Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 300128 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 928 PM EDT SUN MAR 29 2015 .SYNOPSIS...HIGH PRESSURE OVERHEAD WILL MOVE OFFSHORE TONIGHT AHEAD OF A COLD FRONT. THIS COLD FRONT WILL MOVE THROUGH THE REGION MONDAY. ANOTHER COLD FRONT SHOULD MOVE THROUGH THE REGION OVERNIGHT TUESDAY INTO WEDNESDAY. && .NEAR TERM /THROUGH MONDAY/... AS OF 926 PM SUNDAY... THE MAIN FORECAST PROBLEM THIS EVENING IS WHETHER OR NOT A FROST ADVISORY WOULD BE NEEDED IN THE SOUTHEASTERN COUNTIES ALONG I-95 AS LOW TEMPERATURES ARE EXPECTED TO DROP INTO THE MID TO UPPER 30S OVERNIGHT. AFTER SITTING ON THE FENCE FOR A LONG TIME...ULTIMATELY HAVE DECIDED THAT THERE IS NOT ENOUGH EVIDENCE TO WARRANT THE FROST ADVISORY AT THIS TIME FOR SEVERAL REASONS. FIRST THE ARGUMENT FOR AN ADVISORY STEMS FROM THE FACT THAT HIGH RESOLUTION MODELS WERE PICKING UP ON AN AREA OF HIGHER DEWPOINTS ALONG OUR EASTERN COUNTIES THAT DEVELOPED RATHER QUICKLY THIS EVENING AND DID IN FACT COME INTO FRUITION. AT RWI FOR EXAMPLE THE DEWPOINT WENT FROM 16 TO 26 DEGREES IN ONE HOUR. AT THE SAME TIME TEMPS HAVE ALREADY DROPPED INTO THE UPPER 30S. THE RAPID INCREASE IN DEWPOINTS AND DROP IN TEMPERATURES SUPPORTS THE POSSIBILITY OF FROST...PARTICULARLY IN RURAL AREAS WHERE TEMPERATURES ARE NORMALLY COOLER. THOSE SAME HI-RES MODELS HOWEVER ARE SHOWING THAT THE WINDOW FOR TEMPERATURES COLD ENOUGH AND DEWPOINTS HIGH ENOUGH FOR FROST IS VERY SMALL...PARTICULARLY BETWEEN 6-9Z. WHILE DEWPOINTS IN THE EAST WILL CONTINUE TO RISE AFTER THIS TIME PERIOD...TEMPERATURES ARE ALSO EXPECTED TO RISE AS THE HIGH SHIFTS SOUTHEAST AND LIGHT WINDS PICK UP OUT OF THE SOUTHWEST. THIS NOT ONLY MAKES THE WINDOW FOR FROST VERY SHORT BUT THE IMPACTS MINIMAL...ESPECIALLY AFTER LAST NIGHTS HARD FREEZE. THEREFORE WILL FOREGO THE ADVISORY AT THIS TIME. EXPECT LOWS EARLIER THAN NORMAL...AGAIN AROUND 6-9Z WITH A NON-TYPICAL HOURLY TEMPERATURE CURVE THEREAFTER. -ELLIS MOISTURE AND LIFT WILL INCREASE THROUGH MONDAY MORNING. LIFT WILL INCREASE AS THE RIGHT ENTRANCE REGION OF A UPPER LEVEL JET MOVES IN LATE TONIGHT. THIS WILL RESULT IN A BAND OF SHOWERS MOVING THROUGH THE AREA FROM WEST TO EAST...ROUGHLY BETWEEN 09-16Z. POPS WILL QUICKLY DECREASE LATE MONDAY MORNING THROUGH EARLY AFTERNOON. QPF VALUES ARE PROGGED TO BE RATHER LIGHT WITH ONLY A TENTH OF AN INCH OR SO. -KRD && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... AS OF 315 PM SUNDAY... MONDAY NIGHT AND TUESDAY... WEAK SURFACE HIGH PRESSURE WILL BUILD INTO CENTRAL NC IN THE WAKE OF THE EXITING FRONTAL SYSTEM MONDAY NIGHT INTO EARLY TUESDAY. THE APPROACH OF A DISTURBANCE IN THE NW FLOW ALOFT MAY INITIATE A PERIOD OF OROGRAPHIC CIRRUS OVER OUR REGION BY EARLY TUESDAY. THE SURFACE FRONT AND WAVE ASSOCIATED WITH THE DISTURBANCE ALOFT WILL CROSS TO OUR NORTH TUESDAY AFTERNOON AND EVENING. THIS WILL SET-UP A LEE SIDE TROUGH OVER THE WESTERN PIEDMONT BY TUESDAY AFTERNOON. THE PRESSURE GRADIENT IS EXPECTED TO TIGHTEN IN RESPONSE TO THIS LEE SIDE TROUGH AND THE APPROACHING SFC LOW. THE RESULTANT SW LOW LEVEL FLOW WILL AID TO BOOST TEMPS BACK TO NEAR NORMAL LEVELS. MIN TEMPS MONDAY NIGHT UPPER 30S TO AROUND 40. MAX TEMPS TUESDAY UPPER 60S-LOWER 70S. TUESDAY NIGHT AND WEDNESDAY...SFC COLD FRONT WILL SWEEP ACROSS CENTRAL NC PRETTY UNEVENTFUL AS ATMOSPHERE TOO DRY TO SUPPORT PRECIP GENERATION. BULK OF COLD AIR BEHIND THE FRONT WILL REMAIN MOSTLY TO OUR NORTH. 850MB THERMAL TROUGH DOES EXTEND SWD INTO THE NORTHERN COUNTIES ON WEDNESDAY WITH EFFECTS A BIT MORE PRONOUNCED OVER THE NORTHERN COASTAL PLAIN VERSUS THE WESTERN-SOUTHERN PIEDMONT. MIN TEMPS TUESDAY NIGHT MID-UPPER 40S. HIGH TEMPS WEDNESDAY LOW-MID 60S NE TO THE LOWER 70S SW. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 345 PM SUNDAY... THURSDAY...MEDIUM RANGE MODELS IN DECENT AGREEMENT...DEPICTING A WEAKENING MID LEVEL S/W IN THE SOUTHERN STREAM LIFTING ACROSS THE DEEP SOUTH INTO THE SE U.S. MEANWHILE A S/W IN THE NORTHERN STREAM WILL PROGRESS EAST ACROSS THE GREAT LAKES INTO THE NEW ENGLAND...DRAGGING A COLD FRONT TOWARD CENTRAL NC BY THURSDAY NIGHT. BULK OF SHOWERS ASSOCIATED WITH THE SOUTHERN SYSTEM WILL LIKELY OCCUR MORE TO OUR WEST-SW...WITH SHOWER GENERATION DECREASING FARTHER EAST AS SYSTEM SHEARS OUT. SW FLOW AHEAD OF THE APPROACHING COLD FRONT WILL CONTINUE TO PULL WARM AIR INTO CENTRAL NC. THE MIXTURE OF SUN/CLOUDS AND SPOTTY SHOWER COVERAGE SHOULD PERMIT TEMPS TO REBOUND INTO THE 70S AREAWIDE. IF SUN IS MORE PREVALENT THAN CLOUDS THURSDAY AFTERNOON...COULD SEE TEMPS REACH/SLIGHTLY EXCEED 80 DEGREES OVER TEH SE HALF. FRIDAY INTO SATURDAY...SFC COLD FRONT WILL DRIFT SLOWLY EAST-SE THROUGH THIS PERIOD...POSSIBLY EXITING OUR EASTERN COUNTIES BY MID DAY SATURDAY (BASED ON SLOWER GFS). APPEARS BULK OF SHOWERS FRIDAY WILL OCCUR WEST-NORTH OF CENTRAL NC...THOUGH INCREASING ACROSS THE PIEDMONT BY LATE IN THE DAY. SHOWER COVERAGE SHOULD MAXIMIZE FRIDAY NIGHT AS THE FRONT DRIFTS ACROSS THE AREA. MAX TEMPS FRIDAY DEPENDENT ON SHOWER COVERAGE AND CLOUD THICKNESS. POTENTIAL FOR TEMPS TO REACH 80 AGAIN IN THE FAR SE FRIDAY AFTERNOON IF SHOWERS AND CLOUDS ARE DELAYED. SHOULD SEE SLIGHTLY COOLER TEMPS FRIDAY IN THE FAR NORTH-NW DUE TO MORE EXTENSIVE CLOUD COVERAGE. SLIGHTLY COOLER TEMPS ANTICIPATED SATURDAY WITH SHOWER THREAT DIMINISHING NW- SE THROUGHOUT THE DAY. EASTER SUNDAY AT THIS TIME APPEARS DRY AND SEASONABLY COOL AS HIGH PRESSURE BUILDS INTO OUR REGION FROM THE NW. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... AS OF 815 PM SUNDAY... CURRENT VFR CONDITIONS WILL DETERIORATE TO A SHORT PERIOD OF MVFR THEN IFR CONDITIONS MON MORNING INTO EARLY AFTERNOON... WITH MVFR VSBYS IN A PERIOD OF RAIN. HIGH PRESSURE OVER THE AREA THIS EVENING WILL MOVE OFFSHORE AS A COLD FRONT APPROACHES FROM THE NW... BRINGING POOR AVIATION CONDITIONS FOR 4-6 HOURS... STARTING AROUND 12Z AT INT/GSO... AROUND 13Z-14Z AT RDU... AND AROUND 15Z-16Z AT RWI/FAY. IMPROVEMENT BACK TO VFR CIGS/VSBYS IS EXPECTED AROUND 16Z AT INT/GSO... AROUND 18Z AT RDU... AND AROUND 19Z-21Z AT FAY/RWI... AND SHOULD PERSIST THROUGH THE END OF THE TAF VALID PERIOD. ANOTHER AVIATION CONCERN WILL BE STRENGTHENING WINDS IN THE 1200-1800 FT AGL LAYER... POTENTIALLY UP TO 40-50 KTS FROM THE SW. WHILE WE MAY NOT NECESSARILY MEET LOW LEVEL WIND SHEAR CRITERIA... WITH SURFACE WINDS FROM THE SW AT JUST 8-12 KTS... THE INCREASE IN WIND SPEED WITH HEIGHT MAY CAUSE MECHANICAL TURBULENCE AND DIFFICULTY HANDLING SOME AIRCRAFT. THESE STRONGER WINDS ALOFT ARE MOST LIKELY IN THE 06Z-18Z TIME FRAME. LOOKING BEYOND 00Z TUE (EARLY MON EVENING)... VFR CONDITIONS SHOULD DOMINATE THROUGH WED NIGHT... ALTHOUGH ANOTHER WEAK COLD FRONT WILL DROP SE THROUGH THE AREA EARLY WED MORNING CAUSING A SHIFT IN SURFACE WINDS. THE RETURN OF THIS FRONT FROM SW TO NE THROUGH THE AREA AS A WARM FRONT THU AFTERNOON/NIGHT MAY BRING A PERIOD OF MVFR CIGS WITH A FEW SHOWERS. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...KRD/DJF NEAR TERM...ELLIS/KRD SHORT TERM...WSS LONG TERM...WSS AVIATION...HARTFIELD

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