SWODY1
SPC AC 171259
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0659 AM CST TUE FEB 17 2009
VALID 171300Z - 181200Z
...THERE IS A SLGT RISK OF SVR TSTMS THE LWR MS AND TN VLYS...
...SYNOPSIS...
FAIRLY LOW AMPLITUDE PATTERN WILL PREVAIL OVER MUCH OF THE CONUS
THIS PERIOD AS FLAT RIDGE NOW OVER THE OZARKS/SRN PLNS CONTINUES E
TO THE MID/S ATLANTIC CST...AND UPR LOW NOW NEAR SFO DRIFTS E AND
WEAKENS. SHORTWAVE IMPULSE NOW OVER ERN UT EXPECTED TO ACCELERATE E
ACROSS THE CNTRL RCKYS/CNTRL PLNS LATER TODAY/TONIGHT AHEAD OF NRN
STREAM DISTURBANCE AMPLIFYING SE FROM SK/MB.
AT LWR LVLS...A STRENGTHENING SW TO WSWLY 850 JET WILL PREVAIL FROM
E TX AND THE NW GULF OF MEXICO INTO THE TN AND LWR OH VLYS. THIS
JET WILL OVERRIDE A MORE S OR SSWLY FLOW OF MODIFIED POLAR AIR
RETURNING NWD ON BACKSIDE OF RETREATING SFC RIDGE ALONG THE S
ATLANTIC CST.
...LWR MS/TN VLYS...
SATELLITE AND GPS PW DATA SHOW FAIRLY RICH MOISTURE /PW AOA 1 INCH/
IN PLACE OVER THE ERN THIRD OF TX AND WRN LA. THIS MOISTURE WILL
SPREAD ENE INTO THE LWR MS AND TN VLYS WITH 50+ KT LLJ LATER
TODAY/TONIGHT...ATOP SHALLOW LAYER OF COOLER/DRIER AIR AT THE SFC.
ALTHOUGH MODERATE SFC-BASED INSTABILITY MAY DEVELOP WITH DAYTIME
HEATING TODAY OVER E TX...COMBINATION OF LOW CLOUDS AND CAPPING
INVERSION ON S SIDE OF SRN STREAM JET SHOULD PROHIBIT TSTM
DEVELOPMENT. WILL NEVERTHELESS MAINTAIN LOW PROBABILITIES FOR THE
UNLIKELY DEVELOPMENT OF AN ISOLD STORM THERE THIS AFTN. FARTHER
ENE...EXPECT AREA OF WEAK ELEVATED CONVECTION NOW OVER AR AND THE
LWR TN VLY TO BE FOLLOWED BY ADDITIONAL...STRONGER DEVELOPMENT
TONIGHT/EARLY WEDNESDAY AS RICHER ELEVATED MOISTURE INFLOW IS LIFTED
BY STRENGTHENING WAA.
FORCING FOR ASCENT ACROSS REGION WILL BE LIMITED TO 850-700 MB WAA
AS DPVA WITH AFOREMENTIONED UT IMPULSE REMAINS WELL TO THE N AND W.
BUT COMBINATION OF INCREASING MOISTURE AVAILABILITY...FAIRLY STEEP
MID LVL LAPSE RATES...AND 55-65 KT UNIDIRECTIONAL WLY FLOW IN THE
700-500 MB LAYER WILL SUPPORT STORM ORGANIZATION/ SUSTENANCE.
SLIGHTLY ELEVATED ROTATING STRUCTURES AND BOWS WILL POSE A THREAT
FOR SVR HAIL...AND...ESPECIALLY TOWARD 12Z...POSSIBLY DMGG WIND.
IN FAR E TX...WRN/NRN LA AND SRN AR...THERE EXISTS A POSSIBILITY FOR
SFC-BASED STORMS LATE IN THE PERIOD AS RESIDUAL MODIFIED POLAR AIR
IS REPLACED BY MARITIME AIR AT THE SFC. FOR THIS REASON... WILL
MAINTAIN LOW PROBABILITIES FOR TORNADOES AND WIND DAMAGE IN THOSE
AREAS.
...CA...
COLDEST AIR ALOFT ASSOCIATED WITH UPR LOW NOW NEARING SFO WILL CROSS
THE BAY AREA AND CNTRL VLY AROUND MAX HEATING TIME. SATELLITE LOOPS
SUGGEST POTENTIAL FOR SOME BREAKS...WITH SFC HEATING ACTING ON
BOUNDARY LAYER LEFT MOISTENED BY RECENT RAINS. SETUP MAY SUPPORT A
FEW CLUSTERS OF STORMS WITH MARGINALLY SVR HAIL THROUGH LATE AFTN.
..CORFIDI.. 02/17/2009
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