AFDMFL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MIAMI FL 641 PM EST THU MAR 11 2010 .AVIATION...ONGOING CONVECTION WILL CONTINUE TO DIMINISH EARLY THIS EVENING BUT WILL INCREASE AGAIN LATER TONIGHT. HOWEVER, PREVAILING MVFR CIGS WILL OCCUR MUCH OF TONIGHT. MORE WIDESPREAD RAINFALL EXPECTED LATE TONIGHT/EARLY FRIDAY AND HAVE INTRODUCED PROB30 GROUP AFT 14Z TO ACCOUNT FOR THIS. IFR CONDITIONS ARE NOT OUT OF THE QUESTION WITH THIS POTENTIAL WET SYSTEM AND MAY LOWER CONDITIONS IN THE LATE TAF ISSUANCES TO ACCOUNT FOR LATER DETERIORATING TRENDS. KOB && .PREV DISCUSSION... /ISSUED 340 PM EST THU MAR 11 2010/ ..INCREASING FLOODING POTENTIAL FOR LATE TONIGHT AND FRIDAY... ..SLIGHT RISK OF SEVERE WEATHER THROUGH FRIDAY... UPDATED MARINE SECTION. DISCUSSION... LATEST GUIDANCE STILL DEPICTS THE STRONG LOW PRESSURE SYSTEM INTENSIFYING THROUGH TODAY ACROSS CENTRAL CONUS. THIS SYSTEM WILL CONTINUE MOVING EASTWARD, WITH AN ASSOCIATED SHORTWAVE MOVING ACROSS NORTHERN PORTIONS OF THE FLORIDA PENINSULA TODAY. THIS FEATURE WILL BE RESPONSIBLE FOR THE WEATHER THAT SOUTH FLORIDA WILL GET THIS AFTERNOON/EVENING AND EARLY FRIDAY MORNING. MODEL SOUNDINGS SHOW PWATS INCREASING TO AROUND 2.0 INCHES THIS AFTERNOON/EVENING, BUT 18Z SPECIAL SNDG SHOWS THIS INCREASE HAS NOT YET MATERIALIZED. THE MAIN CONCERN AND DEBATE AT THIS MOMENT IS IF ANY ACTIVITY THAT DEVELOPS THIS AFTERNOON AND EVENING WILL DEVELOP IN AN ENVIRONMENT FAVORABLE FOR THUNDERSTORMS...HEAVY RAINFALL...AND/OR SEVERE WEATHER. ALTHOUGH SOME PARAMETERS LIKE HELICITY ARE FAVORABLE FOR SEVERE WEATHER IN THE AFTERNOON AND EVENING, LACK OF LOW LEVEL LIFTING MECHANISMS, MARGINAL CAPES, AND NEARLY MOIST ADIABATIC LAPSE RATES ARE KEEPING DEVELOPMENT RATHER LIMITED ACROSS THE AREA AT THIS TIME. FURTHERMORE...WATER VAPOR LOOP SHOWS WATER VAPOR PLUME FROM THE PACIFIC STREAMING ACROSS THE GULF AND THE PENINSULA TO OUR NORTH WITH SNDGS ACROSS THE STATE INCLUDING OURS SHOWING A SKINNY CAPE PROFILE. THIS IS ALL INDICATIVE OF HEAVY RAIN POTENTIAL BUT THE DEEP MOISTURE ASSOCIATED WITH UPPER MSTR PLUME WILL REALLY NOT GET DOWN INTO SOUTH FLORIDA UNTIL TONIGHT AND MOST LIKELY TOMORROW. SO DECIDED TO LOWER POPS DOWN INTO THE LIKELY RANGE FOR THE REMAINDER OF THIS AFTERNOON AND EARLY EVENING AND LEFT THEN AT 80 OR ABOVE LATE TONIGHT AND THROUGH FRIDAY. FOR FRIDAY, THE STORY IS A LITTLE DIFFERENT. A FRONTAL TROUGH CURRENTLY ACROSS NORTHERN FL IS EXPECTED TO MOVE TOWARDS SOUTH FLORIDA DURING THE DAY BRINGING LOW LEVEL FORCING...HIGHER INSTABILITY...AND MOISTURE LEVELS POTENTIALLY IN EXCESS OF 2 STANDARD DEVIATIONS ABOVE NORMAL. LATEST GFS SOUNDINGS SHOW PWATS REACHING 2.3 INCHES IN THE AFTERNOON AND CAPE OF AROUND 1775 J/KG. GOOD UPPER LEVEL DIVERGENCE, THE LACK OF A MID LEVEL INVERSION AS WELL AS GOOD LOW LEVEL INSTABILITY MAKES THE ENVIRONMENT FAVORABLE FOR CONTINUED HIGH CHANCES OF SHOWERS AND THUNDERSTORMS. HELICITIES IN EXCESS OF 20O TO 300 CONTINUING OVERNIGHT WILL CONTINUE TO SUSTAIN A REMOTE CHANCE OF AN ISOLATED TORNADO BUT AS THE ACTUAL FRONTAL TROUGH GETS CLOSER ON FRIDAY THOSE VALUES WILL DECREASE STEADILY DURING THE DAY WITH THE THREAT DECREASING. THE MAIN CONCERN WE BELIEVE WILL REMAIN THE POTENTIAL THEN FOR STRONG GUSTY WINDS AND LOCALLY HEAVY RAINFALL FOR FRIDAY. WE WILL KEEP MONITORING THIS AND IF THE TRENDS CONTINUE WITH PWAT VALUES RISING TO FORECAST LEVELS AS WE MOVE INTO FRIDAY...AND GIVEN THE POTENTIAL AS IT IS HAPPENING TODAY TO OUR NORTH WITH TRAINING ECHO PATTERNS DEVELOPING WEST TO EAST UNDERNEATH UPPER LEVEL WATER VAPOR PLUME...IT IS NOT OUT OF THE QUESTION AT THIS TIME THAT WE MIGHT NEED A FLOOD WATCH LATER TONIGHT FOR FRIDAY. BY FRIDAY NIGHT THE LOW PRESSURE ACROSS THE SOUTHEASTERN U.S. WILL CONTINUE MOVING EASTWARD, PUSHING ITS COLD FRONT ACROSS THE FLORIDA PENINSULA. SHOWER ACTIVITY WILL CONTINUE ACROSS THE AREA, BUT DECREASING SUBSTANTIALLY OVERNIGHT WITH NICE CONDITIONS OVERALL DEVELOPING THE REMAINDER OF THE WEEKEND. FOR SUNDAY AND MONDAY, DRIER AND COOLER CONDITIONS ARE EXPECTED AS THE AIRMASS BEHIND THE COLD FRONT DOMINATES SOUTH FLORIDA. THIS CONDITIONS WILL CONTINUE UNTIL MID WEEK, WHEN THE NEXT LOW PRESSURE SYSTEM WILL DEVELOP AND APPROACHES SOUTH FLORIDA. MARINE...MARINE WINDS ACROSS THE ATLANTIC WATERS OF 20 TO 25 KNOTS WILL CONTINUE TO GRADUALLY SUBSIDE BY LATE THIS AFTERNOON SO WILL CONTINUE SMALL CRAFT ADVISORY FOR WINDS THROUGH 7 PM THIS EVENING. WINDS ARE EXPECTED TO PICK UP AGAIN AHEAD OF THE FRONT ON FRIDAY AND BEHIND IT ON SATURDAY WHEN EITHER SMALL CRAFT EXERCISE CAUTION OR ADVISORIES MIGHT AGAIN BE NEEDED. SEAS ARE OVERALL EXPECTED TO REMAIN BELOW 7 FEET THROUGH FORECAST PERIOD EXCEPT ALONG THE OFFSHORE WATERS OF COLLIER COUNTY WHERE SEAS ARE FORECAST TO REACH 7 FEET LATE SATURYDAY NIGHT AND SUNDAY BEHIND THE FRONT. FIRE WEATHER...BEHIND THE FRONT AFTERNOON MINIMUM RELATIVE HUMIDITIES WILL GET DOWN TO NEAR MARGINAL LEVELS BY LATE IN THE WEEKEND. AT THIS TIME THE MAIN DAY OF CONCERN LOOKS LIKE SUNDAY. && .PRELIMINARY POINT TEMPS/POPS... WEST PALM BEACH 70 79 60 77 / 80 90 70 20 FORT LAUDERDALE 72 81 64 77 / 80 90 80 20 MIAMI 71 82 64 78 / 80 90 80 20 NAPLES 70 76 61 74 / 80 90 50 10 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...NONE. AM...SMALL CRAFT ADVISORY FOR WINDS UNTIL 7 PM EST THIS EVENING FOR BISCAYNE BAY-COASTAL WATERS FROM DEERFIELD BEACH TO OCEAN REEF, FL OUT 20 NM-COASTAL WATERS FROM JUPITER INLET TO DEERFIELD BEACH, FL OUT 20 NM-WATERS FROM DEERFIELD BEACH TO OCEAN REEF, FL EXTENDING FROM 20 NM TO THE TERRITORIAL WATERS OF THE BAHAMAS-WATERS FROM JUPITER INLET TO DEERFIELD BEACH, FL EXTENDING FROM 20 NM TO 60 NM. GM...NONE. && $$