Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KRAH 020114 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 814 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 210 PM SUNDAY... THROUGH TONIGHT: FAIRLY DEEP MOIST ISENTROPIC UPGLIDE ATOP A CHILLY IN SITU WEDGE AIR MASS CONTINUES TO PRODUCE AREAS OF LIGHT RAIN AND DRIZZLE OVER CENTRAL NC. THE LOSS OF A FEED OF LOW LEVEL DRY AIR IN TO THE AREA TO COUNTERACT THE EFFECTS OF LATENT HEAT RELEASE HAS LED TO A SWITCHOVER TO MOSTLY FREEZING RAIN OVER ALL BUT THE FAR NORTHERN PIEDMONT... AND EVEN HERE IT DOESN`T APPEAR THAT ANY ADDITIONAL ICE IS ACCRUING GIVEN THE NEAR-FREEZING WET BULBS. TRENDS ALL SUGGEST THAT WE CAN LET WHAT`S LEFT OF THE ADVISORY EXPIRE ON SCHEDULE OR PERHAPS BE CANCELLED A BIT EARLY. THE SUPPORTIVE MOIST UPGLIDE WILL BE ON THE WANE THROUGH THE LATE AFTERNOON AND EARLY EVENING... AS THE WEAK 850 MB WAVE HEADS TO OUR NORTHEAST... AND MODEL GUIDANCE ALL POINT TO AN EXIT OF THE RAIN TO THE NORTHEAST THIS EVENING. WILL MAINTAIN A WEST-TO-EAST TAPERING OFF OF POPS ACROSS THE CWA. A WEAK SURFACE MESOHIGH WILL HOLD OVER THE WESTERN AND CENTRAL CAROLINAS OVERNIGHT... WITH A WEAK REMNANT COASTAL FRONT ON ITS EASTERN EDGE AND THE MOUNTAINS ON ITS WESTERN EDGE HINDERING ANY HORIZONTAL DISPERSION... AND A CONTINUED STABILIZING WARM SURGE ALOFT PREVENTING VERTICAL DISPERSION. EXPECT LOW CLOUDS AND FOG TO HOLD TONIGHT WITH HIGHLY STABLE AND MOIST LOW LEVELS. THIS PATTERN AS WELL AS STATISTICAL GUIDANCE SUPPORT TEMPS MOVING VERY LITTLE OVERNIGHT... HOLDING AT ROUGHLY 32 TO 40. TOO MUCH UNCERTAINTY RIGHT NOW REGARDING STRATUS VERSUS FOG DOMINATING TONIGHT... BUT IF OUR SURFACE WINDS DROP TO LESS THAN 4 KTS FOR AN EXTENDED TIME... WE MAY NEED A DENSE FOG ADVISORY FOR A PORTION OF THE CWA OVERNIGHT. 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 SHORT TERM...RAH LONG TERM...RAH AVIATION...RAH/GIH

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.