Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 020258 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 955 PM EST SUN MAR 1 2015 .SYNOPSIS...WEAK BUT COOL HIGH PRESSURE WILL HOLD OVER THE AREA THROUGH TONIGHT. A COLD FRONT WILL PUSH SOUTHWARD THROUGH NORTH CAROLINA ON MONDAY... THEN SETTLE JUST TO OUR SOUTH MONDAY NIGHT AS HIGH PRESSURE NOSES IN FROM THE NORTH. MOIST AIR RIDING UP AND OVER THIS STATIONARY FRONT WILL BRING UNSETTLED WEATHER FOR TUESDAY INTO WEDNESDAY. && .NEAR TERM /THROUGH TODAY/... AS OF 955 PM SUNDAY... A COLD AIR DAMMING AIRMASS IS FIRMLY WEDGED IN PLACE AND WILL REMAIN SO UNTIL A COLD FRONT MOVING IN FROM THE NORTHWEST PROVIDES A BRIEF REPRIEVE ON MONDAY. A SURFACE HIGH ASSOCIATED WITH THE CAD COLD POOL HAS DRIFTED SOUTH TOWARD THE SAVANNAH RIVER BASIN THIS EVENING. ALL MEASURABLE PRECIP HAS SHIFTED EAST OF THE AREA AND THE MAIN FORECAST CONCERN OVERNIGHT IS THE POTENTIAL FOR FOG DEVELOPMENT AS SOME DRIER AIR MOVES IN BETWEEN 925MB AND 700MB. WHILE FORECAST SOUNDINGS DON`T SHOW THE STRONGEST SIGNAL FOR DENSE FOG...STRATUS HAS BEEN SLOWLY LOWERING IN THE PAST COUPLE OF HOURS AND VISIBILITIES HAVE BEEN FALLING OVER THE SOUTHERN FOOTHILLS BEHIND A NOTICEABLE (ON IR IMAGERY) BACK-EDGE OF DEEPER MOISTURE. THE MAIN COUNTER TO WIDESPREAD FOG WILL BE A SLOWLY TIGHTENING PRESSURE GRADIENT IN RESPONSE TO THE COLD FRONT MOVING THROUGH THE OHIO VALLEY....MAINLY ACROSS THE NORTH-NORTHWEST PORTIONS OF THE CWA. A DENSE FOG ADVISORY MAY BE NEEDED IN THE NEXT FEW HOURS...ESPECIALLY FOR THE SOUTHERN HALF OF THE AREA. OTHERWISE... TEMPS WILL HOVER PRETTY CLOSE TO THEIR CURRENT VALUES IN THE MID AND UPPER 30S FOR MUCH OF THE NIGHT. -BLS FOR MON/MON NIGHT: A POTENT NORTHERN STREAM SHORTWAVE TROUGH CROSSING THE GREAT LAKES/ST LAWRENCE VALLEY/NORTHEAST LATE TONIGHT/MONDAY WILL HELP PUSH A WEAK FRONT SOUTHWARD INTO AND THROUGH NC MONDAY... AND AFTER A MURKY AND GRAY MONDAY MORNING... THIS MECHANISM WILL FINALLY SCOUR OUT THE LOW LEVEL MOIST/STABLE POOL FROM NNW TO SSE DURING THE DAY. MODELS DEPICT ENOUGH LOW AND MID LEVEL MOISTURE HOLDING ON OVER SRN NC NEAR THE SOUTHWARD-INCHING FRONTAL ZONE WITH SUFFICIENT LINGERING LOW LEVEL MOISTURE TRANSPORT TO SUPPORT A LOW CHANCE OF SOME PATCHY LIGHT RAIN OVER THE SRN CWA MON FROM LATE MORNING THROUGH MID AFTERNOON... WHILE FURTHER NORTH... WE SHOULD TREND TOWARD PARTIAL CLEARING AS DRIER LOW LEVEL AIR ATTEMPTS TO BUILD IN. HAVE OPTED TO STAY ON THE LOW END OF GUIDANCE FOR HIGHS MONDAY (NEAR 50 NORTH TO THE UPPER 50S SOUTH) AS THERE IS LIKELY TO BE A DELAY AND LIMIT TO THE PARTIAL CLEARING... HOWEVER IF LATER FORECASTS TREND TOWARD MORE SUNSHINE TOMORROW... THESE MAY NEED TO BE BUMPED UP A CATEGORY OR SO. THE RELATIVELY QUIET WEATHER WILL BE SHORT-LIVED... NOT A SURPRISE GIVEN THE STRONG JET LEVEL WINDS OVER THE CENTRAL/SRN CONUS FOSTERING AN ACTIVE WEATHER CYCLE. AN APPROACHING WEAK LOW LEVEL WAVE AND PRECEDING SURGE IN MOISTURE TRANSPORT INTO THE MIDSOUTH AND SOUTHERN APPALACHIANS WILL SUPPORT A SMALL CHANCE POP IN THE SW CWA LATE MON NIGHT. LOWS FROM AROUND 30 NE TO MID-UPPER 30S FAR SOUTHWEST. -GIH && .SHORT TERM /TUESDAY/... AS OF 250 PM SUNDAY... A CAD SCENARIO IS PROGGED TO DEVELOP ON TUESDAY AS A 1032 HIGH TO OUR NORTH DRIFTS EAST OUT INTO THE ATLANTIC...AND FLOW ALOFT BACKS FROM WNW IN THE MORNING TO SW BY AFTERNOON. WITH ISENTROPIC UPGLIDE INCREASING AS 850MB FLOW BACKS TO SW AND INCREASES...LOOK FOR LIGHT RAIN TO DEVELOP TUESDAY MORNING AND LINGER INTO THE AFTERNOON...WITH MODELS SUGGESTING QPF WILL REMAIN AOB 0.15". AS ALWAYS THE CASE WITH CAD...TEMPS WILL REMAIN BELOW GUIDANCE AND WELL BELOW NORMAL...UPPER 30S NW TO AROUND 50 SE. WHILE WE HAVE LOW TEMPS AROUND FREEZING ALONG AND NORTH OF HWY 64 TUESDAY MORNING...THE COMBINATION OF THE LIGHT INTENSITY OF THE RAIN AND BORDERLINE FREEZING TEMPS...FORECAST SOUNDINGS SUGGEST VERY LITTLE IF ANY FREEZING RAIN THREAT ACROSS OUR NORTHERN ZONES TUESDAY MORNING. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... AS OF 250 PM SUNDAY... TUESDAY NIGHT...THE NEXT COLD FRONT WILL APPROACH...AND WITH INCREASING SW LOW LEVEL FLOW AHEAD OF IT...THE CAD SHOULD SCOUR OUT WITH TEMPS TUE NIGHT ACTUALLY RISING THRU THE NIGHT WITH VIGOROUS WAA AHEAD OF THE FRONT. IN FACT...BY- OR SHORTLY AFTER SUNRISE WED...TEMPS WILL BE IN THE 50S ACROSS OUR ENTIRE CWA. WITH FROPA DURING THE AFTERNOON...WE COULD SEE TEMPS RISE WELL INTO THE 60S DURING THE MORNING...PERHAPS BREAKING THE 70 DEGREE MARK ACROSS OUR SE ZONES. AS FOR RAIN CHANCES...LOOK FOR POPS TO INCREASE FROM NW TO SE THRU THE DAY WED...WHILE IT STILL LOOKS LIKE THE BULK OF THE PRECIP WILL BE FOUND RIGHT ALONG OR JUST BEHIND THE FRONT...WHICH WILL LINGER WEDNESDAY NIGHT THROUGH MUCH OF THE DAY THURSDAY AS MIDLEVEL FLOW BECOMES PARALLEL TO THE FRONT...AND A STEADY FETCH OF DEEP MOISTURE IS TRANSPORTED OVERTOP A COOLING POST-FRONTAL LOW LEVEL AIRMASS. SPEAKING OF THE COOLING LOW LEVEL AIRMASS...LOW LEVEL THICKNESSES ARE PROGGED TO PLUMMET IN THE WAKE OF THE FRONT...FROM ~1380M 00Z THU TO ~1265M BY 10Z THU. SOME OF THE GUIDANCE SUGGESTS TEMPS MAY HOLD IN THE 20S DURING THE DAY THU! GIVEN THE AFOREMENTIONED LINGERING MOISTURE PLUME...ASSUMING THIS MODEL SOLUTION HOLDS...ITS BEGINNING TO LOOK A LITTLE MORE LIKELY THAT WE MAY BE DEALING WITH SOME SORT OF WINTER P-TYPE EVENT DURING THE DAYTIME THURSDAY. THE MAIN QUESTION IS HOW MUCH...AS QPF PROGS STILL VARY QUITE A BIT...WITH GFS QPF ROUGHLY TWICE AS MUCH AS THE ECMWF DURING THE 12Z THU TO 00Z FRI PERIOD. PLEASE STAY TUNED! LATEST GFS AND ECMWF ARE IN BETTER AGREEMENT DURING THE LATE-WEEK AND WEEKEND TIMEFRAME...WITH THE OPERATIONAL RUNS BOTH SHOWING THE MOISTURE PLUMES PUSHING SOUTH OF OUR CWA BY 06Z FRIDAY...THEN DRY WEATHER FOR OUR CWA FRIDAY THROUGH SATURDAY WITH HIGH PRESSURE BUILDING OVER THE AREA. LOW LEVEL THICKNESS PROGS RECOVER QUITE QUICKLY DURING THIS TIME...BUT THAT MAY NEED ADJUSTMENT DEPENDING ON WHAT HAPPENS THURSDAY. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... AS OF 810 PM SUNDAY... IN ASSOCIATION WITH A LINGERING COLD AIR DAMMING REGIME CHARACTERIZED BY A CHILLY; SATURATED; AND STABLE LAYER OF AIR IN THE NEAR SURFACE LAYER...INITIALLY MAINLY IFR CONDITIONS...TO SCATTERED MVFR-VFR ONES INCLUDING AT TRIAD TAF SITES...WILL DETERIORATE TO LIFR TONIGHT...THEN IMPROVE TO VFR BY MID-LATE MORNING MONDAY. ANY LINGERING LIGHT RAIN AT KRWI WILL MOVE EAST THROUGH 02Z...WITH OCCASIONAL DRIZZLE EXPECTED OTHERWISE AND ELSEWHERE OVERNIGHT. AN ALTERNATE BUT LESS LIKELY SCENARIO IS THAT SSW WINDS WILL INCREASE AND MIX TO THE SURFACE TONIGHT...IN RESPONSE TO A TIGHTENING MSL PRESSURE GRADIENT AHEAD OF AN APPROACHING COLD FRONT. THE ASSOCIATED MIXING COULD THEORETICALLY MIX OUT THE LOW CLOUDS MUCH EARLIER THAN CURRENTLY REFLECTED IN THE TAFS...OR KEEP THE LIFR CONDITIONS FROM SETTING IN ALTOGETHER. THOUGH CURRENT OBSERVATIONAL TRENDS WOULD SUGGEST THAT PROCESS MAY INDEED ALREADY BE UNDERWAY... PARTICULARLY AT TRIAD TAF SITES WHERE THE LOW OVERCAST HAD ALMOST COMPLETELY SCATTERED OUT AS OF 01Z...THE OVERWHELMING CONSENSUS OF OTHER FACTORS/FORCING MECHANISMS FOR LOW STRATUS/FOG SUGGESTS THIS ALTERNATE SCENARIO IS IMPROBABLE - ONLY AROUND 10-20 PERCENT - AND THAT THE NEAR TERM IMPROVEMENT IS A TEMPORARY ONE. A DRY COLD FRONT WILL CROSS THE REGION AND CAUSE A DRIER NORTHWESTERLY WIND TO ENVELOP CENTRAL NC BETWEEN 12-18Z MON...WITH VFR CONDITIONS EXPECTED THROUGH THE END OF THE 00Z TAF PERIOD. -RAH LOOKING BEYOND 00Z TUE... A DISTURBANCE ALOFT RIDING ALONG THE SURFACE FRONT WILL BRING A THREAT OF MVFR/IFR CONDITIONS STARTING LATE MONDAY NIGHT (INT/GSO) OR TUE AFTERNOON (RDU/RWI/FAY)... ALONG WITH A LLWS RISK. THESE SUB-VFR CONDITIONS SHOULD GIVE WAY TO VFR CONDITIONS AT FAY THEN AT RWI/RDU WED AS A WARM FRONT MOVES NORTHWEST THROUGH THE AREA WITH STRENGTHENING SW WINDS... BUT SUB- VFR CONDITIONS MAY HOLD IN LONGER AT INT/GSO. THIS WARM FRONT WILL DROP BACK DOWN SOUTHEAST THROUGH THE AREA AS A COLD FRONT LATE WED OR WED NIGHT... TURNING SURFACE WINDS BACK AROUND TO NORTH/NORTHEASTERLY FOR THU WITH WIDESPREAD RAIN AND SUB-VFR CONDITIONS. VFR CONDITIONS SHOULD RETURN TO NORTHERN SECTIONS (RDU/RWI/INT/GSO) BY THURSDAY NIGHT/FRIDAY. -GIH && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD/BLS SHORT TERM...RAH LONG TERM...RAH AVIATION...RAH/GIH

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