Isolated Downbursts/Hail CO/NEB/SD/KS
MESOSCALE DISCUSSION 1800
NWS STORM PREDICTION CENTER NORMAN OK
0348 PM CDT WED AUG 22 2012
AREAS AFFECTED...EASTERN CO/WESTERN NEB/SOUTHERN SD/FAR NORTHWEST KS
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 222048Z - 222245Z
PROBABILITY OF WATCH ISSUANCE...20 PERCENT
SUMMARY...ISOLATED DOWNBURST/SEVERE HAIL POTENTIAL WILL EXIST ACROSS
THE HIGH PLAINS INCLUDING PORTIONS OF EASTERN CO/FAR NORTHWEST KS AS
WELL AS WESTERN NEB INTO SOUTHERN SD. A WATCH IS NOT CURRENTLY
ANTICIPATED AS MARGINAL BUOYANCY/VERTICAL SHEAR SHOULD LIMIT THE
OVERALL EXTENT/DURATION OF THE SEVERE RISK.
DISCUSSION...MUCH OF THE REGION IS UNDER THE SOUTH-PERIPHERAL
INFLUENCE OF A SHORTWAVE TROUGH SPREADING EAST-NORTHEASTWARD OVER
THE NORTHERN HIGH PLAINS AND CANADIAN ROCKIES PER WATER VAPOR
IMAGERY. STEADY LEE TROUGH DEVELOPMENT/SHARPENING HAS BEEN OCCURRING
TODAY ACROSS THE CENTRAL HIGH PLAINS IN TANDEM WITH A 1006 MB
SURFACE LOW CENTERED ACROSS SOUTHWEST SD/NORTHWEST NEB AT MID
AFTERNOON. ISOLATED TSTMS HAVE INCREASED SINCE 1930-2000Z IN
VICINITY OF THIS LEE TROUGH ESPECIALLY ACROSS PARTS OF EASTERN
CO...ALTHOUGH ADDITIONAL ISOLATED/WIDELY SCATTERED DEVELOPMENT MAY
OCCUR ACROSS WESTERN NEB TO NEAR THE SURFACE LOW IN SOUTHERN SD
THROUGH EARLY/MID EVENING.
BUOYANCY AND DEEP TROPOSPHERIC WIND SPEEDS ARE BOTH RELATIVELY
WEAK...HOWEVER FACTORS SUCH AS STEEP LAPSE RATES AND WINDS VEERING
WITH HEIGHT MAY RESULT IN SOME SEMI-SUSTAINED HIGH-BASED
STRUCTURES/BRIEF SUPERCELLS. GIVEN A WELL-MIXED BOUNDARY LAYER
/35-50 F SFC TEMPERATURE-DEWPOINT SPREADS/ AND AN AMPLE DCAPE
ENVIRONMENT...ISOLATED DAMAGING WINDS AND PERHAPS SEVERE HAIL WILL
BE POSSIBLE. A COOLING POST-SUNSET BOUNDARY LAYER SHOULD EVENTUALLY
ACCOUNT FOR A WEAKENING TREND ACROSS THE CENTRAL HIGH
PLAINS...ALTHOUGH TSTMS MAY PERSIST A BIT LONGER THIS EVENING ACROSS
NORTHERN NEB AND SOUTHERN SD WITH AID OF A STRENGTHENING LOW LEVEL
JET/WARM ADVECTION REGIME.
..GUYER/MEAD.. 08/22/2012
ATTN...WFO...FSD...ABR...LBF...UNR...GLD...PUB...B OU...CYS...
LAT...LON 44110134 44229957 43719885 42759885 42000101 39510173
38240334 38920433 41970350 44110134
Isolated Damaging Winds CA/NV/AZ/UT
MESOSCALE DISCUSSION 1799
NWS STORM PREDICTION CENTER NORMAN OK
1243 PM CDT WED AUG 22 2012
AREAS AFFECTED...SOUTHEAST CA/SOUTHERN NV TO NORTHWEST AZ/FAR
SOUTHWEST UT
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 221743Z - 221945Z
PROBABILITY OF WATCH ISSUANCE...20 PERCENT
SUMMARY...LOCALLY VERY HEAVY/PERSISTENT RAINFALL WILL LIKELY BE THE
PRIMARY CONCERN...BUT ISOLATED DAMAGING WINDS/MAINLY SUB-SEVERE HAIL
WILL BE POSSIBLE ACROSS PORTIONS OF SOUTHEAST CA/SOUTHERN NV INTO
NORTHWEST AZ/FAR SOUTHWEST UT THROUGH THIS AFTERNOON.
DISCUSSION...A SOUTHERN STREAM UPPER LOW CONTINUES TO SHIFT SLOWLY
EAST-SOUTHEASTWARD OVER SOUTH-CENTRAL CA AT MIDDAY PER WATER VAPOR
IMAGERY...WITH AN ASSOCIATED DIFFLUENT/UPPER JET EXIT REGION
OVERSPREADING MUCH OF NV TO NEAR THE UT/AZ BORDERS. A VERY MOIST
AIRMASS IS IN PLACE ACROSS THE REGION...ESPECIALLY EVIDENT BY AN
EXTREMELY HIGH CLIMO-RELATIVE PRECIPITABLE WATER VALUE OF 1.69
INCHES PER THE 12Z LAS VEGAS OBSERVED SOUNDING...IN ADDITION TO
RECENT GPS-DERIVED PW VALUES AROUND 2-INCHES ACROSS SOUTHEAST CA.
THE DEGREE OF MOISTURE/PW...ALONG WITH INCREASING LARGE
SCALE/OROGRAPHIC ASCENT AND DIURNAL HEATING WILL CONTRIBUTE TO
INCREASING NUMBER/VIGOR OF TSTMS THROUGH THIS AFTERNOON. LOCALLY
VERY HEAVY/PERSISTENT RAINFALL WILL LIKELY BE THE PRIMARY
IMPACT...ALTHOUGH SUFFICIENT VERTICAL SHEAR AND THERMODYNAMIC
CHARACTERISTICS WILL EXIST FOR SOME SEMI-SUSTAINED STORMS/MULTICELLS
CAPABLE OF WIND DAMAGE AND MAINLY SUB-SEVERE HAIL. SAMPLING THE
RELATIVELY STRONG SOUTHWESTERLY MID-HIGH LEVEL WINDS AHEAD OF THE
ADVANCING UPPER LOW...THE 12Z OBSERVED SOUNDING AND MORE RECENT
WSR-88D VWP DATA FROM LAS VEGAS ARE INDICATIVE OF AROUND 25 KT OF
0-6 KM SHEAR...WHILE THERMODYNAMIC ADJUSTMENTS TO THE 12Z VEF
SOUNDING SUGGEST AS MUCH AS 1000-1500 J/KG MLCAPE EXISTS ACROSS THE
LOWER CO RIVER VALLEY WHERE MORE AGGRESSIVE HEATING IS OCCURRING.
..GUYER/MEAD.. 08/22/2012
ATTN...WFO...FGZ...SLC...PSR...VEF...LKN...SGX...
LAT...LON 33371647 35131580 37001592 38151500 37911361 37321304
35751243 34801351 33271469 33371647
Severe Weather Reports 8/21/12
Tornado reports- 1. tornado reported by county sheriff in Utah along Beaver/Lincoln county line. 2. Waterspouts briefly moved onshore near Beach City, Texas.
MD 1795
MESOSCALE DISCUSSION 1795
NWS STORM PREDICTION CENTER NORMAN OK
0950 PM CDT MON AUG 20 2012
AREAS AFFECTED...PORTIONS NW TX AND SOUTH-PLAINS REGION.
CONCERNING...SEVERE THUNDERSTORM WATCH 586...
VALID 210250Z - 210415Z
THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 586
CONTINUES.
SUMMARY...REMAINDER WW MAY BE CLEARED BEHIND MCS MOVING SEWD 30-40
KT ACROSS SERN PANHANDLE AND SOUTH-PLAINS REGION. PRIND SVR THREAT
HAS PEAKED...BUT CORRIDOR OF THREAT FOR DAMAGING WIND REMAINS
BETWEEN CDS-LBB BEFORE COMPLEX ENCOUNTERS PROGRESSIVELY MORE STABLE
AIR AND WEAKENS FURTHER.
DISCUSSION...FORWARD-PROPAGATIONAL MCS THAT PRODUCED SEVERAL SVR
GUSTS IN AMA AREA -- INCLUDING AT LEAST TWO ABOVE 65 KT -- WAS
EVIDENT AT 230Z FROM HALL COUNTY SWWD TO NEAR LBB. MRGLLY SVR/50-KT
GUSTS ALSO WERE MEASURED AT LBB AT 226Z AND TURKEY (HALL COUNTY)
MESONET SITE AT 220Z. NARROW CORRIDOR OF LINGERING SFC-BASED
BUOYANCY IS EVIDENT ALONG AND SW OF QUASISTATIONARY SFC FRONT
ANALYZED FROM HALL COUNTY SEWD TO NEAR ABI...AND ALONG AND E OF
MOIST AXIS DRAWN JUST E OF LBB-SJT LINE. SFC DEW POINTS GENERALLY
MID 50S TO LOW 60S F CONTRIBUTE TO ESTIMATED MLCAPE 300-800 J/KG IN
THAT SWATH. ALONG AND W OF FRONT...MLCAPE WILL CONTINUE DECREASING
TREND WHILE MLCINH INCREASES WITH TIME...AS DIABATIC SFC COOLING
CONTINUES. THIS SHOULD CONTINUE GEN/GRADUAL WKNG TREND ALREADY
EVIDENT IN REFLECTIVITY/BASE-VELOCITY RADAR AND IR-SATELLITE
IMAGERY. HOWEVER...A FEW DAMAGING GUSTS CANNOT BE RULED OUT THROUGH
ABOUT 04Z AS CONVECTION PROCEEDS SEWD OVER CENTRAL/SRN SECTIONS OF
CAPROCK AND ERN SOUTH-PLAINS REGION.
..EDWARDS.. 08/21/2012
ATTN...WFO...OUN...SJT...LUB...MAF...
