Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170715 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 314 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/... 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. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... 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. && .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 310 AM FRIDAY... SUNDAY THROUGH MONDAY NIGHT: THE LATEST GFS/ECMWF/NAM ARE IN GOOD AGREEMENT IN SHOWING EXCELLENT MOISTURE TRANSPORT SUNDAY INTO SUNDAY NIGHT AS A LEAD DISTURBANCE SHIFTS ACROSS THE REGION. PW VALUES ARE EXPECTED TO INCREASE INTO THE 1.5 TO 1.75 INCH RANGE... WHICH IS WELL ABOVE NORMAL FOR THIS TIME OF YEAR. MEANWHILE... THE LATEST ECMWF AND MORESO THE LATEST GFS SHOWS A BACK DOOR FRONT MAKING BETTER INROADS INTO CENTRAL NC FROM THE NORTH AS A 1025 MB SURFACE HIGH BUILDS INTO THE AREA FROM NORTH ON SUNDAY MORNING. HOWEVER... IS STILL UNCLEAR AS TO HOW FAR SOUTH THIS FRONT WILL MAKE IT AND WHERE A POSSIBLE CAD BOUNDARY MIGHT SET UP. NONETHELESS... ANY BOUNDARY SHOULD LIFT BACK THROUGH THE AREA/OR SHIFT TO THE NORTH OF THE AREA SUNDAY NIGHT. HOWEVER... GIVEN THE RATHER STRONG VEERING LOW LEVEL FLOW... 0-1 KM AND ESPECIALLY 0-3 KM SRH VALUES ARE QUITE IMPRESSIVE. THANKFULLY AS THE LOW LEVEL FLOW STRENGTHENS AND SRH VALUES INCREASE THE LATEST MODEL GUIDANCE HAS MINIMAL INSTABILITY AT BEST... WITH BOTH THE GFS/NAM BUFR SOUNDING SHOWING QUITE MOIST SOUNDINGS. TAKING A QUICK LOOK AT THE SHERB VALUES... NOT SEEING ANY VALUES ABOVE 0.5-0.6. VALUES CLOSER TO 1 AND ABOVE WOULD HIGHLIGHT MORE OF A CONCERN FOR A HIGH SHEAR LOW CAPE SVR/TOR EVENT. WHILE THE SVR THREAT IS QUITE SMALL (NOT NIL THOUGH)... WE WILL LIKELY SEE SOME MODERATE TO HEAVY HEAVY RAIN GIVEN THE ABOVE MENTIONED GOOD MOISTURE TRANSPORT AND HIGH PW`S AND GOOD LIFT. THE BULK OF THE PRECIP IS EXPECTED LATE SUNDAY INTO SUNDAY NIGHT... WHEN WE COULD SEE UPWARDS OF 1 TO 2 INCHES OF RAIN.... WITH LOCALIZED HIGHER AMOUNTS. HIGH TEMPS WILL BE A CHALLENGE FOR SUNDAY... DEPENDING THE PLACEMENT OF THE BACKDOOR FRONT AND TIMING OF THE PRECIP AT A GIVEN LOCATION. FOR NOW WILL SHOW HIGHS IN THE MID TO UPPER 60S NW/N TO THE MID TO UPPER 70S SE... KEEPING IN MIND OF THE HIGH BUST POTENTIAL. THE MAIN SURFACE COLD FRONT SHOULD MOVE THROUGH THE REGION LATE MONDAY INTO MONDAY NIGHT. WHILE THE STRONGER MID AND LOW LEVEL FLOW WILL HAVE PUSHED TO THE EAST... WE SHOULD SEE INSTABILITY INCREASE AS SOME DRIER MID LEVEL AIR WORKS INTO THE AREA FROM THE SOUTHWEST ON MONDAY MORNING/AFTERNOON. THIS SHOULD HELP TO YIELD SOME DESTABILIZATION AHEAD OF THE FRONT ON MONDAY RESULTING IN ISOLATED TO SCATTERED SHOWER AND STORMS MONDAY AFTERNOON/EVENING IN ADVANCE OF THE FRONT... WITH POSSIBLY A FEW STRONG TO MAYBE SEVERE STORMS (AS DEEP LAYER SHEAR WILL STILL BE AROUND 25 TO 35 KTS). BEST CHANCE OF ANY SVR AT THIS TIME (KEEP IN MIND WE ARE STILL A WAYS OUT IN TIME) WOULD BE ACROSS EASTERN PORTIONS OF THE AREA WHERE WE COULD SEE MLCAPE VALUES OF UP TO 1500 J/KG. HIGHS MONDAY ARE EXPECTED TO BE IN THE UPPER 70S TO LOWER 80S.. WITH POSSIBLY SOME MID 80S EAST/SOUTHEAST. LOWS TUESDAY MORNING RANGING FROM THE MID 50S NW TO AROUND 60 SE. TUESDAY THROUGH THURSDAY: GENERALLY DRIER WEATHER IS EXPECTED BEHIND THE FRONT ON TUESDAY THROUGH THURSDAY. HOWEVER... A BROAD MID LEVEL TROUGH ACROSS THE EAST COAST WILL REMAIN... WITH A MID LEVEL LOW EXPECTED NEAR THE U.S./CANADIAN BORDER. WHILE CENTRAL NC WILL SEE THE MAIN MID LEVEL TROUGH AXIS PASS LATE TUESDAY INTO WEDNESDAY (CURRENTLY DRY)... ITS NOT ENTIRELY OUT OF THE REALM OF POSSIBILITY THAT WE COULD SEE A FAST MOVING DISTURBANCE IN THE BROAD CYCLONIC FLOW ALOFT DURING THIS TIME FRAME (TUE-THU) PRODUCE SOME LIGHT PRECIP. FOR NOW WILL KEEP THE FORECAST DRY AND TEMPS NEAR NORMAL FOR HIGHS AND LOWS. && .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...BSD AVIATION...WSS

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