Area Forecast Discussion
Issued by NWS Melbourne, FL

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000
FXUS62 KMLB 210912
AFDMLB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MELBOURNE FL
412 AM EST SUN DEC 21 2014

.DISCUSSION...

...MORE HUMID AND WARMER THROUGH WED...
...INCREASED RAIN CHANCES LATE TODAY INTO MON THEN AGAIN LATE TUE
AND WED AHEAD OF NEXT COLD FRONT...

CURRENTLY...
STATIONARY FRONT LAYING INSIDE A WEAK INVERTED TROF EXTENDING FROM
THE SW GOMEX ACRS THE NRN FL PENINSULA. EVENING SOUNDINGS SHOW
INCRSG MOISTURE ACRS THE CENTRAL PENINSULA WITH PWAT VALUES ARND
1.4"...UP FROM 0.8" FROM THE 20/00Z FLIGHT...A FEW POCKETS OF DRY
AIR REMAIN BLO THE H70 LYR THAT INDICATE ADDITIONAL POTENTIAL FOR
MOISTURE LOADING. TO THE S...KMFL HAS MOISTENED TO 1.2" UP FROM 0.9"
FROM 20/00Z BUT STILL SHOWS THE REFLECTION OF A HIGH PRES RIDGE OVER
THE FL STRAITS AND THE CENTRAL BAHAMAS WITH SUBSTANTIAL DRY AIR ABV
A SUBSIDENCE INVERSION IN THE H80-H75 LYR. TO THE N...BOTH KJAX/KTAE
ARE NEARLY SATURATED THRU THE H100-H70 LYR WITH VERY DRY AIR ABV AN
INVERSION IN THE H70-H60 LYR. RUC ANALYSIS INDICATES PLENTIFUL
UPSTREAM MOISTURE WITH H100-H70 MEAN RH VALUES OVER THE GOMEX
LARGELY AOA 80PCT...H85-H50 VALUES AOA 50PCT BUT AS HIGH AS 90PCT
WITHIN THE VCNTY OF THE STATIONARY FRONT.

ALOFT...A 100-120KT ZONAL JET STREAK EXTENDING FROM THE RIO GRANDE
VALLEY TO BERMUDA IS PARALLEL TO THE STATIONARY FRONT AND IS
GENERATING A BROAD LINE OF UPR LVL DIVERGENCE. THOUGH THIS LINE HAS
MARGINAL STRENGTH/ORGANIZATION...VORTICITY AND OMEGA FIELDS SHOW
SIMILAR AXES...WITH ALL THREE NEARLY VERTICALLY STACKED. MODERATELY
COOL AIR REMAINS IN PLACE WITH H50 TEMPS HOLDING ARND -10C. H70-H50
LAPSE RATES STEEPEN FROM ARND 5.5C/KM OVER THE PENINSULA TO
6.0-6.5C/KM OVER THE ERN GOMEX...BUT H85-H70 LAPSE RATES ACTUALLY
DECREASE FROM ARND 5.5C/KM OVERHEAD TO 4.5C/KM UPSTREAM.

TODAY-TONIGHT...
THE ZONAL ORIENTATION OF THE JET WILL MAINTAIN A DEEP W/SW FLOW THRU
THE H85-H30 LYR THAT WILL REMAIN PARALLEL TO THE ORIENTATION OF THE
STATIONARY FRONT. THIS ASSURES THE FRONT WILL NOT MAKE MUCH PROGRESS
S OF THE I-4 CORRIDOR...IF EVEN THAT FAR. RUC40 ANALYSIS CONTINUES
TO SHOW A TIGHT E-W ISENTROPIC GRADIENT THRU THE 300K-315K LYR THAT
WILL COMBINE WITH THE DEEP W/SW FLOW TO EVENTUALLY PRODUCE THE NEXT
RAIN EVENT.

WITH MOST OF THE DRY AIR OVER CENTRAL FL ALREADY ERODED AND
PLENTIFUL MOISTURE UPSTREAM POISED TO PLOW WHAT REMAINS OUT OF THE
WAY...AND A WELL STACKED BAND OF INSTABILITY OVER THE GOMEX...POPS
WILL BE INTRODUCED TO THE ENTIRE CWA...SLGT CHC ALONG AND N OF
THE I-4 CORRIDOR THROUGH EARLY AFTN...BCMG 30-40 FROM VERO BEACH/LAKE
KISSIMMEE NWD. DRIER AIR AND FURTHER DISTANCE FROM THE FRONT WILL
LIMIT PRECIP OVER THE SRN CWA TO 20PCT...MAINLY IN -SHRAS.

PRECIP WILL INCREASE AREAWIDE TONIGHT...BUT AGAIN WILL REFLECT THE
DRIER AIR TO THE S AND THE POSITION OF THE STATIONARY FRONT. PRECIP
PRIMARILY WILL BE AS SHRAS...COOL AIR ALOFT ALONG WITH THE ENHANCED
BAND OF MID/UPR LVL INSTABILITY MAY ALLOW ISOLATED TSRA TO DVLP IN
THE VCNTY OF THE FRONTAL BNDRY. BOTH GFS/ECMWF MOS SHOWS HI POPS
OVER THE NRN CWA...THOUGH ECMWF IS TOO AGGRESSIVE WITH 70POPS CLEAR
DOWN TO LAKE OKEECHOBEE/JUPITER INLET. LIKELY/CATEGORICAL OVER THE
NRN BREVARD/NRN OSCEOLA NWD...SCT FROM SRN BREVARD/SRN OSCEOLA SWD.

ONE FLY IN THE OINTMENT IS THE GFS SOLUTION BTWN 06Z-12Z TONIGHT
WITH QPF BTWN 0.75"-1.5" ALONG THE I-4 CORRIDOR. TIME SECTIONS FOR
THE REGION SHOW VERY STRONG COUPLETS IN THE OMEGA AND DIVERGENCE
FIELDS IN THE PRESENCE OF 90PCT MEAN RH THRU THE ENTIRE H70-H30 LYR.
WHILE THE MOISTURE SOLUTION SEEMS REASONABLE...THE COUPLETS ARE
CLEAR SIGNS OF CONVECTIVE FEEDBACK. PRECIP CHANCES WILL BE HIGH...
NO DOUBT...BUT WILL CAP QPF BTWN 0.25"-0.50".

DESPITE INCREASING CLOUD COVER...LIGHT SRLY WINDS WILL COMBINE WITH
THE SLOW ARRIVAL OF SIG PRECIP TO ALLOW AFTN TEMPS TO WARM INTO THE
M/N70S AREAWIDE...NEAR 80 ALONG THE NE SHORE OF LAKE OKEECHOBEE...
4-8F ABV AVG. CLDY SKIES AND SFC DEWPOINTS IN THE U50S/L60S WILL
KEEP OVERNIGHT MINS IN THE L/M60S...EXCEPT IN THE M/U60S ALONG THE
IMMEDIATE COAST...10-15F ABV AVG.

MON-TUE...A MOIST SOUTHERLY WIND FLOW WILL BE IN PLACE WITH
FRONTAL BOUNDARY JUST TO OUR NORTH. TAIL END OF A BAND OF
CONVECTION NEAR THIS FRONTAL BOUNDARY MAY BE AFFECTING NORTHERN
SECTIONS EARLY MON THEN AS THE BOUNDARY GRADUALLY LIFTS NORTH...
NO LARGE SCALE LIFTING MECHANISMS ARE NOTED. LIKELY POPS IN THE
NORTH MON WILL TAPER BACK TO 30-40 PERCENT TUE. POPS ACROSS THE
SOUTH LOOK TO JUST BE AROUND 20 PERCENT BOTH DAYS. WITH THE HIGH
MOISTURE...THERE WILL PLENTY OF CLOUDINESS...ESPECIALLY MON. MAX
TEMPS SHOULD BE IN THE MID 70S NORTH ON MON AND LOWER 80S SOUTH.
THE LOWER 80S SHOULD LIFT TO CENTRAL SECTIONS ON TUE.

TUE NIGHT-CHRISTMAS...TROUGH IN THE MID SECTION OF THE COUNTRY
WILL DEEPEN WITH BASED DIGGING INTO THE GULF OF MEXICO WED THEN
DAMPENING OUT AS IT LIFTS ACROSS THE SOUTHEAST STATES ON CHRISTMAS.

THIS LATEST MODEL SOLUTION IS SLOWER THAN PREVIOUS RUNS...SO HAVE
BACKED OFF ON PRE FRONTAL CONVECTION UNTIL LATE TUE NIGHT IN THE
NORTH AND ON WED FOR THE REST OF THE AREA. RATHER STRONG LOW LEVEL
WINDS ARE STILL INDICATED AS THE CONVECTIVE BAND MOVES ACROSS THE
AREA. THE ECMWF 850 MB WINDS ARE STRONGER THAN THE GFS (WHICH HAS
BACKED TO AROUND 35 KNOTS). IN ANY EVENT...WITH THE SLOWER
SOLUTION...MODEST DIURNAL HEATING/DESTABILIZATION ON WED COULD
LEAD TO SOME STRONG STORMS.

SHOWER CHANCES MAY LINGER INTO WED NIGHT AND SOME CLOUDINESS INTO
CHRISTMAS MORNING. TEMPS DO NOT LOOK AS COOL WITH THE SLOWER
FRONTAL PASSAGE AND SOME CLOUDINESS. CONSENSUS LOWS ARE NOW IN THE
LOWER/MID 50S WITH HIGHS CHRISTMAS DAY IN THE MID 60S TO LOWER
70S...AND THESE READINGS MAY EVEN BE TOO COOL.

FRI-NEXT SUNDAY...HIGH PRESSURE BEHIND THE COLD FRONT IS FORECAST TO
EXTEND ACROSS THE AREA FRI AND ELONGATE INTO THE ATLANTIC NEXT
WEEKEND. THE MODELS DISAGREE ON TIMING OF THE NEXT COLD FRONT WITH
CONSENSUS SOLUTION SHOWING IT APPROACHING BY SUN (MOST SUPPORTED
BY THE ECMWF). THE GFS SMEARS 15-20 POPS OUT SAT-SUN BUT WILL HOLD
OFF THROWING IN 20 PERCENT UNTIL SUNDAY. AFTER TEMPS CLOSE TO
NORMAL ON FRI...MODERATION TO A LITTLE ABOVE NORMAL IS EXPECTED ON
THE WEEKEND.

&&

.AVIATION...THRU 22/06Z

SFC WNDS:
THRU 21/15Z...VRBL AOB 4KTS. BTWN 21/15Z-21/18Z...S 5-8KTS. BTWN
21/18Z-21/22Z...INTERIOR SITES S/SW 4-7KTS...COASTAL SITES S/SE
6-9KTS. AFT 21/22Z...S/SE AOB 5KTS.

VSBYS:
THRU 21/14Z...AREAS MVFR IN BR...LCL LIFR IN FG MNLY VCNTY
KVRB/KFPR. BTWN 21/14Z-21/18Z...N OF KEVB-KISM SLGT CHC MVFR SHRAS.
BTWN 21/18Z-22/03Z...N OF KMLB-KLAL SCT MVFR/ISOLD IFR SHRAS...S OF
KMLB-KLAL SLGT CHC MVFR SHRAS. AFT 22/03Z...N OF KTIX-KISM
PREVAILING MVFR IN NMRS/WDSPRD RA WITH PDS IFR +RA...S OF KTIX-KISM
CHC MVFR SHRAS.

CIGS:
N OF KMLB-KLAL: THRU 21/14Z...BTWN FL080-100 WITH PDS MVFR BTWN
FL020-030. BTWN 21/14Z-22/03Z...BTWN FL060-080 WITH PDS MVFR BTWN
FL015-025 IN SCT SHRAS. AFT 22/03Z...MVFR BTWN FL010-020.

S OF KMLB-KLAL: THRU 21/14Z...AOA FL120. BTWN 21/14Z-22/03Z...BTWN
FL080-100 WITH PDS MVFR BTWN FL020-030 IN ISOLD -SHRAS. AFT
22/03Z...BTWN FL060-080 WITH PDS MVFR BTWN FL015-025 IN SCT -SHRAS.

&&

.MARINE...
TODAY-TONIGHT...FAVORABLE SEA CONDS THRU DAYBREAK BUT DETERIORATING
WX CONDS AS A WEAK STATIONARY FRONT JUST N OF THE I-4 CORRIDOR
KEEPS THE LCL PGRAD DISRUPTED AND SERVES AS A FOCUS FOR SHRA/TSRA
ACTIVITY. SFC WNDS S-SE BTWN 4-8KTS FROM CAPE CANAVERAL SWD...VRBL
AOB 5KTS N OF THE CAPE IN THE VCNTY OF THE FRONT. SEAS AOB 2FT...
BUILDING TO 2-3FT OVER THE OFFSHORE LEG AFT MIDDAY.

N OF THE CAPE...SCT SHRAS AFT MIDDAY...BCMG NMRS/WDSPRD WITH ISOLD
TSRAS AFT SUNSET. S OF THE CAPE...ISOLD/SCT SHRAS AFT MIDDAY...CONTG
THRU THE OVERNIGHT PD.

MON-WED...SOUTHERLY FLOW WITH 10-15 KNOT SPEEDS INDICATED MON THEN
PUSHING UP TO 15-20 KNOTS TUE AFTERNOON AND EVENING AND NEAR 20
KNOTS WED AS COLD FRONT APPROACHES. SHOWER AND STORM CHANCES MAY
BE 50-60 PERCENT IN THE NORTH MON...THEN DROP OFF TO 20-40 PERCENT
UNTIL FRONTAL BAND CONVECTION APPROACHES LATE TUE NIGHT AND ON WED.

CHRISTMAS...STILL A LITTLE BIT OF A TRICKY FORECAST AS THE GFS IS
A LITTLE SLOWER THAN THE ECMWF WITH THE TIMING OF FRONTAL PASSAGE.
IF THE FRONT IS SLOWER LIKE THE GFS...THE BAND OF SHOWERS/STORMS
MAY STILL BE ACROSS THE WATERS EARLY...BUT OTHERWISE A NORTHWEST
WIND SURGE 15-20 KNOTS IS INDICATED BEHIND THE FRONT...SO BOATING
CONDITIONS DO NOT LOOK GOOD WITH EITHER MODEL.

&&

.PRELIMINARY POINT TEMPS/POPS...
DAB  74  66  76  65 /  40  80  60  40
MCO  77  64  77  64 /  40  70  50  30
MLB  77  67  77  67 /  30  40  40  20
VRB  77  68  79  66 /  20  30  30  20
LEE  76  63  76  64 /  40  80  60  40
SFB  76  63  76  64 /  40  80  60  30
ORL  76  64  76  65 /  40  70  50  30
FPR  77  69  80  66 /  20  30  30  20

&&

.MLB WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
AM...NONE.
&&

$$

SHORT TERM...BRAGAW
LONG TERM....LASCODY



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