Damaging Wind and Heavy Rain in Florida, May 13, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
1033 PM EDT Sat May 12 2012

.DISCUSSION...
The 23 UTC regional surface analysis showed a weak frontal low
over western MS, with a warm (or perhaps quasi-stationary) front
extending east from this low across the western FL Panhandle and
adjacent coastal waters. Vapor imagery and upper air data showed a
short wave trough over western LA, with a few weak impulses
(including small MCVs) well to the east of this trough axis.
Recent radar imagery showed a narrow north-south oriented band of
storms propagating eastward at 5 to 10 KT over the western FL
Panhandle and coastal waters. Although the exact details are
different, all of the latest Convection Allowing Models (CAM)
bring this band (or a similar feature) slowly east through our
forecast area late tonight through Sunday morning. At first glance
the severe storm threat might appear minimal. There isn't a strong low
level or mid level jet stream, no major 500 mb height falls, weak
lapse rates, and a weak surface low moving slowly northeast.
However, the 12 UTC CAM guidance indicates a few strong
mesocyclones across our forecast area, as did their previous runs.
Evidently they may be suggesting that the aforementioned frontal
system in the FL Panhandle will enhance the vertical wind shear
enough for significant updraft rotation. Indeed, local VAD Wind
profiles from our radar network show 0-1 km vertical shear values
of 30 to 35 KT, which is impressive. (The 0-6 km shear magnitude
is only about 30 KT, which is rather weak).

Overnight we expect most of the storms over land to be slightly elevated
due to the stable near-surface layer, but the storms over the Gulf
will be surface based. As the storms over the water cross land,
they may acquire stronger updraft rotation from the convergence of
the coast and the proximity of the frontal system (and backed
surface winds). Most of the storms will become slightly elevated
as they move farther inland, but as the front begins to lift
slowly north late tonight and Sunday morning, some of these storms
may become surface based. This would allow for a storm or two to
produce marginally damaging wind gusts (40-55 KT) and/or a brief
tornado. The severe threat is likely to diminish Sunday afternoon
as the front moves away from the area, resulting in weakened
vertical wind shear.

&&

.AVIATION...
This TAF package will be dominated by an unsettled weather
pattern with scattered to numerous showers and thunderstorms
advancing from southwest to northeast across the region. Local
radars at 00z do show scattered convection already approaching our
western terminals (DHN and ECP). Accompanying the convection will
be periods of MVFR CIGS/VSBYS. No threat overnight for widespread
fog due to cloud extensive cloud cover and convection. Winds on
Sunday will be from the southeast to south in the 10 to 15 knot
range.

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
AL...None.
GA...None.
FL...None.
GM...None.

&&

AVIATION...Barry
REST OF DISCUSSION...Fournier

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TALLAHASSEE FL
928 PM EDT SAT MAY 12 2012

ALZ065>069-FLZ007>019-026>029-034-108-112-114-115-118-127-128-134-
GAZ120>131-142>148-155>161-GMZ730-750-755-765-770-775-140130-
COFFEE-DALE-HENRY-GENEVA-HOUSTON-INLAND WALTON-CENTRAL WALTON-
HOLMES-WASHINGTON-JACKSON-INLAND BAY-CALHOUN-INLAND GULF-
INLAND FRANKLIN-GADSDEN-LEON-INLAND JEFFERSON-MADISON-LIBERTY-
INLAND WAKULLA-INLAND TAYLOR-LAFAYETTE-INLAND DIXIE-SOUTH WALTON-
COASTAL BAY-COASTAL GULF-COASTAL FRANKLIN-COASTAL JEFFERSON-
COASTAL WAKULLA-COASTAL TAYLOR-COASTAL DIXIE-QUITMAN-CLAY-
RANDOLPH-TERRELL-DOUGHERTY-LEE-WORTH-TURNER-TIFT-BEN HILL-IRWIN-
EARLY-MILLER-BAKER-MITCHELL-COLQUITT-COOK-BERRIEN-SEMINOLE-
DECATUR-GRADY-THOMAS-BROOKS-LOWNDES-LANIER-
APALACHEE BAY OR COASTAL WATERS FROM KEATON BEACH TO OCHLOCKONEE
RIVER FL OUT TO 20 NM-
COASTAL WATERS FROM APALACHICOLA TO DESTIN FL OUT 20 NM-
COASTAL WATERS FROM  OCHLOCKONEE RIVER TO APALACHICOLA FL OUT TO
20 NM-
COASTAL WATERS FROM  SUWANNEE RIVER TO KEATON BEACH OUT 20 NM-
WATERS FROM APALACHICOLA TO DESTIN FL FROM 20 TO 60 NM-
WATERS FROM  SUWANNEE RIVER TO APALACHICOLA FL FROM 20 TO 60 NM-
928 PM EDT SAT MAY 12 2012 /828 PM CDT SAT MAY 12 2012/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST ALABAMA...
SOUTHWEST AND SOUTH CENTRAL GEORGIA...AND THE FLORIDA BIG BEND
AND PANHANDLE...AND ADJACENT COASTAL WATERS.

.DAY ONE...TONIGHT...

SHOWERS AND THUNDERSTORMS WILL DEVELOP OVER THE FLORIDA PANHANDLE
AND SOUTHEAST ALABAMA...BECOMING MORE NUMEROUS AS THE NIGHT GOES
ON. SOME OF THIS RAIN MAY SPREAD EAST INTO GEORGIA AND THE FLORIDA
BIG BEND AS WELL. A FEW STORMS COULD BE STRONG TO
SEVERE...PRODUCING MARGINALLY DAMAGING WIND GUSTS OR PERHAPS EVEN
A BRIEF TORNADO...MAINLY IN THE FLORIDA PANHANDLE OR ADJACENT
COASTAL WATERS. SOME OF THE SHOWERS AND STORMS WILL PRODUCE HEAVY
RAIN...WITH LOCALIZED FLOODING POSSIBLE IN LOW LYING AND POOR
DRAINAGE AREAS.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY...

SHOWERS AND THUNDERSTORMS WILL CONTINUE DURING THE DAY ON
SUNDAY...EVEN LINGERING INTO MONDAY BEFORE DRIER WEATHER RETURNS.
ISOLATED SEVERE STORMS WILL REMAIN POSSIBLE SUNDAY MORNING...BUT
THE THREAT FOR SEVERE STORMS IS LIKELY TO DIMINISH IN THE
AFTERNOON AS A WARM FRONT MOVES NORTH...AWAY FROM OUR REGION.
HEAVY RAIN WILL CONTINUE TO BE A THREAT THROUGH SUNDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED LATER TONIGHT OR SUNDAY MORNING.
SPOTTERS SHOULD MONITOR THE LATEST WEATHER INFORMATION...AND BE
CONSIDERED ACTIVATED IF A HAZARDOUS WEATHER WATCH OR WARNING IS
ISSUED.

FOR ADDITIONAL INFORMATION...VISIT THE NATIONAL WEATHER SERVICE
WEBSITE ON THE INTERNET AT WEATHER.GOV...THEN CLICK ON YOUR AREA
OF INTEREST ON THE NATIONAL MAP.

FOURNIER