SWODY1
SPC AC 011954
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0254 PM CDT WED APR 01 2009
VALID 012000Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CNTRL GULF COASTAL
REGION INTO NRN FL...
...THERE IS A SLGT RISK OF SVR TSTMS OVER A PORTION OF THE SRN
PLAINS...
...NRN FL THROUGH THE NERN GULF COASTAL AREA...
CONVECTIVELY ENHANCED OUTFLOW BOUNDARY STRETCHES ACROSS NRN FL.
MODEST BUT PERSISTENT SWLY LOW LEVEL FLOW WILL SUSTAIN LIFT AND
CONVECTIVE DEVELOPMENT ALONG THE BOUNDARY NEXT SEVERAL HOURS. LOW
LEVEL SHEAR IS NOT PARTICULARLY STRONG. HOWEVER...40-50 KT WLY FLOW
ALOFT WITHIN THE SUBTROPICAL JET STREAM WILL MAINTAIN SUFFICIENT
BULK SHEAR FOR A THREAT OF ORGANIZED STORMS INCLUDING SUPERCELLS
WITH STORMS DEVELOPING ALONG THE CONVECTIVE OUTFLOW AS WELL AS ALONG
SEA BREEZE BOUNDARIES. SURFACE HEATING HAS RESULTED IN MODERATE
INSTABILITY (1000-1500 J/KG MLCAPE) OVER CNTRL FL WHERE DISCRETE
STORMS HAVE DEVELOPED ON SEABREEZE. ISOLATED DAMAGING WIND AND LARGE
HAIL ARE THE MAIN THREATS WITH THIS ACTIVITY. HOWEVER...A TORNADO OR
TWO CANNOT BE RULED OUT. THREAT WILL PERSIST AT LEAST INTO THE EARLY
EVENING.
LOW LEVEL JET IS FORECAST TO STRENGTHEN TONIGHT OVER THE NRN GULF IN
ASSOCIATION WITH AN IMPULSE EJECTING ENEWD THROUGH THE SUBTROPICAL
JET STREAM. THIS WILL LIKELY CONTRIBUTE TO SOME NWD RETREAT OF THE
FRONT CURRENTLY OVER THE NWRN GULF. ADDITIONAL STORMS MAY DEVELOP
FARTHER WEST OVER THE CNTRL/NERN GULF WHERE STRENGTHENING LOW LEVEL
JET INTERSECTS THE BAROCLINIC ZONE. IF THE BOUNDARY CAN ADVANCE FAR
ENOUGH INLAND...THREAT WILL EXIST FOR ISOLATED DAMAGING WIND...LARGE
HAIL AND PERHAPS A TORNADO OR TWO.
...SRN PLAINS...
SEE PREVIOUS DISCUSSION.
..DIAL.. 04/01/2009
.PREV DISCUSSION... /ISSUED 1126 AM CDT WED APR 01 2009/
...SYNOPSIS...
LARGE-SCALE PATTERN WILL REMAIN PROGRESSIVE THROUGH THE PERIOD WITH
THE PRIMARY FEATURE OF INTEREST BEING RAPIDLY INTENSIFYING MIDLEVEL
TROUGH WHICH WILL DIG SEWD THROUGH THE FOUR CORNERS REGION BEFORE
SHIFTING MORE EWD INTO THE CNTRL/SRN PLAINS TONIGHT. ELSEWHERE...A
SUBTROPICAL BRANCH OF WESTERLIES WILL BE MAINTAINED ACROSS THE GULF
COAST REGION WITH SEVERAL WEAK PERTURBATIONS EMBEDDED WITHIN THIS
FLOW REGIME.
IN THE LOW LEVELS...LEE CYCLOGENESIS IS UNDERWAY THIS MORNING OVER
CNTRL/ERN CO IN RESPONSE TO THE APPROACH OF MIDLEVEL SYSTEM OVER THE
GREAT BASIN. THIS LOW WILL CONTINUE TO DEEPEN THROUGH THE DAY WHILE
DEVELOPING SEWD THROUGH THE SRN HIGH PLAINS BEFORE MOVING INTO CNTRL
OK BY 02/12Z. MEANWHILE...ATTENDANT PACIFIC FRONT WILL PUSH
EWD/SEWD FROM THE CNTRL/SRN ROCKIES THROUGH THE SRN HIGH PLAINS INTO
CNTRL PARTS OF OK/TX BY THU MORNING. OVER FL...A WEAK SURFACE WAVE
OBSERVED OVER THE PNHDL THIS MORNING WILL LIKELY DEVELOP EWD ACROSS
NRN FL TODAY IN ADVANCE OF A WEAK DISTURBANCE EMBEDDED WITHIN
SUBTROPICAL AIRSTREAM. AS THIS OCCURS...EXPECT OUTFLOW BOUNDARY TO
SLOWLY RETREAT NWD THROUGH THE NRN PENINSULA.
...CNTRL/ERN GULF COAST INTO CNTRL FL...
12Z SOUNDINGS AND GOES SOUNDER DATA INDICATE A RELATIVELY MOIST
LOW-LEVEL AIR MASS IN PLACE TODAY ACROSS THE CNTRL/SRN FL PENINSULA
WITH SURFACE DEWPOINTS IN THE 60S TO AROUND 70F AND PW VALUES OF
1.3-1.5 INCHES. THIS MOISTURE WILL COMBINE WITH STRONGER DIABATIC
HEATING S OF OUTFLOW BOUNDARY TO SUPPORT A MODERATELY UNSTABLE AIR
MASS WITH MLCAPE APPROACHING 1500-2000 J/KG. GIVEN THE RELATIVELY
WEAK CAP...EXPECT TSTMS TO BECOME FOCUSED ALONG OUTFLOW BOUNDARY AND
ERN SEA BREEZE BY LATE MORNING INTO THIS AFTERNOON AS AIR MASS
WARMS/DESTABILIZES.
DESPITE THE RELATIVELY WEAK LOW-LEVEL WIND FIELDS...THE PRESENCE OF
THE SUBTROPICAL JET IS RESULTING IN RATHER STRONG MID AND HIGH-LEVEL
FLOW ACROSS THE NRN AND CNTRL PENINSULA WITH VERTICAL SHEAR QUITE
SUFFICIENT /40-50+ KT/ FOR SUPERCELLS. WHILE DAMAGING WINDS AND
SOME HAIL WILL BE THE PRIMARY SEVERE THREATS...A TORNADO OR TWO WILL
BE POSSIBLE WITH ANY MORE INTENSE SUPERCELLS THAT CAN INTERACT
FAVORABLY WITH THE OUTFLOW BOUNDARY AND/OR SEA BREEZE.
SEE MCD 357 FOR FURTHER DETAILS REGARDING NEAR TERM SEVERE THREAT.
OVERNIGHT...STRENGTHENING LLJ WILL ENHANCE MOISTURE AND WARM THERMAL
ADVECTIONS N OF RETREATING MARINE FRONT...RESULTING IN INCREASING
TSTM ACTIVITY ACROSS THE CNTRL/ERN GULF STATES. LATEST MODEL
GUIDANCE SUGGESTS THAT SURFACE-BASED STORM DEVELOPMENT WILL BE MOST
LIKELY ALONG THE NERN GULF COAST WHERE ENVIRONMENT WILL BECOME
INCREASINGLY SUPPORTIVE OF SUPERCELLS CAPABLE OF DAMAGING
WINDS...HAIL AND PERHAPS TORNADOES. OTHERWISE...EXPECT THE
POTENTIAL FOR SOME HAIL WITH ANY MORE INTENSE ELEVATED TSTMS THAT
MAY DEVELOP.
...SRN PLAINS...
12Z REGIONAL SOUNDINGS INDICATE THAT BOUNDARY LAYER IS RATHER DRY
THIS MORNING IN WAKE OF FRONTAL PASSAGE INTO THE NWRN GULF OF
MEXICO. HOWEVER...GOES SOUNDER DATA SHOW THAT CONSIDERABLY MORE
MOIST CONDITIONS EXIST ALONG FRONT OVER THE SHELF WATERS. THIS
MOISTURE WILL BEGIN TO RAPIDLY RETURN NWD THROUGH THE PERIOD AS SLY
LLJ INTENSIFIES AHEAD OF MATURING SURFACE CYCLONE. THIS PROCESS
WILL OCCUR BENEATH EML/STEEP MIDLEVEL LAPSE RATES PLUME PRECEDING
INTENSIFYING MIDLEVEL SYSTEM. ONLY WEAK CONVECTIVE INSTABILITY IS
FORECAST THROUGH THE DIURNAL HEATING CYCLE AHEAD OF DEVELOPING
DRYLINE/PRE-FRONTAL TROUGH OVER WRN OK INTO NWRN TX. MORE
SUBSTANTIAL DESTABILIZATION IS EXPECTED OVERNIGHT INTO THE ARKLATEX
AS RICHER MOISTURE IS ADVECTED NWD IN ADVANCE OF PACIFIC FRONT.
DESPITE THE PRESENCE OF STEEP LAPSE RATES AND STRENGTHENING VERTICAL
SHEAR...MOISTURE AND RESULTANT CONVECTIVE INSTABILITY WILL REMAIN
LIMITING INGREDIENTS FOR DEEP MOIST CONVECTION AHEAD OF DRYLINE
THROUGH THE DIURNAL HEATING CYCLE. LATEST NAM GUIDANCE CONTINUES TO
SUGGEST THAT ISOLATED TSTMS WILL BE POSSIBLE BETWEEN 02/00-03Z OVER
PARTS OF SWRN/S-CNTRL KS INTO NWRN/N-CNTRL OK WITHIN ZONE OF
SUSTAINED AND CONCENTRATED CONVERGENCE NE OF SURFACE LOW. SHOULD
STORMS DEVELOP AND BECOME SUSTAINED...POTENTIAL WILL EXIST FOR SOME
HAIL AND PERHAPS LOCALLY STRONG WIND GUSTS.
THE GREATER LIKELIHOOD FOR STORM DEVELOPMENT WILL OCCUR TOWARD
02/12Z FROM THE OZARK PLATEAU SWD THROUGH THE ARKLATEX INTO ERN TX.
BY THIS TIME...MORE ROBUST MOIST RETURN/DESTABILIZATION WILL OCCUR
AHEAD OF COLD FRONT...COINCIDENT WITH STRENGTHENING DEEP-LAYER
FORCING FOR ASCENT. FORECAST SOUNDINGS SUGGEST THAT STORMS SHOULD
REMAIN SLIGHTLY ELEVATED ABOVE A SHALLOW NEAR SURFACE INVERSION.
HOWEVER...THE PRESENCE OF STEEP MIDLEVEL LAPSE RATES AND THE
INCREASING LOW-LEVEL MOISTURE WILL RESULT IN MUCAPE RANGING FROM
500-1000 J/KG OVER THE OZARK PLATEAU TO 1000-2000 J/KG OVER ERN TX.
THIS INSTABILITY IN CONJUNCTION WITH STRONG CLOUD-BEARING SHEAR
SUGGESTS THE POTENTIAL FOR SEVERE STORMS CAPABLE OF MAINLY LARGE
HAIL.
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