ACUS01 KWNS 171958
SWODY1
SPC AC 171956
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0256 PM CDT SAT SEP 17 2011
VALID 172000Z - 181200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE SRN AND
CENTRAL PLAINS...
...WEST CENTRAL TO NW TX...AND NWD TO SW-SOUTH CENTRAL KS...
EARLY-MID AFTERNOON OBJECTIVE ANALYSES INDICATED A ZONE OF MODERATE
TO VERY STRONG INSTABILITY /MLCAPE 2000-3000 J PER KG/ EXTENDING
GENERALLY ALONG AND W OF THE I-35 CORRIDOR IN OK AND TX. GIVEN 1/
THE DEVELOPMENT OF STRONGER INSTABILITY FARTHER S...2/ A SIMILAR
INCREASE IN DEEP LAYER SHEAR INTO WEST CENTRAL TX AND 3/ RECENT
INCREASE IN CU INVOF SURFACE BOUNDARY EXTENDING FROM CHILDRESS TX
AREA TO 25 N MAF...THE SLIGHT RISK AREA HAS BEEN EXTENDED SSWWD INTO
WEST CENTRAL TX. OTHERWISE...THE AFTERNOON INCREASE IN CU FIELD
OVER THE NERN TX PANHANDLE INTO NWRN OK AND SEWD ACROSS N CENTRAL OK
INVOF A WARM FRONT APPEARS TO BE THE START OF NEW TSTM DEVELOPMENT.
ASIDE FROM NEW EXTENSION OF THE SLIGHT RISK AREA...THE PREVIOUS
OUTLOOK REMAINS ON TRACK WITH DAY 1 SEVERE WEATHER THREAT.
ADDITIONAL MESOSCALE DETAILS FOR THE SRN PLAINS ARE AVAILABLE IN SPC
MESOSCALE DISCUSSIONS #2183 AND #2184.
ENHANCED LOW LEVEL SHEAR /EFFECTIVE SRH 200-300 M2/S2 PER OBJECTIVE
ANALYSES/ INVOF A WNW-ESE ORIENTED WARM FRONT MOVING NWD ACROSS NRN
OK THIS AFTERNOON WILL BE A FAVORED ZONE FOR TORNADO POTENTIAL.
THIS THREAT WILL SPREAD INTO SRN KS ATTENDANT TO THE NWD MOVING WARM
FRONT/INCREASING BOUNDARY LAYER MOISTURE...AND THUS HAVE EXTENDED
THE 5% TORNADO PROBABILITY AREA FARTHER E ACROSS SOUTH CENTRAL KS
AND NORTH CENTRAL OK.
...GENERAL TSTM FORECAST IN E TX...
GIVEN RECENT TRENDS IN CONVECTION WITH SOME TSTM ACTIVITY TO THE
E/NE OF GLS/HOU...THE GENERAL TSTM LINE /10 PERCENT PROBABILITY/ HAS
BEEN EXPANDED EWD ACROSS MUCH OF E TX.
..PETERS.. 09/17/2011
.PREV DISCUSSION... /ISSUED 1130 AM CDT SAT SEP 17 2011/
...SYNOPSIS...
FAIRLY LOW AMPLITUDE...PROGRESSIVE...MULTI-STREAM PATTERN WILL
CONTINUE ACROSS THE CONUS THROUGH SUN. BAND OF ENHANCED FLOW
EXTENDING FROM THE SRN RCKYS ENE ACROSS SRN HALF OF THE PLNS WILL
REMAIN THE MAIN UPR JET OF NOTE AS FAR AS SVR TSTMS ARE CONCERNED.
AT LWR LVLS...AN AREA OF LOW PRESSURE IN THE LEE OF THE CO
RCKYS...TIED LARGELY TO THE ABOVE-MENTIONED UPR JET...SHOULD REMAIN
QSTNRY OR DRIFT ONLY SLOWLY E/SE THROUGH THE PERIOD AS LARGE
ANTECEDENT SFC RIDGE CONTINUES TO WITHDRAW TO THE E/NE.
...SRN PLNS THIS AFTN THROUGH TNGT...
IMPULSES IN THE SRN STREAM JET WILL ONCE AGAIN MODULATE TSTM
DEVELOPMENT...IN CONJUNCTION WITH SFC HEATING AND LLJ
INFLUENCES...OVER THE SRN PLNS THIS PERIOD. TSTMS WITH LEAD IMPULSE
NOW IN ERN KS SHOULD WEAKEN LATER TODAY AS THAT DISTURBANCE
CONTINUES EWD INTO MO. BY LATE THIS AFTN...SFC HEATING IN SE
QUADRANT OF SW KS SFC LOW...AND THE APPROACH OF UPSTREAM IMPULSE NOW
OVER NE NM/SE CO...SHOULD SUPPORT THE INITIATION OF NEW STORMS OVER
PARTS OF SW/S CNTRL KS AND NW OK.
CURRENT SFC OBSERVATIONS AND THE 12Z RAOB DATA...ESPECIALLY 850 MB
DEWPOINTS OF 17-18C AT BOTH MAF AND AMA... SUGGEST THAT SUBSTANTIAL
MOISTURE INFLOW WILL CONTINUE ACROSS THE NW HALF OF OK AND SW/S
CNTRL KS TODAY. COUPLED WITH RELATIVELY COOL MID LVL TEMPS ALONG
AND N OF SRN STREAM JET...AMPLE INSTABILITY /SBCAPE TO 2000 J PER
KG/ LIKELY WILL DEVELOP TO SUPPORT STRONG UPDRAFTS. WITH 25-30 KT
WLY MID LVL FLOW...SETUP SHOULD YIELD A FEW SUSTAINED
STORMS/SUPERCELLS CAPABLE OF LARGE HAIL/LOCALLY DMGG WIND.
TORNADOES ALSO WILL BE POSSIBLE GIVEN INCREASING LOW LVL MOISTURE
AND THE LIKELIHOOD FOR PERSISTENT BACKED LOW LVL WINDS E/SE OF SW KS
SFC LOW. MORE WIDELY SCTD STORMS MAY DEVELOP SOMEWHAT LATER IN THE
AFTN SW ALONG LEE TROUGH/DRY LINE INTO W CNTRL AND PERHAPS SW TX.
THE STORMS IN WRN/NRN OK AND SRN KS SHOULD EVOLVE INTO ONE OR TWO
MCSS TNGT/EARLY SUN AS MOIST SSWLY LLJ OVER REGION STRENGTHENS BOTH
DIURNALLY...AND IN RESPONSE TO THE APPROACH OF THE NEXT UPR
DISTURBANCE NOW OVER UT/CO. EMBEDDED STORMS MAY CONTINUE TO PRODUCE
SPORADIC HAIL/LOCALLY DMGG WIND.
...CNTRL HI PLNS THIS AFTN/EVE...
A SEPARATE AREA OF STRONG TO ISOLD SVR TSTMS MAY EVOLVE THIS AFTN
OVER ERN CO...ALONG WRN EDGE OF LOW LVL CLOUD FIELD AND IN
COMPARATIVELY MODEST DEEP FLOW FARTHER N OF SRN STREAM JET.
STEEPENING LOW TO MID LVL LAPSE RATES AND LOW LVL CONVERGENCE ALONG
LEE TROUGH COULD SUPPORT SCTD STORMS WITH HAIL AND POSSIBLY A BRIEF
TORNADO.
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