Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 190557 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1255 AM EST FRI DEC 19 2014 .SYNOPSIS...
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HIGH PRESSURE CENTERED OVER THE MID MISSISSIPPI RIVER VALLEY WILL GRADUALLY EXTEND INTO THE CAROLINAS TODAY. A WEAK STORM SYSTEM WILL DEVELOP OVER THE TEXAS GULF COAST TODAY... THEN TRACK EASTWARD ACROSS THE SOUTHEAST STATES ON SATURDAY. WEAK HIGH PRESSURE WILL BRIEFLY EXTEND ACROSS CENTRAL NC ON SUNDAY.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 1020 PM THURSDAY... SATELLITE AND MOST DATA CONFIRM PLENTY OF MID LEVEL MOISTURE WITH MOSTLY CLOUDY SKIES LINGERING OVER TN/NC. THERE WERE SOME BREAKS IN THE CLOUDS IN THE NW. SOME OF THIS DRIER AIR WILL FINALLY WORK INTO THE REGION OVERNIGHT... MAINLY ACROSS THE NORTH. LOWS ARE ON TARGET FOR 30-35 MOST AREAS. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... AS OF 255 PM THURSDAY... FRIDAY AND FRIDAY NIGHT... HIGH PRESSURE OVER THE MIDWEST WILL SLOWLY SETTLE EAST ACROSS THE CENTRAL APPALACHIANS AS THE PARENT HIGH MOVES TOWARD EASTERN CANADA. WE SHOULD BE IN A RELATIVE MIN BETWEEN MID/HIGH CLOUDS TODAY AND MOISTURE SPREADING IN AHEAD OF SATURDAY`S SYSTEM. GUIDANCE SUGGESTS DEWPOINTS WILL FALL INTO THE 20S..THOUGH WOULDNT BE SURPRISED TO SEE SOME UPPER TEENS BASED ON REGIONAL OBSERVATIONS. THICKNESSES SUPPORT HIGHS IN THE LOW TO MID 50S. LOWS FRIDAY NIGHT SHOULD BE ABLE TO FALL INTO THE LOW/MID 30S (ESPECIALLY NORTHEAST) PRIOR TO THE ARRIVAL OF MORE ROBUST CLOUD COVER. SATURDAY... THE SHORTWAVE CURRENTLY OVER THE CALIFORNIA BAJA REGION WILL LIFT NORTHEAST ACROSS THE SOUTHERN-CENTRAL US ON FRIDAY AND THEN TOWARD OUR REGION ON FRIDAY NIGHT. MODELS CONTINUE TO TREND TOWARD MORE DEAMPLIFICATION WITH THE WAVE BY THE TIME IT REACHES THE SOUTHERN APPALACHIANS SATURDAY MORNING. ACCORDINGLY...THE SURFACE LOW EXPECTED TO DEVELOP ALONG THE GULF COAST IS MUCH WEAKER AND ESSENTIALLY MOVES EAST OFF THE SOUTHEAST COAST. HIGH PRESSURE OVER EASTERN CANADA WILL EXTEND DOWN THE EASTERN SEABOARD AND INTO CENTRAL NC. WHILE NOT OVERLY STRONG OR FAR ENOUGH SOUTH... THE HIGH IS IN A MORE FAVORABLE POSITION TO SUPPLY DRY AIR INTO NC THAN FORECAST A FEW DAYS AGO. HOWEVER...WITH WEAKER DYNAMIC FORCING...THE DRY AIR WILL ALSO LIMIT PRECIP...AND THE NAM/GFS/ECMWF ARE ALL DRY OR NEARLY DRY. CAN`T HELP BUT CONTINUE TO CUT BACK ON POPS BASED ON RECENT GUIDANCE...BUT GIVEN THAT THE SHORTWAVE WILL BE INTERACTING WITH AN ASSORTMENT OF NORTHERN STREAM WAVES OVER THE NORTHERN PLAINS...A SMALL SHIFT BACK TO THE NORTH WILL BRING MEASURABLE PRECIP INTO CENTRAL NC. SHOULD NOTE THAT A SHIFT BACK TO THE NORTH COULD STILL CREATE SOME PTYPE ISSUES AS PTYPE NOMOGRAMS HOVER AROUND THE WINTRY MIX AND WETBULB PROFILES REMAIN CURIOUSLY CLOSE TO FREEZING IN THE LOWEST 10K FT. THIS IS A FINE LINE AS WELL...AS THE SHIFT WOULD ALSO BRING SOME WARM AIR BACK NORTH. WILL REDUCE POPS TO CHANCE ACROSS THE NORTH AND LOW-END LIKELY (MAINLY BETWEEN 12Z AND 00Z) NEAR THE SC BORDER...WHICH MAY STILL BE TOO HIGH BUT FOLLOWS A CONSERVATIVE TREND. WILL ALSO RAISE HIGHS A FEW DEGREES...THOUGH NORTHEASTERLY FLOW AND THICK CLOUD COVER WOULD STILL KEEP TEMPS IN THE UPPER 40S NORTHWEST TO NEAR 50 SOUTHEAST. SATURDAY NIGHT....ALL ENERGY ASSOCIATED WITH THIS SYSTEM WILL DEPART SATURDAY NIGHT...ALLOWING FOR SOME MID-LEVEL DRYING AND SCATTERING OF CLOUDS. HOWEVER...MODELS ARE QUICK TO BRING MOISTURE BACK TOWARD THE REGION FROM THE SOUTH AS ANOTHER SYSTEM GETS GOING BY LATE SUNDAY. LOWS IN THE MID/UPPER 30S. && .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 320 PM WEDNESDAY... ...VERY ACTIVE PATTERN DEVELOPING OVER THE LONG TERM PERIOD... BEHIND THE DEPARTING SOUTHERN STREAM SHORT WAVE TROUGH...SHORT WAVE RIDGING MOVES INTO THE CAROLINAS ON SUNDAY AS HIGH PRESSURE CENTERED OVER THE EASTERN GREAT LAKES AND MID ATLANTIC EXTENDS INTO THE REGION. THE NEXT SOUTHERN STREAM WAVE WHICH MOVES ONSHORE ACROSS CA ON FRIDAY REACHES THE WESTERN GULF OF MEXICO ON SUNDAY NIGHT. LOOK FOR INCREASING AND THICKENING CLOUDS ON SUNDAY WITH HIGHS IN THE UPPER 40S TO LOWER 50S. PRONOUNCED ISENTROPIC LIFT WHICH DEVELOPS AHEAD OF THIS SYSTEM SUNDAY EVENING ACROSS THE SOUTHEAST...SPREADS INTO THE CAROLINAS AFTER MIDNIGHT AND PERSISTS FOR MUCH OF MONDAY MORNING. EXPECT A BROAD AREA OF RAIN WITH THIS SYSTEM AND HAVE INCREASED POPS. TEMPERATURES SUNDAY NIGHT WILL FALL INTO THE MID 30S ACROSS THE NORTHERN PIEDMONT AND THE UPPER 30S ELSEWHERE...THESE TEMPERATURES ALONG WITH A PRONOUNCED WARM NOSE AND WET BULB ZERO VALUES HOLDING ABOVE FREEZING SHOULD PRECLUDE AND PTYPE ISSUES. A SURFACE LOW DEVELOPING IN THE NORTHEAST GULF OF MEXICO WILL MOVE NORTHEAST ALONG THE CAROLINA COAST MONDAY AFTERNOON AND FURTHER OFFSHORE MONDAY NIGHT. PRECIPITATION SHOULD BECOME MUCH MORE SCATTERED AND LIGHT MONDAY NIGHT INTO TUESDAY AS THE STRONGEST FORCING ABATES BUT WIDESPREAD CLOUDINESS AND SMALL RAIN CHANCES WILL PERSIST AS A MOIST AIR MASS LINGERS ACROSS THE AREA. AN IMPRESSIVE NORTHERN STREAM SHORTWAVE TROUGH DIVES INTO THE MIDWEST ON TUESDAY AND TUESDAY NIGHT CARVING OUT A HIGH AMPLITUDE LONG WAVE TROUGH DEVELOPS ACROSS THE MISSISSIPPI VALLEY TUESDAY NIGHT AND BECOMES NEGATIVELY TILTED ON WEDNESDAY AS IT BROADENS AND REACHES THE EAST COAST. BOTH THE DETERMINISTIC GFS AND ECMWF ARE VERY SIMILAR WITH THIS PATTERN. AT THE SURFACE...A STRONG SURFACE CYCLONE DEVELOPS ACROSS THE GREAT LAKES ON TUESDAY INTO WEDNESDAY WITH A STRONG COLD FRONT PROGGED TO MOVE ACROSS THE CAROLINA ON TUESDAY NIGHT AND EARLY WEDNESDAY. THIS PATTERN WILL SUPPORT STRONG AND GUSTY WINDS AHEAD OF AND BEHIND THE COLD FRONT WITH A PERIOD OF WIDESPREAD RAIN AND PERHAPS A FEW THUNDERSTORMS ASSOCIATED WITH THE FRONT. THE DEEP LAYER FLOW ATTENDANT TO THE FRONT IS VERY STRONG WITH A SOUTHWEST WIND OF AROUND 40KTS PROGGED AT 1 KFT NEAR RDU ON WEDNESDAY MORNING AND A WESTERLY WIND OF 40 KTS FORECAST AT RDU AT 1.5 KFT WEDNESDAY NIGHT. BOUNDARY LAYER INSTABILITY IS LIMITED BUT BOTH THE GFS AND THE ECMWF SUGGEST A NARROW WINDOW FOR BOUNDARY LAYER DESTABILIZATION AHEAD OF THE FRONT. THE IMPRESSIVE WIND FIELD COMBINED WITH 700-500 MB LAPSE RATES APPROACHING 7 AS NOTED BY THE GFS...LEADS TO AN ELEVATED SHERB VALUE THAT SUGGESTS SOME HIGHER IMPACT HSLC CONVECTION IS POSSIBLE. THE PRECIPITATION QUICKLY ENDS BEHIND THE FRONT WEDNESDAY AFTERNOON WITH DRY WEATHER EXPECTED FOR CHRISTMAS DAY. HIGHS ON TUESDAY WILL RANGE FROM THE LOWER 50S IN THE TRIAD TO NEAR 60 ACROSS THE SOUTHERN COASTAL PLAIN. TEMPERATURES SHOULDN`T FALL MUCH TUESDAY NIGHT WITH THE CLOUDS AND STRONG SOUTHERLY FLOW. RAISED MINS ABOVE GUIDANCE TO THE MID 40S TO AROUND 50. HIGHS WEDNESDAY WILL RANGE FROM 50 IN THE TRIAD TO NEAR 60 IN THE SOUTHEAST WITH CHILLIER MAXES IN THE MID 40S TO NEAR 50 EXPECTED FOR CHRISTMAS DAY. -BLAES && .AVIATION /06Z FRIDAY THROUGH TUESDAY/...
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AS OF 1255 AM FRIDAY... HIGH PRESSURE CENTERED OVER THE LOWER OH VALLEY WILL GRADUALLY EXTEND INTO CENTRAL NC LATER TODAY AND EARLY THIS EVENING. WHILE PATCHES OF MID LEVEL CLOUDS WILL CROSS THE REGION THROUGH 12Z...VFR CONDITIONS WILL PERSIST. FEWER CLOUDS ANTICIPATED LATER THIS MORNING THROUGH THE AFTERNOON WITH LIGHT AND VARIABLE SURFACE WINDS. A LOW PRESSURE SYSTEM WILL ADVANCE TOWARD CENTRAL NC LATER TONIGHT AND CROSS THE REGION SATURDAY. AREAS OF LIGHT RAIN WILL DEVELOP TOWARD DAYBREAK SATURDAY AND CROSS CENTRAL NC SATURDAY MORNING THROUGH EARLY AFTERNOON. THE LIGHT RAIN FALLING THROUGH THE LOWER LEVELS OF THE ATMOSPHERE WILL AID TO MOISTEN THIS LEVEL...LEADING TO THE POTENTIAL FOR PATCHES OF MVFR CEILINGS...MAINLY IN THE 14Z-20Z SATURDAY TIME FRAME. WINDS EXPECTED TO REMAIN LIGHT AND VARIABLE. VFR CONDITIONS EXPECTED SATURDAY NIGHT INTO SUNDAY AS WEAK HIGH PRESSURE EXTENDS ACROSS THE AREA. ANOTHER LOW PRESSURE SYSTEM...THIS ONE STRONGER THAN THE SATURDAY SYSTEM...WILL BEGIN TO AFFECT CENTRAL NC SUNDAY NIGHT INTO SUNDAY...LEADING TO A PERIOD OF WIDESPREAD MVFR/IFR CEILINGS AND AREAS OF RAIN. THE RAIN WILL DIMINISH ACROSS THE REGION BY MONDAY NIGHT THOUGH MVFR/IFR CEILINGS WILL PERSIST MONDAY NIGHT INTO TUESDAY.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...BADGETT SHORT TERM...BLS LONG TERM...BLAES AVIATION...WSS

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