000
FXUS62 KMFL 251426
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
926 AM EST WED NOV 25 2009

.UPDATE...LATEST SURFACE ANALYSIS REVEALS STATIONARY BOUNDARY
ACROSS CENTRAL FLORIDA. THIS IS SUPPORTED BY BOTH AND ANALYSIS OF
THE TEMPERATURE AND DEW POINT FIELDS. BUT THE ACTUAL AXIS OF THE
TROUGH OF LOW PRESSURE BASED ON A CLOSER LOOK AT THE PRESSURE AND
WIND FIELDS IS LOCATED ACROSS THE LAKE OKEECHOBEE REGION WITH
LIGHT SELY FLOW SOUTH OF THE TROUGH AND SLIGHTLY STRONGER OFF THE SE
COASTAL WATERS. 12Z UPR AIR ANALYSIS REVEALS EXCELLENT UPPER LEVEL
DIVERGENCE ACROSS SOUTH FLORIDA AS THIS TIME WITH MID LEVEL TEMPS
OF AROUND -9. THIS HELPED INCREASE INSTABILITY OVERNIGHT WHICH
COUPLED WITH THE DIVERGENCE AND LOW LEVEL CONVERGENT FLOW OFF THE
SOUTH AND SOUTHEAST COASTS HELPED GENERATE CLUSTER OF SHOWERS AND
STORMS CURRENTLY AFFECTING EASTERN HALF OF SOUTH FLORIDA.
SSMI/AMSU/GPSMET BLENDED TOTAL PRECIPITABLE WATER PRODUCT SHOWS
PRECIPITABLE WATER VALUES OF CLOSE TO 2 INCHES WHICH IS IN LINE
WITH THE 12Z SOUNDING. THIS REPRESENTS MOISTURE LEVELS GREATER
THAN TWO STANDARD DEVIATIONS ABOVE NORMAL OR ABOUT 50% TO 60%
ABOVE NORMAL. SBCAPE VALUES ARE RUNNING JUST ABOVE 1000 J/KG AT
THE PRESENT TIME AND EVEN IF WE WARM UP TO NEAR 80 THEY WILL
REMAIN IN THE 1000-1500 J/KG RANGE. AND THAT IS A BIG ASSUMPTION.
UNLESS CLOUDS BREAK SOME LATER THIS AFTERNOON WE WILL STRUGGLE TO
MOVE WELL INTO THE 70S.

SO FROM THIS...WHAT CAN WE EXPECT FOR THE REST OF TODAY AND INTO
TONIGHT. THE LOCAL WRF ARW 9/3KM NEST IS HANDLING THIS SITUATION
REALLY WELL. GFS DEVELOPS A LOW ALONG THE TROUGH DEVELOPING WINDS
THAT ARE TOO STRONG ACROSS OUR ATLANTIC WATERS. SO FROM THIS POINT
ON WILL LEAN MORE TOWARDS THE LOCAL WRF ARW AND NAM FOR THE
EVOLUTION OF THE WINDS OVER THE NEXT COUPLE OF FORECAST PERIODS
FOR THIS UPDATE. AS FAR AS RAIN CHANCES...GIVEN CURRENT TRENDS
WILL THEM AS IS FOR THE MOMENT. CURRENT ACTIVITY ACROSS THE
EASTERN HALF OF THE CWA WILL LIKELY CONTINUE THROUGH LATE MORNING
OR EARLY AFTERNOON BEFORE ABATING A BIT. THEN ACTIVITY CURRENTLY
ACROSS WEST CENTRAL FLORIDA AND THE SE GULF IS LIKELY TO BEING
AFFECTING SOUTH FLORIDA LATER THIS AFTERNOON OR EVENING FROM THE
NW AND LIKELY SPREAD OVER ACROSS THE REMAINDER OF THE CWA
OVERNIGHT. HOW FAR THE ACTIVITY FROM THE NORTH WILL REACH" onClick="return popup(this, 'notes')">REACH SOUTH IS
IN QUESTION NOW BUT THAT WILL BE EVALUATED WHEN THE 12Z DATA COMES
IN.

MAIN CONCERN AT THIS TIME GIVEN ALL OF THIS IS LOCALLY HEAVY
RAINFALL WITH SOME LOCALIZED FLOODING. SEVERE WEATHER THREAT AT
THIS TIME IS MARGINAL GIVEN LOW LEVEL WIND PROFILES ARE NOT
IMPRESSIVE AND NOT EXPECTED TO INCREASE THAT MUCH AND LIMITED
INSTABILITY. HOWEVER...INCREASE IN LOW LEVEL WINDS WILL BE ENOUGH
TO SUPPORT GUSTY WINDS OF UP TO 40 MPH WITH SOME OF THE STORMS.

&&

.PREV DISCUSSION... /ISSUED 600 AM EST WED NOV 25 2009/

PREV DISCUSSION... /ISSUED 428 AM EST WED NOV 25 2009/

DISCUSSION...
A VERY WET WEATHER PATTERN CONTINUES TO UNFOLD FOR SOUTH FLORIDA
THIS MORNING...WITH WATER VAPOR SATELLITE ANIMATION INDICATING
AT LEAST THREE INDIVIDUAL MID-LEVEL SHORTWAVE TROUGHS IN PLACE
OVER THE GULF OF MEXICO...WITH THE STRONGEST WAVE LOCATED OVER THE
WEST CENTRAL GULF TO THE SOUTH OF THE WESTERN LOUISIANA COAST. ONE
OF THE WEAKER FEATURES...LOCATED OVER THE SOUTHEASTERN GULF TO THE
WEST OF THE DRY TORTUGAS...IS LIKELY RESPONSIBLE FOR ENHANCEMENT
OF NOCTURNAL CONVECTION TO THE SOUTHWEST OF THE FORECAST AREA.
EXPECT THIS REGION OF WIDESPREAD RAIN AND THUNDERSTORMS TO
CONTINUE PROGRESSING SLOWLY NORTHWARD THROUGH THE MORNING.

OVERALL...ALTHOUGH THE NAM/GFS/UKMET/ECMWF DISAGREE ON THE TIMING
OF PASSAGE OF INDIVIDUAL MID-LEVEL SHORTWAVE TROUGHS AND THE GFS
IS STILL SUFFERING FROM SUBSTANTIAL GRID SCALE CONVECTIVE
FEEDBACK...THEY ALL AGREE ON ONE THING -- THAT VERY HIGH RAIN
CHANCES ARE IN ORDER FOR VIRTUALLY THE ENTIRE REGION FOR
TODAY...TONIGHT...AND PERHAPS THE FIRST HALF OF THE DAY ON
THANKSGIVING. THERE IS NO REASON TO DISAGREE...WITH PWAT VALUES ON
POINT FORECAST SOUNDINGS FORECAST TO REMAIN IN THE 1.7-2 INCH
RANGE...A WEAK INVERTED TROUGH EXPECTED TO OSCILLATE ACROSS THE
REGION...AND SEVERAL PERTURBATIONS EXPECTED TO MOVE OVERHEAD IN
ACTIVE SUBTROPICAL JET...EACH OF WHICH WILL CONTRIBUTE TO AN
ENHANCEMENT IN LARGE SCALE VERTICAL MOTIONS. THUS...WILL CONTINUE
TO ADVERTISE HIGH POPS TODAY AND TONIGHT...WITH THE ONLY MAJOR
CHANGE BEING TO INCREASE COVERAGE OF THUNDERSTORMS...BASED ON
AMOUNT OF CONVECTION/LIGHTNING ACTIVITY CURRENTLY IN PLACE OVER
THE KEYS. THE MAGNITUDE OF LOW-LEVEL WIND FIELDS SUGGEST THAT A
FEW STRONG STORMS WILL BE POSSIBLE...WITH GUSTY WINDS POSSIBLE
WITH THE DEEPEST CONVECTIVE CELLS...AND WILL MENTION THIS THREAT
IN THE HWOMFL...AS WELL AS POTENTIAL FOR LOCALLY HEAVY RAINFALL.

TRENDS WILL BEGIN TO CHANGE ON THANKSGIVING DAY...AS A POWERFUL
AND COMPACT UPPER LOW -- CURRENTLY DROPPING SOUTHWARD OVER THE
RED RIVER REGION ON MINNESOTA/THE DAKOTAS -- BEGINS TO OPEN INTO
AN AMPLIFIED LONG WAVE TROUGH AS IT SPREADS EASTWARD ACROSS THE
OHIO VALLEY AND TOWARD NEW ENGLAND. THIS WILL OPEN THE DOOR FOR A
STRONG COLD FRONTAL PASSAGE LATE ON THANKSGIVING DAY. HOWEVER...
WITH THE COLD AIR MASS ONLY BEGINNING TO WORK INTO THE REGION
DURING THE DAY...WILL CARRY AT LEAST CHANCE POPS FOR THE SOUTHEAST
HALF OF THE AREA. LOW-LEVEL COLD ADVECTION WILL INCREASE THROUGH
THURSDAY NIGHT/FRIDAY...AS SURFACE RIDGE SETTLING SOUTHWARD OVER
TEXAS BEGINS TO SHIFT EASTWARD ACROSS THE LOWER MISSISSIPPI
VALLEY...AND WITH POTENTIAL FOR HIGH CLOUDS TO PERSIST IN
WESTERLY FLOW ALOFT...TEMPERATURES MAY STRUGGLE TO MAKE IT OUT OF
THE LOWER 70S ON FRIDAY.

THE EXTENDED FORECAST WILL BEGIN WITH A GOOD RADIATIONAL COOLING
EVENT ON FRIDAY NIGHT/SATURDAY MORNING...AT LEAST IF HIGH CLOUDS
CAN DIMINISH SUFFICIENTLY. ALTHOUGH LOW-LEVEL THICKNESS VALUES
HAVE INCREASED...DEW POINTS IN THE LOWER/MID 30S MAY SUPPORT LOW
TEMPERATURES IN THE LOWER/MID 40S NORTHWEST INTERIOR IF WINDS
REMAIN CALM AND SKIES CLEAR. OTHERWISE...VERY QUIET WEATHER AND A
SLOW WARMING TREND IS ANTICIPATED THROUGH THE BEGINNING OF NEXT
WEEK...WITH ZONAL FLOW ALOFT AND ONLY A FEW PASSING MID-LEVEL
WAVES TO PERIODICALLY ENHANCE CLOUD COVER. A STRONGER SYSTEM MAY
AFFECT THE REGION WITH INCREASING RAIN/STORM CHANCES BY THE MIDDLE
OF NEXT WEEK.

MARINE...
NUMEROUS SHOWERS/THUNDERSTORMS WILL AFFECT THE LOCAL WATERS FOR
THE NEXT 24-36 HOURS...WITH PRESENCE OF LOW-LEVEL BOUNDARY AND
SUFFICIENT INSTABILITY TO MAKE WATERSPOUTS THE PRIMARY MARINE
WEATHER CONCERN IN THE SHORT TERM. PREVAILING WINDS OUTSIDE OF
CONVECTION SHOULD REMAIN AROUND 15 KNOTS. WINDS WILL BEGIN TO
INCREASE FROM THE WEST/SOUTHWEST ON THURSDAY MORNING...AND SHOULD
INCREASE FURTHER WHILE VEERING TO NORTHWEST ON THURSDAY EVENING...
AS COLD FRONT SLIDES SOUTHEASTWARD OVER THE REGION. SCEC A GOOD
BET FOR ALL WATERS BY THURSDAY NIGHT/FRIDAY MORNING...WITH SCA
POSSIBLE ON FRIDAY/FRIDAY NIGHT -- AND LINGERING A BIT LONGER FOR
THE GULF STREAM AS SEAS WILL BE SLOWER TO SUBSIDE. MARINE
CONDITIONS WILL IMPROVE BY EARLY NEXT WEEK...BUT PERHAPS
DETERIORATE ONCE AGAIN BY MID-WEEK AS ANOTHER STORM SYSTEM
APPROACHES SOUTH FLORIDA.

FIRE WEATHER...
AT THIS TIME...THE HIGHEST POTENTIAL TIME FRAME FOR FIRE WEATHER
CONCERNS WILL BE ON FRIDAY AND SATURDAY AFTERNOONS...AS A VERY
DRY AIR MASS OF CANADIAN ORIGINS SPREADS OVER THE REGION.
HOWEVER...DUE TO UNCERTAINTY ON AMOUNT OF CLOUD COVER AND COOL
AMBIENT TEMPERATURES EXPECTED...MINIMUM AFTERNOON RH VALUES MAY
NOT MEET CRITERIA FOR RFW. HOWEVER...MINIMUM AFTERNOON RH MAY FALL
INTO THE 35-45 PERCENT RANGE FOR MOST OF THE AREA ON BOTH
AFTERNOONS.

&&

.PRELIMINARY POINT TEMPS/POPS...
WEST PALM BEACH  79  68  79  54 / 90 80 50 10
FORT LAUDERDALE  80  71  81  57 / 90 80 60 10
MIAMI            81  71  82  58 / 90 80 60 10
NAPLES           79  68  77  58 / 90 80 30 10

&&

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

$$

LONG TERM...52/PS
SHORT TERM/AVIATION...50/RLP