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...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.

&&

.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/...
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

&&

.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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