Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 190816 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 315 AM EST FRI DEC 19 2014 .SYNOPSIS...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. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 315 AM FRIDAY... TODAY...MID LEVEL CLOUDS ASSOCIATED WITH WEAK WARM AIR ADVECTION ALOFT WILL DECREASE/DIMINISH EARLY THIS MORNING AS A WEAK S/W RIDGE AND ATTENDANT SFC RIDGE (FROM PARENT HIGH OVER THE MID MS VALLEY) BUILDS INTO THE CAROLINAS. MINOR 850MB THERMAL TROUGH WITH WEAK CAA WILL MAINTAIN A CHILLY AIR MASS WITH HIGH TEMPS 4-5 DEGREES BELOW NORMAL. MAX TEMPS UPPER 40S FAR NE TO THE MID 50S SOUTHERN THIRD. TONIGHT...A S/W LIFTING E-NE FROM THE SOUTHERN PLAINS WILL ADVANCE EAST ACROSS THE LOWER MS VALLEY TONIGHT. WARM AIR ADVECTION AHEAD OF THIS SYSTEM WILL INCREASE MOISTURE ACROSS OUR REGION...RESULTING IN THICKENING CLOUD COVERAGE FROM THE WEST-SW. MODEST ISENTROPIC UPGLIDE MAY CAUSE PATCHES OF LIGHT RAIN TO DEVELOP OVER THE FAR WESTERN-SOUTHERN PIEDMONT PRIOR TO DAYBREAK. MIN TEMPS GENERALLY IN THE LOW-MID 30S THOUGH SOME PLACES IN THE WEST AND SOUTHWEST WILL SEE MIN TEMPS OCCUR SHORTLY AFTER MIDNIGHT...WITH TEMPS HOLDING STEADY THEREAFTER DUE TO THE THICKENING CLOUDS.
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&& .SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
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AS OF 315 AM FRIDAY... S/W CROSSING THE DEEP SOUTH EARLY SATURDAY WILL SPREAD MOISTURE INTO CENTRAL NC. BEST LIFT THROUGH THE COLUMN ASSOCIATED WITH SPEED CONVERGENCE AT 700MB AND MODEST HEIGHT FALLS IN THE MID LEVELS. THE MODEL GUIDANCE HAS BEEN TRENDING DRIER COMPARED TO 48-72 HOURS AGO WITH SOME NEAR TERM MODELS NOW SUGGESTING LITTLE IF ANY MEASURABLE PRECIP OVER THE NORTHERN PIEDMONT. WILL NEED TO MONITOR THE DEVELOPING RAIN SHIELD OVER THE LOWER MS VALLEY TODAY...AND THE TN VALLEY/DEEP SOUTH TONIGHT. PER LATEST MOISTURE PROFILES AND LIFT...FELL THAT A FEW HUNDREDTHS PROBABLE ACROSS THE PIEDMONT SATURDAY MORNING. THUS HAVE ADJUSTED POPS BACK INTO THE LIKELY CATEGORY OVER THE NW PIEDMONT AND MAINTAINED A LIKELY POPS IN THE SOUTH. FOR AREAS NORTH AND EAST OF RDU..CONTINUED CHANCE POPS. AGAIN...WHAT PRECIP THAT OCCURS WILL BE LIGHT WITH AMOUNTS VARYING BETWEEN A TRACE TO LESS THAN A TENTH OF AN INCH. NAM AND GFS BUFKIT SOUNDINGS SUGGEST A BRIEF OPPORTUNITY FOR MIXED PRECIP IN THE NW PIEDMONT AROUND DAYBREAK...COINCIDING WITH THE BEST LIFT. THE GFS AND NAM HAVE TRENDED SLIGHTLY COOLER WITH PARTIAL THICKNESSES SUGGESTING A RAIN/SNOW MIX POSSIBLE IN THE TRIAD AND POSSIBLY THE ROXBORO AREAS...MAINLY WHEN HEAVIER PRECIP INTENSITY IS OCCURRING. WHILE BULK OF PRECIP WILL BE LIQUID...CANNOT RULE OUT THE POSSIBILITY OF SOME SNOW MIXED IN AT TIMES NORTH OF TEH I-85/40 CORRIDOR IN THE TRIAD. HIGH TEMPS SATURDAY DEPENDENT UPON EXTENT OF PRECIP SATURDAY AND WHETHER PRECIP DOES DIMINISH SATURDAY AFTERNOON. HAVE ADJUSTED MAX TEMPS UP A DEGREE OR TWO. HAVE LEANED TOWARD A DRIER FORECAST FOR SATURDAY NIGHT AS SUBSIDENCE IN THE WAKE OF THE DEPARTING S/W SHOULD END THE THREAT OF PRECIP ACROSS THE REGION BY LATE SATURDAY...AND MORE SO SATURDAY EVENING WITH SOME DECREASE IN CLOUDS POSSIBLE AFTER SUNSET. IF ENOUGH CLEARING OCCURS...MAY SEE POCKETS OF FOG DEVELOP AFTER MIDNIGHT. IN ANTICIPATION OF SOME PARTIAL CLEARING...HAVE LOWERED MIN TEMPS A FEW DEGREES FROM THE PREVIOUS FORECAST (LOW-MID 30S).
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&& .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/... 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. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...BLAES AVIATION...WSS

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