FXUS62 KMFL 231943
AFDMFL
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
243 PM EST WED DEC 23 2009
...SHOWER/TSTORM CHANCES INCREASING LATE THURSDAY THROUGH
CHRISTMAS DAY...
...LOCALLY HEAVY RAINFALL POSSIBLE ATLANTIC COAST THURSDAY
EVENING/OVERNIGHT...
.DISCUSSION...HIGH PRESSURE OVER THE MID ATLANTIC WILL CONTINUE
RIDGING DOWN THE FL PENINSULA TONIGHT...MAINTAINING AN EASTERLY
WIND FLOW. GPS MET DATA SHOWS PWATS HAVE DECREASED ACROSS THE AREA
THIS AFTERNOON...NOW ONLY IN THE 0.6 TO 0.8 INCH RANGE. SKIES OVER
THE ATLANTIC OFF PALM BEACH/BROWARD ARE CLEAR OF ANY CU...EVIDENT
OF THE LITTLE MOISTURE PRESENT. THERE ARE NO RETURNS ON RADAR
CURRENTLY. GIVEN ALL OF THIS...DESPITE THE BREEZY EASTERLY
FLOW...DECIDED TO DROP SHOWER MENTION THROUGH TONIGHT.
TEMPS WILL RUN EVEN WARMER THAN LAST NIGHT WITH LOWS STAYING ABOVE
70F ALONG THE ATLANTIC COAST. AGAIN FOLLOWED CLOSER TO THE WRF-ARW
FOR THE EAST COAST WHICH IS A FEW DEGREES ABOVE GFS/NAM MOS.
THE HIGH WILL MOVE EAST TOMORROW AS POWERFUL SHORTWAVE ENERGY DIVES
OUT INTO THE PLAINS STATES INDUCING A MAJOR WINTER STORM (BLIZZARD
IN SOME AREAS) FOR PORTIONS OF THE PLAINS/MIDWEST. AS THIS
OCCURS...A SUBTLE QUASI-WARM FRONTAL BOUNDARY LOOKS TO DEVELOP AND
LIFT FROM SOUTH TO NORTH ACROSS SOUTH FL LATE TOMORROW AFTERNOON
THROUGH TOMORROW NIGHT. THE LATEST GFS AND NAM DEPICT
THIS...ALONG WITH PWATS INCREASING TO AROUND 1.75 INCHES...OR +2
STD DEVIATIONS FROM CLIMATOLOGY BY THU EVENING. SO THERE WILL BE A
CHANCE OF SHOWERS AND EVEN A FEW STORMS ESPECIALLY NAPLES-FLL AND
POINTS SOUTH THU AFTERNOON...BUT THINKING THAT A MORE ACTIVE TIME
COULD BE THU EVENING/OVERNIGHT. LOW LEVEL WINDS WILL INCREASE
ESPECIALLY THU NIGHT. IN FACT...THE LATEST NAM12 SHOWS A LOW LEVEL
JET OF 35+ KNOTS DEVELOPING AT 925 MB. GFS IS LESS
AGGRESSIVE...ABOUT 25 KNOTS. EITHER WAY...VERY GOOD CONVERGENCE
WILL OCCUR ALONG THE ATLANTIC COAST ESPECIALLY AT NIGHT AS WINDS
DECOUPLE INLAND DUE TO NIGHTTIME COOLING AND STRENGTHENING LOW
LEVEL WINDS.
QUESTION IS HOW MUCH ACTIVITY WILL DEVELOP FROM THIS CONVERGENCE.
GFS AND NAM BOTH SHOW CAPE INCREASING TO 1000+ J/KG
OVERNIGHT (AND SREF HAS LIKELY PROBABILITIES OF CAPE >1000)...AND
WITH THE HIGH PWATS IN PLACE...FORESEE IT WETTER THAN GUIDANCE
INDICATES SO HAVE INCREASED POPS INTO THE LIKELY CATEGORY FOR MUCH
OF THE EAST COAST METROPOLITAN AREAS THU NIGHT ALONG WITH TSTORM
MENTION GIVEN THE INCREASED INSTABILITY. KEPT CHANCE POPS
ELSEWHERE EXCEPT DROPPED THE GULF COAST TO SLIGHT CHANCE AS LITTLE
CONVERGENCE WILL BE PRESENT THERE.
ALTHOUGH HEAVY RAIN ON A LARGE SCALE IS NOT EXPECTED...WILL HAVE
TO WATCH OUT FOR "LOCALIZED" HEAVY RAINFALL THAT COULD SET UP
ALONG PORTIONS OF THE EAST COAST BECAUSE THERE ARE SIGNALS
SUGGESTING THIS POSSIBILITY...GIVEN THE AFOREMENTIONED FACTORS.
AN INHIBITING FACTOR WILL BE THAT UPPER DYNAMICS WILL BE LACKING
AS THAT ENERGY WILL BE WELL NORTH OF THE AREA.
TEMPS THU NIGHT WILL BE WARM...ESPECIALLY EAST COAST. WAS TEMPTED
TO GO ABOVE GUIDANCE. HOWEVER...GIVEN THE LIKELY POPS...SIDED WITH
GFS MOS. PLACES THAT DO NOT SEE RAINFALL THU NIGHT WILL LIKELY NOT
DROP BELOW THE MID 70S...WHICH IS IN RECORD HIGH MINIMUM
TERRITORY. DEFINITELY A WARM, MUGGY CHRISTMAS MORNING IS EXPECTED.
ON CHRISTMAS DAY...THE SUBTLE LOW LEVEL BOUNDARY WILL HAVE LIFTED
NORTH OF THE SERVICE AREA BUT A PRE-FRONTAL TROUGH WILL MOVE IN FROM
THE WEST DURING THE AFTERNOON. THIS WILL LEAD TO INCREASING
CHANCES OF SHOWERS AND EVEN A FEW THUNDERSTORMS BY
AFTERNOON...FOCUSED ALONG THE ATLANTIC COAST DUE TO A S-SW MEAN
WIND FLOW.
A COLD FRONT WILL REACH AND MOVE PASS THE AREA LATE FRI NIGHT INTO
EARLY SAT. THIS FRONT DOES NOT LOOK TO PUSH THROUGH "CLEANLY" WITH
STILL QUITE A BIT OF CLOUDINESS EXPECTED BEHIND THE FRONT
ESPECIALLY SATURDAY ALONG WITH THE POSSIBILITY FOR SHOWERS
DEVELOPING DUE TO WEAK ISENTROPIC LIFT. TEMPS GRADUALLY
LOWER...THOUGH NO SIGNIFICANT COLD AIR IS EXPECTED. MADE NO
CHANGES TO THE EXTENDED FCST.
&&
.MARINE...KEPT THE SMALL CRAFT ADVISORY FOR BISCAYNE BAY AND THE
ATLANTIC WATERS OFF THE BROWARD AND MIAMI-DADE COAST FOR TONIGHT
AS WINDS OF AROUND 20 KTS ARE EXPECTED. LAND OBS HAVE BEEN GUSTING
NEAR 25 KT...EVIDENCE OF THE STRONGER LOW LEVEL EASTERLY WIND
FLOW. WINDS LOOK TO POSSIBLY BACK OFF A BIT THU MORNING BEFORE
INCREASING THU AFTERNOON/NIGHT...POSSIBLY AGAIN TO SCA LEVELS.
&&
.FIRE WEATHER...INCREASING MOISTURE WILL LEAD TO NO FIRE WEATHER
CONCERNS.
&&
.PRELIMINARY POINT TEMPS/POPS...
WEST PALM BEACH 69 79 73 82 / 10 20 60 60
FORT LAUDERDALE 72 80 73 82 / 10 30 60 60
MIAMI 71 80 73 82 / 10 30 60 60
NAPLES 60 81 67 80 / - 30 20 40
&&
.MFL WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
AM...SMALL CRAFT ADVISORY UNTIL 5 AM EST THURSDAY FOR AMZ630-AMZ651-
AMZ671.
GM...NONE.
&&
$$
LONG TERM...57/DG
SHORT TERM/AVIATION...50/RLP
