ACUS01 KWNS 171236
SWODY1
SPC AC 171233
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0733 AM CDT WED OCT 17 2007
VALID 171300Z - 181200Z
..THERE IS A MDT RISK OF SVR TSTMS THIS AFTN THROUGH TONIGHT OVER
PARTS OF AR...CNTRL AND ERN OK...ERN KS AND SRN/CNTRL MO...
..THERE IS A SLGT RISK OF SVR TSTMS FROM E TX AND THE LWR MS VLY N
INTO THE LWR MO AND MID MS VLYS...
..SYNOPSIS...
..POTENTIALLY SIGNIFICANT SEVERE WEATHER EPISODE POSSIBLE THIS
AFTERNOON AND TONIGHT...WITH A THREAT FOR A FEW STRONG AND/OR...
LONG-TRACK TORNADOES...
A DEEP CLOSED LOW WILL EVOLVE OVER THE CNTRL PLNS THIS PERIOD
AS STRONG MID/HIGH-LVL IMPULSE NOW IN NM IS PROPELLED NEWD BY STRONG
PACIFIC JET STREAK SWEEPING E/SE ACROSS THE GRT BASIN. THE NM
TROUGH SHOULD REACH CNTRL KS EARLY TONIGHT AND EASTERN IA BY 12Z
THURSDAY WHILE THE PACIFIC JET STREAK CONTINUES E/SE TO THE SRN HI
PLNS.
AT LWR LVLS...LEE CYCLONE NOW IN SE CO EXPECTED TO DEEPEN AS IT
TRACKS NE ACROSS KS TODAY AND REACHES NE NEB/NW IA EARLY THURSDAY.
SFC PATTERN WILL BE COMPLICATED BY OUTFLOW FROM ONGOING STORMS IN
THE SRN PLNS AND LWR MS VLY...AND BY DISJOINTED NATURE OF DEVELOPING
WARM FRONT THAT ATTM EXTENDS FROM THE RED RVR VLY REGION ESE INTO
NRN LA. LEE TROUGH/DRYLINE EXTENDING S FROM THE CO LOW SHOULD MOVE
E INTO WRN OK AND NW TX BY MID TO LATE AFTN...AND LIKELY WILL ALSO
SERVE AS A FOCUS FOR SVR TSTM DEVELOPMENT.
BY 12Z THURSDAY...EXPECT THAT WARM FRONT WILL HAVE BECOME
BETTER-DEFINED AND WILL HAVE MOVED NE INTO THE MID MS/LWR OH VLYS...
WHILE DEVELOPING COLD FRONT ACCELERATES SE ACROSS THE PLNS.
..SRN/CNTRL PLNS INTO THE LWR/MID MS VLYS THROUGH TONIGHT...
BEGINNING OF AN ACTIVE 2-3 DAY SVR WEATHER EPISODE IS UNFOLDING ATTM
AS TSTMS INCREASE IN COVERAGE/INTENSITY OVER THE SRN AND CNTRL PLNS
IN ZONE OF INCREASING WAA/MOISTURE INFLUX AHEAD OF POTENT NM UPR
IMPULSE. THE STORMS SHOULD CONTINUE TO INCREASE AND MOVE/DEVELOP
NEWD THROUGH THE DAY AS SFC HEATING AND PERSISTENT MOISTURE RETURN
FURTHER DESTABILIZE REGION.
STRENGTHENING LOW AND DEEP-LYR WIND FIELDS ACROSS THE MDT AND SLGT
RISK REGIONS WILL BE MORE THAN ADEQUATE FOR STRONG SUPERCELLS...
WITH DEEP SHEAR EXPECTED TO BE AOA 50 KTS OVER A BROAD SWATH FROM
CNTRL/E TX NE INTO THE MID AND LWR MS VLYS THROUGH THE PERIOD.
WHILE RICHEST MARITIME AIR WILL REMAIN CONFINED TO REGION INVOF
DISSIPATING FRONTAL ZONE OVER E TX/LA AND AR...SEASONABLY RICH
MOISTURE /WITH DEWPOINTS WELL INTO THE 60S/ WILL SURGE N BEYOND THE
STL AREA BY EARLY THURSDAY AS 40-50 KT SSWLY LLJ BROADENS IN WARM
SECTOR OF DEEPENING SFC LOW. THE STEEPEST MID LVL LAPSE
RATES...MEANWHILE...WILL SWEEP ENE FROM THE TX/OK PANHANDLE REGION
THIS MORNING TO THE LWR MO VLY BY EVENING...ALONG AND N OF UPR JET.
GIVEN THE COMPLEXITIES POSED BY EXISTING CONVECTIVE CLUSTERS AND THE
DISJOINTED/DIFFUSE NATURE OF SFC BOUNDARIES...IT IS DIFFICULT TO
CONFIDENTLY IDENTIFY A HIGH RISK CORRIDOR WITHIN THE BROAD AREA
OUTLINED BY THE MDT/SGT RISK FORECASTS. PRESENT INDICATIONS
..HOWEVER...ARE THAT THE MOST SUBSTANTIAL SVR THREAT MAY DEVELOP
THIS AFTN THROUGH EARLY TONIGHT FROM CNTRL/ERN OK NNE INTO SE
KS...AS /1/ SFC HEATING.../2/ CONTINUED MOISTURE INFLOW...AND /3/
STRENGTHENING CONVERGENCE ALONG RESIDUAL OUTFLOW BOUNDARIES AND/OR
TROUGH/DRY LINE SEGMENTS CREATE ENVIRONMENT FAVORABLE FOR STORM
INITIATION. COMBINATION OF MODERATE INSTABILITY /1000-1250 J PER KG
SBCAPE/ AND STRONG DEEP SHEAR SUGGESTS HIGH LIKELIHOOD FOR SUSTAINED
SUPERCELLS. GIVEN BREADTH OF DESTABILIZING WARM SECTOR AND EXPECTED
DEGREE OF DIRECTIONAL SHEAR...THESE STORMS COULD YIELD STRONG AND/OR
LONG-TRACK TORNADOES...IN ADDITION TO LARGE HAIL AND DAMAGING WIND.
THE SVR THREAT LIKELY WILL SPREAD INTO WRN/SRN MO AND NW AR EARLY
TONIGHT...AND ERN MO/WRN IL EARLY THURSDAY...AS FORCING FOR ASCENT
IS MAXIMIZED AHEAD EJECTING UPR TROUGH.
FARTHER S...TSTMS EXPECTED TO BECOME INCREASINGLY NUMEROUS TODAY
INVOF DIFFUSE WARM FRONT FROM FAR ERN TX AND LA INTO MUCH OF AR...IN
RESPONSE TO HEATING AND GLANCING INFLUENCE OF NM TROUGH. MID LVL
LAPSE RATES WILL BE COMPARATIVELY WEAK. BUT COMBINATION OF RICH
BOUNDARY LYR MOISTURE...MODERATE DEEP SHEAR AND BACKED LOW LVL FLOW
WILL YIELD AN ENVIRONMENT FAVORABLE FOR CLUSTERS OF
STORMS/SUPERCELLS THAT COULD PRODUCE TORNADOES AND LOCALLY DAMAGING
WIND IN ADDITION TO VERY HEAVY RAIN. THIS REGIME COULD PERSIST WELL
INTO THE NIGHT AND SPREAD NNE ALONG CONFLUENT ERN PART OF BROADENING
LLJ...EXTENDING SVR THREAT INTO PARTS OF MS AND WRN TN EARLY
THURSDAY.
..MID MS VLY THIS AFTN/EVENING...
SUBSTANTIAL DESTABILIZATION IS FORECAST OVER THE ERN MO/SRN IL/WRN
KY AREA THIS AFTN...MORE THAN LIKELY AS ELEVATED MOISTURE ASSOCIATED
WITH STRENGTHENING SSWLY LLJ IS MIXED TO THE SFC INVOF DEVELOPING
WARM FRONT. IF SUFFICIENT HEATING CAN OCCUR...SOMEWHAT UNCERTAIN
GIVEN CURRENT SATELLITE IMAGERY...LOCALIZED CONVERGENCE MAY SUPPORT
DEVELOPMENT OF SCTD SFC-BASED STORMS. IF SFC-BASED DEVELOPMENT IS
NOT REALIZED...ELEVATED ACTIVITY NOW DEVELOPING IN WRN/SRN MO COULD
AFFECT REGION LATER TODAY AS STORMS BECOME ROOTED INCREASINGLY CLOSE
TO THE SFC. GIVEN 40+ KT DEEP WSW SHEAR...SOME OF THIS ACTIVITY
COULD POSE A SVR THREAT LONG BEFORE PREVIOUSLY-DISCUSSED OVERNIGHT
ACTIVITY.
.CORFIDI/GUYER.. 10/17/2007
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