Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS01 KWNS 040546
SWODY1
SPC AC 040544

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1244 AM CDT WED MAY 04 2016

VALID 041200Z - 051200Z

...THERE IS A SLGT RISK OF SVR TSTMS TODAY ALONG CENTRAL AND
SOUTHERN FLORIDA ATLANTIC COASTAL AREAS...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS MUCH OF THE REMAINDER OF
CENTRAL AND SOUTHERN FLORIDA...

...SUMMARY...
THUNDERSTORMS ARE EXPECTED TO IMPACT MUCH OF CENTRAL AND SOUTHERN
FLORIDA TODAY...WITH A RISK FOR SEVERE WEATHER...PARTICULARLY ALONG
THE EAST COAST BETWEEN VERO BEACH AND PALM BEACH.

...SYNOPSIS...
THE SOUTHERN BRANCH OF SPLIT WESTERLIES EMANATING FROM THE
MID-LATITUDE PACIFIC IS BECOMING INCREASINGLY AMPLIFIED ACROSS THE
U.S...AND IS EXPECTED TO REMAIN SO THROUGH THIS FORECAST PERIOD.  A
COUPLE OF CLOSED LOWS ARE FORECAST TO EVOLVE WITHIN THE BASE OF
UPPER TROUGHS FLANKING SHARP RIDGING CENTERED NEAR THE ROCKIES.  ONE
IS EXPECTED TO CONTINUE TO EVOLVE JUST TO THE WEST OF THE CALIFORNIA
COAST...WHILE A SEASONABLY STRONG IMPULSE /NOW DIGGING ACROSS THE
UPPER MIDWEST/ CONTRIBUTES MOST PROMINENTLY TO THE EVOLUTION OF THE
OTHER...ACROSS THE LOWER OHIO/TENNESSEE VALLEYS INTO THE SOUTHERN
APPALACHIANS VICINITY BY 12Z THURSDAY.

ON THE SOUTHERN PERIPHERY OF THIS LATTER FEATURE...MODELS INDICATE
THAT ANOTHER SHORT WAVE IMPULSE OF MID-LATITUDE ORIGINS WILL PIVOT
ACROSS THE NORTHERN GULF OF MEXICO AND GULF COAST REGION...THROUGH
THE FLORIDA PENINSULA BY LATE THIS EVENING.  GUIDANCE ALSO SUGGESTS
THAT THIS WILL BE PRECEDED ACROSS THE FLORIDA PENINSULA BY A
CONVECTIVELY ENHANCED IMPULSE OF SUBTROPICAL PACIFIC ORIGINS.

IN LOWER-LEVELS...A COLD FRONT ASSOCIATED WITH THE EASTERN U.S.
UPPER TROUGHING MAY FINALLY CLEAR THE REMAINDER OF THE ATLANTIC
SEABOARD AND EASTERN GULF COASTAL AREAS...WITH THE EXCEPTION OF THE
FLORIDA PENINSULA...EARLY TODAY.  SEASONABLY MOIST CONDITIONS AND
INSTABILITY SUPPORTIVE OF STRONG THUNDERSTORM DEVELOPMENT WILL
REMAIN CONFINED TO AREAS SOUTH OF THE FRONT.  HOWEVER...WEAK
DESTABILIZATION BENEATH THE SEASONABLY COLD MID-LEVEL AIR MAY
CONTRIBUTE TO AREAS OF LOW TOPPED THUNDERSTORM
ACTIVITY...PARTICULARLY THIS AFTERNOON AND EVENING ACROSS THE LOWER
OHIO INTO TENNESSEE VALLEYS.

AT THE SAME TIME...AHEAD OF A COLD FRONT ADVANCING INTO THE PACIFIC
NORTHWEST COAST...A CONTINUED MOISTENING ON DEEP LAYER SOUTHERLY
FLOW MAY CONTRIBUTE INCREASING DIURNAL THUNDERSTORM ACTIVITY TODAY.
THIS MAY BE MOST NOTABLE ALONG THE NORTHERN SIERRA NEVADA...AND THE
EASTERN SLOPES OF THE SOUTHERN CASCADES INTO THE MOUNTAINS OF
NORTHEASTERN OREGON.

...CENTRAL AND SOUTHERN FLORIDA...
THERE IS ALREADY A SUBSTANTIAL WESTERLY COMPONENT TO THE LOW-LEVEL
FLOW ACROSS THE PENINSULA.  THIS IS EXPECTED TO PERSIST INTO
DAY...WITH MOST GUIDANCE INDICATE CONSIDERABLE STRENGTHENING OF
SPEEDS /30-50 KT/ IN LOWER TO MID-LEVELS...WITH THE APPROACH OF THE
CONVECTIVELY ENHANCED SUBTROPICAL PERTURBATION.  THIS SUGGESTS THAT
STRONGER LOW-LEVEL CONVERGENCE WILL BECOME...AND MAY
REMAIN...FOCUSED ALONG THE SEA BREEZE NEAR THE ATLANTIC COAST.

HOWEVER...SOME GUIDANCE...INCLUDING THE 12Z ECMWF...AND PERHAPS
RECENT RUNS OF THE RAPID REFRESH...SUGGEST MORE AMPLIFIED
LOW/MID-LEVEL WAVE AMPLIFICATION WITH THE UPPER IMPULSE.  THIS MAY
INCLUDE BACKING OF LOW-LEVEL FLOW AHEAD OF AHEAD OF AN ORGANIZED
CLUSTER OF THUNDERSTORMS PROGRESSING INLAND ACROSS THE GULF COAST.
IF THIS OCCURS...THERE WOULD SEEM TO BE GREATER POTENTIAL FOR STORMS
MAINTAINING STRENGTH AS THEY ADVANCE INLAND ...AND PERHAPS ACROSS
THE PENINSULA...WITH AT LEAST A RISK FOR POTENTIALLY DAMAGING
SURFACE GUSTS.

AT THE PRESENT TIME...MORE CERTAINTY EXISTS CONCERNING POTENTIAL FOR
VIGOROUS CONVECTIVE DEVELOPMENT NEAR THE SEA BREEZE ALONG THE
ATLANTIC COAST THIS AFTERNOON...PARTICULARLY NEAR THE VERO BEACH AND
PALM BEACH AREAS.  IN THE PRESENCE OF MIXED LAYER CAPE ON THE ORDER
OF 1000-2000 J/KG...VERTICAL SHEAR PROFILES ARE EXPECTED TO BECOME
CONDUCIVE TO THE DEVELOPMENT OF SUPERCELLS...WITH THE RISK FOR
LOCALLY DAMAGING WIND GUSTS...MARGINALLY SEVERE HAIL...AND PERHAPS A
TORNADO OR TWO.

..KERR/PICCA.. 05/04/2016

$$


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