Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 200815 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 257 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 315 AM SATURDAY... TODAY...S/W EXITING THE DEEP SOUTH EARLY THIS MORNING PROJECTED TO CROSS NEAR OR JUST SOUTH OF CENTRAL NC LATE THIS MORNING-EARLY THIS AFTERNOON. THIS FEATURE APPEARS TO BE ADVANCING A LITTLE FARTHER TO THE NORTH THAN WHAT PREVIOUS MODEL RUNS HAD DEPICTED. STILL EXPECT BULK OF LIGHT PRECIPITATION ASSOCIATED WITH THIS FEATURE TO AFFECT MAINLY OUR SOUTHERN COUNTIES. HOWEVER...POTENTIAL FOR SPOTTY LIGHT PRECIP TO EXTEND AS FAR NORTH AS THE I-40 CORRIDOR BETWEEN THE TRIAD AND THE TRIANGLE THIS MORNING. THUS HAVE ADJUSTED POPS A LITTLE HIGHER ACROSS THE NORTHERN PIEDMONT WHILE MAINTAINING LIKELY POPS ACROSS THE SOUTH. BULK OF LIFT ASSOCIATED WITH THE S/W WILL BEGIN TO EXIT OUR REGION BY MID DAY-EARLY AFTERNOON. THUS SHOULD SEE PRECIP COVERAGE DIMINISH OVER MOST OF THE PIEDMONT BY EARLY AFTERNOON. DUE TO CLOSE PROXIMITY OF THE S/W...PRECIP MAY PERSIST WELL INTO THE AFTERNOON ACROSS THE SANDHILLS AND SOUTHERN COASTAL PLAIN. PARTIAL THICKNESSES OFF THE LATEST MODEL GUIDANCE IN CONJUNCTION WITH EVAPORATIVE COOLING SUGGEST DECENT PROBABILITY OF RAIN MIXED WITH SNOW ACROSS THE NW PIEDMONT EARLY THIS MORNING. HIGH TEMPS TODAY DEPENDENT ON EXTENT OF PRECIP. EXTENSIVE CLOUDINESS WILL LIMIT INSOLATION. IF PRECIP MORE WIDESPREAD THAN ANTICIPATED ACROSS THE PIEDMONT/NORTHERN COASTAL PLAIN...TEMPS MAY STRUGGLE TO MAKE IT OUT OF THE 30S. OVERALL...TEMPS TODAY WILL BE A SOLID 7-10 DEGREES BELOW NORMAL. MAX TEMPS GENERALLY 40-45 DEGREES. 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.
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
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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.
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&& .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 /06Z SATURDAY THROUGH WEDNESDAY/... AS OF 105 AM SATURDAY... AN UPPER LEVEL DISTURBANCE ADVANCING EAST ACROSS THE DEEP SOUTH WILL PASS SOUTH OF CENTRAL NC LATER THIS MORNING THROUGH EARLY AFTERNOON. THIS WEATHER SYSTEM WILL INCREASE CLOUDINESS ALONG WITH PATCHES OF LIGHT RAIN OVER OUR REGION BY DAYBREAK. EXPECT CEILINGS TO LOWER TO THE 4000-6000FT LAYER WITH SCATTERED PATCHES OF STRATOCU WITH CEILINGS 1500-2500FT POSSIBLE BY LATE MORNING THROUGH THE AFTERNOON...MAINLY SOUTH OF HIGHWAY 64. THIS THREAT FOR LOWER CEILINGS WILL AFFECT THE KFAY TERMINAL. SURFACE WINDS WILL BECOME NELY WITH SUSTAINED WINDS AOB 10KTS. WEAK HIGH PRESSURE WILL BUILD INTO CENTRAL NC FROM NORTH TONIGHT AND SUNDAY...MAINTAINING MOSTLY VFR CONDITIONS. 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...WSS SHORT TERM...WSS LONG TERM...BSD AVIATION...WSS

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