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Texas Winter Storm January 9, 2012


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MESOSCALE DISCUSSION 0009

NWS STORM PREDICTION CENTER NORMAN OK

0651 AM CST MON JAN 09 2012

AREAS AFFECTED...PORTIONS W TX.

CONCERNING...HEAVY SNOW

VALID 091251Z - 091745Z

RAIN-SNOW TRANSITION HAS BEGUN OVER LOWER PECOS REGION GENERALLY

FROM INK-FST. PRIND RATES WILL INCREASE TO 1-2 INCHES/HOUR IN

INCREASINGLY WELL-ORGANIZED PRECIP BAND INITIALLY EXTENDING FROM WRN

PECOS COUNTY NWD OVER WINKLER COUNTY. EMBEDDED TSTMS WILL OFFER

LOCALIZED/BRIEF RATES ABOVE 2 INCHES/HOUR.

SNOW AREA SHOULD PIVOT CYCLONICALLY IN KEEPING WITH EWD SHIFT OF

MID-UPPER LOW...WHILE EXPANDING IN COVERAGE BENEATH ELEVATED MOIST

CONVEYOR. THIS WILL OCCUR AS STRONGEST DEEP-LAYER ASCENT WITHIN

OPTIMAL DENDRITIC-GROWTH LAYER MOVES ACROSS REGION. EXPECT INCREASE

IN SNOW RATES OVER MAF AREA AND NWD/NEWD TOWARD PORTIONS

GARZA/LYNN/TERRY COUNTIES...WHILE HEAVY SNOW AREA SNOW

EXPANDS/SHIFTS EWD ACROSS PORTIONS PECOS/CROCKETT/REAGAN/

GLASSCOCK/HOWARD COUNTIES THROUGH 16Z. SFC TEMPS WILL CONTINUE TO

DECREASE THROUGH MID-LOW 30S F FROM W-E...FROM COMBINATION OF

BOUNDARY-LAYER CAA...WEAK WET-BULB COOLING...AND COLUMNAR DYNAMIC

COOLING. MEANWHILE RELATIVE WARM LAYER BETWEEN 700-800 MB WILL

CONTINUE TO COOL...WHILE RH INCREASES WITHIN DENDRITIC GROWTH COLUMN

AS WELL. THESE PROCESSES WILL FOSTER RAIN-SNOW CHANGEOVER IN ERN

PARTS OF DISCUSSION AREA...AND MAINTAIN SNOW AS DOMINANT

WINTER-PRECIP PHASE. OBSERVED 12Z MAF SOUNDING AND MODIFIED RUC

FCST SOUNDINGS INDICATE THIS TREND...AS WELL AS SUFFICIENTLY STEEP

MIDLEVEL LAPSE RATES TO SUPPORT MUCAPE 100-300 J/KG ROOTED NEAR 700

MB AND EXTENDING INTO ICING LAYERS SUITABLE FOR LTG GENERATION.

THEREFORE OCNL THUNDERSNOW IS EXPECTED OVER MORE OF AREA...WITH LTG

ALREADY DETECTED BETWEEN MAF-FST.

..EDWARDS.. 01/09/2012

ATTN...WFO...SJT...LUB...MAF...

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We've already had nearly 4 inches of rain is some areas in SE TX. Training/rotating storms with several TOR Warnings already and some damage reports out of the Bryan/College Station area...

MESOSCALE DISCUSSION 0008

NWS STORM PREDICTION CENTER NORMAN OK

0559 AM CST MON JAN 09 2012

AREAS AFFECTED...PORTIONS S-CENTRAL TX...MIDDLE-UPPER TX COASTAL

PLAIN...SWRN LA.

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 091159Z - 091430Z

CONVECTIVE REGIME DISCUSSED IN EARLIER MESOSCALE DISCUSSION 7 IS

UNDERGOING EWD AND COASTWARD SHIFTS IN GEOGRAPHY AND AMIDST GEN

INCREASE IN TSTM COVERAGE...HOWEVER OVERALL SVR THREAT APPEARS TOO

MRGL/ISOLATED FOR WW ATTM. STILL...THREAT FOR A TORNADO AND/OR

ISOLATED DAMAGING GUST IS NONZERO...AND EXPECTED TO CONTINUE THROUGH

REMAINDER EARLY-MID MORNING WITH SLOW SHIFT EWD OVER AREA.

FURTHERMORE...MID-UPPER LEVEL CYCLONE OVER NRN CHIHUAHUA APPEARS TO

HAVE BEGUN ITS EWD TURN AS PROGGED. AS RELATED FIELDS OF MID-LEVEL

DESTABILIZATION SHIFT EWD...LAPSE RATES AWAY FROM ANTECEDENT TSTMS

SHOULD INCREASE THROUGH REMAINDER MORNING...FROM W-E...WHILE

FAVORABLE DEEP-LAYER SHEAR IS MAINTAINED. AS SUCH...HAIL WILL

BECOME MORE PROBABLE ON EITHER SIDE OF SFC FRONT...SIZES BEING

PRIMARILY SUBSEVERE TO ISOLATED MRGL-SVR BASED ON SOUNDING ANALOGS

AND OUTPUT FROM 2-D HAIL MODEL.

1130Z SFC MESOANALYSIS SHOWED QUASISTATIONARY FRONTAL ZONE FROM

CENTRAL/NRN LA SWWD THROUGH INFLECTION POINT OVER HOUSTON/WALKER

COUNTIES TX...CORRESPONDING CLOSELY TO MESOCYCLONE OF POTENTIALLY

SVR TSTM THERE. FRONT EFFECTIVELY HAS BEEN SHUNTED SOUTHWARD BY

CUMULATIVE OUTFLOW FARTHER SW...PRODUCED BY INCREASINGLY DENSE BAND

OF TSTMS...AND WAS EVIDENT ACROSS PORTIONS GRIMES/COLORADO/KARNES

COUNTIES. FRONT THEN ARCHED THROUGH WAVE LOW THAT HAS MOVED ENEWD

FROM MEX...TO NEAR COT. EXPECT MOST OF FRONT TO SHIFT SEWD THROUGH

REMAINDER MORNING TOWARD COAST...AIDED ON MESOBETA SCALE BY TSTM

OUTFLOW. THIS WILL SHRINK THAT PORTION OF WARM SECTOR CONTAINING

EFFECTIVELY SFC-BASED PARCELS...WITH MLCAPE RANGING FROM AROUND 250

J/KG OVER SWRN LA TO AROUND 1000 J/KG ALONG MIDDLE TX COAST.

PROFILER/VWP DATA INDICATE EFFECTIVE SHEAR AND SRH EACH HAVE

DECREASED SOMEWHAT SINCE 07Z IN RESPONSE TO SOME WEAKENING/VEERING

OF LOW-LEVEL FLOW...BUT STILL REMAIN FAVORABLE FOR OCNL SUPERCELL

ORGANIZATION. STRONGEST LOW-LEVEL MESOCYCLONES AND POTENTIAL FOR A

TORNADO SHOULD BE INVOF FRONT. WITH WEAK CINH...EXPECT OVERALL

INCREASE IN TSTM COVERAGE TO CONTINUE. WITH TIME...THIS WILL

FURTHER COMPLICATE CONVECTIVE MODES...WITH CLUSTERED AND

QUASI-LINEAR STRUCTURES BECOMING MORE PREVALENT.

..EDWARDS.. 01/09/2012

ATTN...WFO...LCH...SHV...HGX...CRP...EWX...

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