SPC AC 302104
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0404 PM CDT WED SEP 30 2009
VALID 302105Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE
CNTRL/SRN PLNS...
UPDATED TO INCLUDE A SLGT RISK ACROSS PORTIONS OF KS...OK AND TX
PNHDL. SFC-BASED INITIATION HAS INDEED OCCURRED INVOF DRYLINE.
PREV DISCUSSION BELOW REMAINS VALID.
.PREV DISCUSSION... /ISSUED 0313 CDT WED SEP 30 2009/
..CNTRL/SRN PLNS...
SERIES OF MESOANALYSIS DEPICTS CONSIDERABLE VEERING OF THE LLVL FLOW
OVER THE HIGH PLNS DESPITE A STRONG UPR TROUGH/JET DIGGING INTO THE
GRT BASIN. INSPECTION OF WATER VAPOR SHOWS THAT A HEALTHY LEAD
MID-LVL SHORTWAVE TROUGH WAS TRANSLATING NE THROUGH ERN CO AND IS
LIKELY THE CULPRIT TO THE VEERING WIND FIELDS. THIS IMPULSE WILL
CONTINUE ENE INTO NEB AND NRN KS TONIGHT WITH THE PRIMARY PV-ANOMALY
ROTATING EWD FROM UT/WRN WY TO THE CNTRL HIGH PLNS OVERNIGHT.
DRYLINE HAS MIXED EWD INTO WRN KS...ERN OK PNHDL...CNTRL TX PNHDL
AND NWRN PORTIONS OF THE TX S PLNS. VSBL SATL SHOWS HI-BASED CU
FORMING WITHIN A HOT AND DEEPLY-MIXED POST-DRYLINE ENVIRONMENT FROM
NEAR KDDC TO NW OF KPVW. MORNING MODEL RUNS UNDERESTIMATED SFC
TEMPERATURES IN THIS REGION...AND MLCAPES/MLCINH ARE HIGHER/WEAKER
THAN EXPECTED. AS SRN PORTIONS OF THE LEAD WAVE BRUSHES ACROSS THE
DRYLINE...ISOLD TSTMS MAY FORM ALONG THE DRYLINE IN SWRN KS SWWD
INTO THE TX S PLNS FROM MID-LATE AFTN. AREA PROFILERS DEPICT ABOUT
30-45 KTS OF DEEP-LAYER SHEAR...MORE THAN SUFFICIENT FOR SUPERCELL
STORMS...ESP GIVEN SUCH STEEP MID-LVL LAPSE RATES. LARGE HAIL WILL
BE THE PRIMARY THREAT. SUSTAINED SFC-BASED STORMS MAY BE
SHORT-LIVED AS ACTIVITY MOVES AWAY FROM THE DRYLINE DURING THE
EVENING. WILL MAINTAIN LOW SVR PROBABILITIES GIVEN THE UNCERTAINTY
IN STORM FORMATION AND THE SHORT TEMPORAL/SMALL COVERAGE EXPECTED
EVEN IF STORMS DO FORM.
WHILE SFC-BASED INITIATION IS NOT LIKELY FARTHER N DUE TO CAPPING
CONCERNS /REF 18Z KLBF SOUNDING/...RISKS FOR ELEVATED TSTMS WILL
INCREASE AFTER DARK AS THE PRIMARY IMPULSE ROTATES CLOSER TO THE
REGION. A 40-50 KT SLY LLJ COUPLED WITH INCREASING SWLY MID-LVL
FLOW AND A SUBSTANTIAL LAPSE RATE IN THE MID-LVLS WILL ENCOURAGE
ORGANIZATION AND LARGE HAIL PRODUCTION. TSTMS SHOULD EVOLVE FROM
SRN SD INTO NEB AND PARTS OF KS AND MOVE ENE TOWARD THE MID/LWR MO
RVR VLY BY 12Z.
..JPR.. 09/30/2009
.PREV DISCUSSION... /ISSUED 1109 AM CDT WED SEP 30 2009/
...CENTRAL PLAINS...
STRONG/COLD TROUGH CONTINUES EWD ACROSS ROCKIES INTO THE HIGH PLAINS
TONIGHT. RATHER COMPLEX SURFACE PATTERN WITH THE PRIMARY COLD FRONT
FROM WRN WY SWD THRU ERN UT INTO NRN AZ. IN RESPONSE TO ONGOING
VIGOROUS LARGE SCALE ASCENT AND MID LEVEL COLD ADVECTION ACTIVE BAND
OF CONVECTION/SURFACE TROUGH HAS DEVELOPED SWD FROM E OF RWL TO WRN
CO THIS MORNING...ACCOMPANIED BY WINDS TO NEAR SVR LEVELS.
A RATHER DISORGANIZED AREA OF LOW PRESSURE OVER WY EXPECTED TO
CONSOLIDATE INTO A CENTER TO LEE OF CENTRAL ROCKIES AND MOVE EWD
TONIGHT ALONG KS/NE BORDER. SLY LOW LEVEL JET HIGH PLAINS WILL
INCREASE TO 60KT OR GREATER TONIGHT AS TROUGH AND 70-80KT MID LEVEL
JET APPROACH FROM THE WEST.
GULF MOISTURE RAPIDLY RETURNING FROM SRN PLAINS AND IN CONCERT WITH
A STEEP EML SPREADING EWD WILL PROVIDE A FAVORABLE CONDITIONAL
ENVIRONMENT FOR SEVERE STORMS. THE PRIMARY CAVEAT WILL BE THE
SUFFICIENT WEAKENING OF THE CURRENT STRONG CAP TO ALLOW SURFACE
BASED STORM INITIATION.
IT NOW APPEARS THAT THE PRIMARY THREAT INTO THE EVENING WILL BE WITH
THE STRONG ASCENT AND COLD ADVECTION THAT IS FORCING THE CURRENT
ACTIVE CONVECTION CENTRAL ROCKIES AS IT ROTATES NEWD INTO HIGH
PLAINS OF NEB/SWRN SD. WHILE MOISTURE WILL BE LIMITED THE
COMBINATION OF VERY STEEP LAPSE RATES...DCAPES OF 1000 J/KG OR
GREATER AND 50KT OF SHEAR...SUPPORTS WIND DAMAGE POTENTIAL WITH
STORMS BY LATER THIS AFTERNOON.
FURTHER S ALONG THE DRY LINE WHICH SETS UP THRU WRN KS INTO TX
PANHANDLE...THE CAP WILL WEAKEN WITH STRONG HEATING...BUT MODEL
SOUNDINGS INDICATE THERE LIKELY WILL STILL BE SUFFICIENT INHIBITION
TO PRECLUDE STORM INITIATION. HAVE THUS REDUCED SOME THE THREAT OF
SEVERE STORM COVERAGE IN KS THRU THE EVENING. HOWEVER WITH THE
SHEAR AND STEEP MID LEVEL LAPSE RATES IN PLACE...ANY STORM THAT IS
ABLE TO FORM OFF THE DRY LINE COULD BECOME QUICKLY SEVERE WITH A
LARGE HAIL AND DAMAGING WIND THREAT.
OVERNIGHT ELEVATED THUNDERSTORMS EXPECTED TO INCREASE IN COVERAGE
AND POTENTIAL SEVERITY ACROSS THE CENTRAL PLAINS. AGAIN THE PRIMARY
THREAT WILL BE LARGE HAIL...HOWEVER A MORE ORGANIZED WIND DAMAGE
THREAT COULD SPREAD EWD ACROSS NE WHERE LARGE SCALE ASCENT WILL BE
GREATEST AHEAD AND N OF THE TRACK OF SURFACE LOW.
...CENTRAL ROCKIES...
WITH THE COLD FRONT NOW ENTERING WRN CO...POTENTIAL FOR A FEW
STRONG/SEVERE WIND GUSTS WILL PERSIST THRU THE AFTERNOON. STEEP
LAPSE RATES AND STRONG UPPER JET WILL ENHANCE WIND POTENTIAL WITH
ANY THUNDERSTORM THAT DEVELOPS VICINITY AND AHEAD OF COLD FRONT.
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