Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 290310 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1009 PM EST WED JAN 28 2015 .SYNOPSIS...HIGH PRESSURE WILL BUILD OVER THE REGION THROUGH EARLY THURSDAY AND THEN OFF THE SOUTHEAST COAST THURSDAY AFTERNOON. A COLD FRONT WILL SWEEP THROUGH THE AREA LATE THURSDAY AND THURSDAY NIGHT. COOL HIGH PRESSURE WILL BUILD BACK IN FROM THE WEST FRIDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 10 PM WEDNESDAY... SURFACE HIGH PRESSURE CENTERED NEAR WESTERN PA AND WESTERN NY THIS EVENING WILL BUILD SOUTHWARD/EXTEND INTO OUR REGION OVERNIGHT. GIVEN THE WEAK MSLP GRADIENT ACROSS THE AREA... WINDS HAVE ALREADY WENT CALM TO LIGHT AN VARIABLE. MEANWHILE... MID LEVEL RIDGING ALOFT WILL BUILD EASTWARD AND BE CENTERED OVER THE REGION BY 12Z THURSDAY. GIVEN THE CURRENT POSITION OF THE MID LEVEL RIDGE WE ARE CLEAR THIS EVENING... WITH ANY CIRRUS STILL TO THE WEST OF OUR AREA. WHILE WE SHOULD SEE AN INCREASE IN HIGH CLOUDS EARLY THURSDAY MORNING AS THE MID LEVEL RIDGE BUILD OVERHEAD BY DAYBREAK... THINK THE CIRRUS SHOULD REMAIN THIN ENOUGH TO NOT HAVE A SIGNIFICANT IMPACT ON LOW TEMPS. THUS... GIVEN THE MOSTLY CLEAR SKIES AND CALM TO LIGHT AND VARIABLE WINDS HAVE LOWERED LOW TEMPS BY A COUPLE OF DEGREES... WHICH IS IN LINE WITH THE COOLER SIDE OF GUIDANCE (MAV). THIS YIELDS LOWS IN THE UPPER TEENS TO LOWER 20S. (WITH MAYBE A FEW MID 20S IN THE URBAN CENTERS). && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 255 PM WEDNESDAY... THURSDAY...HIGH PRESSURE OVER THE AREA EARLY THURSDAY MORNING WILL WEAKEN AND SHIFT SOUTHEAST OF THE SC COAST BY MIDDAY. MEANWHILE...A PAIR OF SHORTWAVES... ONE EMERGING OFF THE CENTRAL ROCKIES AND ANOTHER DIVING SOUTH OUT OF THE CANADIAN ROCKIES WILL IMPACT THE REGION THURSDAY AFTERNOON/NIGHT. WITH THE LEAD WAVE...FORCING IS FOCUSED ALOFT AS THE BRUNT OF THE DCVA PASSES TO OUR NORTH. MOISTURE IS FOCUSED IN THE MID-LEVELS...PER NAM/GFS BUFR SOUNDINGS...AND DECREASES RAPIDLY WITH SOUTHWARD EXTENT. WHILE THE ECMWF PRODUCES A FEW HUNDREDTHS AREAWIDE BETWEEN 18-00Z...THE NAM/GFS/SREF SUGGEST JUST A PASSING SPRINKLE AT BEST DURING THE AFTERNOON...AND THIS LOOKS MOST REASONABLE. SOUTHERLY WIND WILL HELP HIGHS REBOUND THURSDAY ESPECIALLY IN THE WEST...UPPER 40S NORTHEAST TO LOWER 50S SOUTHWEST. THURSDAY NIGHT...ON THE HEELS OF THE LEAD WAVE...THE TRAILING SHORTWAVE...AND ASSOCIATED WEAK COLD FRONT...WILL CROSS THE CWA IN THE 03-09Z TIME FRAME. THE FORCING FOR ACCENT IS MUCH BETTER WITH STRONGER DCVA AND WEAK LOW-LEVEL FRONTAL CONVERGENCE...ALL WITHIN THE LEFT EXIT REGION OF A STRENGTHENING SPEED MAX OVER THE MID- MISSISSIPPI VALLEY REGION. HOWEVER...MOISTURE MAY AGAIN BE TOO LIMITED AS THE DEEPER LAYER FLOW BECOMES WESTERLY. A FEW ISOLATED LIGHT SHOWERS OR SPRINKLES ARE POSSIBLE WITH FRONT...BUT MAJORITY OF THE AREA SHOULD BE DRY. MAY SEE A FEW WIND GUSTS BEHIND THE FRONT WITH THE INITIAL COLD ADVECTION...AS LOWS FALL INTO THE LOW TO MID 30S. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 335 PM WEDNESDAY... FRI THROUGH SAT NIGHT: THE MODELS ARE IN GOOD AGREEMENT REGARDING THE AMPLIFICATION OF A PAIR OF STRONG NORTHERN STREAM SHORTWAVE TROUGHS INTO AND OFFSHORE THE COAST OF THE MIDDLE ATLANTIC STATES ON FRIDAY. THE ASSOCIATED SFC COLD FRONT SHOULD BE NEAR THE COAST AT THE START OF THE PERIOD/12Z FRI...WITH STRONG CAA - OFFSET TO SOME DEGREE BY 30 KTS OF NW DOWNSLOPE FLOW - FOR THE REMAINDER OF THE DAY. THE RESULT WILL BE BLUSTERY NW WINDS TO AROUND 30 MPH WITHIN A DEEPLY MIXED (~5 K FT) BOUNDARY LAYER...AND HIGHS IN THE MIDDLE 40S TO AROUND 50 DEGREES. 1030 MB CONTINENTAL POLAR HIGH PRESSURE WILL BUILD EAST OF THE APPALACHIANS FRI NIGHT. CONSENSUS LL THICKNESS VALUES AROUND 1280 METERS SUPPORT LOWS MOSTLY IN THE LOWER 20S...THOUGH UPPER TEENS WILL BE POSSIBLE WHERE AND IF DECOUPLING/CALM OCCUR TOWARD DAYBREAK. THE SFC RIDGE WILL CREST OVERHEAD SAT...THEN DRIFT OFFSHORE SAT NIGHT. MEANWHILE ALOFT...INITIALLY NW FLOW WILL TRANSITION TO INCREASINGLY ZONAL FLOW DOWNSTREAM OF BOTH A NORTHERN STREAM S/W TROUGH APPROACHING FROM WESTERN CANADA AND AN EVOLVING UPPER LOW NEAR THE BAJA. THE ZONAL FLOW WILL ALLOW ABUNDANT MID-HIGH LEVEL MOISTURE TO STREAM EAST OVER CENTRAL NC LATE IN THE DAY AND PARTICULARLY OVERNIGHT SAT. GIVEN THE INCREASING MOISTURE ALOFT...LOWS WILL BE NOT BE AS COLD - MOSTLY IN THE LOWER (TO PERHAPS MIDDLE) 30S. WHILE THE INCREASING MID-HIGH LEVEL MOISTURE WILL LIKELY RESULT IN WIDESPREAD VIRGA BY EARLY SUN...A DRY SUB- CLOUD LAYER IN EXCESS OF 7-8 THOUSAND FT PER MODEL CROSS SECTIONS SUGGEST IT WILL REMAIN DRY AT THE SFC. *IF* LIFT AND MOISTURE WERE TO INCREASE MORE QUICKLY THAN CURRENTLY FORECAST...PARTIAL THICKNESS AND WET BULB PROFILE VALUES WOULD SUPPORT SNOW AT THE ONSET...BUT PROSPECTS OF THAT HAPPENING ARE VERY LOW. SUN THROUGH MON: THE MODELS HAVE TRENDED FLATTER WITH THE NORTHERN STREAM S/W TROUGH (REFERENCED ABOVE) AS IT AMPLIFIES INTO THE MIDDLE ATLANTIC STATES THROUGH SUN NIGHT OR MON. THE ASSOCIATED SFC LOW REFLECTION IN RECENT NWP RUNS IS CONSEQUENTLY MUCH WEAKER AND MORE SUPPRESSED THAN EARLIER FORECASTS. REGARDLESS OF WHETHER OR NOT THE GUIDANCE TRENDS BACK TOWARD A STRONGER SYSTEM LIFTING UP WEST OF THE APPALACHIANS...THE HIGHEST RAIN CHANCES WILL STILL BE SUNDAY NIGHT IN EITHER SCENARIO. BEFOREHAND...SUNDAY SHOULD BE A CLOUDY DAY FOR CENTRAL NC...WITH RAIN CHANCES INCREASING FROM TOP-DOWN SATURATION OVER MAINLY THE WESTERN AND NORTHERN PIEDMONT...AND WITH HIGHS WELL BELOW FULL SUN VALUES - MOSTLY IN THE MIDDLE 40S TO AROUND 50 DEGREES. THE FLATTER/WEAKER SFC SOLUTIONS DO HAVE RAMIFICATIONS ON PRECIPITATION CHANCES AND TEMPERATURES FOR MON...HOWEVER...SUCH THAT THE BULK OF THE DAY WOULD BE DRY BEHIND THE SYSTEM GIVEN THE LATEST MODEL TRENDS...WITH CAA-DRIVEN TEMPERATURES IN THE MIDDLE 40S TO AROUND 50 DEGREES. MON NIGHT THROUGH WED: BENEATH HEIGHT RISES ALOFT BEHIND THE DEPARTING NORTHERN STREAM S/W TROUGH...POST-FRONTAL...CONTINENTAL POLAR HIGH PRESSURE WILL BUILD OVERHEAD MON NIGHT-TUE...THEN DRIFT OFFSHORE TUE NIGHT-WED. MEANWHILE ALOFT...THE EVOLVING UPPER LOW NEAR THE BAJA IS FORECAST TO EJECT AND TRACK ACROSS THE SOUTHERN US...WITH ACCOMPANYING SFC LOW DEVELOPMENT FROM THE GOM TO THE SOUTHEAST US COAST...THROUGH MID WEEK. THE RESULT WILL BE INCREASING PRECIPITATION CHANCES IN CENTRAL NC...INTO THE SLIGHT TO CHANCE RANGE...BY EARLY WED. PROJECTED PARTIAL THICKNESS VALUES WOULD SUPPORT JUST A CHILLY RAIN. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... AS OF 705 PM WEDNESDAY... 24 HOUR TAF PERIOD: VFR CONDITIONS WILL CONTINUE THROUGH THE 24 HOUR TAF PERIOD. SURFACE HIGH PRESSURE WILL BUILD INTO THE AREA THIS EVENING... THEN SLIDE TO THE SOUTH AND EAST OF THE REGION ON THURSDAY AS A COLD FRONT APPROACHES CENTRAL NC FROM THE WEST. THIS WILL YIELD CLEAR SKIES THIS EVENING INTO THE OVERNIGHT... WITH LIGHT AND VARIABLE TO CALM WINDS. MID AND HIGH LEVEL CLOUDS WILL BEGIN TO INCREASE ACROSS THE AREA ON THURSDAY... WHILE SURFACE WINDS BECOME SOUTH TO SOUTHWESTERLY IN ADVANCE OF THE FRONT... WITH POSSIBLY SOME GUSTS DURING THE AFTERNOON IN THE 15 TO 20 KT RANGE (HIGHEST PROBABILITY OF SEE SOME WIND GUSTS TO 20 KTS WILL BE AT KGSO/KINT). OUTLOOK: A MOSTLY DRY COLD FRONT WILL MOVE THROUGH THE AREA THURSDAY NIGHT. A BRIEF PERIOD OF MVFR CEILINGS MAY ACCOMPANY THE FRONT. BREEZY NORTHWESTERLY WINDS WILL FOLLOW ON FRIDAY. THE NEXT PERIOD OF WIDESPREAD SUB-VFR CONDITIONS WILL LIKELY COME LATE SUNDAY INTO MONDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...BSD SHORT TERM...BLS LONG TERM...MWS AVIATION...BSD/BLS

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