Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 161843 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 245 PM EDT THU APR 16 2015 .SYNOPSIS...CHILLY HIGH PRESSURE WILL EXTEND INTO THE CAROLINAS AND VIRGINIA FROM THE NORTHEAST THROUGH TONIGHT. A WEAK AREA OF LOW PRESSURE WILL DEVELOP OFF THE SOUTHEAST U.S. COAST TODAY AND DRIFT NORTHEAST AND AWAY FROM THE REGION ON FRIDAY. WEAK HIGH PRESSURE WILL EXTEND INTO THE AREA LATE FRIDAY INTO SATURDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1100 AM THURSDAY... VERY WELL DEFINED WEDGE FRONT ASSOCIATED WITH A HYBRID COLD AIR DAMMING EVENT SHOWING UP NICELY IN OBSERVATIONS. TO THE SOUTHEAST...A COASTAL LOW IS DEVELOPING OFF THE COAST OF SC AND FURTHER ENHANCING THE WEDGE BOUNDARY. THIS WILL MAKE TEMPERATURE FORECASTS VERY TRICKY TODAY AS A VERY STRONG GRADIENT WILL BE PRESENT FROM WEST TO EAST WITH VERY COOL HIGHS IN THE WEST AND POTENTIALLY QUITE A BIT WARMER HIGHS IN THE EAST. FOR NOW HAVE MID 50S IN THE WEST AND UPPER 60S IN THE EAST BUT BY LATE IN THE AFTERNOON THIS COULD VERY WELL PAN OUT TO BE LOWER 50S IN THE WEST AND LOWER TO MID 70S IN THE EASTERN TIER OF COUNTIES. PRECIPITATION CONTINUES ACROSS THE CENTRAL PIEDMONT AND THE NORTHEASTERN COUNTIES AIDED BY ISENTROPIC LIFT AND SOME UPPER LEVEL DIVERGENCE AS WE SIT UNDER THE LEFT EXIT REGION OF A 250 MB JET. PRECIPITATION SHOULD BEGIN TO TREND DOWNWARD HOWEVER AS ISENTROPIC LIFT WEAKENS AND SOME VERY DRY MID-LEVEL AIR TO THE NORTHEAST TRIES TO WORK SOUTHWESTWARD INTO THE CWA. THIS IS VERY EVIDENT ON THE SOUNDINGS WHERE THE KMHX SOUNDING HAS A 5 DEGREE DEWPOINT DEPRESSION AT 850 MB AND THE KWAL SOUNDING HAS A 33 DEGREE DEWPOINT DEPRESSION. AS PRECIPITATION MOVES NORTHEAST...COMPOSITE RADAR SHOWS EVAPORATION OF THE PRECIPITATION...MOST LIKELY CAUSED BY THE MID LEVEL DRY AIR. AS FAR AS CONVECTIVE ALLOWING MODELS ARE CONCERNED...ONLY ONE REALLY HAS A HANDLE OF THE CURRENT MODE OF PRECIP AND THAT IS THE HRRR WHICH DEPICTS THE CURRENT PATTERN VERY WELL. GOING INTO THIS AFTERNOON THE RAIN OVER THE CENTRAL PART OF THE CWA PUSHES NORTHEAST AND CHANCES ELSEWHERE DIMINISH THROUGH THE AFTERNOON TO JUST A FEW PATCHES OF DRIZZLE OR LIGHT RAIN BY THIS EVENING. CLOUDS SHOULD REMAIN OVERNIGHT...THUS MODERATING LOWS...MAINLY LOW TO MIDDLE 50S NW TO SE. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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AS OF 245 PM THURSDAY... FRIDAY SHOULD SEE THE BEGINNING OF A SLOW IMPROVEMENT IN SKY CONDITION AND TEMPS. DEVELOPING (THOUGH WEAK) NW FLOW IN THE MID- UPPER LEVELS WILL BEGIN TO SCOUR THE CAD AIR MASS FROM ALOFT. STILL...RESIDUAL LOW LEVEL MOISTURE WILL REMAIN HIGH ENOUGH TO PRODUCE EXTENSIVE CLOUDINESS IN THE MORNING WITH SOME PARTIAL BREAKS DEVELOPING IN THE AFTERNOON. THIS HEATING ALONG WITH THE PASSAGE OF A WEAK MID LEVEL TROUGH MAY PROVIDE ENOUGH LIFT TO GENERATE AN ISOLATED SHOWER OR THUNDERSTORM ACROSS CENTRAL NC. TEMPS WILL BEGIN TO RECOVER FRIDAY THOUGH IF CLOUDS STICK AROUND A LOT LONGER THAN EXPECTED...MAX TEMPS MAY END UP BEING 3-5 DEGREES COOLER THAN CURRENTLY FORECAST...ESPECIALLY ACROSS THE NORTHERN PIEDMONT. MAX TEMPS FRIDAY LOW-MID 70S. FRIDAY NIGHT... PARTIAL CLEARING MAY LEAD TO THE DEVELOPMENT OF FOGGY CONDITIONS AFTER MIDNIGHT. MIN TEMPS 55- 60. -WSS SAT/SAT NIGHT: EXPECT DRY WEATHER AND PLENTY OF SUNSHINE SAT. A WEAK BACKDOOR FRONT WILL DROP THROUGH NC IN THE MORNING... OTHERWISE WE`LL HAVE SURFACE HIGH PRESSURE OVER THE REGION AND A DRY/SUBSIDING COLUMN BENEATH MID LEVEL RIDGING. WE MAY GET WARM AND MOIST ENOUGH IN THE SOUTHEAST FOR POTENTIAL INLAND-MOVING SEA BREEZE CONVECTION... SO WILL RETAIN THE EXISTING ISOLATED MENTION FOR THE AFTERNOON. WITH THICKNESSES LIKELY NEARING 20 M ABOVE NORMAL AND GOOD MIXING EXPECTED... HIGHS IN THE UPPER 70S TO LOWER 80S APPEAR ATTAINABLE. A STRONG VORTICITY MAX AND WAVE CROSSING NRN NEW ENGLAND SAT WILL HELP PROPEL A MORE PRONOUNCED BACKDOOR FRONT SOUTHWARD TO NEAR THE VA/NC BORDER LATE SAT NIGHT... PUSHED BY COOL DENSE HIGH PRESSURE CENTERED OVER WRN QUEBEC. MODELS DIFFER REGARDING HOW FAR (IF AT ALL) THE FRONT GETS INTO NE NC... WITH THE GFS A BIT FARTHER SSW THAN THE NAM/ECMWF. GIVEN THE STRENGTH OF THE PARENT HIGH AND INTENSITY OF THE NEW ENGLAND WAVE... THINK WE`LL SEE ENOUGH PENETRATION INTO OUR CWA FOR BRIEFLY LOWER DEWPOINTS AND TEMPS INTO THE NE CWA. EXPECT LOWS IN THE UPPER 50S TO LOWER 60S EXCEPT MID 50S FAR NE. THE STRONG LOW CLOSING OFF OVER SASK/MANITOBA AND ATTENDING TROUGH THROUGH THE DAKOTAS ULTIMATELY PICK UP THE SRN STREAM LOW OVER THE CENTRAL PLAINS... CULMINATING IN DEEP MID LEVEL TROUGHING THROUGH CENTRAL NOAM BY DAWN SUNDAY. WHILE WE`RE LIKELY TO SEE INCREASING CLOUDS FROM THE SW SAT NIGHT WITH ENCROACHING DPVA ALOFT AND IMPROVING MOIST INFLOW IN THE LOWER LEVELS... ANY LIFT IS TOO WEAK AND THE COLUMN STILL TOO DRY OVERALL TO SUPPORT ANY PRECIP THROUGH DAWN SUNDAY. -GIH
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/...
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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. LOWS AROUND 60 TO THE MID 60S 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
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/... AS OF 205 PM THURSDAY... 24 HOUR TAF PERIOD: VARIABLE CONDITIONS ACROSS THE CWA RIGHT NOW AS PREDOMINANTLY IFR CEILINGS AND MVFR VISIBILITIES HAVE OVERSPREAD THE SOUTHWESTERN COUNTIES...MVFR CONDITIONS OVER THE NW PIEDMONT ARE SETTLING BACK IN AND VFR TO THE EAST. WHILE CONDITIONS WILL VARY THIS AFTERNOON BASED ON CLOUD COVER AND PLACEMENT OF PRECIPITATION THERE WILL BE AN OVERALL TREND OF IMPROVING IN THE EAST THIS AFTERNOON AND HOLDING STEADY IN THE WEST WHERE THE CAD WEDGE HAS MORE INFLUENCE. OVERNIGHT TONIGHT EXPECT CEILINGS TO GO DOWN TO AT LEAST IFR LEVELS IN MOST LOCATIONS. THIS WILL HAPPEN EARLIER IN THE WEST AND LATER IN EAST. CONVERSELY...AFTER SUNRISE FRIDAY EXPECT EASTERN SITES TO RECOVER TO VFR FASTER THAN WESTERN SITES WHICH COULD HOLD MVFR THROUGH THE END OF THE TAF PERIOD. MOSTLY NNE WINDS AT THIS TIME AT 5-10 KTS BUT AS COASTAL LOW DEVELOPS OFF OF NC...BIGGER EASTWARD COMPONENT COMING IN...CURRENTLY NOTED AT KRWI. BIGGEST THREAT TO CEILINGS OVERNIGHT WILL BE LOW CEILINGS WITH VISIBILITIES SECONDARY. RAIN SHOULD TAPER OFF AFTER SUNSET. ONCE THAT HAPPENS SHOULD BE DRY THROUGH THE END OF THE TAF PERIOD. LONG TERM: RETURN TO MAINLY VFR CONDITIONS FRIDAY AFTERNOON THROUGH SATURDAY. CHANCE FOR ADVERSE CONDITIONS WITH A COLD FRONT SUNDAY INTO MONDAY AND THEN IMPROVING CONDITIONS FOR MIDWEEK NEXT WEEK. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...ELLIS SHORT TERM...WSS/HARTFIELD LONG TERM...HARTFIELD AVIATION...ELLIS

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