Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 221205 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 705 AM EST SAT NOV 22 2014 .SYNOPSIS...HIGH PRESSURE REMAINS OVER THE REGION TODAY INTO TONIGHT. A STRONG LOW PRESSURE MOVING FROM THE SOUTHERN PLAINS INTO THE GREAT LAKES SUNDAY WILL SPREAD MOISTURE OVER THE REGION DURING THE DAY ON SUNDAY. ANOTHER COLD FRONT WILL MOVE EAST ACROSS MUCH OF THE AREA MONDAY...WITH LOW PRESSURE MOVING ALONG THE SOUTHEAST COAST TUESDAY INTO WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 AM SATURDAY... THE LATEST SURFACE ANALYSIS SHOWED SURFACE HIGH PRESSURE OVER CENTRAL NORTH CAROLINA...AND THE 00Z UPPER-AIR ANALYSIS NOTED VERY DRY AIR AT 850MB WITH DEW POINT DEPRESSIONS WELL ABOVE 40C. THE TEMPERATURE HAD FALLEN INTO THE UPPER TEENS AT LEAST AT KTDF...AND WATCHING THE KRDU OVERNIGHT LOW SO FAR THE LOW WAS 25 AS OF THIS WRITING. FOR TODAY...BUFR SOUNDINGS ARE CONTINUED DRY AND STABLE. THE HRRR WRF FORECASTS NOTICEABLE HIGH CLOUDS TODAY...BUT OTHER GUIDANCE SUCH AS THE CANADIAN CLOUD COVER MODEL...AND WHAT ONE WOULD CONSIDER LOOKING AT THE UPPER-LEVEL RELATIVE HUMIDITY FORECASTS AND BUFR SOUNDINGS...SUGGEST LESS. SATELLITE DATA UPSTREAM SUGGEST LESS AS WELL...ALONG WITH THE JET LIFTING NORTH. UNDER EXPECTED SUNSHINE HIGHS SHOULD BE 50 TO 55. OVERNIGHT...CLOUDS SHOULD GRADUALLY INCREASE...BUT IT MAY BE A SLOW INCREASE AS THE AIR MASS REMAINS DRY IN THE MEAN AT LEAST THROUGH 06Z MONDAY...AND MOISTURE ALOFT DOES NOT SHOW A STRONG INCREASE ON BUFR SOUNDINGS UNTIL LATE TONIGHT. THE CANADIAN CLOUD COVER MODEL ALSO SHOWS A SLOW AND GRADUAL INCREASE...AND EVEN A FEW AREAS OF MOSTLY CLEAR TO PARTLY CLOUDY CONDITIONS ESPECIALLY NORTHEAST EVEN LATE TONIGHT. OVERNIGHT LOWS WILL BE FORECAST ON THE COLD SIDE OF GUIDANCE AND A FEW OF THESE LOWS MAY EVEN BE TOO HIGH IF LESS CLOUDS OCCUR FOR LONGER PERIODS IN THE OVERNIGHT. UNDER THE WESTWARD EXTENSION OF THE RIDGE...WINDS SHOULD BE LIGHT FOR MUCH OF THE NIGHT. WILL KEEP A DRY FORECAST AS BOTH THE GFS AND NAM SEEM TO BE A LITTLE SLOWER WITH THE APPROACH OF DEEPER MOISTURE. BY 12Z SUNDAY...THE NAM IS FAIRLY MOIST ALOFT...BUT THE SUB-CLOUD LAYER REMAINS VERY DRY. THE 850MB THETA-E GRADIENT IS JUST BEGINNING TO APPROACH CENTRAL NORTH CAROLINA ON BOTH THE NAM AND GFS AT 12Z SUNDAY...AND THOSE MODELS ARE ALSO SUBSIDENT AT THAT LAYER AT THAT TIME. DESPITE THE DRY SUB-CLOUD LAYER...IF ANY PRECIPITATION WOULD OCCUR OVER THE FAR SOUTHWEST PIEDMONT...FOR EXAMPLE...SUFFICIENT WARMING ALOFT PUSHES THICKNESSES WELL INTO THE LIQUID CATEGORY...AND SURFACE WET BULB TEMPERATURES ARE ABOVE FREEZING. IF ANYTHING DOES OCCUR...IT WOULD BE VERY CLOSE TO 12Z SUNDAY AND THEN ALMOST CERTAINLY IN THE FORM OF SPRINKLES. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 300 AM SATURDAY... THE NAM AND THE GFS ARE SLOW TO BRING IN GOOD LIFT TO CENTRAL NORTH CAROLINA SUNDAY. HOWEVER...NUMEROUS PARAMETERS...INCLUDING 850MB THETA-E...K INDICES...GENERAL 850MB LIFT...700MB VORTICITY...AMONG OTHERS SUGGEST THAT PRECIPITATION WILL MOVE IN FROM THE SOUTHWEST WITH THE GREATEST LIKELIHOOD OF RAIN IN CENTRAL NORTH CAROLINA FROM ABOUT 18Z TO 05Z. HAVE CONFINED THE HIGHEST CHANCES IN THE GRIDDED FORECAST FROM 20Z TO 04Z...AND SOME OF THE WRF GUIDANCE IS EVEN SLOWER THAN THAT WITH THE ONSET PARTICULARLY FROM THE TRIANGLE NORTH AND EAST. FUTURE FORECASTS MAY END UP TRENDING A LITTLE SLOWER...BUT FOR PLANNING PURPOSES ANTICIPATE HIGH PROBABILITIES OF RAIN DURING THE AFOREMENTIONED WINDOW. CLOUDS SHOULD INCREASE...THOUGH THE UNCERTAINTY WITH THE ONSET OF RAIN MAKES THE TEMPERATURE FORECAST CHALLENGING. EXCEPT IN THE TRIAD...GUIDANCE HIGHS ARE RELATIVELY CLOSE...AND WILL PLAN TO GO BETWEEN THERE. IF RAIN WOULD MOVE IN EARLIER...WOULD ALMOST CERTAINLY LEAN TOWARD THE COOLER NAM BUT WITH SOME WRF GUIDANCE VOID OF MUCH PRECIPITATION EVEN TO 18Z SUNDAY THINK AT LEAST A BLEND IS WISE. IN TERMS OF THUNDER...BUFR SOUNDINGS PROVIDE FOR GREATEST LAPSE RATES VERY LATE SUNDAY AFTERNOON THROUGH THE EVENING IN ADVANCE OF A DRY SLOT WHICH BOTH THE NAM AND GFS BUFR SOUNDINGS FORECAST MOVING IN FROM THE SOUTHWEST DURING THE NIGHT WITH INCREASING 850MB SUBSIDENCE. 1000-500MB MUCAPE ON THE GFS IS LESS THAN 200J/KG AND THE SHERBS3 IS LESS THAN ONE...BUT THE NAM IS NOTICEABLY MORE UNSTABLE...ALTHOUGH IT IS DIFFICULT TO SEE SURFACE- BASED CONCERNS ON THE NAM BUFR SOUNDINGS WITH A SLIGHT INVERSION JUST OFF OF THE SURFACE. 0-3KM SHEAR AND HELICITY...AS EXPECTED... ARE VERY HIGH AS WINDS JUST OFF OF THE SURFACE INCREASE GREATLY. ADDED A SLIGHT CHANCE OF THUNDER DURING SUNDAY EVENING TO THE FORECAST FOR THE INTERSTATE 95 CORRIDOR AS AT LEAST THERE IS A SLIGHT CHANCE OF AT LEAST ELEVATED THUNDER...AND FOR THE HWO WILL LIKELY ADD A MENTION OF AT LEAST WIND GUSTS TO 40MPH OR A LITTLE HIGHER AS EVEN SHOWERS IN A RAPIDLY TIGHTENING SURFACE GRADIENT... WITH 925MB WINDS APPROACHING 50KT...SHOULD RESULT IN A FEW QUITE NOTICEABLE WIND GUSTS SIMPLY WITH PRECIPITATION. SPC HAS NOTED A SLIGHT RISK OF SEVERE WEATHER WHERE THUNDER WILL BE ADDED TO THE FORECAST AND WILL CERTAINLY NEED TO BE WATCHFUL OF INSTABILITY TRENDS IN LATER FORECASTS...AS OTHER PARAMETERS ARE PLENTY HIGH ENOUGH FOR ISOLATED SEVERE WEATHER. OVERNIGHT LOWS SUNDAY NIGHT NOT MUCH DIFFERENT FROM THE HIGHS SUNDAY...STEADY TO RISING IN THE TRIAD AND MAYBE A DIFFERENCE OF A DEGREE OR TWO ELSEWHERE IN GENERAL. -DJF MONDAY AND MONDAY NIGHT...MID-LEVEL DRY AIR INTRUSION AND SUBSIDENCE IN THE WAKE OF THE EXITING SHORTWAVE LIFTING OFF TO THE NORTH WILL RESULT IN MOSTLY DRY CONDITIONS DURING THE DAY ON MONDAY. THE TRAILING COLD FRONT WILL TRAVERSE THE AREA MONDAY EVENING/NIGHT BUT AIRMASS IS JUST TOO DRY WITH LITTLE TO NO FORCING/LIFT ALOFT TO SUPPORT POPS. TEMPERATURES MONDAY AFTERNOON IN THE PRE-FRONTAL WARM SECTOR WILL WARM INTO THE UPPER 60S/NEAR 70 NW TO MID 70S SE. LOWS MONDAY NIGHT WILL RANGE FROM LOWER 40S NW TO LOWER 50S SE AS CAA SPREADS WEST TO EAST. -CBL && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 300 AM SATURDAY... TUESDAY THROUGH WEDNESDAY: SOUTHERN STREAM TROUGH EMBEDDED AT THE BASE OF THE AMPLIFYING LONG WAVE TROUGH WILL TRAVERSE THE GULF COAST REGION ON TUESDAY AND THEN ACROSS THE SOUTHEAST ON WEDNESDAY. AFTER A DRY START TO THE DAY ON TUESDAY...RAIN CHANCES WILL RETURN TUESDAY EVENING/NIGHT AND INTO THE DAY ON WEDNESDAY AS WESTERN EDGE OF DEEPER MOISTURE AXIS ATTENDANT TO OFFSHORE FRONTAL ZONE RETREATS INLAND IN RESPONSE TO STRONG DPVA AND UPPER LEVEL DIVERGENCE WITHIN THE RIGHT ENTRANCE REGION OF A 140-150KT JETSTREAK. BOTH THE GFS AND EC CONTINUE TO TREND WETTER DURING THIS PERIOD WITH THE POTENTIAL FOR CENTRAL AND EASTERN PORTIONS OF THE STATE TO RECEIVE SIGNIFICANT RAINFALL. AS SUCH... WILL RAISE POPS TO CHANCE IN THE WEST TO LIKELY IN THE EAST. NO P-TYPE ISSUES HERE WITH JUST A COLD RAIN FOR CENTRAL NC. LOWS TUESDAY NIGHT IN THE MID/UPPER 30 NW TO LOWER 40S SE. HIGHS WEDNESDAY IN THE 40S. PRECIP AND CLOUDS PULL OUT WEDNESDAY EVENING/NIGHT WITH LOWS BACK DOWN INTO THE 30S. THURSDAY AND FRIDAY: UNCERTAINTY REMAINS HIGH REGARDING THE APPROACH OF THE NEXT BATCH OF SHORTWAVE ENERGY ROTATING EASTWARD WITHIN THE BASE OF THE LONGWAVE TROUGH...WITH SOME GUIDANCE SUGGESTING A MID- LEVEL SHORT WAVE MAY TRY TO CLOSE OFF OVER THE MID-ATLANTIC OR CAROLINAS. ITS WORTH NOTING THAT NORTHERN STREAM SYSTEMS LIKE THIS ARE OFTEN MOISTURE-STARVED... ESPECIALLY EAST OF THE MOUNTAINS. GIVEN THERE HAS BEEN LITTLE CONTINUITY AMONG THE DETERMINISTIC GUIDANCE ALONG WITH LARGE SPREAD AMONG THE ENSEMBLE MEMBERS...WILL PLAY THE CONSERVATIVE APPROACH AND MAINTAIN A DRY FORECAST FOR THURSDAY AND FRIDAY. IT LOOKS ALMOST CERTAIN HOWEVER THAT THIS SYSTEM WILL DELIVER ANOTHER SHOT OF COLD ARCTIC AIR INTO THE SOUTHEAST BY THE LATE WEEK AND INTO NEXT WEEKEND. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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AS OF 705 AM SATURDAY... FOR THE 12Z VALID TAF PERIOD...VFR CONDITIONS CONTINUE. LIGHT WINDS THIS MORNING GRADUALLY VEER WITH A SLIGHT INCREASE IN WIND SPEEDS AFTER SUNRISE...WITH SUSTAINED VALUES EXPECTED TO BE UNDER 10KT. SURFACE WINDS UNDER HIGH PRESSURE BECOME LIGHT OR CALM AGAIN THIS EVENING BACKING SLIGHTLY. BEYOND THE 12Z VALID TAF PERIOD...CONDITIONS DETERIORATE SUNDAY AND AS AREAS OF RAIN MOVE IN TO CENTRAL NORTH CAROLINA NUMEROUS AREAS OF SUB-VFR...LIKELY IFR...CONDITIONS DEVELOP DURING THE DAY... ESPECIALLY LATER IN THE DAY...CONTINUING AT LEAST INTO SUNDAY EVENING. WINDS OFF OF THE SURFACE WILL ALSO INCREASE SUNDAY AND BY SUNDAY NIGHT REACH OR EVEN EXCEED 50KT BY 2000FT WHICH COULD MAKE LOW-LEVEL WIND SHEAR A PROBLEM BY LATE IN THE DAY INTO THE OVERNIGHT HOURS. IMPROVING AVIATION CONDITIONS ARE POSSIBLE MONDAY AND WHILE SOUTHWEST WINDS OFF THE SURFACE WILL NOT BE AS STRONG...A GUSTY CHARACTER TO THE SURFACE WINDS CONTINUES. AS LOW PRESSURE MOVES ALONG THE SOUTHEAST COAST TUESDAY INTO WEDNESDAY...UNCERTAINTY INCREASES IN TERMS OF THE POTENTIAL FOR A RETURN TO A PERIOD OF SUB- VFR CONDITIONS AND PRECIPITATION...ESPECIALLY EAST OF THE TRIAD. THE NAM MODEL RETURNS THESE CONDITIONS MUCH FASTER TUESDAY...WHILE THE GFS AND ECMWF ARE SLOWER...MORE OVERNIGHT TUESDAY INTO WEDNESDAY. THE CURRENT THINKING IS TOWARD THE SLOWER SOLUTIONS.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DJF NEAR TERM...DJF SHORT TERM...DJF/CBL LONG TERM...CBL AVIATION...DJF

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