SPC AC 121636
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1136 AM CDT SAT JUN 12 2010
VALID 121630Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS SRN HIGH PLAINS ACROSS THE
MIDWEST...
...THERE IS A SLGT RISK OF SVR TSTMS CENTRAL APPALACHIANS FROM NRN
NC AND VA TO PA/NY AND NWRN NJ...
...SRN HIGH PLAINS...
AS INDICATED IN EARLIER OUTLOOKS...FRONTAL SURGE ACROSS THE HIGH
PLAINS HAS ESSENTIALLY COME TO A HALT ACROSS NERN NM AND THE TX
PNHDL THIS MORNING. THIS BOUNDARY EXTENDS NEWD ACROSS KS WHERE IT
INTERSECTS AN OUTFLOW BOUNDARY NEAR DDC. THE OUTFLOW REINFORCED
FRONT THEN EXTENDS NEWD TO A CONVECTIVELY ENHANCED FRONTAL WAVE AND
ASSOCIATED MCV OVER IA. WARM SECTOR AIRMASS ALONG AND SOUTH OF THIS
BOUNDARY...AND AHEAD OF THE DRYLINE...WILL BECOME VERY UNSTABLE BY
AFTERNOON WITH MLCAPE 2000-3000 J/KG.
SUPPORT FOR LARGE SCALE ASCENT ACROSS THE REGION TODAY APPEARS
MARGINAL AS DEEP UPPER TROUGH OVER THE GREAT BASIN AND SOUTHWEST
REMAINS NEARLY STATIONARY. GIVEN NEGLIGIBLE HEIGHT FALLS AND
PRONOUNCED EML/CAP...PERSISTENT LOW LEVEL FRONTAL CONVERGENCE/LIFT
AND DRYLINE MIXING WILL BE THE PRIMARY DRIVERS FOR CONVECTIVE
DEVELOPMENT LATER THIS AFTERNOON FROM SWRN KS SWD ACROSS WEST TX.
SOME HIGHER RESOLUTION MODEL OUTPUT IS INDICATING THAT STORMS MAY
HAVE DIFFICULTY INITIATING WITHIN THE WEAKLY FORCED AND STRONGLY
CAPPED WARM SECTOR. ACTIVITY MAY INITIALLY DEVELOP IMMEDIATELY ALONG
THE FRONT...OR ATOP WEAK POST-FRONTAL STABLE LAYER.
HOWEVER...OUTFLOW FROM THIS INITIAL DEVELOPMENT MAY BE SUFFICIENT TO
OVERCOME REMAINING WARM SECTOR INHIBITION AND RESULT IN TRUE
SURFACE-BASED STORM INITIATION BY LATE AFTERNOON OR EARLY EVENING.
MODERATELY STRONG SWLY MID LEVEL FLOW OF 40-50KT ON THE ERN FLANK OF
THE WRN UPPER TROUGH...COUPLED WITH SELY LOW LEVEL FLOW...WILL
CONTRIBUTE TO ABOUT 30-40KT BULK SHEAR...SUFFICIENT FOR UPDRAFT
INTENSIFICATION/ROTATION IN DISCRETE STORMS AS WELL AS OVERALL STORM
PERSISTENCE. THE COMBINATION OF ANTICIPATED SHEAR AND INSTABILITY
EXISTING IMMEDIATELY ALONG THE FRONT/WIND SHIFT BOUNDARY...AND NEAR
DRYLINE/FRONT AND OUTFLOW INTERSECTIONS...MAY SUPPORT A FEW INTENSE
SUPERCELLS WITH VERY LARGE HAIL. IF STRONGER/PERSISTENT CELLS CAN
PREFERENTIALLY TRACK NEAR/ALONG THE FRONT...AS OPPOSED TO ACROSS THE
BOUNDARY INTO MORE STABLE AIR...AN ENHANCED TORNADO POTENTIAL COULD
EVOLVE.
WEAKER SHEAR BUT DEEPLY-MIXED AND HOT BOUNDARY LAYER CHARACTERIZED
BY HIGH CAPE WILL BE SITUATED FARTHER SOUTH IN WEST TX AHEAD OF THE
DRYLINE. A COUPLE OF INTENSE STORMS POSING A THREAT FOR HIGH WINDS
AND HAIL APPEAR POSSIBLE BUT OVERALL STORM COVERAGE DOES NOT APPEAR
TO WARRANT HIGHER PROBABILITIES AT THIS TIME.
...MIDWEST...
WELL-ORGANIZED CIRCULATION/FRONTAL WAVE WILL APPARENTLY CONTINUE TO
MOVE EAST FROM IA/MO ACROSS THE MS VALLEY AND INTO IL/IND LATER THIS
AFTERNOON. THE LARGER SYSTEM IS PRECEDED BY A SMALLER MCS NOW MOVING
ACROSS CHICAGO AREA. LIFT ASSOCIATED WITH THESE DISTURBANCES WILL
ACT ON AN INCREASINGLY UNSTABLE AIRMASS WITH MLCAPE OF 2000-3000
J/KG FROM ERN MO ACROSS IL AND INTO WRN IND.
STORM COVERAGE AND ORGANIZATION IN THESE AREAS WILL BE POTENTIALLY
INFLUENCED BY STRONG INHIBITION AND LACK OF STRONGER SHEAR. IF
FORCING WITH THE REMNANT MCVS AND HEATING PROVE SUFFICIENT TO
OVERCOME INHIBITION...MAGNITUDE OF INSTABILITY WILL LIKELY OFFSET
LACK OF GREATER SHEAR AND RESULT IN QUASI-ORGANIZED/PERSISTENT
STORMS WITH A THREAT FOR SOME HAIL AND LOCALLY DAMAGING WINDS.
...CNTRL APPALACHIANS EWD FROM NC TO SERN NY...
TWO MECHANISMS APPEAR RESPONSIBLE FOR AN UPSWING IN STRONG TO SEVERE
STORMS FROM NY/PA SOUTH TO VA AND NC THIS AFTERNOON.
FIRST...THE LONG-LIVED MESOVORTEX THAT INITIATED IN MEXICO SEVERAL
DAYS AGO AND PRODUCED DEVASTATING FLOODING IN AR EARLY FRI HAS NOW
CRESTED THE SUB-TROPICAL RIDGE AND WILL MOVE OFF THE MID ATLANTIC
COAST BY SUNDAY MORNING. CONVECTION ASSOCIATED WITH THIS DISTURBANCE
ARCS FROM OH SEWD WITHIN THE TRAILING VORT LOBE CROSSING THE CNTRL
APPALACHIANS ATTM. EXPECT STORM ACTIVITY TO CONTINUE TO SPREAD EAST
OF THE APPALACHIANS INTO A VERY WARM AND INCREASINGLY UNSTABLE
AIRMASS. WITH MID LEVEL FLOW AOB 25KT AND GENERALLY WEAK
SHEAR...CHANCES FOR WIDESPREAD SEVERE WEATHER APPEAR LIMITED.
HOWEVER...WITH CONVECTION EXPECTED TO INCREASE COINCIDENT WITH
MAXIMUM IN DIURNAL HEATING...SCATTERED DAMAGING WIND EVENTS APPEAR
LIKELY.
A POTENTIALLY MORE ORGANIZED BUT ALSO LOCALIZED SEVERE WEATHER
EPISODE MAY UNFOLD AS FRONTAL WAVE TRACKS ESEWD ALONG WARM FRONT
FROM WRN PA/NY TO NRN NJ THROUGH TONIGHT. WEAK SURFACE LOW IS
ASSOCIATED WITH A LOW AMPLITUDE SHORT WAVE TROUGH EMBEDDED WITHIN
BELT OF 35-40KT MID LEVEL FLOW. SATELLITE IMAGERY WOULD SUGGEST
STRONG WARM SECTOR HEATING NEXT FEW HOURS WITH MLCAPE CLIMBING ABOVE
1000 J/KG AHEAD OF THE FRONTAL WAVE. SHEAR AND INSTABILITY...COUPLED
WITH LIFT/FORCING WITH THE TRANSIENT WAVE...SHOULD BE ADEQUATE FOR A
FEW SEVERE STORMS /POSSIBLY IN THE FORM OF SUPERCELLS OR LINE
SEGMENTS/ WITH ATTENDANT THREATS OF HAIL...HIGH WINDS...AND PERHAPS
EVEN A TORNADO.
...FOUR CORNERS...
STRONG LIFT WITHIN LEFT EXIT REGION OF MID/UPPER JET AND COLD AIR
ALOFT WILL CONTRIBUTE TO NUMEROUS LOW-TOPPED TSTMS ACROSS THE FOUR
CORNERS STATES THIS AFTERNOON. WHILE MLCAPE WILL REMAIN MARGINAL
/AOB 500 J/KG/ FOR MORE ROBUST UPDRAFTS...COMBINATION OF CAPE AND
SHEAR ACROSS PARTS NRN AZ/ERN UT AND WRN CO WILL BE SUFFICIENT FOR
SOME PERSISTENT CELLS WITH A THREAT FOR MARGINALLY SEVERE HAIL AND
PERHAPS ISOLATED WIND GUSTS NEARING SEVERE.
..CARBIN/GRAMS.. 06/12/2010
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