SWODY1
SPC AC 041944
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0244 PM CDT SAT JUL 04 2009
VALID 042000Z - 051200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE HIGH
PLAINS...SRN PLAINS...OZARKS AND MID-MS VALLEY...
THE MOST SIGNIFICANT CHANGE TO THE 20Z OUTLOOK IS TO REMOVE THE
SLIGHT RISK FROM PARTS OF NCNTRL OK ENEWD ACROSS SW AND CNTRL MO.
THIS CORRIDOR IS IN THE WAKE OF A LINE OF THUNDERSTORMS WITH THE
AIRMASS CHARACTERIZED BY VERY WEAK INSTABILITY AND SOMEWHAT LIMITED
VERTICAL SHEAR ESPECIALLY ACROSS SW MO. IN ADDITION...REMOVED PARTS
OF CNTRL KY FROM THE SLIGHT RISK AREA WHERE A LARGE AREA OF RAIN IS
STABILIZING THE AIRMASS. ELSEWHERE...THE OUTLOOK REMAINS NEARLY THE
SAME AS THE PREVIOUS OUTLOOK.
..BROYLES.. 07/04/2009
.PREV DISCUSSION... /ISSUED 1130 AM CDT SAT JUL 04 2009/
...SYNOPSIS...
LARGE SCALE UPPER AIR PATTERN CHANGE WAS UNDERWAY THIS INDEPENDENCE
DAY AS SUB-TROPICAL RIDGE AXIS REPOSITIONS TO THE WRN U.S. AND DEEP
UPPER LOW OVER THE NORTHEAST MOVES EAST. BROAD BELT OF WEAK TO
MODEST /20-40KT/ NWLY MID-LEVEL FLOW EXISTS BETWEEN THESE TWO LARGE
SCALE FEATURES FROM THE ROCKIES...ACROSS THE MID MS AND OH
VALLEYS...TO THE EAST COAST.
..MO/AR OZARKS EWD INTO THE LWR OH VALLEY...
CONVECTIVELY ENHANCED LOW AMPLITUDE SHORT WAVE TROUGH AND ASSOCIATED
1010MB SURFACE LOW ARE FORECAST TO TRACK FROM THE MIDWEST TO THE
LOWER OH VALLEY TODAY. WARM FRONT EXTENDS SEWD FROM THE
LOW...CURRENTLY NEAR NWRN MO...TO NRN KY...AND WAS FRACTURED BY MCS
OUTFLOW OVER SRN IL/SERN MO.
GIVEN GENERALLY LIMITED MID-LEVEL LAPSE RATES /AROUND 6.5 C PER KM/
ACROSS THE WARM SECTOR TODAY DIURNAL HEATING WILL BE THE DRIVING
FACTOR IN STRONG DESTABILIZATION AND RAPIDLY WEAKENING INHIBITION
FROM NRN/ERN AR TO KY/WRN TN. LOW LEVEL MASS TRANSPORT/ISENTROPIC
LIFT ON THE NOSE OF WSWLY LOW LEVEL JET...AND WEAK HEIGHT FALLS WITH
THE UPPER TROUGH/MCV SHOULD LEAD TO AN INCREASE IN SURFACE-BASED
CONVECTION ACROSS THE REGION THROUGH THE AFTERNOON. FORECAST
EFFECTIVE SHEAR ON THE LOWER-END THRESHOLD TO SUPPORT SUPERCELLS
/AROUND 30KT/ WILL LIKELY ALLOW SOME STORMS TO MAINTAIN UPDRAFT
INTEGRITY WITH MARGINALLY SEVERE HAIL...AND PERHAPS A BRIEF/WEAK
TORNADO. STORMS SHOULD GROW UPSCALE INTO ONE OR MORE CLUSTERS WITH
CONVECTIVELY-INDUCED COLD POOLS PROMOTING ADDITIONAL LINEAR
DEVELOPMENT/BOWING STRUCTURES. SCATTERED WIND DAMAGE SHOULD BECOME
THE PRIMARY HAZARD IN A GENERALLY NARROW CORRIDOR FROM SERN MO
ACROSS THE MS RIVER TO THE TN VALLEY THROUGH LATE TONIGHT.
..SRN PLAINS...
WEAK COLD FRONT ARCS FROM ERN KS TO THE NRN TX PNHDL AND THEN NWWD
INTO NM/CO. A WELL-DEFINED OUTFLOW/DIFFERENTIAL HEATING BOUNDARY HAS
BECOME ESTABLISHED SOUTH OF THE FRONT...FROM NWRN AR ACROSS CNTRL OK
TO THE ERN TX PNHDL. SIMILAR TO POINTS EAST...MID LEVEL LAPSE RATES
ACROSS THIS REGION ARE NOT PARTICULARLY STEEP AND MID LEVEL FLOW AND
LARGE SCALE ASCENT IS WEAKER. NONETHELESS...AS SWATH OF WEAK
PRE-FRONTAL CONVECTION DECAYS ACROSS NRN OK AND THE OZARKS THIS
MORNING...NEW AND INCREASINGLY STRONG DEVELOPMENT IS LIKELY ALONG
AND SOUTH OF THE OUTFLOW BOUNDARY...FROM NWRN AR WWD ACROSS OK TO
NWRN TX. INTENSE SURFACE HEATING ALONG THIS ZONE WILL RESULT IN
DEEPLY MIXED BOUNDARY LAYER AND SUFFICIENTLY DRY SUB-CLOUD LAYER FOR
DAMAGING TSTM DOWNDRAFTS. RESULTING STORM OUTFLOW INTERACTIONS IN
THE PRESENCE OF ABUNDANT ANTECEDENT INSTABILITY/MOISTURE WILL
SUSTAIN SEVERE WIND/MARGINAL HAIL THREATS SUFFICIENTLY TO SUPPORT
THE SLGT RISK AREA.
ONE AREA OF POTENTIALLY GREATER SEVERE STORM PROBABILITY MAY EXIST
INVOF OUTFLOW/FRONT INTERSECTION ACROSS THE TX PNHDL. STRONG HEATING
NEAR AND SOUTH OF THE BOUNDARY INTERSECTION SHOULD SUPPORT ROBUST
STORM DEVELOPMENT...CERTAINLY AS STRONG AS ANYWHERE ELSE WITHIN THE
SLGT RISK AREA. THIS JUSTIFIES INCREASING SEVERE PROBS THIS AREA TO
RESULT IN A SLGT RISK.
...UPSLOPE AREAS OF CENTRAL AND NRN ROCKIES...
WEAK POST-FRONTAL ELY/UPSLOPE FLOW AND STRONG SURFACE AND
DIFFERENTIAL HEATING SHOULD CONTRIBUTE TO WIDESPREAD TSTMS ACROSS
THE MOUNTAINS/FRONT RANGE THIS AFTERNOON. VEERING LOW LEVEL WIND
PROFILES RESULT IN SFC-6KM SHEAR OF 30-40KT ERN WY/ERN CO...MORE
THAN SUFFICIENT FOR A FEW ROTATING STORMS. PRIMARY THREAT WILL BE
LARGE HAIL AND LOCAL WET MICRO BURSTS.
...NEW ENGLAND...
WEAK DIURNAL DESTABILIZATION...COLD AIR ALOFT...AND MODEST HEIGHT
FALLS WITH SHORT WAVE TRANSITIONING ACROSS THE REGION SHOULD FAVOR A
FEW AFTERNOON STORMS CAPABLE OF PRODUCING HAIL. WEAK FLOW/SHEAR AND
LIMITED INSTABILITY WILL PROBABLY INHIBIT GREATER AREAL COVERAGE OF
THIS THREAT BUT SUFFICIENT DEVELOPMENT SHOULD OCCUR TO WARRANT
INTRODUCTION OF LOW HAIL PROBABILITIES.
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