Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 030309 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1000 PM EST MON MAR 2 2015 .SYNOPSIS...HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH TONIGHT AND WILL SHIFT OFFSHORE DURING THE DAY TUESDAY AS A LOW PRESSURE SYSTEM TRACKS NORTHEAST FROM THE CENTRAL PLAINS INTO THE GREAT LAKES. && .NEAR TERM /TONIGHT THROUGH TUESDAY NIGHT/... AS OF 1000 PM MONDAY... AFTER A PLEASANTLY WARM DAY...COOLER AND DRIER AIR IS WORKING ITS WAY INTO THE AREA FROM THE NORTH-NORTHEAST AS A 1034MB SURFACE HIGH TRANSLATES EAST ACROSS THE MID-ATLANTIC STATES. THE PRIMARY COLD FRONT IS TO OUR SOUTH...BUT THERE APPEARS TO BE A SECONDARY BOUNDARY...WITH NOTICEABLY HIGH DEWPOINTS POOLING ALONG IT...MOVING FROM THE COASTAL PLAIN TOWARD THE PIEDMONT. THIS COMPLICATES THE OVERNIGHT FORECAST AS THE DRIER...SUB-20F DEWPOINT AIR OVER THE THE NORTHWEST PIEDMONT TRIES TO PUSH SOUTH BUT MAY ULTIMATELY BE HALTED OR SHUNTED OFF TO THE WEST. MOST MODEL ARENT HANDLING THIS VERY WELL...EVIDENT IN PART BY THE MUCH DRIER THAN FORECAST BOUNDARY LAYER ON THE 00Z KGSO RAOB...SO WILL LEAN ON THE RAP/HRRR WHICH HAS DEWPOINTS MOSTLY IN THE 20S TO LOWER 30S TUESDAY MORNING. TEMPS WILL CONTINUE TO FALL INTO THE 30S OVERNIGHT...BUT AS SOME 290K ISENTROPIC LIFT AND HIGHER BASED STRATUS SPREAD NORTH AND EAST ACROSS THE AREA...TEMPS SHOULD STABILIZE MOSTLY ABOVE FREEZING. THE BIGGEST FORECAST ISSUES TONIGHT WILL STILL BE 1) WHETHER OR NOT ANY LIGHT RAIN/DRIZZLE SPREADS FAR ENOUGH NORTH AND EAST INTO THE SUB-FREEZING AIRMASS BEFORE A WEAK DIURNAL RECOVERY IN TEMPS BEGINS ON TUESDAY MORNING...OR 2) PRECIP IS EVEN HEAVY ENOUGH WETBULB TEMPS BELOW FREEZING IN AREAS WHERE THEY ARE INITIALLY ABOVE FREEZING. 18Z AND 00Z GUIDANCE CONTINUES TO ONLY SHOW A COUPLE HUNDREDTHS AT BEST AND MOSTLY COMING AFTER 12Z. THE RAP AND HRRR ARE COMPLETELY DRY THROUGH 12Z. WILL LOWER POPS A LITTLE AND JUST MAINTAIN A MENTION JUST FREEZING DRIZZLE IN THE SMALL AREA WHERE TEMPS AT AT OR BELOW 32...WHICH IS CONFINED TO JUST THE NORTH PIEDMONT PRIOR TO 15Z. NO ADVISORY FOR FREEZING RAIN IS NEEDED AT THIS TIME. TEMPS ON TUESDAY WILL MOVE LITTLE OFF MORNING LOWS...MID 30S TO LOWER 40S. A WARM FRONT IS EXPECTED TO LIFT NORTHWARD TOWARD CENTRAL NC TUE NIGHT...WITH TEMPERATURES RISING OVERNIGHT ACROSS MUCH OF THE AREA...ALTHOUGH THEY COULD REMAIN NEAR STEADY IN THE N/NW PIEDMONT. LIGHT RAIN/DRIZZLE COULD TAPER AS THE WARM FRONT LIFTS WITH EXPANDING FOG CONDITIONS POSSIBLE. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... AS OF 300 PM MONDAY... THE FORECAST PROBLEM FOR THIS PART OF THE FORECAST CONTINUES TO BE THE UNCERTAINTY IN TEMPERATURES DUE TO THE POTENTIALLY LINGERING WEDGE AND THE TIMING AND EXTENT TO WHICH THE WARM FRONT RETREATS NORTHWARD. GIVEN THAT THE MODELS HAVE A TENDENCY TO ERODE THE WEDGE TOO QUICKLY...ESPECIALLY IF THERE IS PRECIPITATION FALLING INTO IT...CURRENTLY FORECAST THE WEDGE STICKING AROUND INTO WEDNESDAY AFTERNOON IN THE FAR NW PIEDMONT...WITH A LARGE SPREAD IN TEMPS FROM NW TO SE ACROSS THE AREA. CONFIDENCE REMAINS SOMEWHAT LOW WITH RESPECT TO TEMPS...AS ANY CHANGES TO THE TIMING AND POSITION OF THE WEDGE/WARM FRONT AS THEY ERODE/RETREAT NORTHWARD WILL HIGHLY IMPACT TEMPERATURES. THEY WILL HOWEVER INCREASE GRADUALLY THROUGH AROUND MIDNIGHT THURSDAY BEFORE THE COLD FRONT BEGINS MOVING INTO THE NW. KEEPING IN MIND THE POTENTIAL MARGIN FOR ERRORS...FORECAST HIGH TEMPS IN THE MID 60S NW TO MID 70S SE ON WEDNESDAY. A NORMAL DIURNAL TEMPERATURE CURVE SHOULD RETURN WEDNESDAY NIGHT...ALTHOUGH THE TEMPERATURE GRADIENT WILL BE QUITE LARGE AND WILL DEPEND ON THE TIMING AND POSITION OF THE COLD FRONT...EXPECT LOWS IN THE UPPER 30S NORTH TO LOW 50S SOUTH WEDNESDAY NIGHT AND HIGHS IN THE LOW 40S NORTH TO MID 50S SOUTH ON THURSDAY AND DECREASING BEHIND THE FRONT. PRECIPITATION: THERE WILL BE A SLIGHT CHANCE OF PRECIP...MAINLY ACROSS THE WESTERN PORTIONS OF THE AREA WEDNESDAY...EVEN THOUGH THE MAIN PRE-FRONTAL CONVECTIVE RAINFALL REMAINS LARGELY ALONG OR WEST OF THE APPALACHIANS UNTIL WEDNESDAY AFT/EVE. SOUTHWESTERLY WINDS WILL BE QUITE STRONG ON WEDNESDAY AFT/EVE AS THE GRADIENT TIGHTENS AHEAD OF THE FRONT. LATE WEDNESDAY AFTERNOON IS STARTING TO SHAPE UP AS A HIGH SHEAR/LOW CAPE EVENT. FORECAST SOUNDINGS INDICATE 200-300 JOULES OF CAPE AND 0-3 KM SHEAR VALUES AROUND 35 KTS...MAINLY ALONG AND EAST OF I-95 AT THIS TIME. WITH SURFACE TEMPS EXPECTED IN THE MID 70S AND DEWPOINTS AROUND 60 DEGREES...THUNDERSTORMS WILL BE POSSIBLE WEDNESDAY AFTERNOON...THUS WILL INTRODUCE A SLIGHT CHANCE ACROSS THE EAST WITH THIS AFTERNOON`S FORECAST. THE LATEST 12Z ECMWF AND GFS MODEL RUNS ARE IN BETTER AGREEMENT WITH THE TIMING OF THE FROPA AND THE ASSOCIATED RAINFALL AS IT MOVES THROUGH THE AREA. THE LATEST RUNS SUGGEST THAT RAIN WILL BE LIKELY WEDNESDAY NIGHT... PROGRESSING NW TO SE THROUGH CENTRAL NC THROUGH MIDNIGHT FRIDAY. THIS REMAINS CASE OF THE COLD AIR CHASING THE PRECIP...BUT FOR NOW STILL EXPECT ALL PRECIP TO FALL AS RAIN...HOWEVER THERE IS A SMALL CHANCE THAT A FEW SNOWFLAKES COULD MIX IN ON THE TAIL END OF THE EVENT. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... AS OF 300 PM MONDAY... FRIDAY THROUGH SATURDAY: HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT THURSDAY NIGHT...REMAINING OVER THE REGION INTO THE WEEKEND. EXPECT A DRY FORECAST FRIDAY THROUGH SATURDAY...WITH HIGHS IN THE UPPER 30S TO LOW 40S FRIDAY...INCREASING THROUGH THE WEEKEND AND INTO THE UPPER 50S TO LOW 60S BY MONDAY. LOWS WILL SEE A SIMILAR TREND...INCREASING FROM MAINLY LOW 20S LOW 20S THU AND FRI NIGHTS TO THE LOW TO MID 30S BY SAT AND SUN NIGHTS. THERE IS SOME MODEL DISAGREEMENT TOWARD THE END OF THE PERIOD WITH REGARD TO PRECIP CHANCES...AS THE ECMWF BRINGS PRECIP IN FROM THE SOUTHWEST SUNDAY NIGHT AND THE GFS IS COMPLETELY DRY. WILL FORECAST A SLIGHT CHANCE FOR RAIN SUN NIGHT/MONDAY...ALTHOUGH CONFIDENCE IS LOW AT THIS TIME. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... AS OF 745 PM MONDAY... STRONG (1032 MB) BUT TRANSIENT MODIFIED ARCTIC HIGH PRESSURE WILL RIDGE SOUTH INTO NC TONIGHT...THEN BUILD QUICKLY OFFSHORE ON TUE. INITIALLY VFR CONDITIONS THIS EVENING WILL BE THREATENED WITH FIRST A NARROW BAND OF LOW MVFR CLOUDS THAT NEAR TERM GUIDANCE WILL DEVELOP IN THE VICINITY OF KRWI IN THE NEXT COUPLE OF HOURS...THEN SWEEP...IN NORTHEASTERLY FLOW...TO THE SOUTHWEST ACROSS THE REMAINDER OF CENTRAL NC BETWEEN 02-07Z...LASTING AT ANY ONE LOCATION FOR JUST 2-3 HOURS BEFORE DEPARTING. MEANWHILE...AN AREA OF 4-5 THOUSAND FT CEILINGS OVER SC WILL EXPAND NORTH AS THE FLOW IN THAT LAYER STRENGTHENS AND CAUSES AIR TO GENTLY RISE ATOP THE AFOREMENTIONED RIDGE OF SURFACE HIGH PRESSURE AND ASSOCIATED NORTHEASTERLY FLOW BENEATH. CONFIDENCE IS RELATIVELY HIGH THAT CEILINGS WITHIN THIS AREA OF CLOUDS WILL THEN GRADUALLY LOWER TO INTO MVFR RANGE FROM WSW TO ENE ON TUE - FIRST AT KINT/KGSO AND LAST AT KRWI. THERE IS A LESSER...MEDIUM CHANCE (AROUND 50 PERCENT)... THAT CONDITIONS WILL LOWER TO IFR...WITH ACCOMPANYING PERIODS OF LIGHT RAIN/DRIZZLE MAINLY AT KGSO/KINT...AND PERHAPS AS FAR EAST AS KRDU...TUE MORNING. IF PRECIPITATION WERE TO INDEED OCCUR... TEMPERATURES WILL BE CLOSE TO FREEZING AT KINT/KGSO...WHERE AN ASSOCIATED PERIOD OF FREEZING PRECIPITATION WOULD BE POSSIBLE. OUTLOOK: TUE NIGHT: SUB-VFR CONDITIONS WILL CONTINUE TO DEVELOP NORTHEAST AND LOWER ACROSS CENTRAL NC THROUGH TUE NIGHT...SUCH THAT LIFR CONDITIONS WITH RESPECT TO CEILINGS AND POSSIBLY VISIBILITIES IN DENSE FOG...ARE EXPECTED TO PREVAIL LATE TUE NIGHT-WED MORNING...IN ASSOCIATION WITH THE SLOW RETREAT/APPROACH OF A WARM FRONT FROM THE SOUTHEAST. WED-THU: A RETURN TO VFR WILL BE PROBABLE WITH THE PASSAGE OF THE WARM FRONT LATER WED AT KFAY/KRWI/KRDU...BUT THIS IMPROVEMENT WILL BE DELAYED...OR MAY NOT OCCUR AT ALL AT KINT/KGSO...BEFORE A COLD FRONT AND AREA OF RAIN ARRIVE FROM THE NORTHWEST WED NIGHT...AND PERSIST THROUGH MUCH OF THU. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...CBL/BLS SHORT TERM...KC LONG TERM...KC AVIATION...RAH

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