SPC AC 290558
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1258 AM CDT WED JUL 29 2009
VALID 291200Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE SOUTHERN HIGH PLAINS
TO ARKLATEX...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE MID ATLANTIC STATES
TO SOUTHERN NY/PORTIONS SOUTHERN NEW ENGLAND...
...SYNOPSIS...
MEAN LONGWAVE TROUGH/EXTENSIVE CYCLONIC LARGE SCALE FLOW PATTERN
WILL PERSIST OVER THE CONUS THROUGH TONIGHT. WITHIN THIS
REGIME...LOW AMPLITUDE SHORTWAVE TROUGH OVER THE TN VALLEY VICINITY
EARLY IN THE OVERNIGHT WILL SHIFT NORTHEASTWARD AND INCREASINGLY
PHASE WITH A STRONGER IMPULSE OVERSPREADING EASTERN ONTARIO TO
NORTHERN QUEBEC. MULTIPLE DISTURBANCES EMBEDDED WITHIN NORTHWESTERLY
FLOW ALOFT WILL REINFORCE THE BROAD TROUGH OVER THE NORTHERN/CENTRAL
PORTIONS OF THE ROCKIES AND PLAINS. AT THE
SURFACE...NORTHEAST-SOUTHWEST ORIENTED FRONTAL BOUNDARY WILL SLOWLY
SPREAD EAST-SOUTHEASTWARD ACROSS THE OH VALLEY/LOWER GREAT
LAKES...WHILE BEING CONVECTIVELY MODIFIED/REMAINING QUASI-STATIONARY
ACROSS THE SOUTHERN PLAINS/ARKLATEX IN ADVANCE OF A
SECONDARY/REINFORCING FRONT SPREADING SOUTHWARD ACROSS THE CENTRAL
PLAINS. GIVEN THIS SCENARIO...A BROAD EXTENT OF AT LEAST ISOLATED
SEVERE POTENTIAL IS AGAIN EXPECTED FROM THE SOUTHERN ROCKIES FRONT
RANGE/SOUTHERN PLAINS TO THE NORTHEAST STATES.
...CENTRAL/SOUTHERN HIGH PLAINS TO ARKLATEX/LOWER MS VALLEY...
SCATTERED TSTMS/SOME MODESTLY ORGANIZED CLUSTERS WILL BE ONGOING
THIS MORNING ACROSS WEST/NORTH TX AND PORTIONS OF OK TO THE
ARKLATEX. CLOUD COVER/PRECIPITATION AND NUMEROUS CONVECTIVE OUTFLOWS
COMPLICATE THE DAYTIME DETAILS...BUT EVEN MODEST HEATING SHOULD
RESULT IN A MODERATELY UNSTABLE/WEAKLY CAPPED AIRMASS BY AFTERNOON
GIVEN THE DEGREE OF MOISTURE /14-18 G PER KG MEAN MIXING RATIOS/
THAT WILL REMAIN IN PLACE ACROSS THE SOUTHERN PLAINS/ARKLATEX. AIDED
BY A CONVECTIVELY DISTURBED MID LEVEL TROUGH...WHICH IS EXPECTED TO
SPREAD EASTWARD ACROSS SOUTHERN OK/NORTH TX TO THE ARKLATEX DURING
THE DAY...ISOLATED TO SCATTERED STORMS /MAINLY MULTICELLULAR/ SHOULD
BECOME INCREASINGLY COMMON THROUGH THE AFTERNOON...WITH POTENTIAL
FOR DAMAGING WINDS/HAIL MAINLY THROUGH AROUND SUNSET.
FARTHER WEST...SIMILAR TO TUESDAY...TSTMS SHOULD AGAIN INITIALLY
DEVELOP/INCREASE OVER THE HIGHER TERRAIN/FRONT RANGE OF SOUTHEAST
CO/NORTHEAST NM DURING THE MID AFTERNOON HOURS...AIDED BY NORTHERN
PLAINS HEIGHT FALLS AND THE APPROACH OF A MID LEVEL
PERTURBATION/SPEED MAXIMA EMBEDDED WITHIN MODERATE NORTHWESTERLY
FLOW ALOFT. VEERING WIND PROFILES WILL SUPPORT SCATTERED SUPERCELLS
CAPABLE OF LARGE HAIL/ISOLATED DAMAGING WINDS THROUGH SUNSET. WITH
TIME...UPSCALE DEVELOPMENT INTO ONE OR MORE SOUTH-SOUTHEASTWARD
MOVING MCS/S SEEMS PROBABLE...WITH POTENTIAL FOR DAMAGING WINDS TO
INCREASE ACCORDINGLY ACROSS THE SOUTHERN HIGH PLAINS INCLUDING
PORTIONS OF OK/TX PANHANDLES AND NORTHWEST TX/PERHAPS WESTERN OK.
...MID ATLANTIC STATES TO SOUTHERN NY/SOUTHERN NEW ENGLAND...
EMBEDDED WITHIN THE CYCLONIC LONGWAVE REGIME...MID LEVEL IMPULSE
OVER THE TN VALLEY EARLY IN THE OVERNIGHT IS EXPECTED TO TRANSITION
NORTHEASTWARD ALONG THE APPALACHIANS THROUGH THE DAY...AND REACH NEW
ENGLAND LATER TONIGHT. WITH A MOIST AIRMASS ALREADY IN PLACE ALONG
THE EASTERN SEABOARD /UPPER 60S TO LOWER 70S F SFC DEWPOINTS/...A
NORTHEASTWARD MOISTURE TRANSPORT WILL OCCUR IN TANDEM WITH THE LOW
AMPLITUDE SHORTWAVE TROUGH...WITH INCREASINGLY STRONG LOW/MID
TROPOSPHERIC WIND FIELDS LIKELY TO ACCOMPANY THIS IMPULSE AS WELL.
WITH A MOIST/WEAKLY CAPPED BOUNDARY LAYER AND THE APPROACH OF THE
AFOREMENTIONED SHORTWAVE TROUGH...STORMS SHOULD DIURNALLY
INCREASE/INTENSIFY BY AFTERNOON IN VICINITY OF MODESTLY
DEEPENING/NORTHEASTWARD ADVANCING SURFACE LOW AND ALONG/EAST OF
SURFACE TROUGH. DAMAGING WINDS/PERHAPS SOME HAIL WILL BE
POSSIBLE...AND SUFFICIENT LOW LEVEL SRH IN THE PRESENCE OF A RATHER
MOIST BOUNDARY LAYER MAY SUPPORT THE POSSIBILITY OF A TORNADO OR TWO
AS WELL.
..GUYER/LEVIT.. 07/29/2009
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