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000
FXUS62 KKEY 120843
AFDKEY

AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS
NATIONAL WEATHER SERVICE KEY WEST FL
443 AM EDT WED MAR 12 2014

.DISCUSSION...
CURRENT WEATHER SUMMARY -- LOCAL BREEZES HAVE VEERED OUT OF THE SOUTH
AND FRESHENED OVERNIGHT...MAKING IT MUCH WARMER THAN THE LAST SEVERAL
NIGHTS. CURRENTLY...AIR TEMPERATURES IN MOST ISLAND COMMUNITIES
REMAIN IN THE MID 70S. HUMIDITY HAS CREPT UP AS WELL...WITH CURRENT
DEWPOINTS APPROACHING 70F. A REVIEW OF SATELLITE MOISTURE CHANNEL
ANIMATIONS OVER THE LAST 24 HOURS SHOWS A POTENT AND DEEP SOUTHERN
STREAM CYCLONE EJECTING EASTWARD ACROSS THE GULF BASIN. THE SYSTEM
HAS BEGUN TO OPEN UP AND WEAKEN SLIGHTLY...WITH THE MAIN SHORT-WAVE
TROUGH AXIS EXTENDING FROM THE FLORIDA PANHANDLE TO THE YUCATAN
PENINSULA. MAXIMUM FORCING FOR LARGE-SCALE ASCENT IS PRESENT
CURRENTLY OVER THE NORTHEASTERN QUARTER OF THE GULF OF MEXICO...WITH
ASCENT DIMINISHING EQUATORWARD. EVIDENCE OF LARGE-SCALE ASCENT AND
DESTABILIZATION IS PRESENT ACROSS THE FLORIDA KEYS AND SURROUNDING
COASTAL WATERS IN THE FORM OF INCREASING LOWER AND MIDDLE LEVEL
CUMULIFORM CLOUD DECKS...AS WELL AS A SMALL OUTBREAK OF SHOWERS ALONG
A FEW NORTHWARD-MOVING CONVERGENCE ZONES OVER THE UPPER KEYS AND
ADJOINING WATERS. A SATELLITE-DERIVED SOUNDING NEAR THE LOWER KEYS AT
06Z INDICATED THAT THE 500MB TEMPERATURE HAD COOLED TO ABOUT -10C...
AND THAT THE ATMOSPHERE HAD DESTABILIZED SINCE TUESDAY EVENING.
HOWEVER...OVERALL POTENTIAL BUOYANCY REMAINED WEAK WITH CONSIDERABLE
DRY AIR IN THE LAYER 5000-10000 FEET ABOVE GROUND.

MEANWHILE...A SURFACE ANALYSIS ACROSS THE EASTERN UNITED STATES EARLY
THIS MORNING REVEALED AN INTENSIFYING WAVE CYCLONE EVOLVING OVER THE
OHIO VALLEY...WITH A DEVELOPING COLD FRONT EXTENDING SOUTHWEST ACROSS
TEXAS. THE SURFACE CYCLONE IS SUPPORTED ALOFT BY A VIGOROUS DIGGING
MIDLATITUDE MIDLATITUDE SHORT-WAVE TROUGH WHICH SEEMS TO BE ABSORBING
ENERGY FROM THE LOWER LATITUDE TROUGH APPROACHING FLORIDA.

FORECAST HIGHLIGHTS TODAY THROUGH THURSDAY NIGHT -- LARGE-SCALE
FORCING FOR ASCENT WILL DESTABILIZE THE ATMOSPHERE OVER SOUTH FLORIDA
AND THE KEYS ONLY FOR ANOTHER FEW HOURS BEFORE THE WEAKENING SHORT-
WAVE TROUGH EJECTS EAST OF THE FLORIDA PENINSULA. BY MIDDAY...THE
COLD FRONT WILL HAVE ACCELERATED SOUTHEASTWARD OFF THE TEXAS COAST
AND OVER THE NORTHERN GULF OF MEXICO AS ITS PARENT LOW PRESSURE AREA
INTENSIFIES AND EXPANDS EASTWARD TOWARD THE NORTHEASTERN STATES.
ISOLATED TO SCATTERED SHOWERS IN FAST SOUTHWESTERLY FLOW SEEM
PROBABLE WITH A DIMINISHING CHANCE FOR THUNDER GIVEN WARMING ALOFT. A
PRE-FRONTAL CONVERGENCE LINE PROBABLY WILL INDUCE A BROKEN BAND OF
MOSTLY SHALLOW CONVECTION CELLS OVER THE SOUTHEASTERN GULF OF MEXICO
LATE THIS AFTERNOON...WITH A PROBABLE PASSAGE THROUGH THE FLORIDA
KEYS DURING THE EVENING HOURS. AN EXPANSIVE REGION OF DIFLUENT
NORTHERLY CONTINENTAL POLAR SURFACE FLOW WILL DEVELOP QUICKLY OVER
MUCH OF THE EASTERN AND SOUTHERN UNITED STATES AS THE EASTWARD-MOVING
CYCLONE DEVELOPS INTO A WESTERN NORTH ATLANTIC GALE CENTER AND A HIGH
PRESSURE CELL BUILDS SOUTHEASTWARD OVER THE GULF BASIN. A FRONTAL
PASSAGE WITH A FAIRLY ROBUST BUT SHORT-LIVED NORTHERLY BLOW SHOULD
COMMENCE IN THE KEYS EARLY THURSDAY MORNING...WITH SUBSEQUENT QUICK
CLEARING AND A 24-HOUR PERIOD OF LOW-LEVEL COLD THERMAL ADVECTION.

FORECAST HIGHLIGHTS FRIDAY THROUGH SUNDAY -- AN EASTWARD-MOVING SURFACE
POLAR ANTICYCLONE WILL MODIFY QUICKLY AS IT EVOLVES OVER THE
SUBTROPICAL WESTERN NORTH ATLANTIC BENEATH WEAK MID-TROPOSPHERIC
RIDGING AND FAST ZONAL FLOW ALOFT. LOCAL BREEZES WILL REMAIN FRESH
FRIDAY...AND PROBABLY SATURDAY AS WELL...AS THEY TURN NORTHEAST
FRIDAY...EAST FRIDAY NIGHT...AND SOUTHEAST BY SATURDAY NIGHT. SURFACE
AIR MASS MODIFICATION WILL COMMENCE FRIDAY AND PROCEED THROUGH THE
WEEKEND. IN FACT...A WEAK LOW-LEVEL WARM ADVECTION REGIME MAY BEGIN
AS EARLY AS SATURDAY...WITH SLIGHT SHOWER CHANCES FOR SUNDAY.

FORECAST HIGHLIGHTS MONDAY AND TUESDAY -- FORECAST CONFIDENCE DIPS
SIGNIFICANTLY FOR THESE LATER PERIODS AS MODELS STRUGGLE WITH THE
STRUCTURE...INTENSITY...AND MOVEMENT OF YET ANOTHER CYCLONE IN THE
PROGRESSIVE SOUTHERN STREAM FLOW. NEAR-CLIMO TEMPERATURES...SLIGHT
SHOWERS CHANCES...AND MODERATE BREEZES BETWEEN SOUTH AND EAST FOR
NOW.
&&

.MARINE...
A TROUGH WILL MOVE EASTWARD ACROSS THE FLORIDA PENINSULA THIS
MORNING. A COLD FRONT WILL SWEEP ACROSS THE GULF OF MEXICO THIS
AFTERNOON AND EVENING...REACHING THE FLORIDA KEYS LATER TONIGHT.
MODERATE SOUTHWEST BREEZES TODAY...WILL SHIFT WEST LATER TODAY...AND
NORTHWEST TONIGHT. A PERIOD OF STRONG NORTH BREEZES IS LIKELY
THURSDAY MORNING...AS A HIGH PRESSURE SYSTEM BUILDS IN BEHIND THE
FRONT. THE EXPANSIVE HIGH PRESSURE AREA THEN WILL SHIFT QUICKLY
EASTWARD OVER THE WESTERN NORTH ATLANTIC THURSDAY NIGHT AND
FRIDAY...AND REMAIN THERE THROUGH SUNDAY.
&&

.AVIATION...
12/06Z TAF ISSUANCE...VFR CONDITIONS WILL PREVAIL AT THE KEY WEST
AND MARATHON TERMINALS THROUGH THE EARLY PART OF THE PERIOD. WINDS
WILL GRADUALLY INTENSIFY OUT OF THE SOUTH-SOUTHWEST AND BECOME GUSTY
BY THIS AFTERNOON. RAIN CHANCES WILL GRADUALLY RAMP UP AFTER 18Z...
BUT THE MOST PROMINENT RAIN CHANCES WILL BE FOUND IN THE VICINITY OF
A PASSING COLD FRONT AROUND THE 02Z TIME PERIOD AT THE ISLAND
TERMINALS.
&&

.PRELIMINARY POINT TEMPS/POPS...
KEY WEST  82  70  74  63 / 40 40 10 -
MARATHON  84  70  74  62 / 40 40 10 -
&&

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

$$

PUBLIC/MARINE.........KASPER
AVIATION/NOWCASTS.....MSB

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