Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 050540 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 140 AM EDT TUE MAY 5 2015 .SYNOPSIS...BERMUDA HIGH PRESSURE WILL EXTEND INTO OUR REGION THROUGH MID WEEK. AN AREA OF LOW PRESSURE WILL FORM NEAR THE BAHAMAS AND MEANDER OFF THE SOUTHEAST COAST DURING THE MIDDLE OF THE WEEK. && .NEAR TERM /TONIGHT/... AS OF 1015 PM MONDAY... BENEATH 850-700 MB RIDGING CENTERED OVER THE SOUTHERN APPALACHIANS AND CAROLINAS THIS EVENING...BERMUDA HIGH PRESSURE WILL CONTINUE TO EXTEND WEST ACROSS OUR REGION. THE FLOW AROUND THE RIDGE WILL MAINTAIN A LIGHT SOUTHERLY WIND...WITH TEMPERATURES ON AVG ABOUT A CATEGORY HIGHER THAN THOSE OF MON MORNING OWING TO A SLIGHTLY TIGHTER MSL PRESSURE GRADIENT AROUND THE NOW MORE DISTANT SFC HIGH - IN THE 50S. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... AS OF 245 PM MONDAY... HIGH PRESSURE WILL REMAIN IN PLACE OFFSHORE OF THE CAROLINAS ON TUESDAY. MEANWHILE A COLD FRONT WILL MOVE INTO THE VICINITY OF THE MASON-DIXON LINE AND A SHALLOW UPPER TROUGH OVER THE GULF OF MEXICO WILL DRIFT EAST ACROSS THE FLORIDA. BETWEEN THESE FEATURES...THE ONLY FORCING FOR CONVECTION WILL BE DIFFERENTIAL HEATING ALONG THE MOUNTAIN SLOPES AND A DEVELOPING LEE TROUGH THAT SHOULD REMAIN WEST OF THE TRIAD. FORECAST SOUNDINGS SHOW ANOTHER DAY OF RELATIVELY DEEP MIXING AND LITTLE POTENTIAL FOR INSTABILITY. WHAT CONVECTION THAT DOES FORM TO THE NORTH AND WEST WILL ENCOUNTER A NORTHEASTERLY STEERING FLOW THAT SHOULD FURTHER HELP TO KEEP ANY SHOWERS/STORMS WEST OF THE TRIAD. HIGHS AGAIN IN THE LOWER 80S...MAYBE A DEGREE WARMER THAN TODAY BASED ON A SLIGHT UPTICK IN 1000-850MB THICKNESSES BY 5M OR SO. ANOTHER MOSTLY CLEAR NIGHT EXPECTED ON TUESDAY NIGHT AS LINGERING CLOUD COVER FROM CONVECTION OVER VIRGINIA SHOULD HOLD TO OUR NORTH. SOME VERY THIN HIGH CLOUDS MAY BEGIN TO FILTER IN FROM THE SOUTH AS A SUB-TROPICAL LOW BEGINS TO DEVELOP NEAR THE BAHAMAS. LOWS AGAIN MOSTLY IN THE MID-60S. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... AS OF 215 PM MONDAY... LIKELY LOW PRESSURE DEVELOPMENT OVER THE NRN BAHAMAS DOMINATES THE MEDIUM RANGE FORECAST. WHILE SUCH DEVELOPMENT -- AND A GENERAL DRIFT TO THE NORTH OR NNW -- IS FAIRLY CERTAIN AT THIS POINT... ITS EXACT MOVEMENT... STRENGTH... AND POTENTIAL FOR TROPICAL CHARACTERISTICS REMAINS IN QUESTION. OVERVIEW: A BACKDOOR FRONT IS EXPECTED TO DROP SOUTHWARD TOWARD OUR NRN BORDER BY WED MORNING... BUT LATEST GUIDANCE HOLDS THIS FRONT (AND THE COOLER AIR BEHIND IT) JUST TO OUR NORTH... KEEPING US UNDER THE INFLUENCE OF STACKED FLAT W-E ORIENTED RIDGING THROUGH THE LOW AND MID LEVELS ACROSS NC EARLY WED. SUBTLE NEGATIVELY TILTED TROUGHING ANALYZED OVER THE NE GULF THIS MORNING IS EXPECTED TO TRACK SLOWLY ENE ACROSS FL BEFORE EMERGING OFF THE ERN FL COAST. THE NAM INTENSIFIES THE ASSOCIATED SURFACE LOW MUCH MORE QUICKLY OVER THE NRN BAHAMAS THAN THE GFS/ECMWF... AND THE NAM REMAINS THE STRONGEST AS IT DRIFTS TO THE NORTH WED... WITH THE ECMWF THE WEAKEST (MERELY AN INVERTED TROUGH WED). BY THU EVENING THE NAM/GFS PLACE THE LOW JUST OFF HILTON HEAD SC... AND WHILE THE 00Z OP ECMWF IS A BIT SOUTHEAST OF THIS POSITION... THE ECMWF ENSEMBLE MEAN IS FAIRLY CLOSE TO THE NAM/GFS POSITION. THE GOOD NAM/GFS AGREEMENT LENDS A BIT MORE CONFIDENCE IN THE GFS SOLUTION... WHICH CULMINATES IN THE LOW TRACKING NORTHWESTWARD INTO SC THU NIGHT BEFORE BECOMING STATIONARY (OR MEANDERING) AND WEAKENING JUST INLAND OVER THE SOUTHEAST STATES OVER THE WEEKEND... A FUNCTION OF THE STEERING FLOW AROUND A STRONG WRN ATLANTIC ANTICYCLONE... ALL BENEATH STRONG MEAN EAST COAST MID LEVEL RIDGING. THE OP ECMWF ON THE OTHER HAND HOLDS THE LOW OFFSHORE WITH A MORE NORTHEASTWARD DRIFT AND ACCORDINGLY REMAINS STRONGER THROUGH SAT. WPC AND HPC EXPERTS ARE FAVORING A MORE WESTWARD POSITION AS COMPARED TO EARLIER FORECASTS... A COMPROMISE SOLUTION BETWEEN THE WESTERNMOST GFS AND EASTERNMOST ECMWF WITH A SLIGHT LEAN TOWARD THE GFS... AND AT A SPEED SLIGHTLY SLOWER THAN THE GFS. WHETHER THIS LOW ATTAINS ANY TROPICAL CHARACTERISTICS IS DIFFICULT TO DETERMINE AT THIS TIME... AND ANY SPECULATION WOULD BE JUST THAT... BUT AT LEAST SUBTROPICAL DEVELOPMENT IS NOT OUT OF THE QUESTION GIVEN THAT WATER TEMPS JUST NORTH OF THE BAHAMAS ARE NEAR 80 AND ABOVE CLIMATOLOGY. LATE IN THE WEEK... TROUGHING THAT IS NOW JUST OFF THE PACIFIC NW... AND WHICH WILL STRENGTHEN INTO A CLOSED LOW NEAR VEGAS BY FRI... WILL THEN OPEN UP AND KICK EAST-NORTHEASTWARD THROUGH THE CENTRAL CONUS... HELPING TO DISSIPATE AND PUSH EASTWARD ANY REMNANT LOW OVER THE SOUTHEAST STATES. SENSIBLE WEATHER: WED LOOKS DRY FOR MOST... ALTHOUGH IN THIS WEAK FLOW REGIME... CONVECTION RESULTING FROM DIFFERENTIAL HEATING OVER THE HIGHER TERRAIN AS WELL AS ALONG THE BACKDOOR FRONT TO OUR NORTH MAY DRIFT INTO NRN AND NW SECTIONS LATE IN THE DAY. WILL KEEP LOW CHANCE POPS WED IN THESE AREAS LATE AFTERNOON INTO EARLY EVENING. BY THU AFTERNOON... FOLLOWING THE ABOVE-DISCUSSED TIMING/TRACK... WE SHOULD START SEEING BANDS OF SHOWERS WORKING INTO THE SE CWA... WITH CONVECTION STILL LIKELY FIRING OVER THE HIGHER TERRAIN JUST TO OUR NW. WILL FOCUS CHANCE POPS ON THE SE AND IN THE FAR NW THU. UNCERTAINTY GROWS EXPONENTIALLY BY FRI... BUT WITH A DECENT CHANCE OF A WEAKER BUT STACKED LOW SOMEWHERE OVER THE INTERIOR SOUTHEAST JUST INLAND... WILL LEAN TOWARD CLIMATOLOGICAL SHOWER/STORM CHANCES... HIGHER SOUTH AND SE... FOR FRI AND HEADING INTO THE WEEKEND. IF THE ECMWF IS CORRECT... WE WOULD SEE LOWER CONVECTION COVERAGE WITH STRONGER RIDGING IN PLACE OVER THE SRN APPALACHIANS. RAIN CHANCES SHOULD DIMINISH ONCE AGAIN SUN INTO MON WITH THE LIKELY WEAKENING AND DEPARTURE OF ANY REMNANT LOW OVER OUR REGION... IN RESPONSE TO THE APPROACHING TROUGH FROM THE WEST. TEMPERATURES: LOW LEVEL THICKNESSES ARE EXPECTED TO BE SLIGHTLY ABOVE NORMAL WED AND CONTINUE TO RISE A COUPLE OF METERS EACH DAY THROUGH MON. SHOULD SEE HIGHS WED AROUND 80 AND LOWS WED NIGHT AROUND 60. WITH EXPECTATIONS OF AT LEAST SOME CLOUD COVER AND POSSIBLE SHOWERS THU ONWARD... WILL KEEP HIGHS NEAR TO SLIGHTLY ABOVE NORMAL... TRENDING BACK TO AT LEAST A CATEGORY ABOVE NORMAL SUN/MON AS WE SHOULD HAVE DECREASING CLOUDS AND CONVECTION COVERAGE. ABOVE NORMAL LOWS THROUGH THE PERIOD. -GIH && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 140 AM TUESDAY... HIGH CONFIDENCE OF VFR CONDITIONS PERSISTING THROUGH THE CURRENT TAF PERIOD AS BERMUDA HIGH PRESSURE CONTINUES TO RIDGE WESTWARD INTO THE REGION. DIURNAL CU WILL LIKELY DEVELOP ONCE AGAIN ON TUESDAY DURING THE AFTERNOON HOURS WITH SOUTHERLY WINDS BETWEEN 5 TO 8KT. OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH AT LEAST WEDNESDAY AS BERMUDA HIGH IN PLACE GRADUALLY WEAKENS...ALLOWING A BACK-DOOR COLD FRONT TO SLIP SOUTH INTO THE AREA LATE WEDNESDAY NIGHT/EARLY THURSDAY. MOISTURE IS LIMITED ALONG THE FRONT AND THUS RAIN CHANCES WILL BE SMALL WITH LITTLE AVIATION IMPACTS. MODELS CONTINUE TO SHOW THE DEVELOPMENT OF AN AREA OF LOW PRESSURE AREA NORTH OF THE BAHAMAS WEDNESDAY/THURSDAY TIME FRAME. MODEL SPREAD REMAINS HIGH WITH THE EVENTUAL EVOLUTION TRACK OF THIS SYSTEM AS IT ENTERS A REGION OF WEAK FLOW OFF THE SE COAST WHERE IT COULD MEANDER FOR SEVERAL DAYS. THIS SYSTEM COULD RESULT IN SOME ADVERSE AVIATION IMPACTS LATE IN THE WORK WEEK AND INTO THE WEEKEND...ESPECIALLY ACROSS COASTAL SECTIONS OF NORTH CAROLINA. ADDITIONALLY...ENHANCED EASTERLY ONSHORE FLOW FROM THIS SYSTEM COULD BRING AN INCREASE THREAT FOR MORNING STRATUS/FOG. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...RAH NEAR TERM...RAH SHORT TERM...22 LONG TERM...HARTFIELD AVIATION...CBL

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