000
FXUS62 KMFL 231139
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
639 AM EST MON NOV 23 2009

.AVIATION...
VFR CONDITIONS EXPECTED THROUGH THE PERIOD. LIGHT FLOW PREVAILING
AT ALL TERMINALS THIS MORNING. BY 23/15Z...SE FLOW EXPECTED TO
PICK UP SPEED WITH VCSH ONLY FOR KAPF AND KPBI DUE TO THEIR
PROXIMITY OF THE COLD FRONT. BY 24/03Z...WINDS WILL SLOW DOWN
AGAIN LIKE PREVIOUS NIGHTS. FOR KAPF...SEA BREEZE EXPECTED TO
DEVELOP BY 23/18Z WITH VCSH POSSIBLE.

&&

.PREV DISCUSSION... /ISSUED 427 AM EST MON NOV 23 2009/

DISCUSSION...
GENERALLY QUIET WEATHER CONDITIONS PERSIST ACROSS SOUTH FLORIDA
THIS MORNING...WITH RECENT IR SATELLITE IMAGERY INDICATING A
CONTINUATION OF THE THICK CIRROSTRATUS DECK IN PLACE OVER THE
REGION. DESPITE THE HIGH-LEVEL CLOUD COVER...WILL CONTINUE TO
MONITOR POTENTIAL FOG DEVELOPMENT TOWARD MORNING...ESPECIALLY
INTERIOR ZONES. SHORT TERM MODELS ARE IN FAIRLY GOOD AGREEMENT ON
DEPICTING A CONTINUATION OF STRONG SOUTHWESTERLY FLOW ALOFT OVER
SOUTH FLORIDA FOR THE NEXT COUPLE OF DAYS...WITH A BROAD 590 DM
MID-LEVEL ANTICYCLONE FORECAST TO REMAIN CENTERED NORTH OF THE
GREATER ANTILLES...AND A STRONG UPPER TROUGH EXPECTED TO DIG
SOUTHEASTWARD ACROSS THE NORTHERN ROCKIES...AND DEVELOP INTO
CUTOFF UPPER LOW BEFORE SHIFTING EASTWARD ACROSS THE CENTRAL
PLAINS LATER TODAY AND TONIGHT. OVERALL...WILL FOLLOW A
PERSISTENCE FORECAST FOR TODAY/TONIGHT...WITH HIGHEST POPS (BUT
ONLY LOW CHANCE) IN VICINITY OF A WEAK/STALLED FRONTAL BOUNDARY
ACROSS CENTRAL FLORIDA. ALTHOUGH MOST OF THE PRECIPITATION SHOULD
COME IN THE FORM OF SHOWERS...WOULD NOT BE ENTIRELY SURPRISED IF
AN ISOLATED THUNDERSTORM DEVELOPED. WILL ALSO STICK TO A
PERSISTENCE FORECAST FOR HIGH TEMPERATURES...AND LOWER MOS NUMBERS
BY A 1-3 DEGREES...BASED ON EXPECTED AMOUNT OF HIGH-LEVEL CLOUD
COVER.

THE FORECAST BECOMES A BIT MORE COMPLICATED ON TUESDAY...AS ALL
AVAILABLE GUIDANCE SUGGESTS AN ACTIVE SUBTROPICAL BRANCH OF THE
UPPER LEVEL JET WILL EVOLVE OVER THE AREA...WITH SEVERAL LOW
AMPLITUDE PERTURBATIONS NOTED IN MID-LEVEL VORTICITY FIELDS
EXTENDING FROM THE EASTERN PACIFIC ACROSS CENTRAL MEXICO. ALTHOUGH
THE VARIOUS GLOBAL MODELS OFFER DIFFERENT SOLUTIONS REGARDING
TIMING AND STRENGTH OF THE INDIVIDUAL WAVES AS THEY APPROACH SOUTH
FLORIDA FROM THE WEST...THE GENERAL TREND OF BROAD/VERY WEAK
SURFACE CYCLOGENESIS SOMEWHERE ACROSS THE GULF BY THE MIDDLE OF
THE WEEK IS BECOMING MORE CLEAR. THIS...IN COMBINATION WITH STRONG
SURFACE LOW PRESSURE -- ASSOCIATED WITH CENTRAL PLAINS UPPER LOW
-- MOVING ACROSS THE UPPER MIDWEST SHOULD RESULT IN THE STALLED
FRONTAL BOUNDARY BEGINNING TO LIFT NORTHWARD LATE ON TUESDAY. A
STRENGTHENING LOW-LEVEL WARM ADVECTION REGIME WILL LIKELY BE IN
PLACE BY TUESDAY NIGHT...AND WHEN COUPLED WITH THE ONSET OF
MODERATE EASTERLY FLOW AT THE SURFACE AND PWATS RISING INTO THE
1.75-2 INCH RANGE...SHOULD LEAD TO A FAIRLY WIDESPREAD COVERAGE OF
SHOWER ACTIVITY ALONG AT LEAST THE SOUTHEAST COAST BY WEDNESDAY
MORNING.

A TREND TOWARD WETTER CONDITIONS IS NOW BEING ADVERTISED BY NOT
ONLY THE GFS AND NAM...BUT ALSO THE MORE RELIABLE UKMET AND
ECMWF...WHICH LEADS TO A HIGHER LEVEL OF CONFIDENCE THAT WEDNESDAY
AND THANKSGIVING DAY WILL FEATURE A FAIR AMOUNT OF SHOWER ACTIVITY
ACROSS SOUTH FLORIDA. RICH/DEEP MOISTURE WILL BE IN PLACE DURING
THIS PERIOD...WITH PWATS ON FORECAST SOUNDINGS EXPECTED TO BE NEAR
OR IN EXCESS OF 1.75 INCHES -- WELL ABOVE NORMAL FOR SOUTH
FLORIDA`S DRY SEASON. RAIN CHANCES MAY BE ENHANCED BY THE PRESENCE
OF A WEAK INVERTED LOW-LEVEL TROUGH...AND LOCALLY HEAVY RAINFALL
MAY OCCUR AT TIMES...BUT THERE IS TOO MUCH UNCERTAINTY TO ADDRESS
THIS AS A SUBSTANTIAL HAZARD AT THIS TIME. A WAVE OF LOW PRESSURE
MOVING NORTHEASTWARD ALONG THIS INVERTED TROUGH ON THANKSGIVING
DAY STILL APPEARS AS IF WILL BRING AN END TO RAIN CHANCES AND OPEN
THE FLOOD GATES FOR A MUCH COOLER/DRIER CANADIAN AIR MASS TO
SPREAD OVER THE AREA BEGINNING ON THURSDAY NIGHT. MODERATE COLD
ADVECTION AND POTENTIAL FOR LINGERING HIGH CLOUDS WILL LIKELY KEEP
HIGH TEMPS IN THE UPPER 60S/LOWER 70S ON FRIDAY. SATURDAY MORNING
SHOULD BE THE COOLEST OF THE EVENT...WITH LOW-LEVEL THICKNESS
VALUES NORTHWEST INTERIOR RANGING FROM 1350 M (ECMWF) TO 1335-1340
M (GFS). WITH DEW POINTS POSSIBLY AS LOW AS THE MID/UPPER 30S AND
LIGHT WINDS...THIS MAY ALLOW TEMPS TO FALL INTO THE LOWER 40S NEAR
THE LAKE ON SATURDAY MORNING...AND PERHAPS EVEN A FEW DEGREES
COOLER IN WIND SHELTERED LOCATIONS. A CONTINUATION OF DRY WEATHER
AND A SLOW WARMING TREND IS EXPECTED THROUGH END OF THE WEEKEND.

MARINE...
GENERALLY BENIGN WEATHER CONDITIONS ARE ANTICIPATED ON THE LOCAL
WATERS FOR THE NEXT COUPLE OF DAYS...WITH A MORE PRONOUNCED
EASTERLY COMPONENT TO LOW-LEVEL WINDS BECOMING ESTABLISHED AT 5-10
KNOTS BY MID-WEEK. A STRONG COLD FRONT STILL APPEARS AS IF IT WILL
PASS ACROSS THE LOCAL AREA ON THANKSGIVING DAY...WITH INCREASING
NORTHWEST WINDS FOLLOWING FRONTAL PASSAGE AND SCEC CONDITIONS
LIKELY ON THURSDAY NIGHT. SCA FOR ALL WATERS APPEARS VERY LIKELY
FROM FRIDAY INTO FRIDAY NIGHT...WITH NORTH/NORTHWEST WINDS AROUND
20 KNOTS RESULTING IN INCREASINGLY HAZARDOUS MARINE CONDITIONS...
ESPECIALLY IN THE GULF STREAM. WINDS WILL VEER TO NORTHEAST AND
SLOWLY SUBSIDE THROUGH THE REMAINDER OF NEXT WEEKEND...WITH HIGH
SEAS EXPECTED TO LINGER IN THE GULF STREAM.

FIRE WEATHER...
THERE ARE NO FIRE WEATHER CONCERNS THROUGH FRIDAY. HOWEVER...
DEPENDING ON AMOUNT OF DIURNAL HEATING ON FRIDAY/SATURDAY...RED
FLAG CONDITIONS WILL BE POSSIBLE FOR AT LEAST A PORTION OF THE
FORECAST AREA ON BOTH AFTERNOONS...AS A DRY CANADIAN AIR MASS
SPREADS OVER THE REGION. A SLOW MODIFICATION OF AIR MASS AND
GRADUAL INCREASE IN LOW-LEVEL MOISTURE IS EXPECTED THROUGH THE END
OF NEXT WEEKEND.

&&

.PRELIMINARY POINT TEMPS/POPS...
WEST PALM BEACH  83  70  83  71 / 30 20 20 50
FORT LAUDERDALE  84  75  84  72 / 20 10 20 60
MIAMI            84  74  84  72 / 10 10 20 60
NAPLES           84  68  84  69 / 30 10 30 40

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
AM...NONE.
GM...NONE.

&&

$$

LONG TERM...70/DD
SHORT TERM/AVIATION...17/ERA