Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 271256
SWODY1
SPC AC 271255

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0755 AM CDT MON APR 27 2015

VALID 271300Z - 281200Z

...THERE IS AN ENH RISK OF SVR TSTMS OVER PARTS OF SRN LA...

...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE ABOVE AREA FROM
PARTS OF N TX SEWD TO THE CNTRL GULF CST...

...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE ABOVE AREA FROM
THE RED RVR VLY TO THE GULF CST...

...THERE IS A MRGL RISK OF SVR TSTMS OVER PARTS OF CNTRL AND SRN
FL...

...SUMMARY...
A BAND OF STRONG TO SEVERE THUNDERSTORMS WITH LOCALLY DAMAGING WINDS
AND POSSIBLY A COUPLE TORNADOES WILL CROSS SOUTHERN AND CENTRAL
LOUISIANA THROUGH ABOUT MIDDAY. DURING THE AFTERNOON...OTHER STRONG
TO SEVERE STORMS WITH HAIL...LOCALLY DAMAGING WIND...AND PERHAPS A
TORNADO WILL AFFECT PARTS OF CENTRAL AND NORTHWEST TEXAS. A FEW
STRONG TO POSSIBLY SEVERE AFTERNOON STORMS ALSO MAY OCCUR OVER
CENTRAL AND SOUTHERN FLORIDA.

...SYNOPSIS...
MULTI-STREAM...CONVOLUTED PATTERN OVER THE CONUS WILL FURTHER
AMPLIFY THIS PERIOD AS RIDGE BUILDS ACROSS THE WRN U.S...DOWNSTREAM
FROM VIGOROUS SHORTWAVE TROUGH NOW CROSSING 140W. AMPLIFICATION OF
THE RIDGE AND CONTINUING PRESENCE OF NERN STATES TROUGH SHOULD LIMIT
EWD PROGRESSION OF NM-W TX UPR LOW...WITH THE SYSTEM ONLY REACHING
NW TX THIS EVE...AND THE LWR RED RVR VLY EARLY TUE.

AT LWR LVLS...LA SQLN AND ASSOCIATED NNE-SSW OUTFLOW BOUNDARY
EXPECTED TO CONTINUE ESE ACROSS LA THROUGH MIDDAY. WNW-ESE FRONT
AHEAD OF THE SQLN...NOW STRADDLING SRN LA...THE NERN GULF OF MEXICO
AND NRN FL...SHOULD SETTLE A BIT SWD WITH TIME AS MAIN SFC
LOW/INVERTED TROUGH ASSOCIATED WITH THE NM-TX UPR LOW DEVELOPS SE
INTO THE NWRN GULF.

...CNTRL GULF CST TODAY/TNGT...
E TX SQLN SHOULD CONTINUE GENERALLY ESE ACROSS SRN/CNTRL LA THROUGH
EARLY AFTN. FORWARD-PROPAGATION OF CONVECTIVE SYSTEM WILL BE
FOSTERED BY ELY COMPONENT TO LOW-LVL FLOW NEAR AND IMMEDIATELY N OF
AFOREMENTIONED FRONT. WITH TIME AND EWD EXTENT...HOWEVER...THESE ELY
TRAJECTORIES WILL BECOME INCREASINGLY DRY AS THE FLOW TAPS DRIER
CONTINENTAL AIR NOW OVER THE TN VLY. AS A RESULT...EXPECT THE
STRONGEST PART OF THE SQLN TO SHIFT SWD INTO THE N CNTRL GULF OF
MEXICO BY MID-AFTN...WITH THOSE PORTIONS PASSING MAINLY S OF
GPT-MOB.

ALTHOUGH LINEAR NATURE OF EXISTING CONVECTION WILL LIMIT OVERALL
TORNADO THREAT...APPRECIABLE LOW-LVL DIRECTIONAL SHEAR PROVIDED BY
ELY LOW-LVL WINDS...RICH MOISTURE NEAR FRONT...PRESENCE OF RESIDUAL
MESOVORTICES IN THE CONVECTIVE BAND SUGGEST A CONTINUING RISK FOR
ISOLD TORNADOES...IN ADDITION TO LOCALLY DMGG WIND /REF WW 126/.

IN THE WAKE OF THE SQLN...MOIST...LOW-LVL CONFLUENT FLOW ATOP THE
MCS COLD POOL...AND UPLIFT ALONG INVERTED SFC TROUGH...SUGGEST THE
POTENTIAL FOR SCTD DIURNALLY-ENHANCED STORMS OVER PARTS OF SE
TX...SW LA...AND THE MIDDLE/UPR TX GULF CSTL PLN. ALTHOUGH WIND
PROFILES OVER THE REGION WILL NOT BE OPTIMAL FOR
SUPERCELLS...SUFFICIENT SHEAR WILL BE PRESENT FOR AT LEAST
OCCASIONAL ORGANIZED/SUSTAINED UPDRAFTS...ESPECIALLY GIVEN
CONTINUING PRESENCE OF STEEP MID-LVL LAPSE RATES. THIS SETUP MAY
YIELD A FEW STORMS WITH A RISK FOR SVR HAIL...AND POSSIBLY A TORNADO
OR TWO...THROUGH EARLY TNGT.

LATE IN THE PERIOD...AFTER ABOUT 06Z TUE...A SECONDARY SVR THREAT
MAY EVOLVE OVER SRN LA FROM NEAR LCH E TO AROUND NEW/BVE AS A SFC
WAVE REDEVELOPS OVER THE NWRN GULF OF MEXICO IN RESPONSE TO THE
CONTINUED EWD MOTION OF W TX UPR LOW. ASSOCIATED INCREASE IN
WAA/MOISTURE TRANSPORT IN STRONGLY SHEARED ENVIRONMENT ALONG THE NRN
GULF SFC FRONT MAY YIELD A CONDITIONAL RISK FOR A TORNADO OR TWO OR
LOCALLY DMGG WINDS IF THE BOUNDARY ADVANCES INLAND. UNCERTAINTY
REGARDING THE LIKELIHOOD OF THIS SCENARIO PRECLUDES THE ADDITION OF
GREATER SVR PROBABILITIES ATTM.

...N CNTRL TX THIS AFTN/EVE...
FARTHER NW...A SEPARATE ARC OF STRONG TO POTENTIALLY SVR TSTMS MAY
ARISE THIS AFTN WITH SFC HEATING OVER PARTS OF NW AND N CNTRL
TX...IN DRY SLOT OF SLOWLY-MOVING UPR LOW. CURRENT SFC OBSERVATIONS
AND OVERALL PATTERN SUGGEST THAT A CLOSED SFC LOW WILL NOT BE
PRESENT. BUT CONFLUENCE ALONG INVERTED TROUGH SHOULD BE SUFFICIENT
TO FOSTER STORM DEVELOPMENT IN ANY AREAS OF STRONGER HEATING. GIVEN
COOL MID-LVL TEMPS /AOB MINUS 15C AT 500 MB/ AND 60+ KT SWLY DEEP
SHEAR WITH AN SIZABLE LOW-LVL DIRECTIONAL COMPONENT...A CONDITIONAL
RISK WILL EXIST FOR SUPERCELLS WITH SVR HAIL AND POSSIBLY A FEW
TORNADOES. ANY SUCH STORMS SHOULD DIMINISH AFTER SUNSET.

...CNTRL/S FL THIS AFTN...
A FAIRLY STRONG N-S TEMP GRADIENT WILL DEVELOP OVER THE FL PENINSULA
TODAY AS WAA CLOUDS/SHOWERS PERSIST OVER THE N CNTRL AND NE GULF OF
MEXICO...ALONG AND N OF SWD-SAGGING COLD FRONT. THIS MAY ENCOURAGE
DEVELOPMENT OF SCTD DIURNAL STORMS ALONG AND S OF THE BOUNDARY...AND
ALONG THE E CST SEA-BREEZE FRONT. RICH MOISTURE /PW AROUND 1.75
INCHES/ AND 40-50 KT WLY 700-500 MB FLOW COULD SUPPORT A FEW
SUSTAINED STORMS...AND POSSIBLY A SUPERCELL...WITH LOCALLY DMGG WIND
AND SVR HAIL.

..CORFIDI/COHEN.. 04/27/2015



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