SWOMCD
SPC MCD 180914
FLZ000-181115-
MESOSCALE DISCUSSION 2254
NWS STORM PREDICTION CENTER NORMAN OK
0314 AM CST FRI DEC 18 2009
AREAS AFFECTED...E-CENTRAL/SERN FL PENINSULA COASTAL AREAS...FL
KEYS.
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 180914Z - 181115Z
CONDITIONAL TORNADO POTENTIAL MAY DEVELOP/INCREASE IN THIS CORRIDOR
OVER NEXT SEVERAL HOURS...BUT APPEARS TOO MRGL AND LIMITED IN LAND
AREA TO WARRANT WW ATTM.
WSR-88D UNITS AND TDWRS OVER THIS REGION HAVE INDICATED
INTERMITTENT/SHORT-LIVED AREAS OF STORM-SCALE ROTATION IN RELATIVELY
SUSTAINED/DISCRETE CELLS OFFSHORE MAINLAND. MOST OF THESE ARE NOT
PRODUCING CG LTG...AND HAVE AND WILL CONTINUE TO WEAKEN CONSIDERABLY
AS ACTIVITY NEARS BEACHES AND MOVES INTO SLIGHTLY MORE STABLE AIR
MASS...WHERE SFC TEMPS ARE 5-8 DEG OFF VALUES CHARACTERIZING
HIGH-THETAE AIR MASS OVER GULF STREAM. FARTHER S...CELLS OVER
STRAITS S OF KEYS ARE IN WEAKER SHEAR ENVIRONMENT THAT MAY INCREASE
SOMEWHAT WITH TIME. AS UPPER TROUGH OVER LOWER DELTA REGION AND
CENTRAL GULF CONTINUES MOVING NEWD...EXPECT STRENGTHENING LOW LEVEL
WIND FIELDS JUST ABOVE SFC OVER ENTIRE REGION...WHICH WILL LENGTHEN
HODOGRAPHS...AND WHICH MAY CONTRIBUTE TO GRADUAL DESTABILIZATION OF
BOUNDARY LAYER AIR INVOF IMMEDIATE PENINSULAR COAST THROUGH MIXING
AND ADVECTIVE PROCESSES. MODIFIED RAOBS AND RUC SOUNDINGS THROUGH
12Z SUGGEST ENOUGH MARITIME THETAE TO OFFSET WEAK LAPSE RATES ALOFT
AND YIELD AROUND 1000 J/KG MLCAPE FROM MIA AREA SWWD...DIMINISHING
NWD TO BELOW 250 J/KG BETWEEN VRB-MLB. BY CONTRAST...AS BUOYANCY
WEAKENS...SHEAR INCREASES NWD IN INCREASING PROXIMITY TO STRONGER
MIDLATITUDE WLYS ALOFT AND TO GREATER HEIGHT FALLS ALOFT. THIS
TREND IS EVIDENT ATTM IN NWD-EXPANDING VWP HODOGRAPHS AND IN FCST
SOUNDINGS. EFFECTIVE BULK SHEAR WILL VARY CONSIDERABLY WITH CAPE
DEPTH -- SMALLER FOR SHALLOWER CONVECTIVE PLUMES -- BUT 45-55 KT
VALUES NOW OFFSHORE MAY OCCUR OVER SOME AREAS OF COAST.
WATCH IS NOT LIKELY FOR THIS SPECIFIC SITUATION. HOWEVER...
SEPARATE MCD/WATCH PRODUCTS MAY BE NEEDED LATER THIS MORNING FOR
POTENTIALLY BETTER-ORGANIZED AND MORE WIDESPREAD SVR THREAT
SHIFTING/SPREADING EWD FROM GULF...MORE DIRECTLY RELATED TO APCHG
UPPER TROUGH.
..EDWARDS.. 12/18/2009
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...MFL...MLB...KEY...
LAT...LON 28398057 28168057 27728036 26938004 26738001 25918011
25338021 24998049 24788078 24688108 24518180 24548218
24608211 24578177 24708168 24768141 24758131 24708123
24818092 24898074 24968099 25148102 25328073 25818042
26298026 26958016 27628050 28158072 28398057
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