Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 020258
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
955 PM EST SUN MAR 1 2015

.SYNOPSIS...WEAK BUT COOL HIGH PRESSURE WILL HOLD OVER THE AREA
THROUGH TONIGHT. A COLD FRONT WILL PUSH SOUTHWARD THROUGH NORTH
CAROLINA ON MONDAY... THEN SETTLE JUST TO OUR SOUTH MONDAY NIGHT AS
HIGH PRESSURE NOSES IN FROM THE NORTH. MOIST AIR RIDING UP AND OVER
THIS STATIONARY FRONT WILL BRING UNSETTLED WEATHER FOR TUESDAY INTO
WEDNESDAY.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 955 PM SUNDAY...

A COLD AIR DAMMING AIRMASS IS FIRMLY WEDGED IN PLACE AND WILL REMAIN
SO UNTIL A COLD FRONT MOVING IN FROM THE NORTHWEST PROVIDES A BRIEF
REPRIEVE ON MONDAY. A SURFACE HIGH ASSOCIATED WITH THE CAD COLD POOL
HAS DRIFTED SOUTH TOWARD THE SAVANNAH RIVER BASIN THIS EVENING. ALL
MEASURABLE PRECIP HAS SHIFTED EAST OF THE AREA AND THE MAIN FORECAST
CONCERN OVERNIGHT IS THE POTENTIAL FOR FOG DEVELOPMENT AS SOME DRIER
AIR MOVES IN BETWEEN 925MB AND 700MB. WHILE FORECAST SOUNDINGS DON`T
SHOW THE STRONGEST SIGNAL FOR DENSE FOG...STRATUS HAS BEEN SLOWLY
LOWERING IN THE PAST COUPLE OF HOURS AND VISIBILITIES HAVE BEEN
FALLING OVER THE SOUTHERN FOOTHILLS BEHIND A NOTICEABLE (ON IR
IMAGERY) BACK-EDGE OF DEEPER MOISTURE.  THE MAIN COUNTER TO
WIDESPREAD FOG WILL BE A SLOWLY TIGHTENING PRESSURE GRADIENT IN
RESPONSE TO THE COLD FRONT MOVING THROUGH THE OHIO VALLEY....MAINLY
ACROSS THE NORTH-NORTHWEST PORTIONS OF THE CWA. A DENSE FOG ADVISORY
MAY BE NEEDED IN THE NEXT FEW HOURS...ESPECIALLY FOR THE SOUTHERN
HALF OF THE AREA.  OTHERWISE... TEMPS WILL HOVER PRETTY CLOSE TO
THEIR CURRENT VALUES IN THE MID AND UPPER 30S FOR MUCH OF THE NIGHT.
-BLS

FOR MON/MON NIGHT: A POTENT NORTHERN STREAM SHORTWAVE TROUGH
CROSSING THE GREAT LAKES/ST LAWRENCE VALLEY/NORTHEAST LATE
TONIGHT/MONDAY WILL HELP PUSH A WEAK FRONT SOUTHWARD INTO AND
THROUGH NC MONDAY... AND AFTER A MURKY AND GRAY MONDAY MORNING...
THIS MECHANISM WILL FINALLY SCOUR OUT THE LOW LEVEL MOIST/STABLE
POOL FROM NNW TO SSE DURING THE DAY. MODELS DEPICT ENOUGH LOW AND
MID LEVEL MOISTURE HOLDING ON OVER SRN NC NEAR THE SOUTHWARD-INCHING
FRONTAL ZONE WITH SUFFICIENT LINGERING LOW LEVEL MOISTURE TRANSPORT
TO SUPPORT A LOW CHANCE OF SOME PATCHY LIGHT RAIN OVER THE SRN CWA
MON FROM LATE MORNING THROUGH MID AFTERNOON... WHILE FURTHER
NORTH... WE SHOULD TREND TOWARD PARTIAL CLEARING AS DRIER LOW LEVEL
AIR ATTEMPTS TO BUILD IN. HAVE OPTED TO STAY ON THE LOW END OF
GUIDANCE FOR HIGHS MONDAY (NEAR 50 NORTH TO THE UPPER 50S SOUTH) AS
THERE IS LIKELY TO BE A DELAY AND LIMIT TO THE PARTIAL CLEARING...
HOWEVER IF LATER FORECASTS TREND TOWARD MORE SUNSHINE TOMORROW...
THESE MAY NEED TO BE BUMPED UP A CATEGORY OR SO. THE RELATIVELY
QUIET WEATHER WILL BE SHORT-LIVED... NOT A SURPRISE GIVEN THE STRONG
JET LEVEL WINDS OVER THE CENTRAL/SRN CONUS FOSTERING AN ACTIVE
WEATHER CYCLE. AN APPROACHING WEAK LOW LEVEL WAVE AND PRECEDING
SURGE IN MOISTURE TRANSPORT INTO THE MIDSOUTH AND SOUTHERN
APPALACHIANS WILL SUPPORT A SMALL CHANCE POP IN THE SW CWA LATE MON
NIGHT. LOWS FROM AROUND 30 NE TO MID-UPPER 30S FAR SOUTHWEST. -GIH

&&

.SHORT TERM /TUESDAY/...
AS OF 250 PM SUNDAY...

A CAD SCENARIO IS PROGGED TO DEVELOP ON TUESDAY AS A 1032 HIGH TO
OUR NORTH DRIFTS EAST OUT INTO THE ATLANTIC...AND FLOW ALOFT BACKS
FROM WNW IN THE MORNING TO SW BY AFTERNOON. WITH ISENTROPIC UPGLIDE
INCREASING AS 850MB FLOW BACKS TO SW AND INCREASES...LOOK FOR LIGHT
RAIN TO DEVELOP TUESDAY MORNING AND LINGER INTO THE AFTERNOON...WITH
MODELS SUGGESTING QPF WILL REMAIN AOB 0.15". AS ALWAYS THE CASE WITH
CAD...TEMPS WILL REMAIN BELOW GUIDANCE AND WELL BELOW NORMAL...UPPER
30S NW TO AROUND 50 SE. WHILE WE HAVE LOW TEMPS AROUND FREEZING
ALONG AND NORTH OF HWY 64 TUESDAY MORNING...THE COMBINATION OF THE
LIGHT INTENSITY OF THE RAIN AND BORDERLINE FREEZING TEMPS...FORECAST
SOUNDINGS SUGGEST VERY LITTLE IF ANY FREEZING RAIN THREAT ACROSS OUR
NORTHERN ZONES TUESDAY MORNING.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
AS OF 250 PM SUNDAY...

TUESDAY NIGHT...THE NEXT COLD FRONT WILL APPROACH...AND WITH
INCREASING SW LOW LEVEL FLOW AHEAD OF IT...THE CAD SHOULD SCOUR OUT
WITH TEMPS TUE NIGHT ACTUALLY RISING THRU THE NIGHT WITH VIGOROUS
WAA AHEAD OF THE FRONT. IN FACT...BY- OR SHORTLY AFTER SUNRISE
WED...TEMPS WILL BE IN THE 50S ACROSS OUR ENTIRE CWA. WITH FROPA
DURING THE AFTERNOON...WE COULD SEE TEMPS RISE WELL INTO THE 60S
DURING THE MORNING...PERHAPS BREAKING THE 70 DEGREE MARK ACROSS OUR
SE ZONES. AS FOR RAIN CHANCES...LOOK FOR POPS TO INCREASE FROM NW TO
SE THRU THE DAY WED...WHILE IT STILL LOOKS LIKE THE BULK OF THE
PRECIP WILL BE FOUND RIGHT ALONG OR JUST BEHIND THE FRONT...WHICH
WILL LINGER WEDNESDAY NIGHT THROUGH MUCH OF THE DAY THURSDAY AS
MIDLEVEL FLOW BECOMES PARALLEL TO THE FRONT...AND A STEADY FETCH OF
DEEP MOISTURE IS TRANSPORTED OVERTOP A COOLING POST-FRONTAL LOW
LEVEL AIRMASS. SPEAKING OF THE COOLING LOW LEVEL AIRMASS...LOW LEVEL
THICKNESSES ARE PROGGED TO PLUMMET IN THE WAKE OF THE FRONT...FROM
~1380M 00Z THU TO ~1265M BY 10Z THU. SOME OF THE GUIDANCE SUGGESTS
TEMPS MAY HOLD IN THE 20S DURING THE DAY THU!  GIVEN THE
AFOREMENTIONED LINGERING MOISTURE PLUME...ASSUMING THIS MODEL
SOLUTION HOLDS...ITS BEGINNING TO LOOK A LITTLE MORE LIKELY THAT WE
MAY BE DEALING WITH SOME SORT OF WINTER P-TYPE EVENT DURING THE
DAYTIME THURSDAY. THE MAIN QUESTION IS HOW MUCH...AS QPF PROGS STILL
VARY QUITE A BIT...WITH GFS QPF ROUGHLY TWICE AS MUCH AS THE ECMWF
DURING THE 12Z THU TO 00Z FRI PERIOD. PLEASE STAY TUNED!

LATEST GFS AND ECMWF ARE IN BETTER AGREEMENT DURING THE LATE-WEEK
AND WEEKEND TIMEFRAME...WITH THE OPERATIONAL RUNS BOTH SHOWING THE
MOISTURE PLUMES PUSHING SOUTH OF OUR CWA BY 06Z FRIDAY...THEN DRY
WEATHER FOR OUR CWA FRIDAY THROUGH SATURDAY WITH HIGH PRESSURE
BUILDING OVER THE AREA. LOW LEVEL THICKNESS PROGS RECOVER QUITE
QUICKLY DURING THIS TIME...BUT THAT MAY NEED ADJUSTMENT DEPENDING ON
WHAT HAPPENS THURSDAY.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
AS OF 810 PM SUNDAY...

IN ASSOCIATION WITH A LINGERING COLD AIR DAMMING REGIME
CHARACTERIZED BY A CHILLY; SATURATED; AND STABLE LAYER OF AIR IN THE
NEAR SURFACE LAYER...INITIALLY MAINLY IFR CONDITIONS...TO SCATTERED
MVFR-VFR ONES INCLUDING AT TRIAD TAF SITES...WILL DETERIORATE TO
LIFR TONIGHT...THEN IMPROVE TO VFR BY MID-LATE MORNING MONDAY. ANY
LINGERING LIGHT RAIN AT KRWI WILL MOVE EAST THROUGH 02Z...WITH
OCCASIONAL DRIZZLE EXPECTED OTHERWISE AND ELSEWHERE OVERNIGHT.

AN ALTERNATE BUT LESS LIKELY SCENARIO IS THAT SSW WINDS WILL
INCREASE AND MIX TO THE SURFACE TONIGHT...IN RESPONSE TO A TIGHTENING
MSL PRESSURE GRADIENT AHEAD OF AN APPROACHING COLD FRONT. THE
ASSOCIATED MIXING COULD THEORETICALLY MIX OUT THE LOW CLOUDS MUCH
EARLIER THAN CURRENTLY REFLECTED IN THE TAFS...OR KEEP THE LIFR
CONDITIONS FROM SETTING IN ALTOGETHER. THOUGH CURRENT OBSERVATIONAL
TRENDS WOULD SUGGEST THAT PROCESS MAY INDEED ALREADY BE UNDERWAY...
PARTICULARLY AT TRIAD TAF SITES WHERE THE LOW OVERCAST HAD ALMOST
COMPLETELY SCATTERED OUT AS OF 01Z...THE OVERWHELMING CONSENSUS OF
OTHER FACTORS/FORCING MECHANISMS FOR LOW STRATUS/FOG SUGGESTS THIS
ALTERNATE SCENARIO IS IMPROBABLE - ONLY AROUND 10-20 PERCENT - AND
THAT THE NEAR TERM IMPROVEMENT IS A TEMPORARY ONE.

A DRY COLD FRONT WILL CROSS THE REGION AND CAUSE A DRIER
NORTHWESTERLY WIND TO ENVELOP CENTRAL NC BETWEEN 12-18Z MON...WITH
VFR CONDITIONS EXPECTED THROUGH THE END OF THE 00Z TAF PERIOD. -RAH

LOOKING BEYOND 00Z TUE... A DISTURBANCE ALOFT RIDING ALONG THE
SURFACE FRONT WILL BRING A THREAT OF MVFR/IFR CONDITIONS STARTING
LATE MONDAY NIGHT (INT/GSO) OR TUE AFTERNOON (RDU/RWI/FAY)... ALONG
WITH A LLWS RISK. THESE SUB-VFR CONDITIONS SHOULD GIVE WAY TO VFR
CONDITIONS AT FAY THEN AT RWI/RDU WED AS A WARM FRONT MOVES
NORTHWEST THROUGH THE AREA WITH STRENGTHENING SW WINDS... BUT SUB-
VFR CONDITIONS MAY HOLD IN LONGER AT INT/GSO. THIS WARM FRONT WILL
DROP BACK DOWN SOUTHEAST THROUGH THE AREA AS A COLD FRONT LATE WED
OR WED NIGHT... TURNING SURFACE WINDS BACK AROUND TO
NORTH/NORTHEASTERLY FOR THU WITH WIDESPREAD RAIN AND SUB-VFR
CONDITIONS. VFR CONDITIONS SHOULD RETURN TO NORTHERN SECTIONS
(RDU/RWI/INT/GSO) BY THURSDAY NIGHT/FRIDAY. -GIH

&&

$$
SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD/BLS
SHORT TERM...RAH
LONG TERM...RAH
AVIATION...RAH/GIH



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