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12/15-12/16 MV/GL snow event?

Thundersnow12

By Thundersnow12,
in Central/Western States

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baroclinic_instability

baroclinic_instability

Posted
Posted

For what it is worth, the UK suggests a farther S storm as well. Then there is the GFS/SREF/CMC consensus. NAM is an outlier as it is south as well but has been heading N lately. Given the large east coast retrograding low and the significant arctic high in place I have to think ECM/UK has a slight better chance of verifying. Of course I don't want that since TC area gets little out of this...

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csnavywx

csnavywx

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The greatest forcing with this storm will be dominated in the low levels in the zone of warm air advection and along the frontal zone which is below 700 hpa. You can in a way see that in the thermal profile of the sounding alone. There will be better thermals heading north into the colder air, but the forcing into the dendritic growth zone will be rather weak. The amount of forced ascent through this zone is key to growth. Snow factors across most areas will not be all that high, prolly 10/12-1 on average.

That's pretty much a neutral-moist/low static stability sounding from 700-550mb, wouldn't take much to make that slightly unstable. Generally speaking, model resolution of warm wedges like that are smoothed when it comes to soundings, so it wouldn't surprise me if that were indeed an unstable layer poking into the DGZ. Layers like that can throw a wrench in ratio/accum. forecasting. Otherwise, that sounding looks extra "rimey".

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baroclinic_instability

baroclinic_instability

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Posted

That's pretty much a neutral-moist/low static stability sounding from 700-550mb, wouldn't take much to make that slightly unstable. Generally speaking, model resolution of warm wedges like that are smoothed when it comes to soundings, so it wouldn't surprise me if that were indeed an unstable layer poking into the DGZ. Layers like that can throw a wrench in ratio/accum. forecasting. Otherwise, that sounding looks extra "rimey".

Yeah true, but Friv said that was over LAF. I guess from that standpoint, the mid level height falls are not too impressive that far E as the upper wave weakens and flattens heading eastward. Seems the greatest dynamic induced height falls are over NE IA with the passing shortwave which would yield some mid-level cooling/destabilization. You make a good point and it seems to match up with sref DGZ over NE Iowa. I think the relatively low prob (50%) is for these exact reasons.

Looks like the SREF guidance has a second region of enhanced DGZ over S. Indiana after 0Z once that low level jet kicks in suggesting some weak elevated convective potential...although this will not all be snow so it is rather moot.

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Chicago WX

Chicago WX

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Posted

If I get anything over an inch then the GFS needs to verify. NAM/ECMWF does me no good.

Per Harry about the 12z Euro:

But seriously.. 12z euro did not budge much on track but did add a little more QPF in IA back up into MN/ND.. 1-3/2-4 in your hood down that way perhaps? The .10+ and greater runs from Chicago to Ft Wayne. Less/nadda north of that line.

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Thundersnow12

Thundersnow12

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AREA FORECAST DISCUSSION...CORRECTED FOR ISSUED BY NWS LA CROSSE

NATIONAL WEATHER SERVICE QUAD CITIES IA IL

ISSUED BY NATIONAL WEATHER SERVICE LA CROSSE WI

247 PM CST TUE DEC 14 2010

DEEP-LAYERED 280-305K ISENTROPIC LIFT ALONG WITH SOME 850-500MB FN CONVERGENCE AND

DIVERGENCE ALOFT AHEAD OF THE SHORTWAVE AND IN RIGHT ENTRANCE REGION

OF ONE JET AND LEFT EXIT REGION OF ANOTHER SPREADS INTO/ACROSS THE

AREA WED/WED NIGHT. STRONGER SIGNAL FOR DEEPEST SATURATION OF THE

COLUMN OVER THE CENTRAL/NORTH PARTS OF THE FCST AREA. WITH THE

INCREASING MODEL CONSENSUS...RAISED SNOW CHANCES WED AFTERNOON TO

THE 60-70 PERCENT RANGE OVER MUCH OF THE CENTRAL/NORTH PARTS OF THE

FCST AREA...THEN TO THE 70-80 PERCENT RANGE FOR MUCH OF THE AREA

WED NIGHT. POTENTIAL FOR 1 TO LOCALLY UP TO 5 INCHES OF SNOW ACROSS

MAINLY THE NORTH/NORTHEAST PARTS OF THE FCST AREA FROM LATE WED

THRU THU MORNING BEFORE THE LIFT WEAKENS/MOVES OFF. STILL PLENTY OF

MODEL DIFFERENCES ON SNOW AMOUNTS WITH THIS SYSTEM. IF PRESENT

TRENDS CONTINUE TOWARD SOMETHING SIMILAR TO THE 14.09Z-15Z SREF

MEANS...A WINTER WEATHER ADVISORY WOULD BE NEEDED FOR PORTIONS OF

THE FCST AREA...MAINLY ALONG/NORTHEAST OF A KCID-KMLI LINE. LEFT

HEADLINE DECISIONS TO MID CREW...WHICH WILL HAVE ANOTHER SET OF

MODEL RUNS AND SOME OF THE LOCAL/REGIONAL WRF MODEL RUNS TO HELP

SORT OUT THE DETAILS/POTENTIAL SNOW AMOUNTS.

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baroclinic_instability

baroclinic_instability

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MPX saying 2.5-4.5 for the southwest burbs. i'm supposed to land at msp around 930pm tomorrow... we'll see if that holds up.

nice long afd here:

http://forecast.weat...on=1&glossary=1

thinking 13 or 16 to 1 ratios. we just might pull a WWA out of this.

I dont think we will get in on that high of snow factors, but I do think SW burbs have a good chance to get in on a winter weather advisory possibly extending TC wide. Either way you look solid for snow for your return trip to MN Snowman.gif

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