Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 280727 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 225 AM EST WED JAN 28 2015 .SYNOPSIS...
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HIGH PRESSURE WILL BUILD OVER THE REGION THROUGH EARLY THURSDAY... BEFORE PUSHING TO OUR SOUTH. A CLIPPER LOW PRESSURE SYSTEM AND ASSOCIATED COLD FRONT WILL SWEEP THROUGH THE AREA LATE THURSDAY AND THURSDAY NIGHT. COOL HIGH PRESSURE WILL BUILD BACK IN FROM THE WEST FRIDAY.
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&& .NEAR TERM /OVERNIGHT/... AS OF 912 PM TUESDAY... STRONG NW FLOW IN THE WAKE OF THE DEPARTING LOW PRESSURE SYSTEM WILL FUNNEL DRY CHILLY AIR INTO CENTRAL NC OVERNIGHT. A PERTURBATION ROTATING AROUND THE DEEP CYCLONE WILL CROSS OUR REGION OVERNIGHT. THIS SYSTEM MAY CAUSE A STRATUS DECK TO PERSIST OVER SECTIONS OF HALIFAX AND EDGECOMBE COUNTIES WHILE PATCHY CIRRUS MAY AFFECT THE REST OF THE REGION. CLEAR SKIES SHOULD RETURN BY 3-4 AM. THE COLD AIR ADVECTION WILL YIELD LOW LEVEL THICKNESSES IN THE 1265- 1270M RANGE BY EARLY WEDNESDAY. HISTORICALLY, THESE THICKNESSES HAVE PRODUCED MIN TEMPS AROUND 20-LOWER 20S. UPSTREAM...MIN TEMPS EARLY TUESDAY MORNING WERE IN THE MID TENS-LOWER 20S IN THE COAL FIELDS OF EASTERN KY (WHERE OUR AIR PARCELS ARE ORIGINATING). HOWEVER ATMOSPHERE OVER CENTRAL NC EXPECTED TO REMAIN WELL-MIXED THROUGH MOST OF THE NIGHT (AS EVIDENT OF THE GUST 20-25MPH BEING REPORTED AT A FEW SITES ACROSS THE NORTHERN PIEDMONT), POSSIBLY DECOUPLING BY 4- 5 AM. THUS...THE WINDS MAY AID TO KEEP TEMPS UP A BIT BUT WHEN/IF THE WINDS DECOUPLE...TEMPS SHOULD PLUMMET IN THE BONE DRY ATMOSPHERE. HAVE TWEAKED MIN TEMPS A BIT...YIELDING LOWS MOSTLY IN THE LOW-MID 20S AND NEAR 20 IN THE NORMALLY COLDER LOCATIONS. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 230 PM TUESDAY... HIGH PRESSURE IS FORECAST TO MOVE OVERHEAD WEDNESDAY INTO WEDNESDAY NIGHT. SUNNY SKIES AND LIGHT WINDS WILL TEMPER THE CHILLY AIR MASS. HIGHS ARE EXPECTED TO REACH THE MID TO UPPER 40S (WARMEST SOUTHERN PIEDMONT). IT APPEARS THAT THE HIGH LEVEL MOISTURE WILL HOLD OFF UNTIL THURSDAY. THEREFORE... CLEAR SKIES AND LIGHT WINDS SHOULD LEAD TO LOWS IN THE UPPER TEENS TO LOWER 20S. OPTIMAL RADIATIONAL COOLING SHOULD LEAD TO LOWS BELOW MOS GUIDANCE... ESPECIALLY OVER THE CENTRAL PIEDMONT. HIGH PRESSURE MOVES OFFSHORE AS A SHORT WAVE AND ASSOCIATED SURFACE FRONT MOVES INTO AND ACROSS THE OHIO VALLEY THURSDAY INTO THURSDAY NIGHT. WESTERLY FLOW ACROSS THE SOUTHERN STATES WILL QUASH LOW LEVEL MOISTURE ADVECTION...SO WILL KEEP ONLY A SLIGHT CHANCE POP WITH VERY LIGHT PRECIP AMOUNTS...A FEW HUNDREDTHS AT MOST...LIMITED TO A NARROW WINDOW FROM THURSDAY EVENING THROUGH PERHAPS MIDNIGHT. SOUTHWEST FLOW AHEAD OF THE FRONT WILL ALLOW FOR WEAK WARM AIR ADVECTION AND HIGHS WILL REACH THE UPPER 40S ACROSS THE NORTH TO LOWER 50S IN THE FAR SOUTHERN COUNTIES. EXPECT RAPID CLEARING AFTER MIDNIGHT...BUT MIXING AND LIMITED TIME FOR RADIATIONAL COOLING WILL MODERATE MINS FROM AROUND FREEZING IN THE NORTHWEST TO THE MID 30S ELSEWHERE OVERNIGHT. && .LONG TERM /FRIDAY THROUGH TUESDAY/...
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AS OF 225 AM WEDNESDAY... FRI-SAT NIGHT: DRY AND COOL. LATEST MODEL RUNS UNANIMOUSLY SHOW THE SURFACE FRONT OFF THE NC COAST FRI MORNING WITH COLD AIR ADVECTION COMMENCING... AS SURFACE HIGH PRESSURE INITIALLY CENTERED OVER THE UPPER MIDWEST PUSHES EASTWARD WHILE BUILDING SOUTH INTO NC. GOOD MIXING AND A TIGHT MSLP GRADIENT WILL BRING BRISK NORTHWEST WINDS SUSTAINED UP TO 15-20 MPH... AND MOMENTUM TRANSFER SUPPORTS GUSTS TO 25-30 MPH FROM LATE MORNING THROUGH THE AFTERNOON... ABATING SLOWLY IN THE EVENING WITH THE GRADUAL LOSS OF MIXING. FALLING THICKNESSES FRI INDICATE HIGHS IN THE MID 40S TO AROUND 50 DESPITE PLENTY OF SUNSHINE. WINDS FALL OFF FRI NIGHT BUT DON`T GO COMPLETELY CALM... YET THE CHILLY AIR MASS BUILDING IN WITH CLEAR SKIES AND OTHERWISE DECENT RADIATIONAL COOLING STILL FAVORS LOWS IN THE LOW-MID 20S... AND WOULD NOT BE SURPRISED TO SEE A FEW TEENS IN OUTLYING AREAS. SUNSHINE CONTINUES SAT AS THE HIGH RIDGES SOUTHWARD INTO NC. HIGHS STILL BELOW NORMAL... 44-48. THE MID LEVEL RIDGE AXIS SHIFTS OVER AND JUST EAST OF THE CAROLINAS SAT NIGHT AS THE SURFACE RIDGE MOVES SSE AND OFFSHORE... AND WE SHOULD SEE INCREASING HIGH CLOUDS LATE AS WSW MID LEVEL FLOW STARTS DRAWING IN WEAK SOUTHERN STREAM VORTICITY FROM THE BAJA LOW. LOWS IN THE UPPER 20S TO AROUND 30. SUN-TUE: CONFIDENCE INCREASING THAT WE`LL SEE A GOOD SHOT OF RAIN... LIKELY FOCUSED IN THE SUN NIGHT-MON TIME FRAME. THE ECWMF IS A BIT FASTER THAN THE GFS BY ABOUT 3-6 HRS... AND WILL GO WITH A COMPROMISE TIMING SOLUTION FOR NOW... BUT OTHERWISE THE TWO MODELS ARE IN GOOD AGREEMENT ON AMPLIFICATION AND PRECIP PLACEMENT. A POTENT NORTHERN STREAM SHORTWAVE TROUGH TRACKS THROUGH THE CENTRAL MISS VALLEY SUNDAY/SUN NIGHT AS ITS ASSOCIATED PRIMARY SURFACE LOW MOVES JUST AHEAD OF IT THROUGH THE OH VALLEY... ALL THE WHILE PULLING INCREASING SOUTHERN-STREAM MOISTURE FROM EAST OF THE NW- MEXICO LOW... ALONG AND AHEAD OF THE TRAILING SURFACE COLD FRONT INTO THE GULF STATES AND MID SOUTH. THE ECMWF/GFS COMPROMISE TIMING SUPPORTS BRINGING A CHANCE OF RAIN INTO THE FAR WRN CWA LATE SUN... FOLLOWED BY WIDESPREAD RAIN SPREADING EASTWARD SUN EVENING THROUGH THE FIRST HALF OF MONDAY... AS THE NORTHERN STREAM SHORTWAVE TROUGH CROSSES THE OH VALLEY/CENTRAL APPALACHIANS INTO THE NORTHEAST/MID ATLANTIC REGION. HAVE SLOWED DOWN BOTH THE ARRIVAL AND EXIT OF PRECIP BY A FEW HOURS... AND HAVE RAISED POPS A BIT MORE AT THE EVENT`S PEAK BASED ON GOOD AGREEMENT AMONG THE MODELS AND THEIR ENSEMBLE MEMBERS... AND VERY HIGH VALUES OF LOW LEVEL MOISTURE FLUX AND VIGOROUS DYNAMIC FORCING FOR ASCENT. LOW LEVEL THICKNESSES SOAR OVER CENTRAL NC SUNDAY THROUGH AT LEAST THE FIRST HALF OF MON... ALTHOUGH THERE IS STILL A CHANCE OF A LINGERING COOL STABLE POOL OVER THE NW PIEDMONT. SO WE SHOULD SEE ABOVE NORMAL TEMPS... MAINLY OVER THE SRN AND ERN CWA... DESPITE THE HIGH CHANCE OF SHOWERS. THE GFS DEPICTS A COUPLE HUNDRED J/KG OF MUCAPE AHEAD OF THE FRONT... AND IF THIS WEAK INSTABILITY PERSISTS IN LATER RUNS... A RISK OF THUNDER MAY NEED TO BE ADDED. FRONTAL PASSAGE IS MOST LIKELY MON AFTERNOON... WITH PLUNGING THICKNESSES POST-FRONT AS ANOTHER CANADIAN SOURCE HIGH BUILDS IN FROM THE NW. EXPECT CLEARING SKIES MON EVENING WITH TEMPS RETURNING TO BELOW NORMAL VALUES MON NIGHT THROUGH TUE. -GIH
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 100 AM WEDNESDAY... 24 HOUR TAF PERIOD: VERY HIGH CONFIDENCE OF VFR CONDITIONS THROUGH THE TAF PERIOD AS VERY DRY AIR HAS COME INTO THE REGION WITH DEWPOINTS IN THE TEENS AND SINGLE DIGITS IN SOME SPOTS. WINDS ARE OUT OF THE NORTHWEST WITH SOME GUSTS STILL PREVAILING UP TO 20 KTS. OTHERWISE EXPECT 5-10 KT WINDS OVERNIGHT OUT OF THE NORTHWEST. OTHER THAN SOME SCATTERED CLOUDS AROUND THE 3500 FOOT LEVEL AND POSSIBLY SOME OROGRAPHIC CLOUDS AT THE 5-6 KFT LEVEL DRIFTING OUT OF VA AND INTO OUR NORTHEASTERN AREAS. OTHERWISE AN ALL AROUND PLEASANT AVIATION DAY. LONG TERM: THE NEXT THREAT TO AVIATION CONDITIONS WILL BE THURSDAY NIGHT INTO FRIDAY MORNING AS A FRONTAL SYSTEM CROSSES THE AREA AND THEN ANOTHER SYSTEM SUNDAY INTO MONDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...WSS SHORT TERM...BADGETT LONG TERM...HARTFIELD AVIATION...ELLIS

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