Area Forecast Discussion
Issued by NWS Tampa Bay Area, FL

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 KTBW 200841
AFDTBW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAMPA BAY RUSKIN FL
341 AM EST SAT DEC 20 2014

.SHORT TERM (TODAY - SUNDAY)...
RATHER COMPLEX WEATHER PICTURE THIS WEEKEND WITH AS MANY MODEL
SOLUTIONS AS WE HAVE MODELS. THE OVERALL SYNOPTIC PICTURE LOOKS
SIMILAR IN EACH MODEL...BUT THE SENSIBLE WEATHER DEPICTION IS
ANYTHING BUT SIMILAR.

FOR TODAY AT LEAST...THE LEAD SHORT-WAVE TROUGH WILL PASS HARMLESSLY
BY TO OUR NORTH LEAVING A WEAK FRONTAL BOUNDARY TO MEANER OVER THE
NORTHEAST GULF. WEAK MID-LEVEL RIDGING WILL BE MOVING IN BEHIND THE
DEPARTING SHORT-WAVE AS THE MORE SIGNIFICANT TROUGH BEGINS TO TAKE
SHAPE OUT WEST. MID AND HIGH-LEVEL CLOUDINESS WILL BE ON THE
INCREASE TODAY...ESPECIALLY NORTH OF THE TAMPA BAY AREA. ALL AREAS
WILL SEE AT LEAST SOME SUNSHINE WITH TEMPERATURES CLIMBING INTO THE
LOWER TO MIDDLE 70S NORTH AND CENTRAL AND POSSIBLY APPROACHING 80
DEGREES FAR SOUTH.

TONIGHT WE BEGIN TO FEEL THE EFFECTS OF THE DEEPENING UPPER-LEVEL
TROUGH TO OUR WEST. WARM ADVECTION ALOFT WILL OVER-RUN OUR COOLER
LOW-LEVELS RESULTING IN A LOWERING AND THICKENING OF CLOUDS AND EVEN
THE ONSET OF OVER-RUNNING RAINS. THE SURFACE BOUNDARY WILL BE
SOMEWHERE NEAR OR JUST NORTH OF THE TAMPA BAY AREA...SO BEST RAIN
CHANCES WILL BE NORTH OF THERE. ANY RAIN THAT DOES FALL SHOULD BE ON
THE LIGHT SIDE WITH THE GREATEST CHANCE BEING OVER LEVY AND CITRUS
COUNTIES.

THE MID-LEVEL TROUGH WILL CONTINUE TO DEEPEN AND MOVE INTO THE
NORTHWEST GULF BY LATE SUNDAY. INCREASED LIFT ACROSS THE WEAK
BOUNDARY OVER OUR NORTHERN AREA SHOULD RESULT IN STEADIER/MORE
PERSISTENT RAINFALL. MUCH OF THIS WILL REMAIN OVER THE GULF
WATERS...BUT BELIEVE MOST OF OUR AREA WILL SEE SOME RAIN BY THE
AFTERNOON HOURS AS MID-LEVEL SOUTHWESTERLY FLOW STRENGTHENS TO NEAR
50 KNOTS AND BRINGS DEEPER MOISTURE INTO THE PICTURE. AT THIS TIME I
CHOSE TO LEAVE OUR VERY SOUTHERN AREAS DRY THROUGH SUNDAY. THIS
COULD BE A BIT OPTIMISTIC IF THE CLUSTER OF CONVECTION CURRENTLY
BETWEEN WESTERN CUBA AND THE YUCATAN PENINSULA HOLDS TOGETHER LONG
ENOUGH TO BE STEERED NORTHEASTWARD AHEAD OF THE DEVELOPING TROUGH.
CONFIDENCE IN THE LATTER HALF OF THE WEEKEND IS RATHER LOW DESPITE
THE FACT THAT WE ARE ONLY 36 TO 48 HOURS OUT.

.LONG TERM (SUNDAY NIGHT THROUGH NEXT FRIDAY)...
THE MAIN PLAYERS IN OUR WEATHER FOR SUNDAY NIGHT INTO MONDAY WILL BE
A FRONTAL BOUNDARY ALONG THE NORTHERN GULF COAST AND ITS INTERACTION
WITH PASSING ENERGY/SHORTWAVE ALOFT. BEEN SOME DISAGREEMENT IN THE
GUIDANCE MEMBERS FOR THE 00Z PACKAGE...WITH THE GFS BECOMING AN
OUTLIER IN ITS DEPICTION OF A WET PATTERN FOR THE CENTRAL AND
SOUTHERN FLORIDA PENINSULA...AND THE ECMWF/NAM/SREF ENSEMBLE ALL
SUGGESTING THE BEST LIFT AND BEST RAIN CHANCES WILL REMAIN TO THE
NORTH OF THE I-4 CORRIDOR. IN THIS CASE...AN ENSEMBLE APPROACH WOULD
SUGGEST LEANING TOWARD THE DRIER SOLUTION FOR THE SOUTHERN HALF OF
THE AREA...AND WILL FOLLOW THIS PHILOSOPHY. HOWEVER...THIS MAKES FOR
LOWER THAN AVERAGE CONFIDENCE IN THE FORECAST GIVEN THE AMOUNT OF
POTENTIAL ERROR SHOULD SOMETHING LIKE THE GFS SOLUTION VERIFY.

FOR NOW...THIS IS THE FORECAST AND WE ARE STICKING TO IT (FOR THE
MOMENT). AS THE UPPER ENERGY INTERACTS WITH THE QUASI-STATIONARY
BOUNDARY...THE SURFACE FOCUS INCREASES INTO THE NORTHERN
PENINSULA...AND A DEVELOPING LOW LEVEL JET INDUCES AN ISENTROPIC
UPGLIDE RESPONSE ALONG THE 295-305K SURFACES. SHOULD SEE SHOWERS
BREAKING OUT OVER THE EASTERN GULF AND STREAMING NORTHEAST INTO THE
NATURE COAST BY LATER SUNDAY AND THEN CONTINUE INTO SUNDAY NIGHT.
HAVE KEPT LIKELY/CATEGORICAL POPS TO THE NORTH OF THE TAMPA BAY
AREA...WITH DECREASING RAIN CHANCES AS ONE HEADS FURTHER SOUTH. THE
UPPER SUPPORT LOOKS TO SHEAR OUT AND EXIT TO OUR NORTHEAST EARLY ON
MONDAY...LEAVING THE BOUNDARY LYING ACROSS OR JUST SOUTH OF THE I-10
CORRIDOR. ALTHOUGH WE WILL HAVE LOST THE UPPER SUPPORT...THE LOW
LEVEL FOCUS NEAR THE BOUNDARY SHOULD KEEP DECENT SHOWER CHANCES IN
THE FORECAST TO THE NORTH OF TAMPA FOR THE DAYLIGHT HOURS OF MONDAY
AND MONDAY NIGHT. LIKELY NOT LOOKING AT A LOT OF RAINFALL
ACCUMULATION DURING THIS TIME...BUT RATHER A MOSTLY CLOUDY AND "OFF
AND ON" LIGHT SHOWERS SITUATION. GOING TO KEEP RAIN CHANCES MUCH
LOWER IN THE 20-40% RANGE FOR THE TAMPA BAY AREA AND SOUTHWARD AS
THERE SIMPLY IS NOT MUCH IN THE WAY OF A LIFTING MECHANISM TO
SUPPORT SUSTAINED SHOWER ACTIVITY.

THINGS BECOME MORE INTERESTING AS WE HEAD INTO THE MIDDLE PORTION OF
THE WEEK. DURING TUESDAY WILL BE WATCHING A SIGNIFICANT
AMPLIFICATION TO THE PATTERN ACROSS THE CENTRAL PART OF THE COUNTRY.
THIS TROUGH WILL BEGIN TO QUICKLY SWING EASTWARD ALONG THE NORTHERN
GULF COAST LATER TUESDAY INTO TUESDAY NIGHT. AT THE SURFACE...AN
ASSOCIATED LOW PRESSURE AREA WILL ORGANIZE ACROSS THE LOWER MS
VALLEY AND HEAD NORTHEASTWARD...WHILE A TRAILING COLD FRONT
ORGANIZES AND PUSHES INTO THE NORTH-CENTRAL GULF. DEEP LAYER
SYNOPTIC FORCING SPREADING EASTWARD...ALONG WITH DEVELOPING UPGLIDE
AND DIFFLUENCE ALOFT SHOULD RESULT IN A LARGE AREA OF SHOWERS AND
STORMS BREAKING OUT ACROSS THE EASTERN GULF OF MEXICO THROUGH THE
DAY. MODEL CONSENSUS BRINGS THIS BAND OF SHOWERS/STORMS TOWARD THE
REGION TUESDAY EVENING AND THEN ACROSS THE FORECAST AREA TUESDAY
NIGHT AND WEDNESDAY MORNING. MODELS ARE NOT COMPLETELY IN AGREEMENT
REGARDING THE LARGE SCALE TROUGH STRUCTURE...BUT THE ORGANIZATION OF
THE FRONT AND IMPRESSIVE DIFFLUENCE FIELDS ALOFT SUGGEST LIKELY TO
CATEGORICAL RAIN CHANCES ARE JUSTIFIED TUESDAY NIGHT FOR MUCH OF THE
FORECAST AREA. AS IT STANDS NOW...BOTH THE GFS/ECMWF ARE FORECASTING
45-55KTS OF DEEP LAYER SHEAR...WHICH IS PLENTY ENOUGH TO SUPPORT
ORGANIZED CONVECTION. 40-50KT LOW LEVEL JET (DEPENDING ON YOUR MODEL
OF CHOICE)...COMBINED WITH THE SHEAR SUGGESTS SOME THREAT FOR STRONG
TO SEVERE STORMS...WITH STRAIGHT LINE WINDS THE MAIN HAZARD. ONE
ISSUE WE CAN SEE LOOKING AT THE CONVECTIVE FIELDS IS THE AMOUNT OF
PRE-FRONTAL CONVECTION OVER THE EASTERN GULF IN BOTH THE GFS/ECMWF.
THIS AMOUNT OF CONVECTION WILL RELEASE QUITE A BIT OF LATENT HEAT
INTO THE DOWNSTREAM ENVIRONMENT...AND FURTHER HINDER POTENTIAL
UPDRAFTS IN AN ALREADY MEAGER MID-LEVEL LAPSE RATE ENVIRONMENT.
STILL PLENTY OF TIME TO WATCH THIS SYSTEM DEVELOP...BUT IT REQUIRES
MONITORING.

COLD FRONT AND STORMS SHOULD EXIT THE REGION BEFORE THE END OF
WEDNESDAY AFTERNOON...WITH COOLER...BUT RAIN FREE CONDITIONS
ARRIVING FOR WEDNESDAY NIGHT AND CHRISTMAS DAY. SUBTLE DIFFERENCES
IN TROUGH EVOLUTION RESULT IN BIG DIFFERENCES IN HOW MUCH COLD AIR
FILTERS INTO THE REGION BY THURSDAY MORNING. WITH LITTLE EVIDENCE TO
SIDE ONE WAY OR THE OTHER JUST YET...WILL USE A ECMWF/GFS BLEND FOR
THE END OF THE FORECAST PERIOD...AND AWAIT BETTER AGREEMENT. OF NOTE
THOUGH...IF THE COLDER GFS SOLUTION IN THE LOWER LEVELS WAS TO
VERIFY...THEN THE SETUP WOULD BE FAVORABLE THURSDAY MORNING FOR COLD
AIR STRATUS TO STREAM OFF THE GULF FOR THE FIRST HALF OF THE
DAY.


&&

.AVIATION...
MAINLY VFR NEXT 24 HOURS. ONLY VERY LOW POTENTIAL FOR FOG BUT ENOUGH
CONFIDENCE TO SHOW TEMPO MVFR VISIBILITIES AT PGD THROUGH 12Z.

&&

.MARINE...
THE WEEKEND SHOULD NOT BE TOO BAD FOR BOATERS WITH SOME
DETERIORATION NOTED DURING THE SECOND HALF OF SUNDAY. WINDS AND SEAS
SHOULD STAY BELOW ANY HIGHLIGHT CRITERIA THIS WEEKEND...BUT AN AREA
OF RAIN WITH SOME EMBEDDED STORMS WILL BE DEVELOPING OVER THE GULF
AND MOVING INTO AT LEAST THE NORTHERN HALF OF OUR WATERS SUNDAY
AFTERNOON. WE WILL ALSO SEE AN INCREASE IN HUMIDITY WHICH COULD LEAD
TO SOME PATCHY SEA FOG FROM THE BAY AREA NORTHWARD.

RAIN CHANCES AND SOME SEA FOG WILL STAY IN THE FORECAST FOR SEVERAL
DAYS AS TWO SEPARATE SYSTEMS IMPACT OUR WEATHER. THE SECOND SYSTEM
WILL BRING A SIGNIFICANT INCREASE IN WINDS AND SEAS AS A STRONG COLD
FRONT MOVES INTO THE CENTRAL GULF TUESDAY AND TUESDAY NIGHT THEN
ACROSS THE WATERS ON WEDNESDAY. WINDS WILL INCREASE FROM THE SOUTH
ON TUESDAY AND REACH SMALL CRAFT ADVISORY LEVELS BY TUESDAY NIGHT.
SEAS WILL RESPOND QUICKLY...RISING FROM 4 FEET OR SO TUESDAY TO 7
FEET TUESDAY NIGHT. WINDS WILL SHIFT TO THE WEST AND NORTHWEST ON
WEDNESDAY AT 20 TO 25 KNOTS WITH SEAS CLIMBING TO 10 FEET.

&&

.FIRE WEATHER...
MOISTURE WILL BE ON THE INCREASE OVER THE NEXT SEVERAL DAYS WITH NO
FIRE WEATHER PROBLEMS EXPECTED. A STRONG COLD FRONT WILL BRING
STRONG GUSTY WINDS TO THE REGION TUESDAY NIGHT AND WEDNESDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
TPA  75  62  76  65 /   0  10  30  50
FMY  79  61  79  64 /   0   0  10  30
GIF  76  60  77  63 /   0  10  20  50
SRQ  75  60  77  64 /   0  10  30  40
BKV  75  56  77  62 /   0  10  40  60
SPG  74  62  75  64 /   0  10  30  50

&&

.TBW WATCHES/WARNINGS/ADVISORIES...
FL...NONE.
GULF WATERS...NONE.

&&

$$

SHORT TERM/AVIATION/MARINE/FIRE WEATHER...JILLSON
LONG TERM/DECISION SUPPORT...MROCZKA




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