Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 301802 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 100 PM EST FRI JAN 30 2015 .SYNOPSIS...BREEZY NORTHWESTERLY WINDS TODAY WILL GIVE WAY TO HIGH PRESSURE BUILDING IN FROM THE WEST OVER THE WEEKEND. A LOW PRESSURE SYSTEM WILL THEN CROSS THE REGION LATE SUNDAY AND MONDAY. && .NEAR TERM /THROUGH TODAY/... AS OF 1030 AM FRIDAY... AN UPPER TROUGH IS CURRENTLY SWINGING ACROSS THE AREA WITH A COLD FRONT DEPARTING TO THE EAST. STRONG POST-FRONTAL COLD ADVECTION IS SETTING UP ACROSS THE AREA THIS MORNING WITH THE 12Z KGSO RAOB SHOWING AN ALREADY DEEP MIXED LAYER UP TO 5000 FT AND A GUST TO 38KT AT KGSO. NORTHWESTERLY WINDS ARE STEADILY INCREASING AND GUSTS ARE STARTING TO REACH THE UPPER 20S TO AROUND 30KT AREAWIDE. IT APPEARS THE GUSTS WILL PEAK LATE THIS MORNING AND VERY EARLY AFTERNOON...AS MUCH AS 30-35KT IN SOME AREAS...BEFORE THE PRESSURE GRADIENT BEGINS TO SLOWLY WEAKEN. MEANWHILE...REGIONAL VIS SHOWS A FEW STREAMS OF MOISTURE (JUST ABOVE 850MB PER KGSO/KRNK RAOBS) SPILLING EAST ACROSS THE NORTHERN CWA. THE STRONG INVERSION JUST ABOVE AND STRENGTHENING SUBSIDENCE BEHIND THE UPPER TROUGH WILL KEEP THIS MOISTURE TRAPPED AND THE STRATOCU FAIRLY SHALLOW...SO WE MAINLY EXPECT SKIES VARYING FROM PARTLY CLOUDY SOUTHWEST TO A PERIOD OF MOSTLY CLOUDY NORTHEAST. DRY ADIABATIC MIXING TO 850MB WHILE ACCOUNTING FOR SOME DOWNSLOPE WARMING YIELDS HIGHS IN THE 43-50 RANGE...ONLY ABOUT 3-4 DEGREES OFF CURRENT READINGS. -BLS && .SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... AS OF 300 AM FRIDAY... WINDS WILL DIMINISH TONIGHT UNDER CLEAR SKIES. THERE SHOULD BE ENOUGH OF A GRADIENT FOR AT LEAST A SLIGHT STIR TO THE WIND THROUGH THE NIGHT...AS 925MB WINDS REMAIN TO 35KT. SURFACE DEW POINTS SHOULD CONTINUE TO DRY...AND 1000-850MB THICKNESSES WOULD SUGGEST LOWS FROM THE TEENS TO THE LOWER 20S. THIS WILL ESSENTIALLY BE THE FORECAST FOR LOWS OVERNIGHT...19 TO 20 IN THE NORTHWEST PIEDMONT TO NEAR 25 TOWARD KFAY...CLOSE TO THE AVERAGE OF THE MET AND MAV MOS. ON SATURDAY...925MB WINDS DIMINISH TO AROUND 15KT BY 18Z...AND BUFR SOUNDINGS FROM BOTH THE NAM AND GFS SUGGEST A FEW WIND GUSTS IN THE TEENS KNOTS WITH INITIAL MIXING BEFORE THE WINDS DIMINISH AS HIGH PRESSURE CONTINUES TO BUILD IN FROM THE NORTHWEST. SATURDAY AFTERNOON...A FLAT RIDGE AXIS ALOFT GETS CLOSE TO CENTRAL NORTH CAROLINA AS SOME MID-LEVEL VORTICITY ADVECTION MOVES INTO AND ACROSS CENTRAL NORTH CAROLINA DURING THE LATE AFTERNOON AND NIGHTTIME HOURS...FORECAST BY BOTH THE GFS AND NAM. GFS AND NAM BUFR SOUNDINGS SUGGEST INCREASING UPPER-LEVEL MOISTURE SUCH THAT INCREASING HIGH CLOUDS SHOULD GRADUALLY OCCUR FROM SATURDAY AFTERNOON INTO SATURDAY NIGHT. WITH MOST IF NOT ALL OF CENTRAL NORTH CAROLINA EXPECTED TO BE MOSTLY CLOUDY BY THE MIDDLE OF THE NIGHT SATURDAY...OVERNIGHT LOWS SHOULD BE WARMER...MID TO UPPER 20S IN THE NORTHERN COASTAL PLAIN TO AROUND 30 ELSEWHERE. -DJF MINOR MID-LEVEL IMPULSES EMANATING FROM THE UPPER TROUGH/CLOSED LOW OVER THE SOUTHWEST US WILL GET KICKED EASTWARD...IN ADVANCE OF AN AMPLIFYING NORTHERN STREAM OVER THE CENTRAL PLAINS...ON SUNDAY. ASSOCIATED CYCLOGENESIS WILL TRACK EASTWARD ACROSS THE LOWER MS VALLEY/TN VALLEY ON SUNDAY...THEN ACROSS THE CAROLINAS/VIRGINIA SUNDAY NIGHT BEFORE MOVING OFF THE MID-ATLANTIC COAST MONDAY MORNING. NWP MODEL GUIDANCE CONTINUES TO EXHIBIT CONSIDERABLE SPREAD WITH THE TRACK OF THE SURFACE LOW AS IT MOVES THROUGH THE REGION SUNDAY NIGHT...WITH A DEFINITE NORTHWARD SHIFT OBSERVED IN THE LATEST 00Z/30 MODEL ITERATION. THIS RESULTS IN A SLIGHTLY SLOWER/DELAYED ONSET OF PRECIP ACROSS THE AREA LATE SUNDAY AFTERNOON AND EVENING...BUT IMPORTANTLY DISPLACES THE HEAVIER QPF NORTH OF THE AREA. AS SUCH...SUNDAY WILL END UP MOSTLY DRY ACROSS CENTRAL NC WITH THICKENING CLOUD COVER THROUGH THE AFTERNOON WITH HIGHS RANGING FROM MID 40S NORTH TO LOWER 50S SOUTH. RAIN CHANCES WILL QUICKLY RAMP UP SUNDAY EVENING...WITH CATEGORICAL POPS SUNDAY NIGHT...CUTTING OFF FROM WEST TO EAST MORNING MONDAY AS THE MID-LEVEL DRY SLOT RACES EASTWARD. ESTIMATED QPF AMOUNTS NOW LOOK TO BE IN THE 0.25-0.50" RANGE. WITH ONLY WEAK ELEVATED INSTABILITY AT BEST EXPECTED ACROSS THE COASTAL PLAIN AND WITH THE SURFACE LOW NOW DISPLACED NORTH OF THE AREA...WILL KEEP OUT THE MENTION OF ANY THUNDER ACROSS THE EASTERN ZONES. EXPECT A NON-DIURNAL TEMP TREND SUNDAY NIGHT...WITH LOWS OCCURRING BEFORE MIDNIGHT...THEN TEMPERATURES WARMING OVERNIGHT OWING TO STRONG WAA. LOWS SUNDAY NIGHT IN THE LOWER 40S NORTHWEST TO UPPER 40S SOUTHEAST. -CBL && .LONG TERM /MONDAY THROUGH THURSDAY/... AS OF 300 AM FRIDAY... MONDAY THROUGH TUESDAY: AGGRESSIVE MID-LEVEL DRY AIR INTRUSION WILL OVERTAKE THE AREA FROM THE WEST BETWEEN 12 TO 18Z MONDAY IN ADVANCE OF THE PASSAGE OF THE NORTHERN STREAM TROUGH PASSAGE MONDAY AFTERNOON. THIS WILL BRING AN ABRUPT END TO PRECIP ACROSS THE AREA MONDAY MORNING...WITH RAIN/SHOWERS EXITING THE COASTAL PLAIN BY MID TO LATE MORNING. EQUALLY IMPRESSIVE WILL BE STRONG POST-FRONTAL DRY COLD AIR ADVECTION REGIME...WITH TEMPERATURES FALLING BY THE AFTERNOON AS CONTINENTAL POLAR HIGH PRESSURE BUILDS INTO THE AREA MONDAY NIGHT AND INTO THE DAY ON TUESDAY. IF PROJECTED LOW-LEVEL THICKNESSES VERIFY AND WE DECOUPLE AS THE SURFACE HIGH MOVES OVERHEAD... EXPECT LOWS TUESDAY MORNING IN THE UPPER TEENS TO LOWER 20S. UNDER FULL COMPLIMENTS OF SUN...TEMPS TUESDAY WILL STRUGGLE TO WARM THROUGH THE 30S. HIGHS RANGING FROM MID/UPPER 30S NORTH TO LOWER 40S SOUTH. WEDNESDAY THROUGH THURSDAY: MODEL SPREAD REMAINS HIGH WITH THE EVOLUTION OF THE SLOW MOVING UPPER LOW/TROUGH EJECTING EASTWARD FROM MEXICO AND SUBSEQUENT DEVELOPMENT OF A LOW PRESSURE AREA TRACKING ALONG THE SOUTHEAST COAST. IN A COMPLETE ROLE REVERSAL... THE GFS IS NOW MORE PROGRESSIVE THAN THE EC WITH BRINGING PRECIP BACK INTO THE AREA DURING THE DAY ON WEDNESDAY...WITH THE EC NEARLY 24 HOURS SLOWER...DELAYING UNTIL THURSDAY. GIVEN LATER TIMING OF ONSET OF PRECIP...LOW-LEVEL THICKNESSES CURRENTLY SUPPORT ALL RAIN. HOWEVER IF FUTURE MODEL RUNS SPEED UP THE TIMING OF THE SYSTEM...ANY PRECIP INTO THE AREA TUESDAY NIGHT/EARLY WEDNESDAY MORNING COULD BE OF THE FROZEN VARIETY. WILL CONTINUE TO MONITOR TRENDS...BUT FOR NOW GIVEN UNCERTAINTY WILL KEEP POPS AT SMALL CHANCE FOR WEDNESDAY AND THURSDAY WITH A CONTINUATION OF BELOW NORMAL TEMPERATURES. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... AS OF 100 PM FRIDAY... STRONG NORTHWESTERLY WIND GUSTS (CROSSWINDS FOR MANY RUNWAYS) OF ANYWHERE FROM 25KT TO 35KT ARE OCCURRING ACROSS CENTRAL NC THIS MORNING IN THE WAKE OF A DEPARTING COLD FRONT. THESE GUSTS WILL CONTINUE THIS AFTERNOON AND MAY LINGER INTO THE EVENING HOURS BEFORE SUBSIDING AFTER MIDNIGHT. SCATTERED STRATOCU WILL BE MOSTLY CONCENTRATED FROM KRDU NORTH AND EAST BUT REMAIN ABOVE 5000 FT THIS AFTERNOON. OTHERWISE...HIGH PRESSURE WILL BUILD IN FROM THE WEST THROUGH SATURDAY AND VFR CONDITIONS ARE EXPECTED TO PREVAIL. BEYOND THE 12Z VALID TAF PERIOD... VFR CONDITIONS WILL CONTINUE THROUGH EARLY SUNDAY. A LOW PRESSURE SYSTEM WILL CROSS THE CENTRAL APPALACHIANS SUNDAY NIGHT...WITH A CHANCE OF RAIN AND SUB-VFR CONDITIONS FROM LATE SUNDAY AFTERNOON THROUGH MONDAY AFTERNOON. HIGH PRESSURE AND VFR CONDITIONS WILL RETURN FOR TUESDAY...WITH ANOTHER SYSTEM TO APPROACH THE REGION ON WEDNESDAY. && .FIRE WEATHER... AS OF 300 AM FRIDAY... WIND GUSTS TO 30KT TODAY...OR TO AROUND 35 MPH...ARE CERTAINLY POSSIBLE AS THE SURFACE GRADIENT TIGHTENS BEHIND THE COLD FRONT. SURFACE DEW POINTS WILL FALL BEHIND THE FRONT AS WELL...WITH THE LOWEST GUIDANCE OF THE RAP SUGGESTING SOME DEW POINTS IN SINGLE FIGURES LATE IN THE DAY IN THE NORTHWEST PIEDMONT. THE GFS IS HIGHER...AND THE NAM IS MORE OF A COMPROMISE...WHICH IS CONSISTENT WITH THE MOS GUIDANCE. BY 00Z SATURDAY...THE GRIDDED FORECAST WILL SHOW A DEW POINT NEAR 10F IN THE TRIAD...BUT EVEN THERE THE MINIMUM RELATIVE HUMIDITY IS IN THE UPPER 20S PERCENT. BASED THOSE DEW POINTS...RECENT RAIN...AND EARLIER FORECAST SERVICE COORDINATION... WILL FOR NOW HIGHLIGHT THE ADVERSE CONDITIONS OF THE WIND GUSTS IN THE DISCUSSION OF THE FIRE WEATHER FORECAST. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DJF NEAR TERM...DJF/BLS SHORT TERM...DJF/CBL LONG TERM...CBL AVIATION...BLS FIRE WEATHER...DJF

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