Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 202008
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
308 PM EST SAT DEC 20 2014

.SYNOPSIS...A SHORTWAVE LOW WILL EXIT THE AREA THIS AFTERNOON
INITIATING A BRIEF DRYING TREND FOR SUNDAY. THE PATTERN WILL BECOME
UNSETTLED AGAIN SUNDAY NIGHT AND INTO EARLY NEXT WEEK AS A LOW
PRESSURE SYSTEM DEVELOPS OFF OF THE SOUTHEAST COAST AND MOVES
NORTHWARD INTO THE CAROLINAS FOR THE BEGINNING OF NEXT WEEK.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
AS OF 245 PM SATURDAY...

TODAY AND TONIGHT: VERY LIGHT RAIN STILL FALLING ACROSS EASTERN
COUNTIES THIS HOUR BUT OTHERWISE MUCH OF THE CWA IS CLEARING OUT AS
FAR AS PRECIPITATION. CLOUD COVER IS A DIFFERENT STORY AS THERE IS A
PATCHWORK OF CEILINGS IN THE WAKE OF THE SHORTWAVE ANYWHERE FROM VFR
TO IFR. WESTERN STATIONS FOR THE MOST PART HAVE RETURNED TO VFR AND
SHOULD STAY THERE THROUGH THE AFTERNOON AS DRIER AIR BEGINS TO MOVE
IN BELOW 850 MB. THIS DRIER BOUNDARY LAYER SHOULD FILTER INTO
EASTERN SITES OVER THE NEXT SEVERAL HOURS. AT LEAST VFR CEILINGS
SHOULD HANG ON FOR THE REST OF THE DAY WHICH WILL KEEP MAX TEMPS
DOWN IN THE LOW 40S. SOME NORTHERN SITES WILL NOT GET OUT OF THE
UPPER 30S TODAY.

OVERNIGHT TONIGHT THERE IS A LOW CONFIDENCE FORECAST REGARDING ANY
POTENTIAL CLEARING. THE RESULT OF SUCH CLEARING WOULD BE A GREAT
OPPORTUNITY FOR FOG IN A WINDOW GENERALLY BETWEEN 6-12Z. THIS WILL
ALSO COINCIDE WITH A WINDOW OF POTENTIAL FREEZING TEMPERATURES AS
THICKNESS VALUES ARE AROUND 1310 AND MOST GUIDANCE SUGGESTING LOWS
TONIGHT IN THE UPPER 20S TO LOW 30S. CURRENT FORECAST SOUNDINGS SHOW
THE POTENTIAL ACROSS THE NORTHERN AREAS AND ARE PRETTY FAVORABLE FOR
FREEZING FOG EVEN WITH A POTENTIAL THIN BROKEN TO OVERCAST LAYER
AROUND 5 KFT. COVERAGE OF THE FOG WILL MOST LIKELY BE PATCHY BUT
COULD BE UPGRADED TO AREAS IN SOME LOCATIONS. IMPACTS OF THIS WILL
MOST LIKELY BE INCONSEQUENTIAL BUT CAN NOT RULE OUT SOME SLICK SPOTS
ON ELEVATED SURFACES...BUT IN ALL LIKELIHOOD ROADS SHOULD BE OK.


SUNDAY AND SUNDAY NIGHT: TEMPERATURES WILL QUICKLY REBOUND AND THE
SURFACE LAYER SHOULD DRY OUT AFTER 14Z OR SO. THE ATTENTION THEN
WILL TURN TO THE EVOLVING PATTERN FOR SUNDAY WHICH WILL BE THE
DEVELOPMENT OF TWO FEATURES...ONE BEING A COASTAL LOW ALONG THE
SOUTHEAST COAST AND THE SECOND BEING THE DEVELOPMENT OF A CAD WEDGE
ASSOCIATED WITH A HIGH PRESSURE OVER THE NORTHEAST. MOST OF THE
MOISTURE ASSOCIATED WITH THE LOW WILL REMAIN SOUTH OF THE AREA...SO
SUNDAY SHOULD BE DRY BUT WE WILL SEE SOME CLOUD COVER ENCROACHING
FROM THE SOUTHWEST...WHICH WILL INCREASE THROUGH SUNDAY AFTERNOON.
HIGHS ON SUNDAY WILL BE IN THE UPPER 40S NORTH TO LOW 50S SOUTH.

ON SUNDAY NIGHT THE ISENTROPIC LIFT WILL INCREASE SIGNIFICANTLY AS
THE LOW GETS CLOSER TO THE AREA AND THE WEDGE FRONT SHARPENS UP.
PRECIPITATION CHANCES WILL STEADILY INCREASE OVERNIGHT FROM SLIGHT
CHANCE EARLY ON TO NEAR DEFINITE BY MONDAY MORNING. SOUTHWESTERN
AREAS WILL SEE THE MOST QPF BEFORE DAYBREAK...MOST LIKELY BETWEEN
0.1-0.2 INCHES. BECAUSE OF THE CLOUD COVER...LOWS WILL MODERATE A
LITTLE...MID 30S TO LOWER 40S NORTHEAST TO SOUTHWEST.

&&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
AS OF 310 PM SATURDAY...

HIGH PRESSURE OVER THE CANADIAN MARITIMES WILL EXTEND SOUTHWARD INTO
THE MID ATLANTIC...AND WILL WEDGE SOUTH INTO THE CAROLINAS ON
MONDAY. MINOR SHORTWAVE IMPULSES IN ADVANCE OF THE AMPLIFYING
UPSTREAM TROUGH OVER THE CENTRAL US COUPLED WITH ANOTHER ENSUING SFC
WAVE DEVELOPMENT ALONG THE STALLED OFFSHORE FRONTAL ZONE WILL SPUR
ANOTHER WEAK ISENTROPICALLY DRIVEN PRECIP EVENT ACROSS CENTRAL NC ON
MONDAY. A MORE PRONOUNCED WARM NOSE WILL PRECLUDE ANY P-TYPE
ISSUES...WITH LIKELY TO CATEGORICAL RAIN  AND QPF AMOUNTS IN THE
0.25-0.50 RANGE...WITH THE HIGHEST AMOUNTS INLAND OVER THE MORE
STEEPLY SLOPED PORTION OF THE COLD DOME SURFACE OVER THE PIEDMONT.
MEASURABLE RAIN CHANCES REALLY DECREASE BY MONDAY EVENING AS WE LOSE
SATURATION ALOFT...BUT LIGHT...DRIZZLE AND/OR AT THE VERY LEAST FOG
WILL PERSIST OVERNIGHT AMIDST CONTINUED WEAK SOUTHERLY UPGLIDE.

LITTLE DIURNAL VARIATION THROUGH MONDAY NIGHT. HIGHS IN THE UPPER 30
NW TO MID/UPPER 40S SE. LOWS IN THE MID 30S NW TO NEAR-LOWER 40S SE.


 &&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 308 PM SATURDAY...

TUESDAY: ALTHOUGH THE PARENT HIGH WILL BE WELL REMOVED(OVER OF JUST
OFF THE CANADIAN MARITIMES)...INITIALLY WEAK SOUTHERLY UPGLIDE
DOWNSTREAM OF THE AMPLIFYING TROUGH WILL KEEP THE WEDGE OF COLD AIR
LOCKED FIRMLY IN PLACE ACROSS THE PIEDMONT UNDERNEATH A SHROUD OF
LOW CLOUDS AND POSSIBLY DRIZZLE...WITH A RETURN OF MEASURABLE RAIN
CHANCES BY THE LATE AFTERNOON/EVENING WITH THE RESURGENCE OF LOW-
LEVEL CONVERGENCE ALONG THE RETREATING WEDGE FRONT. MADE MINOR
ADJUSTMENTS TO INHERITED GRID FORECAST WHICH MAINTAINS A CLASSIC CAD
CLIMATOLOGY...BUT CONFIDENCE IS BELOW AVERAGE...ESPECIALLY ON THE
SOUTHERN/EASTERN FRINGES OF COLD DOME. HIGHS RANGING FROM MID 40S NW
TO NEAR 60 SOUTHEAST.

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT: MODELS ARE IN VERY GOOD
AGREEMENT REGARDING EVOLUTION OF A HIGH-AMPLITUDE UPPER TROUGH THAT
IS FORECAST TO ADVANCE SLOWLY EASTWARD
...LIKELY ASSUMING A NEGATIVE TILT AS IT CROSSES THE
SOUTHERN/CENTRAL APPALACHIANS ON WEDNESDAY. EXPECT WET CONDITIONS
TUESDAY NIGHT WITH THE PASSAGE OF THE WARM FRONT THROUGH THE
AREA...FOLLOWED BY  WET...WINDY AND POSSIBLY STORMY CONDITIONS
DURING THE DAY CHRISTMAS EVE AS THE OCCLUDED FRONT PUSHES THROUGH
THE AREA. MODELS HAVE BACKED OFF FROM THE TRIPLE POINT LOW ACROSS
THE CAROLINAS BUT REGARDLESS...DEEP LAYER SHEAR OF 50-60KTS WILL BE
MORE THAN  SUFFICIENT TO SUPPORT STRONG TO SEVERE CONVECTION. THE
BIGGEST QUESTION AT THIS POINT WILL BE THE AVAILABILITY/PRESENCE OF
WEAK INSTABILITY...WHICH MODELS CURRENTLY INDICATE MUCAPE 100-200
J/KG WITH WEAK LAPSE RATES ALOFT OF 5.0-5.5 C/KM. FOR NOW WILL ADD
AN ISOLATED CHANCE TO FAVORED CLIMO REGION OF THE SANDHILLS AND
COASTAL PLAIN. TEMPERATURES VERY CHALLENGING...WARMING TUESDAY NIGHT
WITH PASSAGE OF THE WEDGE FRONT INITIALLY AND THEN THE WARM FRONT
DURING THE PREDAWN HOURS. WARM SECTOR SHOULD EXTEND WELL INTO THE
PIEDMONT ON WEDNESDAY WITH MUCH OF THE AREA WARMING INTO THE
60S...WITH THE EXCEPTION OF THE NW PIEDMONT WHERE THEY MAY HOLD IN
THE 50S.  RAPIDLY CLEARING AND COOL AIR ADVECTION WILL COMMENCE
CHRISTMAS EVE EVENING/NIGHT WITH LOWS CHRISTMAS MORNING IN THE 30S.
DEEPENING SURFACE LOW OVER THE GREAT LAKES WILL RESULT IN BREEZY
CONDITIONS ON CHRISTMAS DAY. OTHERWISE DRY WITH SEASONABLE
TEMPERATURES CONTINUING INTO FRIDAY AS HIGH PRESSURE BUILDS IN FROM
THE NORTHERN GULF. NEXT SYSTEM WILL APPROACH THE AREA LATE
SATURDAY/SATURDAY NIGHT.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
AS OF 1240 PM SATURDAY...

24 HOUR TAF PERIOD: A REAL VARIATION IN AVIATION CONDITIONS OUT
THERE THIS AFTERNOON DEPENDING ON WHERE YOU ARE. IN GENERAL
PRECIPIATION HAS ENDED WEST OF HIGHWAY 1 BUT EAST OF HIGHWAY 1 SOME
LINGERING RAIN/SNOW SHOWERS WILL CONTINUE FOR THE NEXT COUPLE OF
HOURS AS A SHORTWAVE SYSTEM MOVES EASTWARD. IN THE WAKE OF THE
PRECIPIATION CONDITIONS RANGE ANYWHERE FROM VFR TO IFR WITH A LOT OF
VARIATION IN BETWEEN. THEREFORE IT WILL BE A LOW CONFIDENCE FORECAST
THROUGH THE AFTERNOON WITH SOME IMPROVEMENT IN CONFIDENCE LATER IN
THE TAF PERIOD. AFTER PRECIPITATION WRAPS UP BY 21Z OR SO...THERE IS
SOME QUESTION TO WHETHER OR NOT CLOUD COVER WILL SCATTER OUT. IT MAY
DECREASE A BIT IN COVERAGE BUT MORE LIKELY BROKEN CEILINGS WILL
PREVAIL...MAINLY BETWEEN 5-6 KFT. THE DEGREE OF CLEARING WILL SET
THE STAGE FOR ANOTHER LOW CONFIDENCE FORECAST OVERNIGHT AND THAT IS
IN REGARDS TO WHETHER OR NOT WE WILL SEE SOME FOG. THIS WILL BE MOST
LIKELY AT KINT...KGSO AND POSSIBLY KRDU AS WELL. THE TIMING IS A
LITTLE UNCERTAIN BUT A BIG WINDOW OF 6-12Z WOULD COVER MOST OF THE
POSSIBLE TIMING. THERE IS STILL A THIN LAYER OF MOISTURE AT 6KFT
DURING THE OVERNIGHT HOURS THAT COULD KEEP BROKEN TO OVERCAST
CEILINGS AROUND OVERNIGHT. DESPITE THIS...FORECAST SOUNDINGS STILL
CALL FOR SATURATION AT THE SURFACE. IN ADDITION...THE DEGREE OF
CLEARING WILL ALSO AFFECT TEMPERATURES. ENOUGH OF A CLEARING COULD
RESULT IN SOME FREEZING FOG...MAINLY BETWEEN 9-12Z AT THE THREE
SITES MENTIONED BEFORE. AGAIN THIS IS A LOW CONFIDENCE FORECAST BUT
THERE IS ENOUGH OF AN INDICATION TO PUT FOG IN THE TAFS AND MENTION
THE POSSIBILITY OF FREEZING FOG IN THE DISCUSSION. FURTHER SOUTH AND
EAST FOG IS NOT AS LIKELY BUT CANNOT BE RULED OUT.

AFTER SUNRISE THINGS CALM DOWN AND CONDITIONS SHOULD FOR THE MOST
PART RETURN TO VFR WITH SOME LINGERING MVFR CEILINGS POSSIBLE ON
SUNDAY AFTERNOON. WINDS WILL BE LIGHT OUT OF THE NORTHEAST AROUND 5
KTS.

LONG TERM: UNSETTLED PATTERN FOR THE BEGINNING OF NEXT WEEK WILL
RESULT IN SOME ADVERSE AVIATION CONDITIONS POSSIBLE FOR MONDAY
THROUGH WEDNESDAY BEFORE CLEARING OUT AND RETURNING TO VFR FOR
CHRISTMAS DAY.

&&

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

&&

$$

SYNOPSIS...ELLIS
NEAR TERM...ELLIS
SHORT TERM...CBL
LONG TERM...CBL
AVIATION...ELLIS


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