Severe Thunderstorm Warning 153, NWS Tallahassee, FL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
220 PM EDT FRI AUG 18 2000

CURRENTLY: VISIBLE SATELLITE SHOWED LOW/MID CLOUDS INCREASING OVER
NRN AL/GA AHEAD OF AN APPROACHING FRONT OVER OH VALLEY. CLOSER TO
HOME...E-W SURFACE RIDGE SPRAWLED FROM WRN ATLANTIC THRU FL INTO
GULF. AXIS OF UPPER RIDGE STILL TO OUR W W/ N-NE FLOW. GULF SEA
BREEZE CU RESTICTED TO NEAR THE COAST W/ A FEW MID CLOUDS ASSOCD W/
E-W BOUNDARY LAYER SHEAR AXIS FROM WRN FL BIG BEND INTO ERN FL
PNHDL. SHOWERS REPORTED EARLIER THIS MORNING MOVED INTO COASTAL
WATERS & DISSIPATED. TEMPS RANGE FROM MID-UPR 90S INLAND (HOT SPOTS
DHN& ABY AT 99) TO 85-90 IMMEDIATE COAST. PREVAILING WINDS WERE W-SW
5-10 KTS.

SHORT-RANGE/ZFP: 18/12Z MODEL SUITE IN GOOD AGREEMENT WITH LARGE
SCALE FEATURES. BROAD UPPER RIDGE OVER SRN 1/2 CONUS W/ AXIS OVER TX
RETROGRADES SLIGHTLY AS SHORT WAVE ENERGY CURRENTLY IN THE UPPER MS
AND OH VALLEYS MOVES E AND AMPLIFIES AN E COAST TROUGH WHICH REMAINS
IN PLACE THROUGH SAT BEFORE LIFT NEWD SAT NIGHT/SUN. MEANWHILE...A
COLD FRONT IN THE OH VALLEY MOVES SWD INTO SRN AL/GA LATE SAT INTO
SUN. THE FRONT THEN STALLS ACROSS OUR CWFA AS WEAK WAVES FORM ON IT.

THE 1000-700 MB FLOW WILL BE GENERALLY NW 10 KT OR GREATER SAT W/ A
SLIGHT WLY COMPONENT SUN. THIS REGIME FAVORS HIGHER POPS MOST
AREAS...PARTICULARLY SE AL & ERN FL BIG BEND. MODEL SOUNDINGS IN
CONCENSUS W/ GRADUAL INCREASE IN PRECIP WATER (ETA THE WETTEST AT 2)
THRU EARLY SUN. TIME-HEIGHT SECTIONS SIMILAR GREATER THAN 60% RH BELOW
650 MB. SOME LIFT NOTED LATE SAT/EARLY SUN (STRONGEST W/ ETA -8
MB/SEC) IN PROXIMITY TO FRONTAL BOUNDARY. MODEL QPFS DO DIVERGE. ETA
MORE PLAUSIBLE SOLUTION AS NGM OVERDOES PCPN TONIGHT & SAT ASSOCD W/
SHEAR AXIS OVER FL. ETA QPF AMOUNTS W/ FRONT ARE LIGHT...GENERALLY
LESS THAN A HLAF INCH.

FOR POPS...WILL KEEP LESS THAN 20% FL ZONES & 20% ELSEWHERE TONIGHT.
WILL INCREASE POPS TO CHANCE CATEGORY SAT (HIGHEST SE AL/SW GA ZONES
IN CLOSER PROXIMITY TO FRONT). CHANCE CONTINUES SAT NIGHT AS FRONT
DROPS S INTO SE AL/S GA. TAPER POPS OFF SUN FROM N TO S AS FRONT STALLS
NEAR FL/GA BORDER. FOR TEMPS...AIRMASS BEHIND FRONTAL BOUNDARY NOT
SIG COOLER OR DRIER W/ ONLY SLIGHT MODERATION IN HIGH TEMPS
EXPECTED. TRENDED CLOSER TO FWC NUMBERS.

MEDIUM-RANGE/EFP: 18/00Z MRF BRINGS FRONT THRU ALL BUT EXTREME SE
PORTION OF OUR CWFA & STALLS IT JUST S OF A JAX-CTY LINE SUN & MON
AS SERIES OF WEAK SURFACE WAVES FORM & RIDE NEWD ALONG BOUNDARY.
FRONT THEN BECOMES DIFFUSE OR WASHES OUT TUE. MEAN 1000-700 MB FLOW
REMAINS NE-E 10 KTS OR LESS THRU PERIOD. MRF LAYER RH FOR SAME
PERIOD SHOWS SOME DRYING OVER OUR NW ZONES W/ RH VALUES <40%
SUN...BUT ATLANTIC/GULF MOISTURE INCREASES & SPREADS NWWD MON & TUE.
BOTTOMLINE: RETURN TO NEAR CLIMO TEMPS & POPS W/ EMPHASIS ON
MAINLY AFTN/EVE CONVECTION.

MARINE: MOSTLY SW WINDS 5-10 KTS TONIGHT...INCREASING TO 10-15 KTS
SAT AFTN & NIGHT AS SFC/BNDRY LAYER PRESSURE GRADIENT TIGHTENS AHEAD
OF APPROACHING COLD FRONT. SEAS LIKEWISE BUILD FROM 1-2 FT TONIGHT
TO 3-4 FT SAT NIGHT. ISOLD MAINLY LATE NIGHT/MORNING CONVECTION BECOMES
WDLY SCT TO SCT SAT NIGHT.

FIRE WX: NO CONCERNS W/ DEWPTS IN THE 70S & LOWEST MIN RH/S AT OR
ABOVE 45%.

PRELIM CCF...
TLH 074/097 074/093 1335
PFN 079/091 080/090 1335
DHN 076/095 075/092 2433
ABY 076/095 074/092 2433
VLD 074/096 073/093 2334

.TLH...
AL...NONE.
GA...NONE.
FL...NONE.

MAJ