Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170708 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 310 AM EDT FRI APR 17 2015 .SYNOPSIS...LOW PRESSURE WILL MOVE SLOWLY AWAY FROM THE SOUTHEAST US COAST THROUGH TONIGHT. HIGH PRESSURE WILL OTHERWISE EXTEND ACROSS THE MIDDLE ATLANTIC STATES THROUGH SATURDAY. A LOW PRESSURE SYSTEM WILL BEGIN TO AFFECT OUR AREA SUNDAY...BRINGING A DECENT CHANCE FOR SHOWERS LATE SUNDAY INTO MONDAY && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 310 AM FRIDAY... A NEARLY SATURATED AIR MASS IN THE LOWEST 10K FT OF THE ATMOSPHERE WILL MAINTAIN EXTENSIVE CLOUDINESS ACROSS CENTRAL NC THIS MORNING. MAY STILL SEE AN ISOLATED SHOWER OR SPOTS OF DRIZZLE BUT A LIFTING MECHANISM FOR PRECIP GENERATION LARGELY ABSENT. MAIN FORECAST CHALLENGE CENTERS ON WHEN/IF WE DISSIPATE ENOUGH OF THE CLOUDS BY THIS AFTERNOON TO WARM TEMPS BACK TO NEAR NORMAL LEVELS. AS IS OFTEN THE CASE...RESIDUAL CAD AIR MASS WILL LIKELY BE SLOW TO ERODE AS NO DISCERNIBLE SCOURING MECHANISM (SUCH AS A COLD FRONT PASSAGE) NOTED. APPEARS WE WILL HAVE TO RELAY ON MIXING OF DRIER AIR FROM ALOFT TO ERODE THE CLOUDS...AND PER MODEL SOUNDINGS THIS MAY TAKE SOME TIME. CLOUD DECK APPEARS TO BE THINNER OVER THE FAR EAST- NE SO THIS REGION MAY SEE PARTIAL SUN INITIALLY. SIMILARLY...WEAK DOWNSLOPE COMPONENT TO THE LOW LEVEL FLOW MAY AID TO ERODE THE CLOUD COVER OVER OUR WESTERN PERIPHERY BY THIS AFTERNOON. THIS SUGGEST THAT AREAS CLOSEST TO THE HIGHWAY 1 CORRIDOR MAY BE THE LAST TO SEE PARTIAL SUN SOMETIME THIS AFTERNOON (PROBABLY LATE AFTERNOON). THUS...MAY SEE A FAIRLY UNIFORM MAX TEMPS FIELD WITH HIGH TEMPS IN THE MID 70S. TEMPS HIGHLY DEPENDENT ON SOME EROSION OF CLOUD DECK. IF SKIES REMAIN OVERCAST...MAX TEMPS WILL BE CLOSER TO 70-LOWER 70S. WHILE BULK OF REGION WILL BE A DRY...A WEAK S/W IN THE NORTHERN STREAM WILL PASS NORTH OF OUR REGION LATE THIS AFTERNOON. THIS FEATURE MAY DRAG A WEAK SFC TROUGH INTO OUR REGION. WEAK CONVERGENCE ALONG THIS FEATURE COUPLED WITH AFTERNOON HEATING MAY TRIGGER AN ISOLATED SHOWER OR STORM...MAINLY ACROSS THE NORTHERN COUNTIES AND CLOSER TO THE VA BORDER. TONIGHT...WHAT PARTIAL CLEARING THAT OCCURS LATER TODAY/THIS EVENING WILL DETERMINE THE EXTENT OF FOG DEVELOPMENT LATE TONIGHT-EARLY SATURDAY MORNING. CURRENTLY EXPECT ENOUGH PARTIAL CLEARING ALONG WITH A SATURATED TOP SOIL TO CAUSE FOG TO DEVELOP MOST LOCATIONS AFTER MIDNIGHT. NOT EXPECTING WIDESPREAD DENSE FOG AT THIS TIME BUT COULD SEE POCKETS OF FOG REDUCE THE VISIBILITY TO NEAR ZERO. IF CLOUD COVER PERSISTS WELL INTO THE AFTERNOON-EVENING HOURS...THEN FOG PRODUCTION MAY BE LIMITED. MIN TEMPS MILD IN THE UPPER 50S-LOWER 60S.
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&& .SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
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AS OF 310 AM FRIDAY... SATURDAY...MIXING OF DRIER AIR ALOFT SHOULD AID TO QUICKLY ERODE ANY FOG/LOW CLOUDS BY MID MORNING SATURDAY. WITH LOW LEVEL THICKNESSES SEVERAL METERS ABOVE NORMAL...SHOULD SEE TEMPS CLIMB ABOVE 80 DEGREES MOST LOCATIONS WITH SOME SPOTS IN THE SOUTH APPROACHING 85 DEGREES. AFTERNOON INSTABILITY MAY SUPPORT AN ISOLATED SHOWER OR STORM IN THE FAR SE ASSOCIATED WITH AN INLAND MOVING SEABREEZE. A WEAK SFC COLD FRONT MAY SLIDE INTO OUR FAR NORTHERN-NE COUNTIES LATE IN THE DAY SATURDAY OR EARLY EVENING. FRONTAL PASSAGE SHOULD BE UNEVENTFUL THOUGH COULD SEE SFC DEWPOINTS DIP INTO THE UPPER 40S OVER THE FAR NORTH-NE SATURDAY EVENING. OTHERWISE...MAY SEE CLOUDS INCREASE/THICKEN AFTER MIDNIGHT OVER THE FAR SOUTH AND WEST AHEAD OF THE NEXT APPROACHING LOW PRESSURE SYSTEM. THIS WILL LEAD TO MILD OVERNIGHT TEMPS IN THE 55-60 DEGREE RANGE.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 245 PM THURSDAY... SUN-MON NIGHT: A WET AND POTENTIALLY STORMY PERIOD. MID LEVEL FLOW OVER OUR REGION BECOMES INCREASINGLY CYCLONIC AS THE SLIGHTLY POSITIVELY TILTED BUT SLOWLY DAMPENING LARGE SCALE TROUGH APPROACHES FROM THE WSW. AT THE SURFACE... THE ASSOCIATED FRONTAL SYSTEM WILL OCCLUDE OVER THE UPPER MIDWEST AND GREAT LAKES SUN/SUN NIGHT... WITH THE BACKDOOR FRONT AROUND THE NC/VA BORDER SLOWLY RETREATING BACK TO THE NNE AS A WARM FRONT... WHILE THE PRIMARY COLD FRONT EXTENDS FROM A TRIPLE POINT LOW OVER LOWER MICH DOWN THROUGH THE MID/LOWER MISS VALLEY. MECHANISMS TO FORCE ASCENT SUCH AS MID LEVEL DPVA... UPPER DIVERGENCE... AND LOWER LEVEL (850-925 MB) MASS CONVERGENCE WILL BE STRENGTHENING (ESPECIALLY OVER WRN NC/SW VA) LATE SUN... PERSISTING THROUGH SUN EVENING AND INTO THE NIGHT... AND MOISTURE WILL BE ABUNDANT WITH AN INFLUX OF PW VALUES OVER 1.5"... OR WELL OVER 200% OF NORMAL. GIVEN THIS PLENTIFUL WATER CONTENT AND GOOD LIFT... TRAINING BANDS OF MODERATE RAIN COULD BRING LOCALIZED FLOODING PROBLEMS. MODELS CONTINUE TO SLOW DOWN THE ARRIVAL OF THE MID LEVEL TROUGH AND ITS ACCOMPANYING PRECIP... 6-9 HRS SLOWER THAN YESTERDAY MORNING`S RUNS... AND WILL CONTINUE TO REFLECT THIS IN THE FORECAST. WILL RAMP UP POPS TO LIKELY WEST/SMALL CHANCE EAST SUN MORNING... THEN GO TO CATEGORICAL WEST/GOOD CHANCE EAST SUN AFTERNOON... BEFORE GOING CATEGORICAL AREAWIDE SUN EVENING/NIGHT. WHILE THE LARGE SCALE MODELS DON`T DEPICT MUCH INSTABILITY AT ALL SUNDAY WITH PRIMARILY MOIST ADIABATIC FORECAST PROFILES... I DO HAVE SOME CONCERN ABOUT POCKETS OF CONVECTION AND AN ISOLATED THREAT OF A QUICK WEAK SPIN-UP IN OUR FAR NORTHWEST LATE SUNDAY INTO SUNDAY NIGHT... ESPECIALLY NEAR A WEAK ALONG-FRONT LOW THAT THE GFS/ECMWF DEVELOP OVER SOUTH CENTRAL VA. UPPER DIVERGENCE REACHES A HEFTY MAXIMUM OVER THE SRN APPALACHIANS SUN EVENING... WITH A 40-50 KT 850 MB JETLET FROM THE SSE... AND THE RETREATING BACKDOOR FRONTAL ZONE AND AFOREMENTIONED LOW COULD PROVIDE A SOURCE FOR ENHANCED LOW LEVEL VORTICITY WITH FORECAST SOUNDINGS SHOWING A STRONGLY CURVED HODOGRAPH. WILL CONTINUE TO MONITOR. TOTAL RAINFALL IS LIKELY TO REACH AT LEAST ONE INCH IN MOST SPOTS THROUGH SUN NIGHT... AND WITH A DEEP WARM LAYER (LCL TO 0C) NEAR 3.5 KM FAVORING WARM RAIN PROCESSES... LOCALLY HIGHER TOTALS ARE POSSIBLE. WILL TAPER POPS DOWN MON MORNING WEST TO EAST AS THE MID LEVEL TROUGH AXIS AND CONVEYOR BELT OF PEAK MOISTURE PUSHES TO OUR NORTHEAST... PLACING US FULLY IN THE WARM SECTOR WITH A PUNCH OF MID LEVEL DRY AIR ARRIVING FROM THE SW. ANY HEATING AT ALL WILL PUSH UP MUCAPE TO 1500-2000 J/KG (AS THE GFS SUGGESTS) MON AFTERNOON WITH 25-30 KT WSW 850 MB WINDS AND BULK SHEAR NEAR 30-35 KTS. THE SLOWLY LOWERING DYNAMIC FORCING FOR ASCENT MAY LIMIT THE THREAT OF SEVERE STORMS... BUT STILL EXPECT AT LEAST A FEW STRONG CELLS... ESPECIALLY IF WE DO INDEED GET SOME HEATING AHEAD OF THE COLD FRONT. AFTER A DOWNWARD TREND TO RAIN WEST TO EAST IN THE MORNING... WILL REBOUND WITH SCATTERED SHOWERS AND STORMS MON AFTERNOON INTO EARLY EVENING. A FEW OF THESE COULD PRODUCE STRONG GUSTY STRAIGHT LINE WINDS GIVEN INDICATIONS OF A STRAIGHT LINE HODOGRAPH. HIGHS FROM AROUND 70 NW TO THE MID 70S SE SUN... AND MID 70S TO LOWER 80S MON. LOWS AROUND 60 TO THE MID 60S SUN NIGHT AND MID 50S TO LOWER 60S MON NIGHT... WITH THE FRONT LIKELY NOT COMING THROUGH UNTIL LATE. TUE-THU: FAIRLY QUIET AND DRY WITH SURFACE HIGH PRESSURE BUILDING IN FROM THE WEST. LARGE/DEEP MID LEVEL LOW PRESSURE CENTERED OVER AND NORTH OF THE NRN GREAT LAKES WILL COVER MUCH OF CENTRAL AND EASTERN NOAM... BRINGING SEASONABLY COOL TEMPS AS IT SITS AND SPINS THROUGH MID WEEK. WE COULD SEE A QUICK SHOT OF LIGHT PRECIP WITH A FRONT APPROACHING FROM THE NW WED NIGHT OR THU... HOWEVER OUR MOISTURE SOURCES WILL REMAIN UNTAPPED AND LIFT APPEARS WEAK... SO THIS SHOULD AMOUNT TO ONLY LIGHT PRECIP AT MOST... AND WILL KEEP POPS WED NIGHT/THU BELOW CLIMATOLOGY. TEMPS SHOULD HOLD NEAR OR JUST BELOW NORMAL THROUGH THE PERIOD. -GIH && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... AS OF 115 AM FRIDAY... VARYING AVIATION CONDITIONS WILL BE THE NORM ACROSS CENTRAL NC TODAY AND TONIGHT A MOIST AIR MASS IN THE LOWEST 10K FT OF THE ATMOSPHERE WILL RESULT IN CEILINGS OF VARYING HEIGHTS. DO EXPECT CEILINGS TO LOWER INTO THE LOW END MVFR-IFR RANGE DURING THE PRE-DAWN HOURS AS ATMOSPHERE NOCTURNALLY COOLS/STABILIZES. AFTER 12Z...CEILINGS WILL SLOWLY LIFT AND SHOULD BE ON THE ORDER OF HIGH END MVFR/LOW END VFR AT MOST TAF SITES BY 18Z...AND SCATTERED-BROKEN 3500-5000FT BY LATE AFTERNOON. SFC WINDS WILL BE LIGHT AND VARIABLE. THE MOIST AIR MASS NEAR THE SURFACE TONIGHT WILL LIKELY CAUSE AREAS OR WIDESPREAD FOG TO DEVELOP LATE TONIGHT-EARLY SATURDAY MORNING...RESULTING MVFR/IFR CONDITIONS. THIS FOG AND/OR LOW CLOUDS SHOULD LIFT AND DISSIPATE 13-15Z SATURDAY. EXPECT VFR CONDITIONS FOR THE REMAINDER OF SATURDAY. MAY SEE SPOTS OF FOG DEVELOP AGAIN SATURDAY NIGHT BUT THE FOG SHOULD NOT BE AS PREVALENT AS WHAT IS EXPECTED TONIGHT/EARLY SATURDAY. AVIATION CONDITIONS EXPECTED TO TAKE ANOTHER DOWNTURN SUNDAY THROUGH MONDAY AS A LOW PRESSURE SYSTEM AND ATTENDANT SFC COLD FRONT AFFECTS OUR REGION. IMPROVING AVIATION CONDITIONS ANTICIPATED FOR TUESDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...HARTFIELD AVIATION...WSS

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