Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 181240
SWODY1
SPC AC 181239

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0739 AM CDT FRI APR 18 2014

VALID 181300Z - 191200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS FL PENINSULA...

...SUMMARY...
SEVERE THUNDERSTORMS ARE POSSIBLE THROUGH THIS EVENING OVER THE
FLORIDA PENINSULA.  THE MAIN ACTION AREA WILL MOVE FROM THE GULF OF
MEXICO ONTO THE WEST COAST THEN INLAND...BUT A FEW STRONG TO SEVERE
STORMS ARE POSSIBLE AHEAD OF THAT.  DAMAGING WIND IS THE MAIN
HAZARD.  THESE STORMS ALSO MAY OFFER LARGE HAIL AND A TORNADO OR
TWO.

...SYNOPSIS...
MID-UPPER LEVEL PATTERN FEATURES SHORTWAVE TROUGH OVER INLAND PAC
NW...RIDGING OVER ROCKIES...AND BROADLY CYCLONIC FLOW ACROSS MUCH OF
SERN CONUS AND GULF OF MEXICO.  SHORTWAVE TROUGH -- NOW EVIDENT IN
MOISTURE-CHANNEL IMAGERY OVER WRN AR AND EXTREME E TX -- IS FCST TO
AMPLIFY AS IT MOVES ESEWD INTO PRE-EXISTING CYCLONIC REGIME.  THIS
PROCESS SHOULD YIELD CLOSED 500-MB LOW OVER FL PANHANDLE BY
06Z..MOVING EWD ROUGHLY ALONG I-10 TO FL COASTAL BEND/SWRN GA AREA
NEAR END OF PERIOD.  THIS WILL SPREAD STRONGLY DIFLUENT BUT ALSO
INCREASING WINDS ALOFT OVER OUTLOOK AREA.  MEANWHILE...BROAD/WEAK
SRN-STREAM CYCLONE NOW OFFSHORE SRN CA WILL MOVE EWD TO AREAS NEAR
OR S OF LAS...WITH TROUGH SWD ACROSS LOWER CO RIVER VALLEY AND
NRN/CENTRAL BAJA BY 12Z.

AT SFC...CYCLONE NOW SE OF MS RIVER MOUTH IS PROGGED TO MOVE OR
RE-DEVELOP THROUGH NRN PART OF ONGOING TSTM COMPLEX OVER NERN
GULF...THEN MOVE NEWD ACROSS NWRN FL LATE AFTN INTO EVENING.
DIFFUSE WARM FRONTAL ZONE WAS ANALYZED AT 11Z FROM THAT LOW ESEWD
THROUGH ERN-GULF PRECIP AREA AND CENTRAL FL PENINSULA.  ACCOMPANYING
BAROCLINIC ZONE WILL SHIFT NWD SLOWLY TODAY...WITH SFC DEW POINTS TO
ITS S MAINLY UPPER 60S/LOW 70S F.

...FL PENINSULA...
MAIN SVR THREAT IS EXPECTED TO SHIFT EWD OVER FL WITH TSTM COMPLEX
NOW OVER ERN GULF...WHICH SHOULD CONTINUE TO MOVE SLOWLY EWD THROUGH
MORNING INTO AFTN BEFORE ACCELERATING.  ADDITIONAL DEVELOPMENT IS
POSSIBLE TO ITS E AND SE TODAY OVER PENINSULA...AND THIS EVENING
ACROSS STRAITS/KEYS AND EXTREME ERN GULF...MOVING EWD TO NEWD ACROSS
S FL.  LOW-LEVEL SHEAR SHOULD BE WEAKER WITH SWD DISTANCE AWAY FROM
FRONTAL ZONE...ESPECIALLY ACROSS S FL...AND THIS FACTOR RENDERS
UNCONDITIONAL SVR PROBABILITIES MORE MRGL WITH SWD EXTENT.

LOW-LEVEL THETAE ADVECTION NEAR WARM FRONT...ALONG WITH MUTED SFC
HEATING...SHOULD CONTRIBUTE TO ANTECEDENT DESTABILIZATION AND
500-1500 J/KG MLCAPE.  DEEP SHEAR IS EXPECTED TO INCREASE GRADUALLY
THIS AFTN AHEAD OF MAIN MCS AS AFOREMENTIONED SHORTWAVE TROUGH
STRENGTHENS/APCHS...DESPITE VEERING OF SFC WINDS TO SLY BEHIND WARM
FROPA.  HODOGRAPH SIZE WILL BE LIMITED BY LACK OF MORE ROBUST
NEAR-SFC WINDS...EVEN ALONG AND JUST N OF WARM FRONT WHERE FLOW IS
MORE BACKED.  STILL...A FEW SUPERCELLS ARE POSSIBLE IN ADDITION TO
ORGANIZED CLUSTERS/BOWS/LEWPS.

MOST MODELS...INCLUDING SREF MEMBERS...APPEAR TOO SLOW ALREADY WITH
EWD PROGRESS OF GULF TSTMS AND LIKELY TOO LATE WITH ITS PASSAGE
ACROSS FL THIS AFTN INTO EVENING.  SOME PRECURSORY/ANTECEDENT
CONVECTION MAY OCCUR BEFORE MAIN MCS ARRIVES -- ESPECIALLY ALONG SEA
BREEZES IN SRN PENINSULA WHERE STRONGEST DIABATIC HEATING IS
EXPECTED AND THEREFORE MOST VIGOROUS SOLENOIDAL LIFT IS POSSIBLE.
HOWEVER...THIS POTENTIAL APPEARS MORE AND MORE CONDITIONAL/LIMITED
WITH NWD AND WWD EXTENT AS THICK ANVIL MATERIAL SPREADS EWD OVER
MOST OF FL.

..EDWARDS/ROGERS.. 04/18/2014




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