seem to at least hint at that. GFS if it stays on its current path the next run would in all likelihood inundate Northern IL and Southern WI with 6-10 inches of snow, we are talking over 120 hours here so the certainty is definitely in question. From a personal standpoint I hope this storm is record breaking, nothing I can't stand more than 3 inches of snow then 5 degree temps to follow

 

[Jeff Miller]

00z coming in...

Storm developing stronger and with higher QPF in Nebraska and South Dakota...

http://rap.ucar.edu/weather/model/gfs084hr_sfc_prcp.gif

Also, minimum pressure 3mb lower than the previous run so we have a wetter and stronger solution with the 00z run with what we have right now up to the 108. The overall path looks to be on basic target, but a little faster. How this will play with the overall snowfall/frozen potential has yet to be seen.

A change however is occuring with this run at 108 with the low opening up and weakening once it gets to the Chicago area - same basic path but an obviously weaker solution.

As the model gets back to Michigan - again, no change in path this run, SE Lower Michigan, the low deepens again, and a moderate rain changes to snow and wind over Chicagoland by the 120.

by 132 the low bombs near Toronto with a minimum pressure of 983 and a great deal of light to moderate snow and wind over practically all the Great Lakes!

at 144 we have a tremendous powerhouse of a low with a pressure of 979 and snowshowers and light snow with strong winds continuing over the Great lakes as arctic air rapidly intrudes over the Northern Plains.

So far then with this run, same general path, but some fluctuations in intensity and in timing with higher snowfall accumulations in Nebraska at the onset then first predicted last run at the 12Z.

Here is the latest GFS predicted total snowfall accumulations. This is up to hour 99. Note the increase in total predicted snowfall over the FSD area - some predictions bringing total accumulations to near 16"!

 

[V. Gensini]

Question for those knowledgable with relation to this system:

Is this SIGMA referring to SIGMA Theta or SIGMA the [SIZE=-1]System of Icing Geographic identification in Meteorology? And with that said, how does this point to a record storm.

Jeff:

Sigma is referring to the deviation from the norm. For purposes you probably could care less about Statisticians use standard deviation (sigma) to refer to the deviation of a data set about a mean (average). The 4 sigma category would put the system in the 99th percentile (only 1 percent of storms would rank above it).

Anyway, back to the storm The model differences we are seeing right now are IMHO purely due to the fact that we are not getting good sampling of either systems at the moment! How are the models supposed to resolve these features 100+ hrs out, if they are interpolating data to begin with? Everyone should sit back and let this storm get on shore before making any proclamations! After all, its still 5 days away!

On a side note, I had the pleasure to sit in at DVN today and I must say that there was some disagreement as to what was put in the HWO & AFD. You must remember that these are written solely by one forecaster with little collaboration. (One forecaster working short term, one working long term). Therefore, things such as this should be taken with a grain of salt. Isn't it much more fun to form your own opinion about the storm anyway?

 

[Jeff Miller]

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.

 

[Joel Wright]

Boy it's gonna be a challenging forecast for areas just north of where that surface low tracks. It's showing a period of snow, changing to sleet and freezing rain, and even all rain in areas of northern MO, the southern half of IA, and about the northern half of IL. Some pretty strong warm air advection just off the surface most of the day on Saturday over those areas.

Much of NE, southern SD, the northern half of IA, up into parts of MN and WI may get a lot of snow.

It's interesting the way the storm weakens, and then regains strength again out east.

 

[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.