Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 211217
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0717 AM CDT THU MAY 21 2015
VALID 211300Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER ERN NC...
...THERE IS A SLGT RISK OF SVR TSTMS OVER FAR WRN TX...
...THERE IS A MRGL RISK OF SVR TSTMS FROM CNTRL NM SEWD ACROSS
SWRN/SRN TX EWD THROUGH THE CNTRL GULF COAST...
...THERE IS A MRGL RISK OF SVR TSTMS FROM SERN VA INTO ERN SC...
...SUMMARY...
ISOLATED TO WIDELY SCATTERED SEVERE STORMS ARE MOST PROBABLE OVER
FAR WESTERN TEXAS AND ACROSS EASTERN NORTH CAROLINA THIS AFTERNOON.
SEVERAL STRONG STORMS ARE ALSO POSSIBLE ALONG PARTS OF THE GULF
COAST AND RIO GRANDE VALLEY.
...SYNOPSIS...
A SHORT-WAVE TROUGH OVER BAJA THIS MORNING WILL EJECT NEWD INTO THE
CNTRL/SRN HIGH PLAINS BY 12Z/FRI IN ADVANCE OF A MID/UPPER-LEVEL LOW
AND ASSOCIATED JET STREAK WHICH WILL MOVE ONSHORE OVER SRN CA AND
NRN BAJA LATE TONIGHT. ELSEWHERE...PHASED VORTICITY MAXIMA OVER NRN
ONTARIO AND THE MIDWEST WILL TRANSLATE INITIALLY SEWD THEN
EWD...PROMOTING THE INTENSIFICATION OF A LONG-WAVE TROUGH OVER ERN
NORTH AMERICA.
AT THE SURFACE...STRENGTHENING MID-LEVEL FLOW ACROSS THE
APPALACHIANS COUPLED WITH THE INFLUENCE OF A LOW-AMPLITUDE
PERTURBATION MOVING THROUGH WRN NC AS OF 12Z WILL CONTRIBUTE TO THE
SLIGHT DEEPENING OF AN AREA OF LOW PRESSURE WHICH WILL DEVELOP EWD
ACROSS NC TODAY. A TRAILING COLD FRONT WILL ADVANCE SEWD THROUGH
THE SRN APPALACHIANS AND CNTRL GULF COAST STATES WITH THE WRN
EXTENSION OF THIS BOUNDARY BECOMING QUASI-STATIONARY OVER S-CNTRL
TX.
...ERN NC THIS AFTERNOON...
INCREASED FORCING FOR ASCENT AHEAD OF THE ABOVE-MENTIONED VORTICITY
MAXIMUM AND ASSOCIATED SURFACE LOW WILL FOSTER THE DEVELOPMENT OF
TSTMS BY EARLY AFTERNOON WITH ACTIVITY INTENSIFYING WHILE MOVING EWD
TOWARD THE COAST. WHILE MID-LEVEL LAPSE RATES WILL REMAIN
WEAK...DAYTIME HEATING COUPLED WITH BOUNDARY-LAYER DEWPOINTS RISING
INTO THE UPPER 60S WITH THE PASSAGE OF THE WARM FRONT WILL YIELD
MLCAPE APPROACHING 1000 J/KG. AT THE SAME TIME...A TIGHTENING
MID-LEVEL HEIGHT WILL PROMOTE INCREASING WLY FLOW ALOFT AND A
RESULTANT ENHANCEMENT OF VERTICAL SHEAR WITH THE ENVIRONMENT
BECOMING SUPPORTIVE OF SUSTAINED LINE SEGMENTS AND EPISODIC
SUPERCELL STRUCTURES. DAMAGING OUTFLOW WINDS WILL BE THE PRIMARY
HAZARD...THOUGH SOME MARGINALLY SEVERE HAIL AND A BRIEF TORNADO ARE
POSSIBLE.
...RIO GRANDE VALLEY TODAY THROUGH EVENING...
A LONG-LIVED CLUSTER OF TSTMS /INCLUDING EMBEDDED...PERIODIC
SUPERCELL STRUCTURES/ IS IN PROGRESS OVER THE LOWER RIO GRANDE
VALLEY NEAR LRD WITH THIS ACTIVITY LIKELY BEING AIDED BY DCVA
ATTENDANT TO A WEAK SHORT-WAVE TROUGH APPROACHING THE TX BIG BEND.
THE INFLOW AIR MASS TO THESE STORMS IS QUITE MOIST AND ALREADY
MODERATELY UNSTABLE WITH MLCAPE OF 1000-2000 J/KG. LOW-LEVEL UPLIFT
ALONG THE EXISTING MCS COLD POOL SHOULD SUPPORT A CONTINUED SEWD
PROPAGATION OF THE SYSTEM INTO DEEP SOUTH TX WITH SOME
INTENSIFICATION POSSIBLE. ISOLATED OCCURRENCES OF DAMAGING WINDS
AND LARGE HAIL WILL BE POSSIBLE...AS WILL A BRIEF TORNADO.
FARTHER THE NW...DEEPENING OROGRAPHIC CIRCULATIONS WILL BE AUGMENTED
BY INCREASING HEIGHT FALLS/DCVA ASSOCIATED WITH THE BAJA IMPULSE TO
GIVE RISE TO ISOLATED STORMS THIS AFTERNOON FROM CNTRL NM INTO FAR
WRN TX. LOW-LEVEL MOISTURE QUALITY WILL REMAIN SOMEWHAT MARGINAL
WITHIN THE POST-FRONTAL AIR MASS...THOUGH STEEPENING LOW TO
MID-LEVEL LAPSE RATES MAY BOOST MLCAPE TO 500-1000 J/KG LATER TODAY.
MOREOVER...A 50-60 KT MID-LEVEL JET STREAK ATTENDING THE MIGRATORY
SHORT-WAVE TROUGH WILL OVERSPREAD THE REGION BY LATE AFTERNOON/EARLY
EVENING...ENHANCING VERTICAL SHEAR. AS SUCH...THE SETUP WILL BE
SUPPORTIVE OF UPDRAFT ROTATION AND A RISK FOR MAINLY SEVERE HAIL
INTO THIS EVENING.
...GULF COAST THIS AFTERNOON...
PRE-EXISTING OUTFLOW BOUNDARIES REMNANT FROM WED AFTERNOON/EVENING
STORMS...THE SWD-MOVING COLD FRONT AND THE DEVELOPING SEA BREEZE
FRONT WILL FOCUS SCATTERED AFTERNOON TSTMS AMIDST A MOIST AND
MODERATELY UNSTABLE AIR MASS. WHILE VERTICAL SHEAR WILL REMAIN
WEAK...COALESCING...WATER-LOADED DOWNDRAFTS MAY YIELD A FEW LOCALLY
DAMAGING WIND GUSTS LATER TODAY.
..MEAD/LEITMAN.. 05/21/2015
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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