Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 190104
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
804 PM EST THU DEC 18 2014

.SYNOPSIS...HIGH PRESSURE OVER THE MISSISSIPPI RIVER VALLEY WILL
EXTEND EASTWARD INTO THE MID ATLANTIC AND CAROLINAS THROUGH TONIGHT.
A LOW PRESSURE SYSTEM EXPECTED TO DEVELOP ALONG THE GULF COAST ON
FRIDAY WILL REMAIN SOUTH OF NORTH CAROLINA AS IT TRACKS OFFSHORE THE
SOUTHEAST COAST ON SATURDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 920 AM THURSDAY...

AN ALREADY LOW AMPLITUDE TROUGH ALOFT OVER THE MID-MISSISSIPPI RIVER
VALLEY THIS MORNING WILL CONTINUE TO DEAMPLIFY AS IT SKIRTS ACROSS
THE TENNESSEE VALLEY AND VIRGINIA THROUGH TONIGHT. AN AREA OF LIGHT
RAIN MOVING ACROSS EASTERN TENNESSEE...FOCUSED NEAR THE H925-H85
FRONTAL ZONE WHERE ISENTROPIC LIFT IS GREATEST...CONTINUES TO
GRADUALLY WEAKEN WITH EASTWARD EXTENT.  EXPECT THIS TREND TO THE
CONTINUE AS THE UPPER DISTURBANCE MOVES OFF TO THE EAST-NORTHEAST
AND THE FORCING DECOUPLES.  SO NO PRECIP IS EXPECTED OVER CENTRAL
NC.  EAST OF THE MOUNTAINS...THE AIRMASS REMAINS VERY DRY WITH ALL
MOISTURE ABOVE 12K FT.   WHILE THERE IS A FAIR AMOUNT OF HIGH LEVEL
MOISTURE UPSTREAM...GUIDANCE SUGGESTS  THERE WILL PERIODS OF SUN
MIXED IN WITH THE HIGH CLOUDS (POTENTIALLY OROGRAPHICALLY ENHANCED
AT TIMES THIS MORNING. TEMPS SHOULD GET TO WITHIN A COUPLE DEGREES
OF THE CURRENT FORECAST HIGHS OF 49-55.  IF ANYTHING...THEY WILL END
UP ON THE COOLER SIDE.

SKIES WILL BEGIN TO CLEAR OFF BY EARLY FRIDAY MORNING WITH THE
PASSAGE OF THE AFOREMENTIONED MID LEVEL TROUGH. GIVEN A RATHER WEAK
MSLP GRADIENT ACROSS THE AREA WITH SURFACE HIGH PRESSURE EXTENDING
INTO THE AREA FROM THE WEST... WE SHOULD SEE LIGHT AND VARIABLE TO
CALM WINDS OVERNIGHT. THIS COMBINED WITH CLEAR SKIES WILL ALLOW US
TO COOL QUITE NICELY TONIGHT. EXPECT LOW TEMPS WILL RANGE FROM THE
UPPER 20S TO AROUND 30 (WITH MAYBE EVEN A FEW MID 20S) IN THE USUAL
RURAL COLD LOCATIONS TO THE LOWER 30S ELSEWHERE.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 255 PM THURSDAY...

FRIDAY AND FRIDAY NIGHT... HIGH PRESSURE OVER THE MIDWEST WILL
SLOWLY SETTLE EAST ACROSS THE CENTRAL APPALACHIANS AS THE PARENT
HIGH MOVES TOWARD EASTERN CANADA. WE SHOULD BE IN A RELATIVE MIN
BETWEEN MID/HIGH CLOUDS TODAY AND MOISTURE SPREADING IN AHEAD OF
SATURDAY`S SYSTEM. GUIDANCE SUGGESTS DEWPOINTS WILL FALL INTO THE
20S..THOUGH WOULDNT BE SURPRISED TO SEE SOME UPPER TEENS BASED ON
REGIONAL OBSERVATIONS.  THICKNESSES SUPPORT HIGHS IN THE LOW TO MID
50S.  LOWS FRIDAY NIGHT SHOULD BE ABLE TO FALL INTO THE LOW/MID 30S
(ESPECIALLY NORTHEAST) PRIOR TO THE ARRIVAL OF MORE ROBUST CLOUD
COVER.

SATURDAY... THE SHORTWAVE CURRENTLY OVER THE CALIFORNIA BAJA REGION
WILL LIFT NORTHEAST ACROSS THE SOUTHERN-CENTRAL US ON FRIDAY AND
THEN TOWARD OUR REGION ON FRIDAY NIGHT. MODELS CONTINUE TO TREND
TOWARD MORE DEAMPLIFICATION WITH THE WAVE BY THE TIME IT REACHES THE
SOUTHERN APPALACHIANS SATURDAY MORNING.  ACCORDINGLY...THE SURFACE
LOW EXPECTED TO DEVELOP ALONG THE GULF COAST IS MUCH WEAKER AND
ESSENTIALLY MOVES EAST OFF THE SOUTHEAST COAST. HIGH PRESSURE OVER
EASTERN CANADA WILL EXTEND DOWN THE EASTERN SEABOARD AND INTO
CENTRAL NC.  WHILE NOT OVERLY STRONG OR FAR ENOUGH SOUTH... THE HIGH
IS IN A MORE FAVORABLE POSITION TO SUPPLY DRY AIR INTO NC THAN
FORECAST A FEW DAYS AGO.  HOWEVER...WITH WEAKER DYNAMIC
FORCING...THE DRY AIR WILL ALSO LIMIT PRECIP...AND THE NAM/GFS/ECMWF
ARE ALL DRY OR NEARLY DRY.

CAN`T HELP BUT CONTINUE TO CUT BACK ON POPS BASED ON RECENT
GUIDANCE...BUT GIVEN THAT THE SHORTWAVE WILL BE INTERACTING WITH AN
ASSORTMENT OF NORTHERN STREAM WAVES OVER THE NORTHERN PLAINS...A
SMALL SHIFT BACK TO THE NORTH WILL BRING MEASURABLE PRECIP INTO
CENTRAL NC.  SHOULD NOTE THAT A SHIFT BACK TO THE NORTH COULD STILL
CREATE SOME PTYPE ISSUES AS PTYPE NOMOGRAMS HOVER AROUND THE WINTRY
MIX AND WETBULB PROFILES REMAIN CURIOUSLY CLOSE TO FREEZING IN THE
LOWEST 10K FT.  THIS IS A FINE LINE AS WELL...AS THE SHIFT WOULD
ALSO BRING SOME WARM AIR BACK NORTH.  WILL REDUCE POPS TO CHANCE
ACROSS THE NORTH AND LOW-END LIKELY (MAINLY BETWEEN 12Z AND 00Z)
NEAR THE SC BORDER...WHICH MAY STILL BE TOO HIGH BUT FOLLOWS A
CONSERVATIVE TREND.  WILL ALSO RAISE HIGHS A FEW DEGREES...THOUGH
NORTHEASTERLY FLOW AND THICK CLOUD COVER WOULD STILL KEEP TEMPS IN
THE UPPER 40S NORTHWEST TO NEAR 50 SOUTHEAST.

SATURDAY NIGHT....ALL ENERGY ASSOCIATED WITH THIS SYSTEM WILL DEPART
SATURDAY NIGHT...ALLOWING FOR SOME MID-LEVEL DRYING AND SCATTERING
OF CLOUDS.  HOWEVER...MODELS ARE QUICK TO BRING MOISTURE BACK TOWARD
THE REGION FROM THE SOUTH AS ANOTHER SYSTEM GETS GOING BY LATE
SUNDAY.  LOWS IN THE MID/UPPER 30S.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
AS OF 320 PM WEDNESDAY...

...VERY ACTIVE PATTERN DEVELOPING OVER THE LONG TERM PERIOD...

BEHIND THE DEPARTING SOUTHERN STREAM SHORT WAVE TROUGH...SHORT WAVE
RIDGING MOVES INTO THE CAROLINAS ON SUNDAY AS HIGH PRESSURE CENTERED
OVER THE EASTERN GREAT LAKES AND MID ATLANTIC EXTENDS INTO THE
REGION. THE NEXT SOUTHERN STREAM WAVE WHICH MOVES ONSHORE ACROSS CA
ON FRIDAY REACHES THE WESTERN GULF OF MEXICO ON SUNDAY NIGHT. LOOK
FOR INCREASING AND THICKENING CLOUDS ON SUNDAY WITH HIGHS IN THE
UPPER 40S TO LOWER 50S. PRONOUNCED ISENTROPIC LIFT WHICH DEVELOPS
AHEAD OF THIS SYSTEM SUNDAY EVENING ACROSS THE SOUTHEAST...SPREADS
INTO THE CAROLINAS AFTER MIDNIGHT AND PERSISTS FOR MUCH OF MONDAY
MORNING. EXPECT A BROAD AREA OF RAIN WITH THIS SYSTEM AND HAVE
INCREASED POPS. TEMPERATURES SUNDAY NIGHT WILL FALL INTO THE MID 30S
ACROSS THE NORTHERN PIEDMONT AND THE UPPER 30S ELSEWHERE...THESE
TEMPERATURES ALONG WITH A PRONOUNCED WARM NOSE AND WET BULB ZERO
VALUES HOLDING ABOVE FREEZING SHOULD PRECLUDE AND PTYPE ISSUES.

A SURFACE LOW DEVELOPING IN THE NORTHEAST GULF OF MEXICO WILL MOVE
NORTHEAST ALONG THE CAROLINA COAST MONDAY AFTERNOON AND FURTHER
OFFSHORE MONDAY NIGHT. PRECIPITATION SHOULD BECOME MUCH MORE
SCATTERED AND LIGHT MONDAY NIGHT INTO TUESDAY AS THE STRONGEST
FORCING ABATES BUT WIDESPREAD CLOUDINESS AND SMALL RAIN CHANCES
WILL PERSIST AS A MOIST AIR MASS LINGERS ACROSS THE AREA.

AN IMPRESSIVE NORTHERN STREAM SHORTWAVE TROUGH DIVES INTO THE
MIDWEST ON TUESDAY AND TUESDAY NIGHT CARVING OUT A HIGH AMPLITUDE
LONG WAVE TROUGH DEVELOPS ACROSS THE MISSISSIPPI VALLEY TUESDAY
NIGHT AND BECOMES NEGATIVELY TILTED ON WEDNESDAY AS IT BROADENS AND
REACHES THE EAST COAST. BOTH THE DETERMINISTIC GFS AND ECMWF ARE
VERY SIMILAR WITH THIS PATTERN. AT THE SURFACE...A STRONG SURFACE
CYCLONE DEVELOPS ACROSS THE GREAT LAKES ON TUESDAY INTO WEDNESDAY
WITH A STRONG COLD FRONT PROGGED TO MOVE ACROSS THE CAROLINA ON
TUESDAY NIGHT AND EARLY WEDNESDAY. THIS PATTERN WILL SUPPORT STRONG
AND GUSTY WINDS AHEAD OF AND BEHIND THE COLD FRONT WITH A PERIOD OF
WIDESPREAD RAIN AND PERHAPS A FEW THUNDERSTORMS ASSOCIATED WITH THE
FRONT. THE DEEP LAYER FLOW ATTENDANT TO THE FRONT IS VERY STRONG
WITH A SOUTHWEST WIND OF AROUND 40KTS PROGGED AT 1 KFT NEAR RDU ON
WEDNESDAY MORNING AND A WESTERLY WIND OF 40 KTS FORECAST AT RDU AT
1.5 KFT WEDNESDAY NIGHT. BOUNDARY LAYER INSTABILITY IS LIMITED BUT
BOTH THE GFS AND THE ECMWF SUGGEST A NARROW WINDOW FOR BOUNDARY
LAYER DESTABILIZATION AHEAD OF THE FRONT. THE IMPRESSIVE WIND FIELD
COMBINED WITH 700-500 MB LAPSE RATES APPROACHING 7 AS NOTED BY THE
GFS...LEADS TO AN ELEVATED SHERB VALUE THAT SUGGESTS SOME HIGHER
IMPACT HSLC CONVECTION IS POSSIBLE. THE PRECIPITATION QUICKLY ENDS
BEHIND THE FRONT WEDNESDAY AFTERNOON WITH DRY WEATHER EXPECTED FOR
CHRISTMAS DAY. HIGHS ON TUESDAY WILL RANGE FROM THE LOWER 50S IN THE
TRIAD TO NEAR 60 ACROSS THE SOUTHERN COASTAL PLAIN. TEMPERATURES
SHOULDN`T FALL MUCH TUESDAY NIGHT WITH THE CLOUDS AND STRONG
SOUTHERLY FLOW. RAISED MINS ABOVE GUIDANCE TO THE MID 40S TO AROUND
50. HIGHS WEDNESDAY WILL RANGE FROM 50 IN THE TRIAD TO NEAR 60 IN
THE SOUTHEAST WITH CHILLIER MAXES IN THE MID 40S TO NEAR 50 EXPECTED
FOR CHRISTMAS DAY. -BLAES

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AS OF 805 PM THURSDAY...

24-HR TAF PERIOD: VFR CONDITIONS AND LIGHT WINDS WILL RULE THROUGH
THE TAF PERIOD IN ASSOCIATION WITH DRY HIGH PRESSURE EXTENDING INTO
THE REGION FROM THE NORTHWEST. ASIDE FROM LINGERING 6-8 KFT CEILINGS
THIS EVENING...EXPECT CEILINGS TO REMAIN AT OR ABOVE 10 KFT.

LOOKING AHEAD: FORECAST CONFIDENCE DECREASES LATE THIS WEEKEND
THROUGH EARLY NEXT WEEK. CEILINGS WILL REMAIN AT OR ABOVE 5 KFT AS A
FAST-MOVING UPPER LEVEL DISTURBANCE CROSSES THE REGION. CEILINGS
WILL LOWER DURING THE DAY SUNDAY AS A LOW PRESSURE SYSTEM DEVELOPS
ALONG THE GULF COAST...FALLING TO MVFR AND EVENTUALLY IFR/LIFR FROM
THE SOUTH SUNDAY NIGHT/MONDAY (LINGERING THROUGH TUESDAY) AS THE LOW
TRACKS NORTHEAST OFFSHORE THE CAROLINA COAST. SIGNIFICANT WEATHER IN
THE FORM OF LOW CEILINGS/VISBYS...HEAVY SHOWERS...AND STRONG WINDS
APPEAR LIKELY LATE TUE INTO WED AS A POWERFUL STORM SYSTEM DEVELOPS
OVER THE EASTERN CONUS. -VINCENT

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...BSD/BLS
SHORT TERM...BLS
LONG TERM...BLAES
AVIATION...VINCENT



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