Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 230000
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
700 PM EST SAT NOV 22 2014

.SYNOPSIS...HIGH PRESSURE WILL CONTINUE TO SHIFT OFFSHORE TONIGHT. A
STRONG LOW PRESSURE MOVING FROM THE SOUTHERN PLAINS INTO THE GREAT
LAKES SUNDAY WILL SPREAD MOISTURE OVER THE REGION DURING THE DAY ON
SUNDAY. ANOTHER COLD FRONT WILL MOVE EAST ACROSS MUCH OF THE AREA
MONDAY...WITH LOW PRESSURE MOVING ALONG THE SOUTHEAST COAST TUESDAY
INTO WEDNESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 305 PM SATURDAY...

HIGH PRESSURE OFFSHORE EXTENDS EAST TO WEST ACROSS THE STATE
TODAY...WHILE A FEW PATCHES OF CIRRUS DRIFT OVERHEAD IN THE
SOUTHWESTERLY FLOW ALOFT.  OTHERWISE...REGIONAL VIS SAT IMAGERY
SHOWS VERY LITTLE CLOUD COVER UPSTREAM...WITH MOISTURE JUST NOW
BEGINNING TO SURGE INLAND FROM THE GOMEX ACROSS SOUTHERN GA/AL.
EXPECT SKIES WILL BE MOSTLY CLEAR FOR AT LEAST THE FIRST HALF OF
NIGHT...BEFORE THICKER CIRRUS AND CIRROSTRATUS BEGIN TO ADVECTION IN
FROM THE SOUTH.  IN ADDITION...MOISTURE RETURN AROUND THE SURFACE
HIGH MAY LEAD TO SOME STRATUS LATE TONIGHT....WITH SREF
PROBABILITIES SHOWING THE BEST CHANCE OVER THE WESTERN
PIEDMONT...WHICH SEEMS REASONABLE GIVEN THE AMOUNT OF DRY AIR
CURRENTLY OVER CENTRAL AND EASTERN NC.  LOWS ACROSS THE
NORTH...WHERE RADIATIONAL COOLING WILL BE BEST FOR MOST OF THE
NIGHT...MAY DIP INTO THE LOWER 30S...WHILE AREAS TO THE SOUTH WILL
SEE MID AND UPPER 30S.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 410 PM SATURDAY...

A SHORTWAVE TROUGH CURRENTLY OVER SOUTHWEST TX WILL EJECT
NORTHEASTWARD SUNDAY MORNING...DEAMPLIFYING AS IT LIFTS TOWARD THE
GREAT LAKES REGION.  WHILE THE SURFACE LOW WILL ALSO LIFT WELL WEST
OF THE MOUNTAINS...A 50-60KT LLJ WILL BRING PW OF OVER 1.75 INCHES
WITHIN THE ASSOCIATED WARM CONVEYOR BELT LATE SUNDAY EVENING/NIGHT.
BASED ON A CONSENSUS OF MODEL ISENTROPIC FIELDS...RAIN WILL BEGIN TO
SPREAD INTO THE AREA FORM THE SOUTH MID-MORNING... THOUGH PRECIP
WILL INITIALLY HAVE TO OVERCOME THE RATHER DRY AND ONLY SLOW
MOISTENING AIRMASS OVER NC.  THE HEAVIER PRECIP ACCOMPANYING THE
SURFACE/850MB WARM FRONTS WILL BEGIN TO SPREAD INTO THE AREA AFTER
21Z...AND IT LOOKS AS THOUGH THE 00-06Z TIME FRAME WILL BE THE BEST
FOR THE HEAVIEST RAIN.

TEMPS... WITH DEWPOINTS IN THE 30S IN THE WESTERN PIEDMONT EARLY
SUNDAY...EVAPORATIVE COOLING WILL LIKELY LEAD TO AT LEAST A
WEAK...STABLE WEDGE AIRMASS OVER THE NORTHWEST PIEDMONT.  HIGHS IN
THE TRIAD MAY STRUGGLE TO GET OUT OF THE UPPER 40S...WHILE TEMPS
WILL HAVE LITTLE MORE TIME TO WARM INTO THE 50S TO LOWER 60S TO THE
EAST.  TEMPS ARE THEN EXPECTED TO HOLD STEADY OR CONTINUE RISING
SLOWLY INTO THE UPPER 50S TO MID 60S OVERNIGHT AS THE WARM FRONT
SURGES NORTH THROUGH THE AREA.  WHETHER OR NOT THE WEDGE AIRMASS IS
ERODED IN THE NORTHWEST PIEDMONT...AS MODELS INDICATE...IS
UNCERTAIN.  BUT FOR MANY AREAS...HIGHS WILL LIKELY OCCUR WELL AFTER
SUNSET.

SEVERE THREAT... STRONG WARM ADVECTION WILL LEAD TO SOME WEAK
DESTABILIZATION...ELEVATED TO THE NORTHWEST AND NEAR SURFACE BASED IN
THE SOUTHEAST.  MODELS HAVE TRENDED A LITTLE FURTHER INLAND WITH THE
BETTER PUSH OF THE MARITIME AIR...WITH THE NAM SHOWING AS MUCH AS
200-600 J/KG MLCAPE AT KFAY AS DEWPOINTS RISE INTO THE MID 60S.
THIS APPEARS TO BE THE HIGHEST MLCAPE GENERATED BY ANY OPERATIONAL
NWP...WITH THE GFS/SREF SHOWING 100-300 J/KG...AND NOCTURNAL
STABILIZATION WILL FURTHER LIMIT CAPE. EFFECTIVE DEEP LAYER SHEAR
INCREASING TO 50-70KT SHOULD SUPPORT SOME LOW-TOPPED SUPERCELLULAR
STORMS EMBEDDED WITHIN THE BANDS OF SHOWERS AND STORMS CROSSING SC
AND SOUTHEASTERN NC.  IN ADDITION...THERE WILL BE A 4-6 HOUR WINDOW
LATE SUNDAY EVENING WHEN THE WEAK INSTABILITY WILL LINE UP WITH
STRONG CYCLONICALLY CURVED LOW-LEVEL HODOGRAPHS...AND LOW-END
TORNADO THREAT MAY EXIST ALONG AND EAST OF I-95.  FURTHER TO THE
NORTHWEST...ELEVATED INSTABILITY WILL ALSO BE WEAK..BUT DPVA FROM
THE VORT LOBE ATTENDANT TO THE MAIN SHORTWAVE MAY ALSO BE ENOUGH FOR
AN ISOLATED STORM EVEN BACK TOWARD THE TRIAD. -BLS

MON AND MON NIGHT: THE AXIS OF A 50 KT LLJ...IN DEEP SW FLOW
ALOFT...WILL CROSS CENTRAL NC DURING THE DAY MONDAY...IN ADVANCE OF
THE SURFACE COLD FRONT THAT IS FORECAST TO CROSS THE AREA LATE MON
AND MON EVENING - A SOLUTION BEST REPRESENTED BY THE SLOWER 12Z
ECMWF/NAM GUIDANCE. THE PASSAGE OF THE LLJ AND ASSOCIATED MOISTURE
TRANSPORT...THEN LATER FRONTAL FORCING/LOW LEVEL CONVERGENCE...WILL
SUPPORT SCATTERED SHOWERS - AND ISOLATED THUNDER IN AN AXIS OF LOWER
TO MIDDLE 60S SURFACE DEWPOINTS IN THE COASTAL PLAIN - ENDING FROM
WEST TO EAST DURING THE AFTERNOON AND EVENING HOURS. STRONG AND
INCREASINGLY UNIDIRECTIONAL DEEP LAYER FLOW...AFTER THE EARLY
MORNING WARM FRONTAL PASSAGE...WILL SUPPORT A CONDITIONAL RISK OF
SEVERE WEATHER IN THE COASTAL PLAIN. IN ADDITION...MIXING OF THE
STRONG LLJ WILL RESULT IN A VERY BREEZY SW WIND...SUSTAINED AROUND
20 MPH...WITH GUSTS BETWEEN 30 AND 40 MPH PROBABLE PER ~35 KT MIXED
LAYER WIND FORECASTS. HIGHS GENERALLY IN THE LOWER TO MIDDLE 70S.

AFTER PERHAPS A LINGERING SHOWER IN THE COASTAL PLAIN DURING THE
EVENING...COLD AND DRY ADVECTION...AND CLEARING...WILL DEVELOP
EASTWARD AND RESULT IN LOWS RANGING FROM AROUND 40 WEST TO LOWER 50S
EAST.  -MWS

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 350 PM SATURDAY...

TUE-WED: 1025 MB SURFACE HIGH PRESSURE WILL BUILD SOUTHEAST ACROSS
THE HIGH PLAINS TUE...THEN EASTWARD INTO THE MIDDLE ATLANTIC STATES
TUE NIGHT. MEANWHILE...THE APPROACH OF A POSITIVELY-TILTED TROUGH
ALOFT FROM THE MS VALLEY WILL INDUCE COASTAL CYCLOGENESIS...ALONG AN
OLD FRONTAL ZONE OFF THE SOUTH EAST...REFERENCED IN THE SHORT TERM
DISCUSSION ABOVE. THERE REMAINS CONSIDERABLE MODEL SPREAD WITH THE
DEVELOPMENT AND TRACK OF THIS COASTAL LOW AS IT LIFTS UP THE
SOUTHEAST AND MIDDLE ATLANTIC COASTS THROUGH MID WEEK...RANGING FROM
THE WELL OFFSHORE AND TOTALLY DRY-FOR-CENTRAL-NC CANADIAN SOLUTIONS
OF RECENT DAYS...TO THE CLOUDY AND WET SOLUTIONS DEPICTED BY THE
PAST FEW ECMWF AND GFS RUNS. GIVEN THE POSITIVE TILT AND ONLY SLOW
EASTWARD PROGRESSION OF THE TROUGH ALOFT...THE MORE WESTWARD (AND
WET) SOLUTIONS OF THE OFFSHORE FRONT AND INCIPIENT COASTAL LOW ARE
FAVORED...WITH A LOW TRACK MOST PROBABLE ALONG THE WESTERN WALL OF
THE GULF STREAM.

THE RESULT WOULD BE RAIN DEVELOPING FROM THE SOUTH LATE TUE AND
ESPECIALLY TUE NIGHT...WITH A COLD RAIN LIKELY AND  TEMPERATURES IN
THE UPPER 30S TO MIDDLE 40S...ON WED. THOUGH THE AFOREMENTIONED
PARENT POLAR HIGH IS FORECAST TO BE RELATIVELY WEAK (AROUND 1025 MB)
AND POSITIONED FARTHER SOUTH (OVER THE MIDDLE ATLANTIC STATES) THAN
IS TYPICAL FOR SNOW IN CENTRAL NC...THE TRACK OF THE COASTAL LOW AND
RESULTANT PARTIAL THICKNESSES ON THE WEST/NW SIDE SUGGEST AT LEAST A
THREAT OF A LITTLE WEST SNOW MIXING IN WITH THE RAIN OVER THE
PIEDMONT. GIVEN THE MARGINALLY COLD THERMODYNAMIC PROFILES...AND
FREEZING LEVELS AROUND 1000 FT OVER THE PIEDMONT PER GFS BUFR
FORECAST SOUNDINGS...ANY SUCH SNOW WOULD LIKELY BE DRIVEN BY
PRECIPITATION RATES...AND THE EXCEPTION RATHER THAN THE RULE.

WED NIGHT-SAT: MEDIUM RANGE GUIDANCE HAS COME INTO SOMEWHAT BETTER
AGREEMENT (THAN RECENT DAYS) REGARDING THE DEVELOPMENT OF A BROAD
TROUGH ALOFT FROM NORTH-CENTRAL CANADA TO THE MIDDLE ATLANTIC COAST
LATE WEEK INTO NEXT WEEKEND. SUCH A PATTERN WOULD FAVOR THE RE-
ESTABLISHMENT OF ARCTIC HIGH PRESSURE ACROSS THE NORTHERN HALF OF
THE CONUS EAST OF THE ROCKIES (JUST TO THE NORTH OF NC)...AND
MILDER/MORE MODIFIED HIGH PRESSURE OVER THE SOUTHEAST STATES. THIS
PATTERN OF NW TO WNW FLOW ALOFT WOULD RESULT IN DRY AND COOL
CONDITIONS OVER CENTRAL NC.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
AS OF 700 PM SATURDAY...

VFR CONDITIONS ARE EXPECTED TO CONTINUE ACROSS MOST OF THE AREA
THROUGH THE OVERNIGHT HOURS AS HIGH PRESSURE REMAINS JUST OFFSHORE.
HOWEVER...RETURN FLOW ON THE BACK SIDE OF THE DEPARTING HIGH
(ESPECIALLY ACROSS THE WESTERN PORTIONS OF NC) MAY BRING SOME
STRATUS ACROSS THE TRIAD LATE TONIGHT...BUT CONFIDENCE IN THIS
OCCURRENCE IS NOT VERY HIGH. ANY SUB VFR CONDITIONS THAT MAY DEVELOP
WILL IMPROVE BY MID-MORNING. HOWEVER...THESE VFR CONDITIONS WILL BE
SHORT LIVED AS AVIATION CONDITIONS DETERIORATE FROM THE SOUTH/WEST
TO NORTH/EAST AS A LOW PRESSURE SYSTEM APPROACHES FROM THE
SOUTHWEST. CIGS/VSBYS WILL GRADUALLY FALL INTO THE IFR RANGE THROUGH
THE AFTERNOON HOURS...AS PRECIP OVERSPREADS THE AREA FROM SOUTH TO
NORTH.

OUTLOOK...ADVERSE AVIATION CONDITIONS WILL CONTINUE INTO SUNDAY
NIGHT AS RAIN...HEAVY AT TIMES...IMPACTS THE AREA. A STRONG 50-60KT
LOW LEVEL JET MAY CAUSE SOME LOW-LEVEL WIND SHEAR...ESPECIALLY AT
KGSO/KINT...WHILE SOME 30-40KT WIND GUSTS MAY BE POSSIBLE OVER
EASTERN NC WHERE THUNDERSTORMS DEVELOP. CONDITIONS WILL IMPROVE SOME
ON MONDAY AS DRIER AIR ALOFT MOVES IN FROM THE WEST...THOUGH LOW
CEILINGS MAY LINGER AT EASTERN TERMINALS. THERE MAY ALSO BE SOME
GUSTY SOUTHWESTERLY WINDS (GUSTS UP TO 35-40 MPH) MONDAY AFTERNOON
AHEAD OF A COLD FRONT. BEYOND MONDAY..ANOTHER SYSTEM WILL IMPACT THE
REGION BY MIDWEEK...THOUGH THERE IS SOME UNCERTAINTY AS TO HOW MUCH
OF THE AREA WILL BE IMPACTED BY PRECIPITATION AND ADVERSE AVIATION
CONDITIONS AS A SURFACE LOW MOVES ALONG THE EAST COAST.

 &&

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

&&

$$

SYNOPSIS...DJF
NEAR TERM...BLS
SHORT TERM...BLS/MWS
LONG TERM...MWS
AVIATION...KRD/BLS


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