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.