Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 210035 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 645 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 /00Z SUNDAY THROUGH THURSDAY/...
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AS OF 700 PM SATURDAY... 24 HOUR TAF PERIOD: THICKER CLOUDINESS HAS MOVED OFFSHORE WITH ONSET OF DRYING ALOFT. CEILINGS ARE WIDESPREAD 3-6K FEET...WITH IFR CONDITIONS AT RDU AND FAY WHICH BOTH RECEIVED HIGHER PRECIP AMOUNTS TODAY. THE BOTTOM OF LOW LEVEL INVERSION IS AT 1200 FEET ON THIS EVENINGS GSO SOUNDING...WHICH WOULD BE A GOOD ESTIMATE FOR THE EVENTUAL CLOUD BASE AS THE COLUMN COOLS OVERNIGHT. THUSLY...WILL MAINTAIN PREDOMINANT IFR CEILINGS AT RDU AND FAY THROUGH SUNRISE...WITH IFR/MIFR CONDITIONS DEVELOPING 06-13Z AT THE REMAINING SITES. FOG IS A GOOD BET...BUT AM NOT CONFIDENT IN HOW DENSE/WIDESPREAD CONSIDERING THE AMOUNT OF CLOUD COVERAGE TO OFFSET RADIATIONAL COOLING...BUT THINK A PRE-SUNRISE PERIOD (09-13Z) OF IFR FOG IS MORE LIKELY THAN NOT. EXPECT VFR CONDITIONS TO RETURN AFTER 13-14Z AND CONTINUE THROUGH THE DAY WITH LIGHT (5KT-ISH) NORTHEAST WINDS. 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.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...ELLIS NEAR TERM...ELLIS SHORT TERM...CBL LONG TERM...CBL AVIATION...MLM

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