Major Winter Storm For Much of The W/Central US This Week.

[Dave]

Indianapolis NWS Weather Briefing

http://www.crh.noaa.gov/ind/?n=webbriefing

Surface Maps Tues to Thurs

[Dave]

New thread in USA weather for the tornado - thunderstorm risk in the South due to this winter storm in the plains & great lakes regions.

http://www.storm2k.org/phpbb2/viewtopic.php?f=24&t=107181




MESOSCALE DISCUSSION 2215
NWS STORM PREDICTION CENTER NORMAN OK
1212 PM CST TUE DEC 08 2009

AREAS AFFECTED...PARTS OF LA INTO SWRN AND CENTRAL MS

CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY

VALID 081812Z - 081945Z

SEVERE/TORNADO THREAT CONTINUES TO SLOWLY INCREASE ACROSS THE LOWER
MS VALLEY REGION. A TORNADO WATCH WILL LIKELY BE REQUIRED IN THE
NEXT 1-2 HOURS.

A POWERFUL STORM SYSTEM CONTINUES MOVING OUT OF THE ROCKIES AND INTO
THE CENTRAL U.S. THIS AFTERNOON...WITH STRONG ASCENT -- HIGHLIGHTED
BY STRONG PRESSURE FALLS FROM MO SWD INTO LA ATTM -- CONTINUING TO
OVERSPREAD THE CENTRAL CONUS.

MOST OF THE DEVELOPING CONVECTION REMAINS ELEVATED ATTM FROM NRN LA
NWD...WHERE A COOL/STABLE BOUNDARY LAYER PERSISTS.
HOWEVER...MOISTENING/DESTABILIZING AIRMASS CONTINUES TO SPREAD NWD
WITHIN STRONG SLY LOW-LEVEL FLOW FIELD ACROSS THE LOWER MS VALLEY
REGION...WITH SURFACE LOW DEVELOPMENT UNDERWAY INVOF ERN OK/WRN AR
AND VICINITY. AS MOISTENING/DESTABILIZING CONTINUES...SURFACE-BASED
CONVECTION -- NOW SHOWING INITIAL SIGNS OF DEVELOPMENT OVER SRN LA
-- SHOULD SLOWLY INCREASE WITHIN BROAD ZONE OF WARM ADVECTION OVER
THE LOWER MS VALLEY.

AREA VWPS REVEAL LOW-LEVEL SLYS/SELYS WHICH VEER/INCREASE QUICKLY
WITH HEIGHT...YIELDING FAVORABLE SHEAR FOR ORGANIZED/ROTATING
STORMS. AS AIRMASS CONTINUES TO BECOME MORE SUPPORTIVE OF SUSTAINED
DEEP CONVECTION WITH TIME...AND AS FLOW ALOFT INCREASES WITH THE
APPROACH OF THE UPPER SYSTEM...SUPERCELLS ARE EXPECTED TO EVOLVE
THROUGH THIS AFTERNOON. AS SEVERE/TORNADO POTENTIAL SLOWLY
INCREASES...TORNADO WATCH WILL LIKELY BECOME NECESSARY -- INITIALLY
OVER PARTS OF LA AND INTO CENTRAL AND SRN MS.

..GOSS.. 12/08/2009


ATTN...WFO...JAN...LIX...LCH...SHV...

LAT...LON 30649358 31519321 32079248 32799007 32578967 31108934
30779021 30499250 30649358

[Dave]

MESOSCALE DISCUSSION 2216
NWS STORM PREDICTION CENTER NORMAN OK
1214 PM CST TUE DEC 08 2009

AREAS AFFECTED...PORTIONS OF THE APPALACHIAN MTNS OF ERN WV...WRN
VA/MD

CONCERNING...FREEZING RAIN

VALID 081814Z - 082245Z

AREAS OF FREEZING RAIN WILL LIKELY DEVELOP BY 21Z...WITH
PRECIPITATION RATES INCREASING TO BETWEEN 0.05 TO 0.10 IN/HR TOWARDS
00Z.

MESONET OBSERVATIONS CONFIRM A NARROW CORRIDOR OF SUB-FREEZING
TEMPERATURES PERSISTS ACROSS PORTIONS OF THE APPALACHIAN
MTNS...ROUGHLY CENTERED FROM GARRETT COUNTY MD TO ALLEGHANY COUNTY
VA. 12Z NAM/HI-RES WRF FORECASTS REMAIN TOO SLOW WITH A LARGE PLUME
OF WAA-DRIVEN PRECIPITATION ACROSS THE TN VALLEY. 12Z GFS APPEARS TO
HAVE A BETTER HANDLE ON THIS AREA OF PRECIPITATION EXPANDING NEWD
ACROSS THE CNTRL APPALACHIANS LATER THIS AFTERNOON. THE STRENGTH OF
THE WAA WILL BE FAVORABLE FOR AN INCREASINGLY LARGE WARM NOSE OF
ABOVE-FREEZING TEMPERATURES /AS SAMPLED UPSTREAM BY 12Z BNA RAOB AND
RECENT AMDAR DATA INVOF SDF/...ATOP THE SUB-FREEZING SURFACE LAYER.
ALTHOUGH SLEET APPEARS POSSIBLE...THE DEPTH OF THE SUB-FREEZING
SURFACE LAYER IS LIKELY TO BE RATHER SHALLOW BASED ON FORECAST
SOUNDINGS AND OBSERVED SURFACE TEMPERATURES AOA THE UPPER 20S. THIS
SHOULD SUPPORT FREEZING RAIN AS THE PRIMARY PTYPE.

..GRAMS.. 12/08/2009


...NOTICE...
SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A
SCHEDULED BASIS FROM DECEMBER 1 THROUGH FEBRUARY 28...FOUR
TIMES A DAY...AROUND 00 UTC...06 UTC...12 UTC...AND 18 UTC
FOR SIGNIFICANT SHORT RANGE WINTER WEATHER EVENTS.

ATTN...WFO...CTP...LWX...RNK...PBZ...RLX...

LAT...LON 39407969 39817941 39767893 39007898 38107936 37628011
37718042 38178029 38918000 39407969

[HarlequinBoy]

It's crazy that all of Iowa is under a blizzard warning!

[RL3AO]

Two inches have fallen at my house so far.

[srainhoutx]

Thanks for the updates ai9d. I've been very busy today. Stay Safe All.

[RL3AO]

NWS Twin Cities has extended the blizzard warning and now includes me.

[Siberian Express]

NWS Twin Cities has extended the blizzard warning and now includes me.

Weather radio just went off, for Blizzard conditions/warning. Kinda rare to hear that emergency signal in the Winter time. The NWS is treating this pretty seriously, as they should.

[RL3AO]

NWS Twin Cities has extended the blizzard warning and now includes me.

Weather radio just went off, for Blizzard conditions/warning. Kinda rare to hear that emergency signal in the Winter time. The NWS is treating this pretty seriously, as they should.

Mine too.

I just measured. Around 2.75" so far. No wind yet.

[srainhoutx]

Up to a foot in NE KS now...


0515 PM HEAVY SNOW SCANDIA 39.79N 97.78W
12/08/2009 E12.0 INCH REPUBLIC KS LAW ENFORCEMENT

[Dave]

MESOSCALE DISCUSSION 2219
NWS STORM PREDICTION CENTER NORMAN OK
0600 PM CST TUE DEC 08 2009

AREAS AFFECTED...MUCH OF IA...NRN IL...SERN MN AND SRN-CENTRAL WI

CONCERNING...HEAVY SNOW

VALID 090000Z - 090500Z

SNOWFALL...WITH RATES UP TO 1 IN/HR...IS EXPECTED TO TRANSLATE NEWD
FROM IA INTO PORTIONS OF SERN MN...NRN IL AND SRN-CENTRAL WI THROUGH
06Z.

POWERFUL UPPER LEVEL JET /140 KT 9-10 KM FLOW BASED ON JTN PROFILER
OBSERVATION AT 22Z/ CURRENTLY NOSING ACROSS W TX/OK IS FORECAST TO
INDUCE RAPID DOWNSTREAM RIDGING OVER ONTARIO/QUEBEC DURING THE
NIGHT. THIS WILL LEAD TO A COUPLED JET STRUCTURE AND RESULTANT
STRONG UPPER LEVEL DIVERGENCE/LARGE SCALE ASCENT OVER THE UPPER MS
VALLEY AND GREAT LAKES REGIONS. AS THIS OCCURS...DEEPENING SURFACE
LOW IS FORECAST TO LIFT INTO WRN-CENTRAL IL BY 06Z...WHICH WILL
MAINTAIN SURFACE FREEZING LINE FROM ROUGHLY FAR SERN WI SWWD INTO
SERN IA/NERN MO. MEANWHILE...NORTH OF THE ORGANIZING CYCLONE...LOW
TO MID LEVEL FRONTOGENESIS IS FORECAST TO STRENGTHEN WITHIN WWD
CURVING BRANCH OF WARM CONVEYOR BELT...WHICH WILL MAINTAIN A ZONE OF
MESOSCALE FORCING ACROSS THE REGION AS STRONGER LOW LEVEL WAA SHIFTS
EAST. THE COMBINATION OF A DEEPLY SATURATED ATMOSPHERE AND MODERATE
TO STRONG ASCENT WITHIN THE DENDRITIC GROWTH ZONE WILL RESULT IN THE
POTENTIAL FOR 1 IN/HR SNOWFALL RATES SHIFTING FROM PORTIONS OF
CENTRAL IA TOWARD THE MS RIVER DURING THE 00-03Z TIME PERIOD...AND
THEN FARTHER NEWD INTO SRN-CENTRAL WI BY 06Z. AREAS ALONG THE SRN
FRINGE OF THE DISCUSSION AREA /I.E. SERN IA INTO NWRN-NRN IL/ WILL
EXPERIENCE STRONGER LOW LEVEL WAA THROUGH 03Z...WITH A CHANGE OVER
TO FREEZING RAIN OR RAIN POSSIBLE AS 850 MB WARM NOSE AND SURFACE
FREEZING LINE WAVER ACROSS THE AREA.

..GARNER.. 12/09/2009