SWOMCD
SPC MCD 181139
FLZ000-181345-
MESOSCALE DISCUSSION 2255
NWS STORM PREDICTION CENTER NORMAN OK
0539 AM CST FRI DEC 18 2009
AREAS AFFECTED...S FL...FL KEYS...AND NARROW PORTIONS ERN AND WRN
COASTAL REGIONS NWD TO CENTRAL FL.
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 181139Z - 181345Z
INLAND COVERAGE OF SFC-BASED TSTMS...SOME OF WHICH MAY BE
SUPERCELLS...SHOULD INCREASE THROUGH AT LEAST 15Z...AS HIGHER-THETAE
MARINE AIR OVERSPREADS GREATER PORTION OF FL...ESPECIALLY COASTAL
AND INLAND AREAS NEAR AND S OF LAKE OKEECHOBEE.
SFC MESOANALYSIS SHOWS SYNOPTIC WARM FRONTAL ZONE ACROSS NRN FL WITH
NOCTURNALLY STABILIZED AND SOMEWHAT DRIER AIR MASS LINGERING ACROSS
MOST OF INTERIOR PENINSULA. MLCAPE IS ESTIMATED AROUND 1000 J/KG
INVOF KEYS...MIA AND SRN EVERGLADES...DIMINISHING NWD WITH RAPID
INCREASE IN CINH W OF LAKE OKEECHOBEE. AS LARGE-SCALE ASCENT
INCREASES -- BOTH IN FORM OF LOW LEVEL WAA AND MIDLEVEL DPVA -- MORE
FAVORABLE INSTABILITY AND GREATER TSTM COVERAGE SHOULD RESULT...
INCLUDING POTENTIAL FOR SUPERCELLS SUCH AS THOSE ALREADY OBSERVED
OVER GULF AND STRAITS SURROUNDING S FL AND KEYS. LOW-LEVEL
HODOGRAPHS...MID-UPPER FLOW...AND DEEP-LAYER SHEAR IN THIS AIR MASS
EACH ARE FCST TO STRENGTHEN GRADUALLY THROUGH MID-LATE MORNING AS
MID-UPPER TROUGH NOW OVER LOWER DELTA REGION AND CENTRAL GULF LIFTS
NEWD.
FARTHER N UP E COAST...POTENTIAL WILL REMAIN MRGL/CONDITIONAL FOR A
FEW MORE HOURS...WITH CONDITIONS REMAINING VERY NEARLY AS DISCUSSED
IN PREVIOUS MCD 2254 BUT SLOWLY SHIFTING NWD. STRONGEST-RIGHTWARD
CELL DEVIANCE WILL OCCUR WITH MOST TORNADO-PRONE STORMS...BUT ALSO
WILL TEND TO FAVOR OFFSHORE TRANSLATION GIVEN ORIENTATION OF
COASTLINE.
FARTHER N UP W COAST...AIR MASS WILL TAKE LONGER TO DESTABILIZE.
COMBINATION OF LAND BREEZE AND AMBIENT/ISALLOBARIC FORCING CONTINUES
ELY COMPONENT...WITH LATTER BEING DOMINANT PROCESS. GRADUAL VEERING
OF NEAR-COASTAL WINDS WILL PERMIT MORE FAVORABLE MARINE AIR MASS NOW
BEING SHUNTED OFFSHORE TO APCH COASTAL AREAS AND RENDER RELATIVELY
STABLE/LOW-DEWPOINT LAYER OF INLAND AIR MORE SHALLOW. SVR THREAT
FROM FMY VICINITY NWD ACCORDINGLY WILL TAKE LONGER TO DEVELOP...BUT
MAY REQUIRE WW LATER THIS MORNING.
..EDWARDS.. 12/18/2009
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...MFL...MLB...KEY...TBW...
LAT...LON 28758069 28448050 28418057 28198057 27788038 26938004
26648000 25878012 25438019 25048044 24838071 24688110
24628132 24638144 24528179 24528217 24588219 24628210
24598171 24698169 24808144 24828126 24728111 24808091
24898071 24938090 25018103 25148116 25218118 25368113
25498123 25628126 25788137 25908164 25818166 25888175
26178181 26448196 26438202 26418211 26458220 26698229
26838228 27018244 27238254 27418270 27518276 27688273
27828284 28158274 28838265 28668239 28008245 27368233
26688167 26388113 26468054 27108043 28298077 28688089
28758069
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