Area Forecast Discussion
Issued by NWS Miami, FL

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000
FXUS62 KMFL 111153
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
753 AM EDT FRI JUL 11 2014

.AVIATION...
DRIER AIR WILL BE WORKING INTO SOUTH FLORIDA TAF SITES TODAY FROM
THE ATLANTIC WATERS. THIS WILL REDUCE THE THE COVERAGE OF SHOWERS
AND THUNDERSTORMS OVER SOUTH FLORIDA TODAY. SO AT THIS TIME WILL
ONLY SHOW VCSH FOR THE EAST COAST TAF SITES FOR TODAY...AND VCTS
FOR KAPF TAF SITE AFTER 18Z DUE TO THE WEST COAST SEA BREEZE
DEVELOPING AND PUSHING INLAND.

THE WINDS WILL ALSO BE FROM THE EAST AT 5 TO 10 KNOTS TODAY OVER
MOST OF THE TAF SITES...EXCEPT AT KAPF TAF SITE WHERE THE WIND
WILL SHIFT TO A WESTERLY DIRECTION AFTER 18Z. THE CEILING AND VIS
WILL ALSO REMAIN IN THE VFR CONDITIONS TODAY FOR MOST OF THE TAF
SITES ACROSS SOUTH FLORIDA. THE ONLY EXCEPTION TO THIS IS OVER
KAPF TAF SITE WHERE THE CEILING COULD FALL INTO MVFR CONDITIONS
WITH THE PASSAGE OF ANY STORMS. HOWEVER...THE TIMING OF THE STORMS
IS NOT KNOWN AT THIS TIME. SO WILL KEEP VFR CONDITIONS FOR KAPF
AND ADMIN WHEN NEED BE ON THE CEILING AND VIS.

&&
.AVIATION...54/BNB


.PREV DISCUSSION... /ISSUED 327 AM EDT FRI JUL 11 2014/

DISCUSSION...

DRY AIR ASSOCIATED WITH SUBSIDENCE AROUND THE EDGE OF THE ATLANTIC
MID LEVEL RIDGE IS MOVING WESTWARD ACROSS SOUTH FLORIDA ON FRIDAY.
IT IS DURING THE MID MORNING HOURS AND EARLY AFTERNOON OF FRIDAY
WHEN THE DRIEST AIR IS EXPECTED TO AFFECT THE AREA. IN ADDITION, BUT
NOT DIRECTLY ASSOCIATED TO THIS MID LEVEL DRYING, THERE IS SOME
SAHARAN AIR AT THE LOW LEVELS THAT BEGAN TO BE PRESENT IN SOUTH
FLORIDA THURSDAY MORNING. THIS SAHARAN AIRMASS IS WELL MIXED SINCE
ITS ORIGIN FROM AFRICA AND HAS A HIGH CONTENT OF MOISTURE DUE TO ITS
PASSAGE THROUGH THE ATLANTIC OCEAN. THEREFORE, ITS EFFECT ON THE
REDUCTION OF THE THUNDERSTORM ACTIVITY IS LESS. SAL CAN BE NOTED
IN THE 00Z SOUNDING FROM JUL 11 AS A VERY SLIGHT DRYING AROUND 2
KM. THE MODEL SOUNDINGS ALSO SHOW THIS SLIGHT DRYING BELOW 700 MB.
THE SAHARAN AIRMASSES THAT HAVE THE GREATEST EFFECT REDUCING
THUNDERSTORMS IN SOUTH FLORIDA ARE THOSE THAT MAKE A RAPID TRANSIT
THROUGH THE ATLANTIC ESPECIALLY DUE TO A FAST EXPANSION OR
WESTWARD DISPLACEMENT OF THE AZORES HIGH PRESSURE.

THE MODEL SOUNDINGS SHOW A DISTINCT DRYING OF THE MID LEVELS OF THE
ATMOSPHERE BEGINNING DURING THE MORNING HOURS OF FRIDAY ASSOCIATED
WITH SUBSIDING AIR FROM THE BERMUDA HIGH. THIS IS SEEN VERY CLEARLY
IN THE WATER VAPOR IMAGERY APPROACHING SOUTH FLORIDA FROM THE EAST.
THIS DRYING IS TRANSIENT, WITH AN INCREASE IN MOISTURE AGAIN FOR
SATURDAY. THERE IS VERY LITTLE CHANGE IN THE 5OO MB TEMPERATURES,
STAYING AROUND -8C FOR THE ENTIRE FORECAST PERIOD. THE LARGE SCALE
WEATHER PATTERN SHOWS A TROUGH OF LOW PRESSURE DEEPENING OVER THE
CENTRAL PORTIONS OF THE US BY THE BEGINNING OF NEXT WEEK. AS THE
TROUGH SLOWLY MOVES EAST A PLUME OF DRIER AIR AT THE LOW AND MID
LEVELS OF THE ATMOSPHERE IS FORECAST TO MOVE FROM THE GULF OF
MEXICO, WHICH COULD DECREASE THE PRECIPITATION COVERAGE BY THE END
OF NEXT WEEK. HOWEVER, THE CONFIDENCE OF THIS IS LOW AT THIS POINT.
BACKWARD TRAJECTORY ANALYSIS SHOWS THAT THE ORIGIN OF THE SURFACE
AIRMASS AT SOUTH FLORIDA WILL REMAIN FROM AROUND LONGITUDE -40 IN
THE CENTRAL ATLANTIC AND AT A SIMILAR LATITUDE THAN SOUTH FLORIDA
FOR THE NEXT SEVEN DAYS.

THE POPS REFLECT THE REASONING DESCRIBED ABOVE. FOR FRIDAY AFTERNOON
POPS ARE DECREASED TO 30 PERCENT FOR MOST OF THE INTERIOR AND 40
PERCENT FOR THE LAKE AREA. FOR SATURDAY AND SUNDAY 40 AND 50 PERCENT
IS INCLUDED FOR THE INTERIOR WEST. SIMILAR POPS TO SATURDAY ARE
FORECAST FOR MOST OF NEXT WEEK.

MARINE...

WINDS WILL BE FROM THE EAST THIS MORNING THROUGH THIS WEEKEND
WITH WIND SPEEDS BELOW 10 KNOTS. THIS WILL KEEP THE SEAS AROUND 2
FEET IN BOTH THE ATLANTIC AND GULF WATERS OF SOUTH FLORIDA THROUGH
THIS WEEKEND. BOATING CONDITIONS SHOULD BE GOOD OVER SOUTH FLORIDA
WATERS OUTSIDE OF ANY SHOWERS OR THUNDERSTORMS.

AVIATION...(ISSUED 122 AM EDT FRI JUL 11 2014)

MOSTLY VFR IS EXPECTED THROUGH THE FORECAST WITH SEA BREEZE ALONG
BOTH COASTS BY LATE MORNING/EARLY AFTERNOON. DRIER AIR MOVING IN
FROM THE ATLANTIC WILL RESULT IN LESS TSRA THAN PAST SEVERAL DAYS
AND FOR THIS REASON ONLY PLACED VCSH FOR THE EAST COAST TERMINALS
WITH A FEW SHRA CURRENTLY MOVING ONTO THE COAST. THIS WILL LIKELY
PERSIST UNTIL 14Z WHEN ACTIVITY WILL SHIFT TO INLAND AND WEST COAST
AREAS. HOWEVER, DO NOT EXPECT COVERAGE TO BE MORE THAN ABOUT 30% SO
KEPT FORECAST AT VCTS FOR KAPF.

&&

.PRELIMINARY POINT TEMPS/POPS...
WEST PALM BEACH  88  77  89  77 /  20  20  30  20
FORT LAUDERDALE  88  79  89  79 /  20  20  20  20
MIAMI            89  78  89  79 /  20  20  30  20
NAPLES           90  75  91  76 /  30  20  30  20

&&

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

$$

SHORT TERM...21/KM
LONG TERM....71/JE
AVIATION...54/BNB


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