Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 271959
SWODY1
SPC AC 271957

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0257 PM CDT MON APR 27 2015

VALID 272000Z - 281200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM N-CNTRL TX TO THE CNTRL
GULF COAST...

...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLIGHT RISK
OVER THE GENERAL AREA...

...THERE IS A MRGL RISK OF SVR TSTMS FOR PORTIONS OF CNTRL AND SRN
FL...

...SUMMARY...
ISOLATED STRONG TO SEVERE STORMS WITH HAIL...LOCALLY DAMAGING
WIND...AND PERHAPS A TORNADO OR TWO MAY AFFECT PARTS OF
NORTH-CENTRAL INTO EASTERN TEXAS AND PERHAPS SOUTHWEST LOUISIANA.  A
FEW STRONG TO POSSIBLY SEVERE STORMS ALSO MAY OCCUR OVER CENTRAL AND
SOUTHERN FLORIDA.

THE ONLY SUBSTANTIAL CHANGES THIS OUTLOOK UPDATE INCLUDE...
1) THE REMOVAL OF 5 PERCENT TORNADO PROBABILITIES OVER SERN LA.  THE
EARLY DAY MCS HAS MOVED INTO THE GULF AND THE AIRMASS HAS BECOME
LESS UNSTABLE IN ITS WAKE.  ANOTHER ROUND OF STORMS IS EXPECTED TO
MOVE INTO SERN LA LATER TODAY/TONIGHT AND STRONG WIND PROFILES WILL
SUPPORT A CONDITIONAL SEVERE THREAT FOR ORGANIZED STORMS.
2) ADDED LOW SEVERE PROBABILITIES FOR MUCH OF THE SRN HALF OF THE FL
PENINSULA AS RECENT ITERATIONS OF CONVECTION-ALLOWING MODELS SHOW
THE NRN GULF OF MEXICO MCS CONTINUING ESEWD AND AFFECTING THE FL
PENINSULA TONIGHT.

..SMITH.. 04/27/2015

.PREV DISCUSSION... /ISSUED 1118 AM CDT MON APR 27 2015/

...SYNOPSIS...

A MID TO UPPER-LEVEL LOW WILL EDGE SLOWLY EWD ACROSS THE SRN PLAINS
IN RESPONSE TO AN AMPLIFYING UPSTREAM RIDGE OVER THE GREAT BASIN
INTO NRN ROCKIES.  A MID-LEVEL JET STREAK OBSERVED WITHIN THE BASE
OF THE UPPER LOW PER 12Z OBSERVED SOUNDINGS WILL PROGRESS GENERALLY
EWD INTO THE CNTRL GULF COAST.

AT THE SURFACE...AN AREA OF LOW PRESSURE OVER N-CNTRL TX WILL
DEVELOP SEWD INTO SRN LA ALONG A COLD FRONT ADVANCING SEWD THROUGH
CNTRL AND SRN PARTS OF TX.  MEANWHILE...VISIBLE SATELLITE AND
SURFACE OBSERVATIONS AS OF MID MORNING INDICATE AN OUTFLOW BOUNDARY
ASSOCIATED WITH THE BOW ECHO OVER SERN LA EXTENDING WWD THROUGH THE
UPPER TX COAST BEFORE CURVING NWWD ALONG A BAZ-SEP LINE WHERE IT
LINKS WITH THE SURFACE LOW AND ASSOCIATED COLD FRONT.

...SERN TX INTO THE CNTRL GULF COAST TODAY INTO TONIGHT...

A WELL-DEFINED BOW ECHO WITH A HISTORY OF FAIRLY WIDESPREAD DAMAGING
WINDS SHOULD CONTINUE ESEWD THROUGH THE REMAINDER OF FAR SERN LA
LATE THIS MORNING INTO EARLY AFTERNOON WITH A RISK FOR DAMAGING
WINDS AND PERHAPS A TORNADO OR TWO OVER THOSE LOCATIONS.  IN THE
WAKE OF THIS MCS...IT APPEARS THAT WAA/ISENTROPIC ASCENT ATOP THE
TRAILING OUTFLOW BOUNDARY COUPLED WITH DEEPER-LAYER FORCING FOR
ASCENT RELATED TO THE ABOVE-MENTIONED MID-LEVEL JET STREAK MAY
SUPPORT THE DEVELOPMENT OF TSTMS THIS AFTERNOON INTO TONIGHT FROM
SERN TX EWD INTO LA.

BASED ON THE 12Z SOUNDINGS AT CRP AND BRO...AMPLE LOW-LEVEL MOISTURE
SURMOUNTED BY A WELL-DEFINED EML WILL SUPPORT MODERATE AFTERNOON
INSTABILITY AND THE POTENTIAL FOR ORGANIZED STORM MODES INCLUDING
SUPERCELLS GIVEN 40-50 KT OF DEEP-LAYER SHEAR.  WHILE LARGE HAIL
APPEARS TO BE THE PRIMARY HAZARD...LOCALLY DAMAGING WINDS AND
PERHAPS A BRIEF TORNADO OR TWO ARE POSSIBLE.

...N-CNTRL INTO ERN TX THIS AFTERNOON/EVENING...

AS MENTIONED ABOVE...CONSIDERABLE OVERTURNING OF THE AIR MASS HAS
OCCURRED OVER ERN INTO N-CNTRL TX IN THE WAKE OF THE MCS NOW OVER
LA.  HOWEVER...COLD MID-LEVEL TEMPERATURES COUPLED WITH A WARMING
BOUNDARY LAYER SHOULD SUPPORT AIR MASS DESTABILIZATION BY AFTERNOON
AHEAD OF THE SURFACE LOW AND COLD FRONT WITH MLCAPE APPROACHING
1000-1500 J/KG.  FORCING FOR ASCENT IN ADVANCE OF THE DEEP-LAYER
CYCLONE IS EXPECTED TO FOSTER THE DEVELOPMENT OF SURFACE-BASED
STORMS BY AFTERNOON AMIDST A KINEMATIC ENVIRONMENT FEATURING
VERTICALLY VEERING AND STRENGTHENING WINDS WITH HEIGHT.  AS
SUCH...SUPERCELLS ARE POSSIBLE WITH THE RISK FOR LARGE
HAIL...DAMAGING WINDS AND A COUPLE OF TORNADOES SPREADING SEWD INTO
PARTS OF ERN TX.  THIS SEVERE WEATHER THREAT SHOULD BEGIN TO WANE BY
MID TO LATE EVENING AS THE BOUNDARY LAYER BEGINS TO COOL AND
STABILIZE.

...FL PENINSULA THIS AFTERNOON...

PRONOUNCED WLY DEEP-LAYER FLOW OBSERVED BY 12Z SOUNDINGS WILL
PERSIST TODAY WITH DIURNAL STORM DEVELOPMENT LIKELY REMAINING
CONFINED TO THE EAST COAST SEA BREEZE.  WHILE MID-LEVEL LAPSE RATES
WILL REMAIN POOR...DAYTIME HEATING COUPLED WITH A MOIST BOUNDARY
LAYER WILL YIELD MODERATE AFTERNOON INSTABILITY AND THE POTENTIAL
FOR A FEW STRONG TO MARGINALLY SEVERE STORMS THIS AFTERNOON WITH A
RISK FOR LOCALLY DAMAGING WIND GUSTS.




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