SWODY1
SPC AC 201945
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0145 PM CST WED JAN 20 2010
VALID 202000Z - 211200Z
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN THRU TONIGHT
ACROSS PARTS OF THE SERN PLAINS THRU THE LWR MS VLY/CNTRL GULF
COAST...
...20Z UPDATE...
...SERN PLAINS INTO THE LWR MS VLY/GULF COAST REGION...
STRENGTHENING LARGE SCALE ASCENT ASSOCIATED WITH WARM ADVECTION
APPEARS TO BE ONGOING ACROSS MUCH OF THE REGION...DOWNSTREAM OF THE
SHORT WAVE TROUGH NOW TURNING EAST OF THE SOUTHERN ROCKIES.
ELEVATED MIXED LAYER AIR ADVECTING FROM THE SOUTHWEST IS SLOWING
CONVECTIVE DEVELOPMENT ACROSS EASTERN TEXAS AND SOUTHEAST OKLAHOMA
INTO MUCH OF ARKANSAS AND LOUISIANA...BUT INCREASING DISCRETE STORM
ACTIVITY PROBABLY WILL COMMENCE ACROSS THE ARKLATEX REGION BY EARLY
EVENING...AS MID/UPPER FLOW BECOMES MORE DIFLUENT/ DIVERGENT WITH
THE APPROACH OF THE UPPER IMPULSE. THE ABSENCE OF CONVECTION TO
THIS POINT HAS ALLOWED FOR CONSIDERABLE BOUNDARY LAYER MOISTENING
AND DESTABILIZATION...AND THE TORNADIC POTENTIAL IS BECOMING MORE OF
A CONCERN. THIS RISK MAY NOT BECOME APPRECIABLE UNTIL CLOSER TO
03-06Z...WHEN A SOUTHERLY 850 MB JET IS PROGGED TO FINALLY INTENSIFY
INTO THE 40-50 KT RANGE...AS A SURFACE LOW DEEPENS OVER THE RED
RIVER VALLEY. BUT...TORNADOES NOW SEEM MORE OF A PROBABILITY AS FAR
NORTH AS SOUTHERN ARKANSAS INTO NORTHERN MISSISSIPPI.
OTHERWISE...THERE HAS BEEN LITTLE CHANGE TO THE 1630Z OUTLOOK.
..KERR.. 01/20/2010
.PREV DISCUSSION... /ISSUED 1021 AM CST WED JAN 20 2010/
...ERN HALF OF SRN PLAINS INTO THE CENTRAL GULF COAST STATES...
LEAD MID/UPPER LEVEL LOW WILL CONTINUE EJECTING NEWD AND WEAKEN
THROUGH THE DAY OVER THE UPPER MS RIVER VALLEY REGION...WHILE NEXT
IMPULSE NOW OVER THE 4-CORNERS BECOMES NEGATIVELY-TILTED AS IT
EJECTS ACROSS THE SRN PLAINS LATER TODAY AND TONIGHT. THIS TRAILING
IMPULSE WILL PROVIDE IMPETUS FOR WIDESPREAD THUNDERSTORM DEVELOPMENT
FROM ERN PORTIONS OF THE SRN PLAINS ACROSS THE LOWER MS RIVER
VALLEY/MID SOUTH THROUGH THE LATTER HALF OF THE PERIOD. IN
ADDITION...PERSISTENT DEEP ASCENT ALONG LEFT EXIT REGION OF STRONG
UPPER LEVEL JET WILL MAINTAIN SWLY LOW LEVEL WAA AND SCATTERED
THUNDERSTORM DEVELOPMENT ACROSS THE NWRN GULF BASIN INTO THE LOWER
MS RIVER VALLEY THROUGH THE DAY.
LEADING ACTIVITY ASSOCIATED WITH MORE DIFFUSE MID/UPPER LEVEL
PATTERN OVER THE LOWER MS RIVER VALLEY SHOULD REMAIN SOMEWHAT
ELEVATED GIVEN STRENGTH OF CAPPING ON MORNING SOUNDINGS AND LITTLE
COOLING ALOFT. REGARDLESS...MID LEVELS REMAIN SUFFICIENTLY COOL FOR
HAIL GROWTH...ESPECIALLY WITH 40-50 KT EFFECTIVE SHEAR SUSTAINING
ROTATING UPDRAFTS. GRADUAL MOISTENING OF THE BOUNDARY LAYER
COMBINED WITH PERSISTENT DEEP ASCENT WILL WEAKEN CAP DURING THE
EARLY TO MID AFTERNOON AND MAY SUPPORT SURFACE-BASED STORMS LATER
THIS AFTERNOON/EVENING. SHOULD THIS OCCUR...MODEST LOW LEVEL SHEAR
WOULD SUPPORT ROTATION AND POSSIBILITY OF TORNADOES/DAMAGING WINDS
AS DEEP LAYER SHEAR MAINTAINS RISK OF SUPERCELLS AND SMALL BOWING
SEGMENTS...ESPECIALLY INVOF SURFACE WARM FRONT EXPECTED TO DEVELOP
NW-SE FROM CENTRAL AND SRN LA/MS INTO THE CENTRAL GULF COAST.
CLUSTER OF STORMS SHOULD INCREASE IN COVERAGE/INTENSITY LATER
TODAY/THIS EVENING AS LLJ INTENSIFIES IN RESPONSE TO EJECTING SRN
PLAINS IMPULSE...WHICH MAY SUPPORT UPSCALE DEVELOPMENT INTO A LINEAR
MCS SHIFTING ENEWD OVERNIGHT. SEVERE RISK ATTENDANT TO THIS
ACTIVITY WILL REMAIN CONTINGENT ON QUALITY OF SURFACE-BASED
INSTABILITY TONIGHT...WITH SOME QUESTIONS ABOUT DESTABILIZATION NWD
AWAY FROM THE COAST GIVEN AMOUNT OF EARLY DAY CONVECTION.
SEPARATE AREA OF STRONG/SEVERE THUNDERSTORM DEVELOPMENT TIED MORE TO
MID/UPPER LEVEL IMPULSE SHIFTING ACROSS THE SRN HIGH PLAINS IS
EXPECTED INTO PORTIONS OF SERN OK/N-CENTRAL AND ERN TX...POSSIBLY AS
EARLY AS 21Z. MORNING ANALYSES INDICATE CAPPING AND PRECEDING
STRATUS WILL BE PROBLEMATIC FOR TSTM DEVELOPMENT MUCH OF THE DAY.
HOWEVER...HEATING FROM THE WEST AND INCREASING CONVERGENCE INVOF N-S
ORIENTED SURFACE TROUGH/DRY LINE TOWARDS THE I-35 CORRIDOR MAY
SUFFICE FOR WEAKENING CAP AND MODEST MLCAPE INTO THE RED RIVER
VALLEY. EVEN IF THIS ACTIVITY REMAINS SLIGHTLY ELEVATED...VERY
STEEP LAPSE RATES AND 40-50 KT EFFECTIVE SHEAR WILL REMAIN
SUPPORTIVE OF SUPERCELLS WITH PRIMARY THREAT OF LARGE HAIL.
ALTHOUGH LOW LEVEL SHEAR IS NOT FORECAST TO BE IMPRESSIVE THIS FAR
NW...FORECAST SOUNDINGS SUGGEST AN ISOLATED TORNADO COULD NOT BE
RULED OUT SHOULD CAPPING BREAK LATER TODAY AND EARLY THIS EVENING.
THIS ACTIVITY SHOULD ALSO INCREASE INTO A MCS AND TRACK ACROSS THE
ARKLATEX AND INTO THE MID SOUTH REGION OVERNIGHT. LARGE HAIL MAY
REMAIN PRIMARY SEVERE HAZARD...ALTHOUGH STRONG SHEAR AND INCREASING
DEEP ASCENT MAY SUPPORT ISOLATED DAMAGING WINDS/TORNADO THREAT
SHOULD BOUNDARY LAYER NOT BECOME TOO STABLE OVERNIGHT.
...SRN-CENTRAL CA COAST...
MOIST PLUME PRECEDING NEXT STRONG IMPULSE WILL SHIFT ACROSS MUCH OF
CA TODAY WITH SUFFICIENT LIFT AND WEAK INSTABILITY SUSTAINING
POTENTIAL FOR ISOLATED THUNDERSTORMS NEAR THE COAST. MORE
ROBUST...LOW-TOPPED THUNDERSTORMS WITHIN POST-FRONTAL OPEN-CELL CU
FIELD ATTENDANT TO MID LEVEL COLD POCKET SHOULD SHIFT INTO CENTRAL
CA THIS AFTERNOON AND SRN CA LATER THIS EVENING/OVERNIGHT. SMALL
HAIL AND WATERSPOUT DEVELOPMENT MAY ACCOMPANY STRONGER CORES AS THIS
ACTIVITY MOVES ASHORE.
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