Area Forecast Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KKEY 291835
AFDKEY

AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS
NATIONAL WEATHER SERVICE KEY WEST FL
235 PM EDT TUE JUL 29 2014

.DISCUSSION...IN THE MID AND UPPER LEVELS...(700-200 MB)...LATEST
AVAILABLE IR IMAGERY OVERLAID WITH SATELLITE IMAGERY AS OF 200 PM
THIS AFTERNOON CONTINUES TO DEPICT AN EXCEPTIONALLY DEEP MID AND
UPPER LONGWAVE PATTERN FOR LATE IN JULY...WITH THE AXIS OF AN EAST
COAST TROUGH EXTENDING SOUTHWARD TO THE SOUTH CAROLINA LOW COUNTRY
FROM AN UNSEASONABLY CHILLY LOW PRESSURE SYSTEM JUST TO THE SOUTH OF
JAMES BAY. TO THE SOUTH OF THAT...THERE REMAINS AN ELONGATED EAST TO
WEST MID AND UPPER WARM CORE ANTICYCLONIC RIDGE SITUATED FROM THE
PECOS RIVER VALLEY OF FAR WEST TEXAS EAST SOUTHEASTWARD TO ACROSS
SOUTHERN FLORIDA THENCE INTO THE WESTERN ATLANTIC ALONG 27 NORTH.

AT THE SURFACE AND IN THE LOWER LEVELS...(SURFACE TO 700 MB) LATEST
IR IMAGERY OVERLAID WITH AVAILABLE MARINE AND LAND SURFACE
OBSERVATIONS AND ANALYSIS AS OF 200 PM DETAILS A COLD FRONT
EXTENDING SOUTHWARDS THEN WESTWARDS ALONG THE THE LENGTH OF THE
ENTIRE NORTHERN GULF COAST FROM A COOL 999 MB LOW PRESSURE NEAR
PRINCE EDWARD ISLAND. AS SUCH...A LIGHT TO GENTLE WESTERLY FLOW
PATTERN IS CURRENTLY IN PLACE ACROSS THE FLORIDA KEYS AND
SURROUNDING WATERS.

.CURRENTLY...AS OF 200 PM...SKIES ARE MOSTLY SUNNY RIGHT OVER THE
LENGTH OF THE KEYS ISLAND CHAIN...BUT VISIBLE SATELLITE IMAGERY
CLEARLY DELINEATES NARROW WELL DEVELOPED CUMULUS CLOUD LINES JUST
INSIDE HAWK CHANNEL PARALLELS TO THE MIDDLE AND UPPER KEYS. KEY WEST
RADAR DOES DETECT SHOWERS WITHIN THIS CLOUDLINE...AS WELL AS OTHER
SHOWERS ON CLOUDLINES SITUATED IN THE OFFSHORE GULF WATERS.

.SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT...THE HIGHLY AMPLIFIED
MID AND UPPER TROUGH WILL REMAIN IN PLACE TONIGHT THROUGH WEDNESDAY
NIGHT...BEFORE BREAKING DOWN THURSDAY AND THURSDAY NIGHT. A SURFACE
FRONTAL BOUNDARY NOW ANALYZED ACROSS NORTHERN FLORIDA WILL MOVE
SOUTHWARDS DOWN THE FLORIDA PENINSULA BEFORE LOOSING ANY IDENTITY
DURING THURSDAY AND THURSDAY NIGHT. AS A RESULT OF THIS
FEATURE...LOWER LEVEL CONFLUENT FLOW...SURFACE TO 700 MB...WILL
CONTINUE ACROSS THE LENGTH OF THE KEYS ISLAND CHAIN. BUT GIVEN THE
DEARTH OF DRIER AIR IN THE MIDDLE LEVELS...THE BEST SHOT FOR SHOWERS
AND ISOLATED THUNDERSTORMS WILL CONTINUE TO REMAIN DOWNWIND OF
SOUTHEASTERN FLORIDA...OR ACROSS THE UPPER KEYS AND SURROUNDING
WATERS. HENCE A SPLIT WHICH WAS PERFORMED ON THE OVERNIGHT FORECAST
CYCLE WILL BE MAINTAINED FOR AT LEAST THE NEXT TWO PERIODS.

SINCE THE AVAILABLE MODEL FORECAST SOUNDINGS ILLUSTRATE
PWAT(PRECIPITABLE WATER) NEAR 1.50 INCHES...CUMULUS CLOUD LINES WILL
REQUIRE A FAVORABLE ALIGNMENT IN THE LOWER TO MIDDLE LEVEL WINDS.
SO CONFIDENCE IN GOOD CUMULUS LINE FORMATION RIGHT OVER THE LOWER
AND MIDDLE KEYS REMAINS TO LOW TO INCREASE POPS...THEREFORE SLIGHT
CHANCE WILL REMAIN ACROSS THE LOWER AND MIDDLE KEYS THROUGH
WEDNESDAY NIGHT. ANY CHANCES FOR RAIN WILL BE PRIMARILY DUE TO
BOUNDARY SCALE INTERACTIONS IN THE LOWER LEVEL CONFLUENT FLOW. THE
OTHER STORY IS THAT GIVEN LIGHT TO GENTLE WESTERLY
FLOW...TEMPERATURES WILL RISE A FEW DEGREES ABOVE NORMAL AGAIN ON
WEDNESDAY...AND GIVEN THE VERY HIGH RELATIVE HUMIDITIES...THE HEAT
INDEX MAY REACH AROUND 105 DEGREES OVER THE ISLANDS.

ON THE THURSDAY THE WINDS WILL COLLAPSE AGAIN ACROSS THE KEYS AND
SURROUNDING WATERS...WHICH WILL PROVIDE BETTER CONDITIONS FOR
CUMULUS CLOUD LINE FORMATION GIVEN AVAILABLE BOUNDARY LAYER
MOISTURE...SO KEPT LOW CHANCE POPS IN THE GRIDS ATTM.

EXTENDED...FRIDAY THROUGH TUESDAY...ALL AVAILABLE INDICATIONS ARE
SUGGESTING THAT TYPICALLY WEAKER LOWER LEVEL RIDGING WILL REMAIN
NORTH OF THE FLORIDA KEYS...HOWEVER...SEVERAL WEAK IMPULSES ARE
HINTED IN THE MODELS...AND GIVEN MODEL FORECAST SOUNDINGS
ILLUSTRATION OF AROUND 2.00 INCHES COLUMNAR PWAT...WILL MAINTAIN
MIDDLE OF THE ROAD CHANCE POPS FOR RAIN THROUGH THE PERIOD. THIS IS
ACTUALLY ONLY 10 PERCENT ABOVE CLIMATOLOGY AS WE ENTER AUGUST. THE
TROPICS REMAIN QUIET WITH THE EXCEPTION OF A WELL DEVELOPED LOW
PRESSURE SYSTEM IN THE EAST CENTRAL ATLANTIC BEYOND 7 DAYS IN TIME
FROM ANY IMPACTS TO THIS REGION...IF THERE WILL EVER BE ANY AT ALL.

&&

.MARINE...LIGHT TO GENTLE WEST TO NORTHWEST WINDS THROUGH THE
EVENING WILL BECOME LIGHT AND VARIABLE AGAIN AFTER MIDNIGHT. LIGHT
TO GENTLE SOUTHWEST TO WEST WINDS WEDNESDAY AND WEDNESDAY NIGHT MAY
FAVOR CUMULUS CLOUD LINES AGAIN IN HAWK CHANNEL...SO CONDITIONS MAY
BE CONDUCIVE FOR ROUNDS OF WATERSPOUTS AGAIN. LIGHT AND VARIABLE
WINDS DURING THURSDAY AND THURSDAY NIGHT WILL BECOME GENTLE AND
SOUTHEASTERLY FRIDAY THROUGH THE WEEKEND...WITH MODERATE BREEZES
POSSIBLE FOR A TIME SATURDAY AND SATURDAY NIGHT.

&&

.AVIATION...THIS AFTERNOON AND EVENING...MAINLY WEST-NORTHWEST WINDS
OF AROUND 10 KNOTS AT THE EYW AND MTH TERMINALS. STEERING FLOW OF
WEST TO NORTHWEST ORIGIN IS NORMALLY ASSOCIATED WITH BELOW NORMAL
CHANCES OF PRECIPITATION. SATELLITE BASED MOISTURE PRODUCTS INDICATE
LAYERS OF DRY AIR WILL INHIBIT SHOWER DEVELOPMENT WITHIN THE LEE OF
THE ISLAND CHAIN. HOWEVER...COLLISIONS BETWEEN CUMULUS LINES HAVE
BEEN EFFECTIVE THIS MORNING IN PRODUCING PRECIPITATION...AND
ADDITIONAL COLLISIONS ARE LIKELY LATER THIS AFTERNOON.

&&

.CLIMATE...ON THIS DATE IN KEYS WEATHER HISTORY...IN 1996...1.23
INCHES OF RAIN FELL AT KEY WEST INTERNATIONAL AIRPORT. THIS SET THE
DAILY RECORD FOR MAXIMUM RAINFALL MEASURED IN KEY WEST ON JULY 29TH.
RAINFALL RECORDS AT KEY WEST DATE BACK TO 1871.

&&

.PRELIMINARY POINT TEMPS/POPS...
KEY WEST  83  92  82  93  82 /  20  20  20  30  30
MARATHON  82  94  81  91  82 /  20  20  20  30  30

&&

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
GM...NONE.

&&

$$

PUBLIC/MARINE/FIRE/DIGITAL............DAF
AVIATION/NOWCASTS.....................CLR
UPPER AIR/DATA ACQUISITION............BF/MP/SC

VISIT US ON THE WEB AT WWW.WEATHER.GOV/KEYWEST

FOLLOW US ON FACEBOOK AND TWITTER AT...

WWW.FACEBOOK.COM/NWSKEYWEST
WWW.TWITTER.COM/NWSKEYWEST













USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.