Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201440 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 940 AM EST SAT DEC 20 2014 .SYNOPSIS...A FAST MOVING DISTURBANCE WILL TRACK EASTWARD ACROSS THE REGION TODAY. WEAK HIGH PRESSURE WILL EXTEND ACROSS CENTRAL NORTH CAROLINA SUNDAY. ANOTHER DISTURBANCE AND ASSOCIATED SURFACE LOW PRESSURE SYSTEM WILL AFFECT OUR AREA SUNDAY NIGHT INTO MONDAY. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 940 AM SATURDAY... FOR TODAY: SHORT WAVE CONTINUES TO CROSS THE CWA THIS MORNING. HRRR DEPICTS THE WETBULB ZERO LINE ACROSS THE I-40 CORRIDOR THROUGH THE TRIAD AND TRIANGLE AND THEN UP THE I-95 CORRIDOR. STILL SOME POCKETS OF BRIEF SNOW OUT THERE BUT TEMPERATURES STARTING TO RISE AND PRECIPITATION RATES HAVE BACKED OFF AND THUS SNOW REPORTS ARE BECOMING MORE AND MORE SCARCE ACROSS THE AREA. THIS TREND WILL CONTINUE WITH ALL SNOW CEASING OVER THE NEXT HOUR OR TWO. PRECIPITATION IN THE FORM OF RAIN WILL CONTINUE TO LINGER ON BUT THE BACK EDGE OF THE MOISTURE HAS ALREADY REACHED SOME OF THE WESTERN COUNTIES AND WILL PROGRESS FROM WEST TO EAST ACROSS THE CWA. THEREFORE EXPECT MOST OF THE PRECIPITATION TO BE DONE THIS AFTERNOON WITH THE SOUTHERN AND EASTERN COUNTIES MOST LIKELY TO HANG ONTO IT THE LONGEST. ONLY A FEW HUNDREDTHS OF AN INCH OF LIQUID ACCUMULATION EXPECTED. SKIES SHOULD REMAIN OVERCAST FOR THE DAY AND THIS WILL HELP KEEP TEMPERATURES DOWN BELOW NORMAL WITH HIGHS IN THE LOW TO MIDDLE 40S EXPECTED ACROSS THE CWA. COOLEST TEMPS IN THE NORTH AND POTENTIALLY WARMER IN THE SOUTH BUT IF PRECIPITATION HANGS ON THE MIDDLE 40S COULD BE TOO HIGH THERE AS WELL. NORTHEASTERLY WINDS AT AROUND 5 KTS WILL CONTINUE TODAY. -ELLIS TONIGHT...WEAK SUBSIDENCE IN THE WAKE OF THE DEPARTING S/W AND SFC RIDGE NOSING SWD INTO OUR REGION SHOULD AID TO DIMINISH THE CLOUD COVERAGE OVER OUR REGION. MODELS DIFFER ON EXTENT OF CLEARING WITH THE GFS A LITTLE MORE AGGRESSIVE THAN MOST. ANY PRECIP OCCURRING AT SUNSET ACROSS THE FAR SE SHOULD DIMINISH/DISSIPATE BEFORE 10 PM. STILL EXPECT SOME RESIDUAL CLOUDINESS OVERNIGHT. IF GFS VERIFIES BEST...THEN MIN TEMPS TONIGHT MAY END UP BEING 2-4 DEGREES COLDER THAN CURRENTLY FORECAST. MIN TEMPS UPPER 20S/AROUND 30 NORTH TO THE LOWER 30S SOUTH. -WSS
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... AS OF 315 AM SATURDAY... SFC RIDGE EXTENDS SOUTH ACROSS THE AREA...AIDED ALOFT BY A MINOR S/W RIDGE. THIS SHOULD PROVIDE PARTLY-MOSTLY SUNNY SKIES TO START THE DAY. A S/W EXITING THE SOUTHERN PLAINS WILL BACK THE FLOW ALOFT TO A SWLY FLOW AND BEGIN TO ADVANCE MID-HIGH LEVEL CLOUDINESS FROM THE SOUTH LATE IN THE DAY. LOW LEVEL THICKNESSES IN THE 1315M- 1330M RANGE...SUPPORTIVE OF MAX TEMPS ABOUT A CATEGORY OR TWO BELOW NORMAL. MAX TEMPS NEAR 50-LOWER 50S. IF CLOUDS ARE DELAYED ACROSS THE SOUTH...MAX TEMPS MAY END UP BEING 2-3 DEGREES WARMER. SUNDAY NIGHT...SOUTHERN STREAM S/W PROJECTED TO CROSS THE LOWER MS VALLEY AND INDUCE WEAK SFC WAVE DEVELOPMENT OFF THE SC COAST BY EARLY MONDAY. WHILE A DRY AIR SFC RIDGE WILL MAINTAIN A PRESENCE OVER CENTRAL NC...DEVELOPING SLY FLOW A FEW THOUSAND FEET ALOFT WILL INITIATE AN OVERRUNNING EVENT LEADING TO A CLASSICAL OR HYBRID COLD AIR DAMMING EVENT. AS SLY FLOW STRENGTHENS TOWARD 06Z...EXPECT RAIN TO OVERSPREAD THE REGION FROM THE SOUTH...LOCKING IN THE CAD AIR MASS. WILL START OUT WITH CHANCE POPS ACROSS THE SOUTH IN THE EVENING...RAMPING UP TO LIKELY POPS ACROSS THE SOUTH HALF AFTER MIDNIGHT...AND CHANCE POPS ELSEWHERE. IF MODEL TRENDS CONTINUE IN LATER MODEL RUNS...AN INCREASE IN POPS TO LIKELY NORTH AND CATEGORICAL SOUTH WOULD BE WARRANTED. MIN TEMPS MAINLY 35-40 DEGREES. && .LONG TERM /MONDAY THROUGH FRIDAY/... AS OF 255 AM SATURDAY... MONDAY THROUGH WEDNESDAY: A SOUTHERN STREAM S/W DISTURBANCE WILL LIFT NORTHEASTWARD OUT FROM THE GULF COAST STATES ON SUNDAY NIGHT INTO MONDAY MORNING... SPREADING WIDESPREAD RAIN ACROSS ALL OF CENTRAL NC AS ISENTROPIC LIFT RAMPS UP. WITH A 1030 MB SURFACE HIGH STILL EXPECTED TO BE EXTENDING SOUTHWARD INTO OUR AREA (AS IT EVER SO SLOWLY SHIFTS EASTWARD) EXPECT WE WILL SEE A PRONOUNCED DAMMING EVENT DEVELOP.... WITH TEMPS FALLING INTO THE MID TO UPPER 30S MONDAY MORNING ACROSS THE NORTHERN AND NORTHWEST PIEDMONT... WITH TEMPS IN THE 40S ELSEWHERE. HOWEVER... BOTH THE GFS AND ECMWF CONTINUE TO DEPICT AN ALL RAIN EVENT ACROSS THE AREA... WITH A PRONOUNCED WARM NOES AT AROUND 4-5KFT COMBINED WITH SURFACE WETBULB TEMPS IN THE MID 30S AT WORST WHEN THE PRECIP SPREADS INTO THE AREA. THE MORE SUBSTANTIAL PRECIP WILL COME TO AN END BY EARLY TO MID AFTERNOON AS THE BEST MOIST ISENTROPIC UPGLIDE BEGINS TO WANE ALONG WITH DRIER AIR ALOFT FILTERING INTO THE AREA. STILL WE SHOULD SEE SOME LINGERING AREAS OF LIGHT RAIN AND DRIZZLE REMAINING. WITH A GOOD AREAWIDE QUARTER TO A HALF INCH OF RAIN EXPECTED WE SHOULD BE ABLE TO LOCK IN THE DAMMING AIRMASS. THUS.. HAVE LOWERED HIGH TEMPS... ESPECIALLY ACROSS THE EASTERN/SOUTHEASTERN PORTION OF CENTRAL NC. EXPECT HIGH TEMPS TO RANGE FROM THE UPPER 30S N/NW TO THE MID TO UPPER 40S E/SE. TEMPS MONDAY NIGHT/TUESDAY MORNING ARE EXPECTED TO REMAIN NEAR STEADY OR EVEN SLOWLY BEGIN TO RISE A LITTLE. THUS... WILL GO WITH LOWS RANGING FROM THE UPPER 30S TO MID 40S. A NORTHERN STREAM DISTURBANCE WILL HAVE FORMED A DEEP TROUGH BY TUESDAY MORNING WITH STACKED LOW PRESSURE OVER THE UPPER MIDWEST. BOTH THE GFS AND ECMWF ARE IN GOOD AGREEMENT IN SHOWING THE DEEP ASSOCIATED TROUGH AXIS SHIFTING EASTWARD ON TUESDAY INTO WEDNESDAY WHILE TAKING ON MORE OF A NEGATIVE TILT... WITH THE ASSOCIATED SURFACE FRONT (AND A POSSIBLE TRIPLE POINT LOW) MOVING ACROSS CENTRAL NC ON WEDNESDAY MORNING INTO THE EARLY AFTERNOON (AS IT STANDS NOW... STILL SEVERAL DAYS OUT THOUGH). QUESTIONS REMAIN AS TO WHERE A POSSIBLE TRIPLE POINT LOW MAY FORM THOUGH... AS FINER DETAILS LIKE THIS ARE HARD TO NAIL DOWN THIS FAR OUT IN THE FORECAST. HOWEVER... WITH THE POTENTIAL FOR A RETREATING CAD BOUNDARY AND STRENGTHENING LOW LEVEL WIND FIELD... WE WILL NEED TO KEEP AN EYE ON HOW THIS SYSTEM COMES TOGETHER. THIS WOULD BE A HSLC TYPE OF SYSTEM. GIVEN THE TIME OF YEAR IT IS QUITE HARD TO GET THE NEEDED INSTABILITY FOR POSSIBLE SEVERE STORMS THOUGH. AS THE EFFECTIVE FRONT APPROACHES AND MOVES THROUGH THE AREA ON WEDNESDAY MORNING INTO THE AFTERNOON WE SHOULD SEE A BAND OF RAIN/SHOWERS ALONG AND IN ADVANCE OF IT (WITH POSSIBLY A FEW THUNDERSTORMS)... WITH THINGS DRYING OUT QUICKLY BEHIND THE EFFECTIVE FRONT ON WEDNESDAY AFTERNOON. HIGHS ON TUESDAY WILL BE TRICKY AND DEPEND ON HOW MUCH THE CAD BOUNDARY RETREATS. FOR NOW WILL GO WITH HIGHS IN THE UPPER 40S NW TO AROUND 60S SE. TEMPS BY WEDNESDAY MORNING WILL NOT FALL MUCH... WITH LOWS WEDNESDAY MORNING IN THE UPPER 40S NW TO MID 50S SE/E. TEMPS ARE EXPECTED TO WARM WEDNESDAY AHEAD OF THE FRONT INTO THE UPPER 50S NW TO THE UPPER 60S E. WEDNESDAY NIGHT THROUGH THURSDAY: WE SHOULD SEE RAPID CLEARING ON WEDNESDAY NIGHT AND CONTINUING FOR THE REST OF THE WEEK... WITH A RETURN TO QUITE WEATHER. LOWS THURSDAY MORNING ARE EXPECTED TO BE IN THE 30S... WITH HIGHS THURSDAY AND FRIDAY AFTERNOONS IN THE 50S. WE COULD BE A BIT BREEZE ON THURSDAY AS MODELS ARE SHOWING THE POTENTIAL FOR SUSTAINED WINDS OUT OF THE WSW IN THE 14 TO 20 MPH RANGE... WITH MAYBE SOME GUSTS OF UP TO 25 MPH. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... AS OF 639 AM SATURDAY... AN UPPER LEVEL DISTURBANCE ADVANCING EAST ACROSS GEORGIA EARLY THIS MORNING WILL PASS SOUTH OF CENTRAL NC LATER THIS MORNING THROUGH EARLY AFTERNOON. THIS WEATHER SYSTEM WILL SPREAD MOISTURE OVERHEAD ALONG WITH LIFT TO PRODUCE PATCHES FO LIGHT RAIN...ESPECIALLY SOUTH OF HIGHWAY 64. SOME OF THE LIGHT RAIN MAY MIX WITH A LITTLE SNOW ALONG AND NORTH OF TEH I-40 CORRIDOR BETWEEN THE TRIAD AND KRDU THROUGH 15Z. OTHERWISE EXPECT WIDESPREAD CEILINGS 5000-8000FT WITH POCKETS OF MVFR CEILINGS (1500-2500FT) POSSIBLE. SURFACE WINDS WILL BECOME NELY WITH SUSTAINED WINDS AOB 10KTS. WEAK HIGH PRESSURE WILL BUILD INTO CENTRAL NC FROM NORTH TONIGHT AND SUNDAY. DRY AIR ASSOCIATED WITH THE RIDGE SHOULD AID TO DIMINISH SOME OF THE CLOUD COVERAGE LATER THIS EVENING INTO THE OVERNIGHT HOURS. A STRONGER UPPER LEVEL DISTURBANCE AND ASSOCIATED SURFACE LOW PRESSURE SYSTEM WILL BRING A HIGH PROBABILITY OF ADVERSE AVIATION CONDITIONS TO CENTRAL NC SUNDAY NIGHT INTO MONDAY. WIDESPREAD MVFR/IFR CEILINGS AND AREAS OF RAIN ARE EXPECTED. THESE CONDITIONS WILL SPREAD NORTH INTO SOUTHERN SECTIONS OF CENTRAL NC SHORTLY AFTER SUNSET SUNDAY THEN CONTINUE NORTHWARD SUNDAY NIGHT. A DECENT TO HIGH THREAT FOR MVFR CEILINGS WILL LINGER MONDAY NIGHT INTO TUESDAY AS THE LOW LEVEL AIR MASS REMAINS MOIST. A STRONG COLD FRONT WILL APPROACH TUESDAY NIGHT AND CROSS THE REGION WEDNESDAY. GUSTY SLY WINDS ARE EXPECTED AHEAD OF THE FRONT TUESDAY NIGHT ALONG WITH HEAVY SHOWERS AND POSSIBLY A THUNDERSTORM OR TWO. THE FRONT WILL CROSS THE AREA WEDNESDAY WITH BLUSTERY WESTERLY WINDS EXPECTED IN ITS WAKE. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...ELLIS/WSS SHORT TERM...WSS LONG TERM...BSD AVIATION...WSS

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