SPC AC 280559
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT TUE JUL 28 2009
VALID 291200Z - 301200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
PLAINS...CNTRL PLAINS AND SRN OZARKS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE
MID-ATLANTIC...ERN PA...NJ AND SERN NY...
...SRN PLAINS AND CNTRL PLAINS/OZARKS...
A POSITIVELY-TILTED SHORTWAVE TROUGH OVER THE NRN HIGH PLAINS
WEDNESDAY WILL DIG SEWD INTO THE SRN AND CNTRL PLAINS WEDNESDAY
NIGHT. AT THE SFC...A COLD FRONT IS FORECAST TO MOVE SEWD INTO THE
CNTRL HIGH PLAINS DURING THE DAY. SOUTH OF THE BOUNDARY...SELY SFC
WINDS SHOULD EXIST HELPING TO REINFORCE A VERY MOIST AIRMASS WITH
SFC DEWPOINTS LIKELY IN THE LOWER 70S F ACROSS MUCH OF THE SRN
PLAINS. THE MODELS ARE NOW IN MUCH BETTER AGREEMENT FOR WEDNESDAY
DEVELOPING A LARGE AREA OF MODERATE TO STRONG INSTABILITY FROM THE
TX AND OK PANHANDLES ESEWD ACROSS OK INTO THE SRN OZARKS. ELEVATED
THUNDERSTORM ACTIVITY MAY BE ONGOING DURING THE MORNING NEAR THE
COLD FRONT IN THE CNTRL HIGH PLAINS OR IN THE SRN HIGH PLAINS WHERE
A LOW-LEVEL JET IS FORECAST TO BE LOCATED.
ALTHOUGH MODEL SOLUTIONS VARY SIGNIFICANTLY CONCERNING THUNDERSTORM
DEVELOPMENT WEDNESDAY AFTERNOON...ONE PLAUSIBLE SCENARIO WOULD BE
FOR INITIATION OF SFC-BASED CONVECTION TO OCCUR ALONG THE NWRN EDGE
OF THE STRONGER INSTABILITY BY LATE AFTERNOON IN SERN CO...SW KS OR
THE OK/TX PANHANDLES WITH AN MCS ORGANIZING AND MOVING ESEWD ACROSS
THE REGION. THIS IDEA IS SUPPORTED BY THE NAM AND GFS SOLUTIONS
WHICH STRENGTHEN A WELL-DEFINED 30-40 KT LOW-LEVEL JET ACROSS THE
SRN PLAINS BY EARLY EVENING. SUBSTANTIAL LOW-LEVEL FLOW AND
INCREASING FLOW ALOFT SHOULD CREATE MODERATE TO STRONG VERTICAL
SHEAR PROFILES SUFFICIENT FOR AT LEAST ISOLATED SEVERE STORMS AND
POSSIBLY SOME SUPERCELLS. FORECAST SOUNDINGS ACROSS THE REGION SHOW
STEEP MID-LEVEL LAPSE RATES FAVORABLE FOR ISOLATED LARGE HAIL. AN
INCREASING WIND DAMAGE THREAT COULD ALSO EXIST IF AN MCS CAN BECOME
WELL-DEVELOPED AND PERSIST INTO THE EVENING. AN UPGRADE IN SEVERE
PROBABILITIES MAY BE NECESSARY ACROSS THE REGION ONCE MODEL
SOLUTIONS BECOME IN BETTER AGREEMENT AND CERTAINTY INCREASES.
THUNDERSTORMS WILL ALSO LIKELY DEVELOP DURING THE AFTERNOON ALONG
THE COLD FRONT MOVING SEWD ACROSS CNTRL AND SRN NEB INTO NRN KS.
MARGINALLY SEVERE WIND GUSTS AND HAIL WILL BE POSSIBLE DURING THE
LATE AFTERNOON WHEN INSTABILITY IN THIS REGION SHOULD BE MAXIMIZED.
...MID-ATLANTIC/ERN PA/NJ/SERN NY...
SOUTHWEST FLOW WILL REMAIN IN PLACE TODAY ACROSS THE NERN STATES AS
A LOW-LEVEL JET MOVES NEWD FROM THE CNTRL APPALACHIAN MTNS INTO THE
MID-ATLANTIC REGION. PARTIAL CLEARING AND SFC HEATING SHOULD ALLOW
SCATTERED THUNDERSTORMS TO INITIATE DURING THE AFTERNOON ALONG AN
AXIS OF MODERATE INSTABILITY FORECAST TO EXTEND FROM ERN VA AND MD
NNEWD ACROSS ERN PA INTO SERN NY. FORECAST SOUNDINGS ALONG THIS
CORRIDOR WEDNESDAY AFTERNOON SHOW A RAPID INCREASE IN BOUNDARY LAYER
FLOW AS THE LOW-LEVEL JET APPROACHES FROM THE WEST SOUTHWEST. THIS
COMBINED WITH ABUNDANT LOW-LEVEL MOISTURE /SFC DEWPOINTS IN THE
LOWER 70S F/ AND STEEP LOW-LEVEL LAPSE RATES SHOULD BE FAVORABLE FOR
ISOLATED DAMAGING WIND GUSTS WITH THE STRONGER CELLS.
...TN VALLEY/SRN APPALACHIAN MTNS...
A BROAD WARM SECTOR IS FORECAST TO EXIST ACROSS THE REGION WEDNESDAY
FROM THE MID-MS VALLEY EWD ACROSS THE TN VALLEY INTO THE CAROLINAS.
SCATTERED THUNDERSTORMS APPEAR LIKELY TO DEVELOP IN AREAS WHERE
INSTABILITY BECOMES MAXIMIZED WEDNESDAY AFTERNOON. ALTHOUGH VERTICAL
SHEAR APPEARS ON THE WEAK SIDE FOR SEVERE STORMS...A FEW MARGINALLY
SEVERE WIND GUSTS WILL BE POSSIBLE AS LOW-LEVEL LAPSE RATES BECOME
QUITE STEEP DURING THE LATE AFTERNOON.
..BROYLES.. 07/28/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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