Area Forecast Discussion
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757 FXUS62 KTAE 200825 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 425 AM EDT MON APR 20 2015 .NEAR TERM [THROUGH TODAY]...
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AT 08 UTC, A LARGE CLUSTER OF THUNDERSTORMS WAS BEGINNING TO DEVELOP UPSTREAM NEAR COASTAL LOUISIANA; THIS WILL LIKELY BE THE NEXT ROUND OF STORMS TO AFFECT THE AREA LATER THIS MORNING. THE STORMS WERE DEVELOPING JUST AHEAD OF AN ADVANCING COLD FRONT AND IN THE LEFT EXIT REGION OF A STRONG 120-140 KNOT UPPER LEVEL JET. BOTH HI-RES AND GLOBAL MODELS ARE IN GOOD AGREEMENT IN ADVANCING THIS CONVECTION INTO OUR AREA LARGELY BETWEEN 12 UTC AND 18 UTC, ALTHOUGH SLIGHT TIMING DIFFERENCES (+/- 2 HOURS) STILL EXIST. THEY ALSO AGREE THAT THE BULK OF THE CONVECTION WILL BE CONCENTRATED OVER THE SOUTHERN HALF OF OUR FORECAST AREA - PRIMARILY OUR FLORIDA ZONES AND PERHAPS THE SOUTHERN ROW OR TWO OF GEORGIA ZONES. WE ADDED LIKELY POPS OF 60 TO 70 PERCENT IN THOSE AREAS FOR THE MORNING HOURS. THE QUESTION THEN BECOMES WHAT THE WARM SECTOR WILL LOOK LIKE THIS AFTERNOON AS THE SYNOPTIC COLD FRONT BEGINS TO ARRIVE IN OUR AREA. MODELS THAT MAINTAIN SOME INSTABILITY IN THE NORTHERN HALF OF OUR AREA AFTER THE MORNING ROUND OF CONVECTION ARE INDICATING MORE AFTERNOON CONVECTION, AS WOULD BE EXPECTED. THEREFORE, AFTERNOON RAIN CHANCES WILL BE TIED TO HOW THINGS UNFOLD THIS MORNING. FOR NOW WE PLACED 20 TO 30 PERCENT POPS IN THE NORTHERN HALF OF OUR AREA THIS AFTERNOON. THE UPSTREAM STORMS APPEAR TO BE DEVELOPING IN THE CUSP OF A PLUME OF STEEPER MID-LEVEL LAPSE RATES ASSOCIATED WITH AN ELEVATED MIXED LAYER, BASED ON THE LATEST RAP ANALYSIS AND 00Z SOUNDINGS FROM THE WESTERN GULF COAST. AS INCREASING ASCENT LEADS TO SOME MID-LEVEL COOLING, AND THE EML PROPAGATES EAST, LAPSE RATES SHOULD STEEPEN ACROSS OUR AREA EARLY THIS MORNING. MODEL FORECAST SOUNDINGS SHOW 7 C/KM 700-500MB LAPSE RATES AT TLH BY 12-15Z. COMBINED WITH THE LOW- LEVEL MOISTURE IN PLACE ACROSS THE AREA, THIS IS EXPECTED TO GENERATE CAPE VALUES ON THE ORDER OF 2000-2500 J/KG, WHICH WILL ALSO COINCIDE WITH 0-6KM BULK SHEAR VALUES AROUND 50 KNOTS. ALL OF THESE ARE INDICATORS OF A FAVORABLE ENVIRONMENT FOR SEVERE STORMS: ORGANIZED CONVECTIVE LINES (WHICH SEEMS LIKE IT WILL BE THE DOMINANT MODE THIS MORNING) OR SUPERCELLS. STRAIGHT-LINE HODOGRAPHS THIS MORNING WOULD FAVOR SPLITTING SUPERCELLS IF THEY WERE TO OCCUR, AND IN A HIGHLY SHEARED ENVIRONMENT WITH STEEP LAPSE RATES AND LOW WET- BULB ZERO HEIGHTS (~8500 FT) LARGE HAIL WOULD BE A GREATER THREAT. THEREFORE, THIS MORNING WE EXPECT THE MAIN THREATS TO BE ASSOCIATED WITH LARGE HAIL AND DAMAGING WINDS. IF ISOLATED TO SCATTERED STORMS CAN DEVELOP IN THE AFTERNOON ALONG THE COLD FRONT, SUPERCELLS WOULD AGAIN BE POSSIBLE AND GREATER LOW LEVEL SHEAR WOULD MEAN THAT ISOLATED TORNADOES WOULD ALSO BE A THREAT IN ADDITION TO HAIL AND WINDS. HOWEVER, NEW CONVECTION MAY BE FIGHTING BOTH DIMINISHED INSTABILITY AND INCREASINGLY DRY MID-LEVEL AIR WHICH CAN DILUTE UPDRAFT STRENGTH. THEREFORE, CONFIDENCE IS LOWER FOR BOTH RAIN CHANCES AND SEVERE WEATHER CHANCES IN THE AFTERNOON. TO RECAP: MORNING ROUND OF STORMS IS LIKELY - MAINLY SOUTH. SOME OF THOSE MAY BE SEVERE WITH LARGE HAIL AND DAMAGING WINDS. THE COMBINATION OF STRONG INSTABILITY AND STRONG SHEAR IS A BIT UNUSUAL, SO A SIGNIFICANT SEVERE REPORT OR TWO CAN`T BE RULED OUT. IN THE AFTERNOON, ISOLATED STORMS MAY REDEVELOP - ESPECIALLY NORTH. THE CHANCES OF SEVERE WEATHER MAY BE LOWER AFTER 18 UTC. .SHORT TERM [TONIGHT THROUGH WEDNESDAY]... THE SEVERE THREAT SHOULD PRETTY MUCH BE OVER BY TONIGHT WITH JUST SOME ISOLATED TO SCATTERED SHOWERS AND STORMS OVER OUR EASTERN ZONES UNTIL AROUND MIDNIGHT. WE WILL THEN FINALLY COME UNDER THE INFLUENCE OF SURFACE HIGH PRESSURE WHICH WILL BRING US A RARE TWO-DAY STRETCH WITHOUT APPRECIABLE POPS, AND SOME SUNSHINE AND LOWER HUMIDITY TO BOOT. TEMPERATURES WILL BE MUCH CLOSER TO SEASONAL LEVELS AS WELL, ESPECIALLY AT NIGHT. .LONG TERM [WEDNESDAY NIGHT THROUGH MONDAY]... RAIN CHANCES AND NIGHTTIME TEMPERATURES WILL GRADUALLY CREEP UP ONCE AGAIN AS SURFACE HIGH PRESSURE MOVES EAST OF THE AREA AND OUR FLOW BECOMES ONSHORE ONCE AGAIN. DAYTIME HIGHS WILL GENERALLY BE IN THE LOWER 80S. THE SOUTHERN BRANCH OF THE JET WILL CONTINUE TO PULL IMPULSES OF ENERGY ACROSS THE REGION AS A SURFACE FRONT SETS UP JUST NORTH OF THE REGION, OCCASIONALLY DIPPING INTO OUR NORTHERN ZONES. THESE FEATURES AND THE SEA BREEZE WILL GENERATED SCATTERED THUNDERSTORMS EACH DAY. SHEAR AND INSTABILITY LOOK SUFFICIENT FOR SOME SOME STRONG STORMS ON THURSDAY WITH SEVERE STORMS POSSIBLE FRIDAY AND SATURDAY.
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&& .AVIATION...
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[THROUGH 06Z TUESDAY] SOME LOW CIGS AND PATCHY FOG WILL BE POSSIBLE THIS MORNING AT ALL TERMINAL SITES WITH IFR CONDITIONS LIKELY FOR A TIME AND LIFR POSSIBLE. CONDITIONS SHOULD IMPROVE TO MVFR-VFR AFTER ABOUT 14-15 UTC OVERALL. HOWEVER, TEMPORARY VIS RESTRICTIONS IN THUNDERSTORMS WILL BE POSSIBLE. ONE ROUND OF STORMS WILL MOVE IN DURING THE MORNING HOURS - REACHING ECP AROUND 13 UTC, TLH AROUND 15 UTC, AND VLD AROUND 16 UTC (+/- 2 HOURS AT EACH SITE). SOME OF THESE STORMS COULD BE QUITE STRONG AND PRODUCE HAIL OR BRIEF GUSTS IN EXCESS OF 30 KNOTS. ISOLATED STORMS MAY REDEVELOP IN THE AFTERNOON, AFFECTING MAINLY DHN AND ABY.
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&& .MARINE...
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STRONG TO SEVERE STORMS WILL BE POSSIBLE TODAY ACROSS THE WATERS. EVEN OUTSIDE OF THUNDERSTORMS, WINDS ARE EXPECTED TO REACH CAUTIONARY LEVELS AT TIMES TODAY AND TONIGHT BEFORE DIMINISHING ON TUESDAY AS HIGH PRESSURE MOVES EAST ALONG THE COAST. THIS HIGH WILL THEN MOVE OFF THE EAST COAST OF FLORIDA AND BRING A PERIOD OF LIGHT ONSHORE WINDS FROM WEDNESDAY THROUGH FRIDAY.
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&& .FIRE WEATHER...
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WETTING RAINS ARE EXPECTED TODAY ACROSS PRIMARILY THE SOUTHERN HALF OF THE AREA (FLORIDA ZONES AND THE SOUTHERN ROW OF ZONES IN GEORGIA). RH WILL STAY ABOVE 60 PERCENT IN MOST AREAS. DRIER AIR WILL ARRIVE TOMORROW, BUT IT SHOULD NOT BE SUFFICIENTLY DRY FOR RED FLAG CONDITIONS AND FUEL MOISTURES SHOULD STILL BE HIGH. RAIN CHANCES AND HIGHER RH RETURN BY THURSDAY.
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&& .HYDROLOGY...
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MINOR FLOODING IS OCCURRING ALONG PARTS OF THE CHOCTAWHATCHEE RIVER AND IS EXPECTED TO CONTINUE. BRUCE IS FORECAST TO EVENTUALLY REACH MODERATE FLOOD STAGE IN A COUPLE OF DAYS, ALBEIT JUST BARELY. MINOR FLOODING IS ALSO OCCURRING ON THE KINCHAFOONEE CREEK AT DAWSON. THE APALACHICOLA RIVER AT BLOUNTSTOWN IS NOW FORECAST TO CREST JUST BARELY BELOW FLOOD STAGE, BUT THAT COULD QUICKLY CHANGE IF MORE RAIN FALLS IN THE BASIN THAN THE CURRENTLY PREDICTED HALF INCH FOR TODAY.
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&& .PRELIMINARY POINT TEMPS/POPS...
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TALLAHASSEE 81 62 82 57 85 / 70 20 10 10 10 PANAMA CITY 78 63 76 63 79 / 70 10 0 10 10 DOTHAN 78 57 77 56 81 / 30 10 0 10 10 ALBANY 78 58 78 55 82 / 50 10 0 10 10 VALDOSTA 80 61 79 55 84 / 60 20 10 10 10 CROSS CITY 83 64 82 58 84 / 70 30 10 10 10 APALACHICOLA 79 65 79 63 81 / 70 20 10 10 10
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&& .TAE WATCHES/WARNINGS/ADVISORIES...
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FL...HIGH RIP CURRENT RISK THROUGH LATE TONIGHT FOR COASTAL BAY- COASTAL GULF-SOUTH WALTON. GA...NONE. AL...NONE. GM...NONE.
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&& $$ NEAR TERM...LAMERS SHORT TERM...WOOL LONG TERM...WOOL AVIATION...LAMERS MARINE...WOOL FIRE WEATHER...WOOL HYDROLOGY...WOOL

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