Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230729 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 325 AM EDT WED APR 23 2014 .SYNOPSIS...A COLD FRONT CROSSING THE REGION WILL MOVE OFFSHORE EARLY THIS MORNING. HIGH PRESSURE WILL BUILD IN FROM THE NORTHWEST THROUGH THURSDAY. ANOTHER COLD FRONT WILL APPROACH FROM THE WEST ON FRIDAY. && .NEAR TERM /THROUGH THURSDAY NIGHT/... AS OF 305 AM WEDNESDAY... FOR TODAY/TONIGHT: COLD FRONT CURRENTLY MAKING ITS WAY THROUGH CENTRAL NC. PATCHY FOG HAS FORMED IN THE COMPARATIVELY LIGHT FLOW AND HIGHER-DEWPOINT AIR AHEAD OF THE FRONT... BUT EXPECT CLEAR SKIES WITH RAPID DRYING BEHIND THE FRONT ALONG WITH A WIND SHIFT TO WNW THEN NW. STRONG SHORTWAVE TROUGH AND VORTICITY MAX PASSAGE OVER THE NORTHEAST AND MIDATLANTIC COAST MAY BRING A FEW CLOUDS ACROSS NORTHEAST SECTIONS... BUT OTHERWISE SKIES WILL BE GENERALLY CLEAR TODAY WITH A DRY AND STABLE COLUMN NOTED UPSTREAM AND ON FORECAST SOUNDINGS. THICKNESSES INDICATE HIGHS OF 68-74. BRISK WINDS FROM THE NW ARE EXPECTED TO BE SUSTAINED AT 13-18 MPH WITH PERIODIC GUSTS TO 20-25 MPH. THIS WIND COMBINED WITH THE DROP IN HUMIDITY TO AROUND 25% WILL BRING ABOUT A RISK FOR ADVERSE FIRE BEHAVIOR (SEE DISCUSSION BELOW). CONTINUED CLEAR TONIGHT WITH LIGHT WINDS AS THE HIGH PRESSURE RIDGE NOSES IN FROM THE NORTH. LOWS TONIGHT 37-44... COLDEST IN THE VA BORDER COUNTIES AND IN OUTLYING AREAS OF NRN PIEDMONT. THE POTENTIAL EXISTS FOR PATCHES OF FROST IN THESE ISOLATED SPOTS... BUT EVEN THESE COLDER LOWS ARE A BIT ABOVE WHAT WE NORMALLY NEED FOR A FROST ADVISORY... SO WILL HOLD OFF FOR NOW A REASSESS THE NEED LATER TODAY. FOR THU/THU NIGHT: ANOTHER GENERALLY CLEAR DAY EXPECTED... WITH ANOTHER REINFORCING FRONT DROPPING THROUGH FROM THE NORTH TO KNOCK THICKNESSES BACK DOWN TO READINGS NEARLY 30 M BELOW NORMAL. DESPITE PLENTY OF SUNSHINE WITH A SURFACE RIDGE NOSING IN FROM THE NORTH AND WEAK MID LEVEL RIDGING BUILDING IN FROM THE WEST... WE SHOULD SEE BELOW-NORMAL HIGHS OF 67-73. A WARM FRONTAL ZONE WILL APPROACH CENTRAL NC FROM THE SW LATE THU NIGHT... RESULTING IN A STRENGTHENING FLOW FROM THE SW AND QUICKLY INCREASING LOW LEVEL MOISTURE FROM SW TO NE. MOIST ISENTROPIC UPGLIDE RAMPS UP AROUND 295K ESPECIALLY IN THE SW HALF OF THE CWA... SO WILL TREND TOWARD INCREASING CLOUDINESS AREAWIDE AND MENTION PATCHY DRIZZLE OVER THE FAR SW CWA (INCLUDING WINSTON-SALEM / ASHEBORO / ALBEMARLE / WADESBORO / LAURINBURG) LATE THU NIGHT. MILDER LOWS OF 46-53. -GIH && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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AS OF 325 AM WEDNESDAY... A PROGRESSIVE SHORTWAVE AND ASSOCIATED SURFACE FRONTAL ZONE WILL MOVE INTO THE TENNESSEE AND OHIO VALLEYS FRIDAY MORNING...THEN ACROSS THE MOUNTAINS DURING THE DAY ON FRIDAY. MODEL SOLUTIONS HAVE ACTUALLY DIVERGED A BIT REGARDING THE TIMING OF THE BEST FORCING AND SUBSEQUENT QPF. THE GFS CONTINUES TO BE THE FASTER SOLUTION...WITH THE UPPER TROUGH AND LOBE OF VORTICITY MOVING ACROSS CENTRAL NC BY MIDDAY...WHILE THE TRAILING FRONTAL ZONE CROSSES THE AREA DURING THE AFTERNOON AND EVENING. THIS SEEMS TO SUGGEST POSSIBLE SHOWERS EARLIER IN THE DAY LESS POTENTIAL FOR HEATING AND DESTABILIZATION AHEAD OF THE FRONT. THE ECWMF HAS TRENDED SHARPER AND A BIT DEEPER WITH THE TROUGH...WHICH LEADS TO A SLOWER SOLUTION BUT BETTER HEATING...PARTICULARLY OVER THE COASTAL PLAIN. LOW-LEVEL MOISTURE RETURN AHEAD OF THE FRONT IS WEAK BUT SHOULD ALLOW DEWPOINTS TO RISE INTO THE UPPER 50S AND LOWER 60S...WHICH COMBINED WITH FORECAST HIGHS IN THE 75-81 RANGE BUT WEAK MID-LEVEL LAPSE RATES...SHOULD YIELD WEAK INSTABILITY...MAYBE 500-1000 J/KG MAINLY ACROSS THE SOUTH AND EAST. DEEP LAYER IS FORECAST TO BE ON THE ORDER OF 25- 35KT...THOUGH STRONGEST TO THE NORTH AWAY FROM BETTER INSTABILITY. POTENTIAL FOR SEVERE SEEMS LIMITED GIVEN THE MARGINAL SHEAR/INSTABILITY...BUT THE SLOWER TREND WITH THE ECMWF AND STRONGER DCVA WOULD SUPPORT A LITTLE BETTER CHANCE. GIVEN THAT THE MID-LEVEL FLOW WILL BE WESTERLY AND DRYING...WILL KEEP POPS IN THE CHANCE RANGE WITH HIGHS IN THE MID 70S WEST TO LOWER 80S EAST. THE COLD FRONT SHOULD PUSH EAST OF THE CWA BY MIDNIGHT FRIDAY NIGHT AND BRING PRECIP CHANCES TO AN END. A SECONDARY FRONTAL ZONE IS FORECAST TO APPROACH BUT REMAIN NORTH OF THE AREA. THUS THE MAIN SENSIBLE IMPACT WILL BE LOWER HUMIDITY ON SATURDAY...WITH FORECAST HIGHS IN THE UPPER 70S AND LOWER 80S.
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&& .LONG TERM /SUNDAY THROUGH TUESDAY/...
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AS OF 325 AM WEDNESDAY... THE PROGRESSIVE FLOW OVER THE CONUS THIS WEEK IS FORECAST TRANSITION TO A MORE AMPLIFIED AND EVEN BLOCKED FLOW NEXT WEEK...THOUGH THE GFS AND ECMWF DONT YET AGREE ON THE DEGREE OF BLOCKING IN THE FLOW. IN GENERAL...A STRONG TROUGH WILL EJECT OUT OF THE SOUTHERN PLAINS THIS WEEKEND AND THEN LIKELY CLOSE OFF INTO AN UPPER LOW OVER THE MIDWEST STATES BY MONDAY.....WITH ANOTHER LOW OVER THE NORTHERN ATLANTIC AND A SHORTWAVE RIDGE IN BETWEEN. THE BIG QUESTION WILL BE WHERE A FRONTAL ZONE TO OUR NORTH ENDS UP ON SUNDAY AND THEN HOW QUICKLY PRECIP SPREADS EAST ALONG THE FRONT MONDAY AND TUESDAY AS THE UPPER LOW MOVES SLOWLY TO THE EAST. THE GFS SUGGEST THE FRONT WILL UNDERCUT THE UPPER RIDGE AND SLIP BACKDOOR INTO THE AREA BY SUNDAY...WHILE THE ECMWF KEEP THE FRONT WELL NORTH OF NC. PRECIP CHANCES SHOULD INCREASE DRAMATICALLY BY TUESDAY AS THE UPPER LOW FINALLY MOVES EAST OF THE MISSISSIPPI RIVER. TEMPS DURING THE TIME FRAME WILL BE MOSTLY AROUND NORMAL...THOUGH UNCERTAINTY GROWS INTO MONDAY AND TUESDAY AS THE POTENTIAL FOR CLOUD COVER AND PRECIP GROW.
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 110 AM WEDNESDAY... A COLD FRONT NOW MOVING INTO THE NC FOOTHILLS FROM THE WNW WILL SWEEP ESE THROUGH CENTRAL NC EARLY THIS MORNING. AHEAD OF THE FRONT... WHERE THE SURFACE HUMIDITY LEVELS REMAIN HIGH... THERE IS A SMALL CHANCE OF MVFR FOG EARLY THIS MORNING... PRIOR TO 08Z AT INT/GSO... 09Z AT RDU/RWI... AND BEFORE 10Z AT FAY. AFTER THESE TIMES... HUMIDITY LEVELS WILL DROP WITH PASSAGE OF THE COLD FRONT. OTHERWISE... HIGH CONFIDENCE IN VFR CONDITIONS TODAY THROUGH TONIGHT... WITH FEW TO NO CLOUDS AND NO FURTHER RESTRICTIONS TO VSBYS AS HIGH PRESSURE BUILDS IN FROM THE NW. OF SOME CONCERN HOWEVER IS THE SHIFT OF WINDS WITH FRONTAL PASSAGE... TO NORTHWESTERLY AT ALL SITES (FROM NW TO SE) 07Z-10Z. SUSTAINED WINDS OF 12-16 KTS MAY GUST UP TO 25 KTS FROM DAYBREAK THROUGH LATE AFTERNOON. THIS MAY CAUSE CROSSWIND PROBLEMS AT GSO/RDU/RWI/FAY TODAY. WINDS WILL DIMINISH SOON AFTER 22Z. LOOKING BEYOND 06Z EARLY THU MORNING: CONTINUED VFR THROUGH THU EVENING WITH A HIGH PRESSURE RIDGE IN PLACE ACROSS CENTRAL NC. A WARM FRONT WILL APPROACH FROM THE SW THU NIGHT... BRINGING WINDS FROM THE SW AND A GOOD CHANCE OF IFR CONDITIONS... WHICH SHOULD GRADUALLY IMPROVE TO MVFR FRI MORNING WITH SCATTERED SHOWERS AND STORM FROM FRI MORNING INTO THE AFTERNOON. A COLD FRONT WILL THEN MOVE THROUGH BY FRI EVENING... WITH HIGH PRESSURE TO FOLLOW... BRINGING LIGHT WINDS AND VFR CONDITIONS OVER THE WEEKEND. -GIH && .FIRE WEATHER /WEDNESDAY INTO WEDNESDAY EVENING/... AS OF 207 PM TUESDAY... INCREASED FIRE DANGER FOR WEDNESDAY ACROSS ALL OF CENTRAL NC. NORTHWEST WINDS AT 15 TO 20 MPH WILL GUST TO 30 BEHIND A COLD FRONT WEDNESDAY AFTERNOON INTO EARLY WEDNESDAY EVENING. LOW MINIMUM RELATIVE HUMIDITIES AROUND 25 PERCENT CAN BE EXPECTED WEDNESDAY AFTERNOON. FINE FUEL MOISTURE LEVELS WILL DRY OUT. IN COORDINATION WITH WAKEFIELD AND BLACKSBURG - AND THE FORESTRY OFFICIALS... WE WILL ISSUE AN INCREASED FIRE DANGER STATEMENT FOR WEDNESDAY. .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...SMITH LONG TERM... SMITH AVIATION...HARTFIELD FIRE WEATHER...BADGETT

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