Area Forecast Discussion
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FXUS62 KKEY 170154
AFDKEY

AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS
NATIONAL WEATHER SERVICE KEY WEST FL
954 PM EDT TUE SEP 16 2014

.DISCUSSION...
A REVIEW OF UPPER-AIR DATA OVER THE LAST 24 HOURS REVEALS WIDESPREAD
GEOPOTENTIAL HEIGHT FALLS OVER MUCH OF THE EASTERN THIRD OF THE
UNITED STATES. ASSOCIATED LARGE-SCALE CYCLONIC FLOW ALOFT HAS SPREAD
HAS FAR SOUTH AS THE NORTHERN HALF OF THE FLORIDA PENINSULA. THIS
UPPER FLOW EVOLUTION HAS LED TO A RAPID DESTRUCTION OF THE SOUTHWARD-
MOVING SUBTROPICAL RIDGE AT THE SURFACE. ALTHOUGH THE RIDGE IS MUCH
CLOSER TO THE FLORIDA KEYS NOW THAN IT WAS YESTERDAY AT THIS TIME...
MEAN SEA LEVEL PRESSURES ACTUALLY HAVE FALLEN ABOUT 3 MILLIBARS IN
THE LAST 24 HOURS. LOCAL GRADIENT FLOWS ARE WEAKENING RAPIDLY...AND
SURFACE WINDS OVER THE LAST SEVERAL HOURS HAVE BEEN MODULATED
PRIMARILY BY A COMBINATION OF DIFFERENTIAL HEATING AND CONVECTIVE
OUTFLOW.

DATA COLLECTED FROM THE KEY WEST EVENING RADIOSONDE BALLOON INDICATE
WEAK-MODERATE CONDITIONAL INSTABILITY WITH SOME SIGNIFICANT
CONVECTIVE INHIBITION ENERGY AT LOW ALTITUDES. HOWEVER...AN APPRAISAL
OF RECENT DOPPLER RADAR DATA SHOWS THAT SHORT-LIVED DEEP CONVECTION
CELLS HAVE BEEN INITIATING ALONG SURFACE BOUNDARIES. MOST OF THESE
BOUNDARIES HAVE MOVED SOUTHWARD OVER THE STRAITS OF FLORIDA...AND
THAT IS WHERE MOST PRECIPITATION IS DETECTED AT THIS HOUR. ONLY TWO
LIGHTNING STRIKES HAVE BEEN DETECTED IN THE SERVICE AREA FOR THE LAST
SEVERAL HOURS...BOTH IN ASSOCIATION WITH A CELL SOUTH OF THE FLORIDA
REEF TRACT NEAR PELICAN SHOAL.

BOTH DIGITAL AND DERIVED FORECASTS HAVE BEEN ADJUSTED ALREADY TO
ACCOUNT FOR NEAR-TERM TRENDS IN SURFACE WIND OBSERVATIONS. ALSO...WE
HAVE REDUCED RAIN PROBABILITIES THROUGH 600 AM...BASED ON RADAR
TRENDS...AND DIMINISHING MESOSCALE FORCING FOR ASCENT OVERNIGHT.
&&

.MARINE...
NO ADVISORIES AND NO HEADLINES. A WEAK PRESSURE PATTERN WILL DEVELOP
TONIGHT ACROSS FLORIDA KEYS COASTAL WATERS...AND PERSIST THROUGH
FRIDAY. THIS WILL SUPPORT LIGHT AND VARIABLE BREEZES EXCEPT IN AN
NEAR SHOWERS AND THUNDERSTORMS.
&&

.AVIATION...
VFR SHOULD PREVAIL OVERNIGHT. PASSING SHOWERS SHOULD FORM OVER THE
COASTAL WATERS...BUT NIGHTTIME WINDS WILL BE LIGHT AND VARIABLE
ENOUGH THAT THEY SHOULD PREVENT ADEQUATE MOTION OF THESE SHOWERS
ACROSS THE KEYS AT THE ISLAND TERMINALS. CONTINUED LIGHT WINDS
TOMORROW SHOULD BRING A CHANCE OF CLOUD LINES FORMING DIRECTLY OVER
THE ISLAND CHAIN...BUT TIMING DOES NOT WARRANT EXPLICIT MENTION IN
THE TAF AT THIS TIME.
&&

.CLIMATE...
SEPTEMBER 16 -- ON THIS DATE IN FLORIDA KEYS CLIMATE HISTORY...IN
1935...THE DAILY RECORD RAINFALL OF 5.04" WAS RECORDED. PRECIPITATION
RECORDS HAVE BEEN KEPT IN KEY WEST SINCE 1871.
&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
GM...NONE.
&&

$$

PUBLIC/MARINE.........KASPER
AVIATION/NOWCASTS.....MSB
DATA COLLECTION.......FLING

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