Area Forecast Discussion
Issued by NWS Miami, FL

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FXUS62 KMFL 210121
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
921 PM EDT SUN APR 20 2014

.UPDATE...
NO CHANGES REQUIRED TO THE FORECAST THIS EVENING. LOW PRESSURE
REMAINS OFF THE CAROLINA COASTLINE AND WILL ONLY MOVE SLOWLY TO
THE NORTHEAST OVER THE NEXT 24-HOURS. THIS WILL KEEP A LIGHT
NORTHERLY LOW LEVEL FLOW ACROSS SOUTH FLORIDA. LOW LEVEL MOISTURE
TRAPPED BELOW THE INVERSION WILL KEEP CLOUD COVER AROUND
OVERNIGHT. THE CLOUD COVER WILL PREVENT TEMPERATURES FROM FALLING
VERY FAR. A SMALL CRAFT ADVISORY FOR SEAS IN EFFECT FOR THE GULF
STREAM EAST OF PALM BEACH COUNTY BEGINNING AT 06Z TONIGHT. A HIGH
RISK FOR RIP CURRENTS IS EXPECTED AT THE PALM BEACH COUNTY BEACHES
ON MONDAY.

&&

.PREV DISCUSSION... /ISSUED 735 PM EDT SUN APR 20 2014/

AVIATION...
PATCHES OF BKN035-040 CLOUDS STILL AFFECTING PARTS OF SOUTH
FLORIDA IN ASSOCIATION WITH WRAP-AROUND MOISTURE ON BACK SIDE OF
ATLANTIC LOW PRESSURE AREA. OVERALL CLOUDINESS HAS DIMINISHED SOME
IN THE PAST FEW HOURS, AND EXPECT THIS GENERAL TREND TO CONTINUE
AS THE LOW GRADUALLY MOVES AWAY FROM THE AREA AND HIGH PRESSURE
BEGINS TO MOVE IN AND DRY THE LOW LEVELS. NEVERTHELESS, STILL
EXPECT PERIODS OF BKN CLOUDS OVERNIGHT, ESPECIALLY PBI AREA.
MOSTLY SCT COVERAGE ON MONDAY, WITH PERIODS OF BKN035-040 IN THE
AFTERNOON. BACKGROUND WINDS WILL BE N-NE AROUND 10 KT, WITH
TERMINAL WINDS LARGELY DRIVEN BY LAND/SEA BREEZE CIRCULATIONS.
KAPF SEABREEZE EXPECTED AROUND 17Z MONDAY AND E COAST SITES
BETWEEN 19Z-21Z. /MOLLEDA

PREV DISCUSSION... /ISSUED 208 PM EDT SUN APR 20 2014/

SHORT TERM (TONIGHT-TUESDAY NIGHT)...
IF WE CAN JUST GET PAST TODAY AND THIS EVENING, THE FORECAST IS
MOSTLY BENIGN. THE BIGGEST CHALLENGE HAS BEEN THE EXTENSIVE CLOUD
COVER THAT IS TRAPPED BENEATH THE VERY STRONG INVERSION WITH ITS
BASE AT 4K ACCORDING TO THE MORNING SOUNDINGS WITH CURRENT ACARS
DATA SHOWING THE INVERSION STILL INTACT. THIS IS INDICATIVE OF HOW
STABLE THE LOWER LAYERS ARE AND THE CLOUD DECK IS NOT MIXING OUT
MAKING A VERY TRICKY FORECAST ESPECIALLY FOR AVIATION INTERESTS.
AT ANY RATE, IT APPEARS THE CLOUD COVER IS NOT GOING TO BE
THINNING UNTIL MUCH LATER THAN ORIGINALLY THOUGHT DELAYING THE
WIND SHIFT AND ALSO KEEPING AFTERNOON TEMPERATURES DOWN BY SEVERAL
DEGREES. THE OTHER CONCERN IS THAT THE CLOUDS ARE SHOWING SOME
SIGNS OF THINNING SOME BUT IF THEY DO NOT BREAK TOO MUCH BEFORE
SUNSET, THEN WILL THEY REFORM INTO A LOW STRATUS DECK KEEPING
MINIMUM TEMPERATURES HIGHER THAN FORECAST. I DID ADJUST THE WIND
KEEPING A NORTH-NORTHWEST DIRECTION WITH THE LANDMASS REMAINING
COOLER.

THE 500MB TROUGH WILL BEGIN TO ACCELERATE EASTWARD ON MONDAY AS
ANOTHER UPSTREAM TROUGH MOVES FROM THE SOUTHERN PLAINS INTO THE
SOUTHEAST STATES. A RIDGE WILL THEN AMPLIFY BETWEEN THESE TWO
TROUGHS OVER THE FLORIDA PENINSULA. HOWEVER, AT THE SAME TIME MODELS
SHOW A SECONDARY SURFACE TROUGH MOVING ACROSS SOUTH FLORIDA LATE
TONIGHT INTO EARLY MONDAY MORNING EXTENDING TO THE SOUTHWEST OF THE
MOST EASTERN TROUGH AND THIS COULD ENHANCE CLOUD COVER AGAIN.
FORECAST SOUNDINGS SHOW SOME DRYING TAKING PLACE UNDER THE INVERSION
AND THIS SHOULD HELP THIN THE CLOUD COVER AND MORE SUN IS EXPECTED
ON MONDAY. SURFACE HIGH PRESSURE WILL BUILD OVER THE EASTERN
SEABOARD MONDAY NIGHT AND THEN SHIFT EAST INTO THE ATLANTIC BY
TUESDAY AS A COLD FRONT ASSOCIATED WITH THE SECOND MID LEVEL TROUGH
MOVES INTO THE SOUTHEAST STATES. ALL OF THESE SYSTEMS COMBINED WILL
KEEP SOUTH FLORIDA DRY WITH THE INVERSION REMAINING IN PLACE AND
TEMPERATURES NEAR THE AVERAGE FOR MID APRIL.

LONG TERM (WEDNESDAY-SUNDAY)...
THE UPPER FLOW PATTERN WILL RETURN TO A ZONAL FLOW ON WEDNESDAY AND
THURSDAY. THERE WILL BE SLIGHT INCREASE IN A CHANCE FOR A SHOWER OR
TWO BY THE END OF THE WEEK AND INTO NEXT WEEKEND AS THE SUBSIDENCE
CAP ERODES AND ALLOWING FOR PWAT TO CLIMB BACK TO NEAR 1.3 INCHES
FROM THE CURRENT HALF INCH. ALSO, A STRONG MID LEVEL TROUGH WILL
DEEPEN ACROSS THE NEW ENGLAND REGION IN THIS TIME FRAME AND ITS
ASSOCIATED COLD FRONT MAY MOVE INTO NORTH FLORIDA BY THE WEEKEND.
THIS ALSO WOULD ALLOW FOR THE INVERSION TO FADE MAKING THE LOW  AND
MID LEVELS A TAD BIT MORE UNSTABLE ACROSS SOUTH FLORIDA.

AVIATION...
DRY AND STABLE CONDITIONS COMBINED WITH A STRONG SUBSIDENCE
INVERSION HAVE ALLOWED THE 3-4 KFT CLOUD DECK TO HANG AROUND TODAY
LONGER THAN ORIGINALLY ANTICIPATED. THIS HAS LED TO NEARLY STEADY
TEMPERATURES ACROSS THE LOCAL AREA TODAY...WHICH HAS REDUCED THE
CHANCES FOR AN EAST COAST SEA BREEZE DEVELOPING. ALTHOUGH A FEW
HIRES MODELS DO CONTINUE TO INDICATE THIS POSSIBILITY THROUGH THE
MID-AFTERNOON HOURS...THEY ARE NOT HANDLING THE CLOUD COVERAGE WELL.
THEREFORE...THE NW FLOW WILL REMAIN IN THIS PACKAGE THROUGH THE
REMAINDER OF THE AFTERNOON AND GRADUALLY BEGIN TO VEER TO THE NNE
LATER TONIGHT THROUGH THE EARLY MORNING HOURS MONDAY AS HIGH
PRESSURE BUILDS EAST NORTH OF THE AREA.

MARINE...
WINDS WILL INCREASE TO AROUND 15 KNOTS RANGE TONIGHT OR SLIGHTLY
HIGHER MAINLY OFF THE PALM BEACH WATERS AND SPREAD SOUTH ON
MONDAY BEFORE BEGINNING TO SUBSIDE MONDAY NIGHT. THIS IN ITSELF
WILL BE SUFFICIENT FOR SMALL CRAFT EXERCISE CAUTION. HOWEVER, THIS
WILL ALSO COMBINE WITH A SWELL THAT IS EXPECTED TO ENTER THE
ATLANTIC WATERS STARTING TONIGHT AND PEAK MONDAY THROUGH TUESDAY
AROUND 3 FEET OFF THE PALM BEACH WATERS AND 2 FEET OFF THE BROWARD
AND MIAMI DADE WATERS TO BRING SEAS UP TO 7 FEET OFF THE PALM
BEACH WATERS AND PORTIONS OF THE BROWARD WATERS MAINLY MONDAY AND
MONDAY NIGHT BEFORE STARTING TO SLOWLY SUBSIDE. THEREFORE, SCEC
FOR TONIGHT AND SCA FOR MONDAY WILL LIKELY BE NEEDED LATER FOR
THOSE WATERS.

&&

.PRELIMINARY POINT TEMPS/POPS...
WEST PALM BEACH  65  79  67  82 /  10  10  10  10
FORT LAUDERDALE  67  81  70  83 /  10  10  10  10
MIAMI            66  82  70  83 /  10  10  10  10
NAPLES           63  80  66  81 /  10   0  10  10

&&

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
AM...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 2 AM TO 8 PM EDT
     MONDAY FOR AMZ650-670.

GM...NONE.
&&

$$

SHORT TERM...84/AK
LONG TERM....30/KOB


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