DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0244 PM CDT MON JUL 20 2009
VALID 202000Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE PLAINS STATES...
...THERE IS A SLGT RISK OF SVR TSTMS IN SRN TX...
...THERE IS A SLGT RISK OF SVR TSTMS IN THE NC/VA AREA...
...PLAINS STATES...
AFTERNOON WATER VAPOR IMAGERY SUGGESTS ONE SHORTWAVE TROUGH WAS
MOVING THROUGH WRN SD/NWRN NEB...WHILE ANOTHER IMPULSE WAS MOVING
THROUGH ERN CO. EXPECT BOTH SYSTEMS TO INITIATE THUNDERSTORMS OVER
PORTIONS OF WRN/CENTRAL NEB SWD INTO KS DURING THE NEXT FEW HOURS.
THESE STORMS ARE EXPECTED TO EVOLVE INTO SEWD MOVING MCS/S...WITH
THE POTENTIAL FOR WIND DAMAGE INCREASING INTO THE EVENING HOURS.
ELEVATED THUNDERSTORMS/CLOUDS WILL LIKELY LESSEN THE THREAT FOR
SEVERE MCS TO MOVE INTO ERN NEB/KS...WITH GREATEST POTENTIAL FOR
WIND DAMAGE FROM WRN/CENTRAL KS S/SEWD INTO OK. SUPERCELLS WITH
LARGE HAIL STILL APPEAR POSSIBLE WITH THE INITIAL SURFACE BASED
STORM DEVELOPMENT.
...SRN TX...
MCV LOCATED NEAR SJT HAD AIDED IN THE STORMS DEVELOPING ON THE ERN
SIDE OF THIS FEATURE. AS STORMS TRACK S/SEWD TOWARD COT/SAT/AUS AND
ENCOUNTER TEMPERATURES IN THE 90S...MLCAPES NEAR 2500 AND 25-30 KT
OF DEEP LAYER SHEAR...ENVIRONMENT WOULD BE SUPPORTIVE FOR DAMAGING
WINDS AND POSSIBLY HAIL.
...SRN NV/AZ...
NUMEROUS THUNDERSTORMS HAD DEVELOPED IN MOIST AND MODERATELY
UNSTABLE ENVIRONMENT ACROSS SRN NV/NRN AZ. THIS AREA IS LOCATED
BENEATH THE UPPER HIGH/LIGHT WINDS...SO STORM UPDRAFTS WILL BE
SHORT-LIVED. HOWEVER...THE AMOUNT OF INSTABILITY MAY SUPPORT SOME
HAIL AS WELL AS GUSTY WINDS GIVEN THE HOT SURFACE TEMPERATURES...AOA
100 DEGREES.
OTHERWISE...ONLY MINOR THUNDER/SEVERE LINE ADJUSTMENTS FROM 1630Z
OUTLOOK BASED ON ONGOING TRENDS.
..IMY.. 07/20/2009
.PREV DISCUSSION... /ISSUED 1114 AM CDT MON JUL 20 2009/
...CENTRAL/NRN PLAINS...
TROUGHING CONTINUES TO DEVELOP SEWD INTO THE PLAINS AS THE LARGE
SWRN UPPER HIGH GRADUALLY WEAKENS. STRONGER NWLY FLOW WILL BE
SPREADING SEWD FROM NRN ROCKIES INTO PLAINS BY TONIGHT.
ACCOMPANYING COLD FRONT CURRENTLY ERN ND SWWD INTO CENTRAL WY PUSHES
SWD THRU CENTRAL HIGH PLAINS TONIGHT WHILE A SURFACE TROUGH
EXTENDING FROM CENTRAL SD SWD THRU WRN NEB/KS EXPECTED TO BE PRIMARY
FOCUS FOR SEVERE THUNDERSTORM INITIATION THIS AFTERNOON.
25-30 KT SLY LOW LEVEL FLOW E OF SURFACE TROUGH HAS TRANSPORTED A
MOIST BOUNDARY LAYER NWD THRU KS INTO NEB AND WITH DAYTIME HEATING
WILL LEAD TO MDT INSTABILITY WITH MLCAPES AOA 2500 J/KG. GIVEN THE
NWLY FLOW REGIME...SHEAR WILL BE FAVORABLE FOR BOTH DEVELOPMENT OF
SUPERCELLS LATER THIS AFTERNOON AND FORWARD PROPAGATING MCS/S
OVERNIGHT AS COLD POOLS ARE GENERATED. LARGE HAIL IS LIKELY WITH
ANY SUPERCELL THAT DEVELOPS LATER THIS AFTERNOON GIVEN THE STEEP
LAPSE RATES...8C/KM...AND INSTABILITY. CONDITIONS WILL BE ONLY
MARGINALLY FAVORABLE FOR ISOLATED TORNADOES.
HAVE EXTENDED THE SEVERE RISK FURTHER NEWD INTO NRN PLAINS ALONG AND
AHEAD OF THE FRONT. WHILE SHEAR WILL BE LESS FAVORABLE...STEEP
LAPSE RATES AND INCREASING LARGE SCALE ASCENT WITH APPROACH OF UPPER
TROUGH SHOULD GENERATE SURFACE BASED STORMS THIS AFTERNOON ALONG
WITH A LARGE HAIL/WIND DAMAGE THREAT.
OVERNIGHT ONE OR MORE MCS/S WILL DROP SWD THRU CENTRAL PLAINS WITH A
CONTINUED WIND DAMAGE/LARGE HAIL THREAT REACHING OK PRIOR TO 12Z.
HAVE EXTENDED THE RISK WWD INTO ERN WY/NERN CO AS UPSLOPE FLOW
DEVELOPS IN THE WAKE OF COLD FRONT WHICH SHOULD REACH NERN CO BY
THIS EVENING. 35-40 KT NWLY MID LEVEL FLOW ALONG WITH STEEP LAPSE
RATES WILL SUPPORT A FEW SEVERE THUNDERSTORMS. ACTIVITY WILL
INITIATE OVER HIGHER TERRAIN ERN WY AND THEN MOVE SEWD WITH
SUFFICIENT INSTABILITY FOR A FEW SUPERCELLS. PRIMARY THREAT WILL BE
LARGE HAIL AND LOCALLY DAMAGING DOWNBURSTS WINDS THRU THIS EVENING
INTO THE CENTRAL HIGH PLAINS.
...TX...
LOOSELY ORGANIZED MCS HAS DEVELOPED THIS MORNING NCENTRAL TX AND
WILL MOVE SWD INTO AN INCREASINGLY UNSTABLE AIR MASS. GIVEN THE 30KT
OF DEEP LAYER SHEAR AND MLCAPES AOA 3000 J/KG BY PEAK
HEATING...SURFACE BASED STORMS SHOULD LEAD TO A SEVERE THREAT. SEE
ADDITIONAL INFO ON THIS AREA IN MCD 1624.
...EASTERN STATES...
LITTLE CHANGE IN THE AREA OR REASONING FOR THE SEVERE THEAT IN THIS
REGION.
A LARGE UPPER TROUGH IS IN PLACE THIS MORNING OVER THE OH/TN
VALLEYS. THE PRIMARY VORTICITY MAX ASSOCIATED WITH THIS TROUGH IS
EXPECTED TO DRIFT SLOWLY NORTHEASTWARD INTO PARTS OF OH/WV BY THIS
EVENING. LARGE SCALE LIFT AND MODERATE INSTABILITY ARE EXPECTED
FROM GA/SC INTO OH/WV...LEADING TO SCATTERED SHOWERS AND
THUNDERSTORMS. MOST MODELS AGREE ON THE DEVELOPMENT OF A CLUSTER OF
STRONG THUNDERSTORMS THIS AFTERNOON ACROSS PARTS OF VA/NC/SC WHERE
GREATEST DESTABILIZATION IS EXPECTED. RATHER COOL TEMPERATURES
ALOFT AND FAVORABLE EFFECTIVE SHEAR WILL PROMOTE ORGANIZED MULTICELL
OR ISOLATED SUPERCELL STORMS CAPABLE OF HAIL AND DAMAGING WINDS.
SOME RISK OF FUNNEL CLOUDS AND/OR AN ISOLATED TORNADO WILL ALSO
EXIST FROM SOUTHEAST OH INTO THE CAROLINAS.
...SWRN DESERTS...
AGAIN TODAY VERY HOT CONDITIONS WILL LEAD TO SCATTERED THUNDERSTORMS
DEVELOPING OVER THE HIGHER TERRAIN MUCH OF THE SWRN U.S. WITH THE
WEAKENING OF THE UPPER HIGH...STEERING FLOW FOR STORM PROPAGATION IS
EXPECTED TO BE MUCH LESS THAN LAST COUPLE DAYS. HOWEVER ANY
THUNDERSTORM DEVELOPMENT OVER HIGHER TERRAIN WILL LEAD TO LOCALIZED
STRONG OUTFLOWS INTO THE ADJACENT DESERT VALLEYS BY THIS EVENING.
ANY SEVERE WILL BE ISOLATED GIVEN THE OVERALL WEAK UPPER SUPPORT
