SPC AC 271725
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1225 PM CDT SAT JUN 27 2009
VALID 281200Z - 291200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE UPPER OH AND TN
VALLEYS TO THE MID SOUTH...
...SYNOPSIS...
SHORT WAVE TROUGH/CLOSED LOW AMPLIFYING ACROSS THE NRN PLAINS/ UPPER
MS VALLEY DURING DAY 1 WILL PROGRESS ESEWD INTO THE GREAT LAKES AND
OH VALLEY ON SUNDAY. BAND OF 60-70 KT WNWLY MID LEVEL WINDS ALONG
SRN PERIPHERY OF THIS TROUGH WILL SPREAD INTO THE OH VALLEY. AN
ATTENDANT COLD FRONT INITIALLY EXTENDING FROM THE GREAT LAKES SWWD
THROUGH THE MID SOUTH TO SRN PLAINS EARLY SUNDAY WILL MOVE EAST AND
SE EXTENDING FROM THE NERN...MID ATLANTIC AND SERN STATES WWD
THROUGH TX BY THE END OF THE PERIOD.
...UPPER OH AND TN VALLEYS THROUGH PORTION OF THE SERN STATES...
27/12Z UPPER AIR DATA AND MID MORNING SURFACE ANALYSES INDICATED A
RICH BOUNDARY LAYER EXTENDED FROM THE LOWER MS VALLEY THROUGH THE TN
VALLEY WITH SURFACE DEWPOINTS IN THE LOWER 70S. THE ERN EXTENT OF
THIS MOISTURE AXIS WILL ADVECT NEWD INTO THE UPPER OH VALLEY ON DAY
2. DESPITE MODEST MID LEVEL LAPSE RATES /6-6.5 C/KM/ ACROSS THE
SLIGHT RISK AREA ON SUNDAY...SURFACE HEATING WITHIN THE VERY MOIST
PRE-FRONTAL WARM SECTOR WILL RESULT IN MODERATE INSTABILITY.
SOME STORMS MAY BE IN PROGRESS AHEAD OF THE FRONT EARLY SUNDAY
ACROSS A PORTION OF THE OH VALLEY. ACTIVITY WILL MOST LIKELY BE
SLIGHTLY ELEVATED ABOVE A STABLE SURFACE LAYER WITH LOW SEVERE
POTENTIAL. STORMS WILL LIKELY REDEVELOP ALONG FRONT OR PRE-FRONTAL
OUTFLOW BOUNDARIES AND SUBSEQUENTLY ADVANCE EWD AND SEWD AS THE
ATMOSPHERE DESTABILIZES. THE MID LEVEL JET ROTATING THROUGH BASE OF
THE UPPER TROUGH WILL RESULT IN 30-40 KT WLY UNIDIRECTIONAL BULK
SHEAR...GENERALLY FROM OH VALLEY SWD TO THE KY/TN BORDER. STORMS
SHOULD ORGANIZE INTO LINE SEGMENTS OR CLUSTERS AS THEY DEVELOP SEWD
WITH A THREAT OF ISOLATED DAMAGING WIND AND HAIL THROUGH MID
EVENING. ALTHOUGH DEEP LAYER SHEAR WILL BE WEAKER ACROSS THE TN
VALLEY...STRONGER INSTABILITY SHOULD COMPENSATE AND SUPPORT A SEVERE
WEATHER THREAT AS THE FRONT MOVES INTO THIS REGION.
...SERN GA...
A COLD FRONT IS EXPECTED TO MOVE OFF THE CAROLINA COAST SATURDAY
NIGHT...WHILE THE WRN EXTENT OF THIS BOUNDARY SHOULD EXTEND WNWWD
FROM NEAR SAV TO NRN GA AND SERN TN AT 12Z SUNDAY. A MODERATELY
UNSTABLE AIR MASS SHOULD PROVE FAVORABLE FOR TSTM DEVELOPMENT ALONG
THE EXTENT OF THIS BOUNDARY. STRONGEST LOW LEVEL CONVERGENCE SHOULD
OCCUR WHERE THIS FRONT INTERACTS WITH THE SEA BREEZE BOUNDARY IN
SERN GA SUNDAY AFTERNOON. EFFECTIVE BULK SHEAR AROUND 25 KT MAY
SUPPORT A FEW ORGANIZED STORMS WITH AN ISOLATED THREAT FOR SEVERE
WEATHER.
...NM EWD TO NRN TX...
UPPER FLOW AND SHEAR PROFILES WILL REMAIN WEAK IN THIS REGION DUE TO
PROXIMITY OF UPPER RIDGE. DESPITE LACK OF LARGE SCALE UPPER
FORCING...FRONTAL CONVERGENCE SHOULD BE SUFFICIENT TO INITIATE
STORMS BY MID-LATE AFTERNOON ACROSS PARTS OF TX. OTHER STORMS WILL
LIKELY DEVELOP OVER THE HIGHER TERRAIN OF NM AIDED BY WEAK IMPULSES
TRACKING ACROSS THIS REGION. STEEP LOW LEVEL LAPSE RATES
AND LARGE TEMPERATURE-DEWPOINT SPREADS WILL SUPPORT A THREAT OF
ISOLATED DOWNBURSTS. MARGINALLY SEVERE HAIL COULD ALSO ACCOMPANY
THE STRONGER STORMS. THREAT DOES NOT WARRANT MORE THAN 5% SEVERE
PROBABILITIES...AND STORMS SHOULD WEAKEN RAPIDLY DURING THE EVENING
WITH ONSET OF NOCTURNAL COOLING.
...NERN CO/SWRN NEB...
THE SRN EXTENT OF A WEAK FRONT SPREADING E/SEWD ACROSS THE NRN
PLAINS/UPPER MS VALLEY TODAY SHOULD BECOME STATIONARY FROM NWRN KS
INTO NERN CO BY 12Z SUNDAY. RESIDUAL MOISTURE ALONG THIS BOUNDARY
INTO NERN CO COMBINED WITH STEEP LAPSE RATES WILL RESULT IN MODERATE
INSTABILITY SUNDAY AFTERNOON. A WEAK IMPULSE TRACKING SEWD ACROSS
THIS REGION BY LATE SUNDAY AFTERNOON SHOULD AID IN SUPPORTING TSTM
DEVELOPMENT...WITH EFFECTIVE BULK SHEAR AROUND 25 KT SUGGESTING A
FEW STORMS COULD PRODUCE STRONG GUSTS/HAIL.
..PETERS.. 06/27/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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