Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 161749 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 150 PM EDT TUE SEP 16 2014 .SYNOPSIS...A COLD FRONT WILL APPROACH FROM THE NORTHWEST LATER TODAY... THEN PUSH SOUTHEAST THROUGH THE REGION TONIGHT. COOL HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH ON WEDNESDAY... AND HOLD OVER THE AREA THROUGH THE REST OF THE WORK WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1010 AM TUESDAY... REST OF TODAY: MUCH OF THE LOW CLOUDINESS FROM EARLIER THIS MORNING HAS THINNED OR DISSIPATED ENTIRELY... LEAVING PLENTIFUL SUNSHINE ACROSS ALL BUT THE FAR SOUTHEAST... WHERE CLOUDS LINGER BUT ARE PROGRESSING EASTWARD. THE SURFACE TROUGH (EVIDENT UP THROUGH 850 MB) IS HOLDING OVER THE ERN CWA... AND LOW LEVEL NWRLY DOWNSLOPE FLOW IS HELPING WITH THE DISSOLUTION OF THE LOW CLOUDS. A MID LEVEL SHORTWAVE NOW MOVING INTO THE TN VALLEY... ROTATING AROUND THE BASE OF THE LARGE CENTRAL/ERN NOAM TROUGH... WILL SHIFT INTO THE SRN APPALACHIANS LATE TODAY BEFORE CROSSING CENTRAL NC. WHILE PW VALUES WILL BUMP UP TO NEAR 1.5" AS THIS WAVE APPROACHES... INSTABILITY IS PROJECTED TO BE MARGINAL ESPECIALLY ACROSS THE NORTH... AS MUCAPE OF 500-1000 J/KG WILL BE CONFINED TO SOUTHERN SECTIONS TODAY. DEEP LAYER SHEAR OF JUST 20-25 KTS WILL ALSO BE BORDERLINE... BUT GIVEN THE INVERTED-V PRESENTATION OF FORECAST SOUNDINGS RESULTING FROM THE AFOREMENTIONED DOWNSLOPE DRYING AND SLIGHTLY LOWER DEW POINTS... A FEW SHOWERS AND STORMS COULD PRODUCE STRONG GUSTY WINDS. EXPECT SCATTERED CONVECTION TO ARRIVE SOON AFTER 19Z IN THE WEST... THEN TRACK EASTWARD THROUGH 04Z... TAPERING OFF THEREAFTER BUT WITH LINGERING CHANCES ESPECIALLY IN THE EAST AND NORTH OVERNIGHT. CURRENT TEMPS ARE RUNNING 5-10 DEGREES ABOVE YESTERDAY`S PACE AT THIS TIME... AND CURRENT FORECAST HIGHS IN THE LOW-MID 80S APPEAR ATTAINABLE... AND ARE IN LINE WITH LATEST HIGH-RES GUIDANCE. -GIH TONIGHT...SCATTERED CONVECTION WILL GRADUALLY WEAKEN WITH LOSS OF HEATING AND EXITING OF MID LEVEL DISTURBANCE. STILL...COULD SEE A FEW SHOWERS PERSIST PAST MIDNIGHT TO THE EAST-SOUTH OF RDU. CLOUDINESS AND LACK OF APPRECIABLE LOW LEVEL CAA SUGGEST MIN TEMPS A FEW DEGREES WARMER THAN EARLIER THINKING. MIN TEMPS LOW-MID 60S.-WSS && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 330 AM TUESDAY... WEDNESDAY...ABUNDANT LOW LEVEL MOISTURE TRAPPED BENEATH A LOW LEVEL INVERSION SHOULD RESULT IN EXTENSIVE CLOUDINESS OVER MOST OF THE REGION WEDNESDAY MORNING...AND POTENTIALLY LINGERING INTO THE AFTERNOON ACROSS THE PIEDMONT. (THIS MAY BE CLASSIFIED AS A HYBRID OR INSITU DAMMING EVENT THOUGH PARENT HIGH RELATIVELY WEAK AND QUITE TRANSITORY). IF EXTENSIVE CLOUDS DO LINGER PAST MID DAY ACROSS THE PIEDMONT...THIS MAY CREATE A DIFFERENTIAL HEATING BOUNDARY BETWEEN THE PIEDMONT AND THE SANDHILLS/SOUTHERN COASTAL PLAIN. THE APPROACH OF YET ANOTHER DISTURBANCE IN THE WEST-NW FLOW ALOFT INTERACTING WITH THIS FEATURE MAY TRIGGER MORE SCATTERED CONVECTION...MAINLY OVER THE SE THIRD OF OUR FORECAST AREA. THE LOW LEVEL STABLE AIR MASS SUGGEST MAINLY PATCHY STRATIFORM RAIN OVER THE NORTHERN PIEDMONT (OR ELEVATED SHOWERS. SINCE LEANING TOWARD MORE CLOUDINESS ACROSS THE PIEDMONT...HAVE LOWERED MAX TEMPS A COUPLE OF DEGREES BUT RAISED MAX TEMPS TO NEAR/ABOVE 80 OVER THE SE COUNTIES. CONTINUED CYCLONIC FLOW ALOFT WILL MAINTAIN CLOUDINESS WEDNESDAY NIGHT ALONG WITH A SMALL THREAT FOR SHOWERS...MAINLY EAST OF HIGHWAY 1. MIN TEMPS SEVERAL DEGREES COMPARED TO THE PREVIOUS NIGHT. MIN TEMPS UPPER 50S NW TO LOWER 60S SE. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 330 AM TUESDAY... THE MEDIUM RANGE WILL FEATURE A LONGWAVE TROUGH THAT WILL MOVE OFFSHORE THE EAST COAST THU AND CONSEQUENTLY YIELD TO RISING HEIGHTS ALOFT AS A FLAT MID LEVEL RIDGE RIDGE BRIEFLY BUILDS EAST FROM THE SOUTHERN PLAINS AND LOWER MS VALLEY FRI-SAT. THE RE-ESTABLISHMENT OF A WESTERN NOAM RIDGE WILL THEN RESULT IN DOWNSTREAM TROUGH AMPLIFICATION FROM SOUTH-CENTRAL CANADA TO THE EAST-CENTRAL US SUN- MON...THE LEAD SHORTWAVE TROUGH OF WHICH WILL INCLUDE THE REMNANTS OF TROPICAL STORM ODILE. MEANWHILE AT THE SFC...A CANADIAN-SOURCE SFC HIGH (AROUND 1030 MB) WILL BUILD FROM CENTRAL CANADA TO THE CANADIAN MARITIMES AND RIDGE SOUTH/SOUTHWESTWARD IN DAMMING ORIENTATION EAST OF THE APPALACHIANS THU THROUGH THE WEEKEND...FOLLOWED BY A COLD FRONTAL PASSAGE - DRIVEN BY THE AFOREMENTIONED RE-AMPLIFICATION OF THE LONGWAVE TROUGH INTO THE EAST-CENTRAL US - ON MON. THE RESULT WILL BE A RELATIVELY PROLONGED PERIOD OF EAST TO NORTHEAST LOW LEVEL FLOW AND ASSOCIATED BELOW NORMAL TEMPERATURES... TEMPERED FURTHER BY PERIODS OF BKN MULTI-LAYERED CLOUD COVER...THROUGH EARLY THIS WEEKEND. THE RELATIVE GREATEST CLOUD COVERAGE WILL LINGER THU (FROM WED NIGHT)...WHEN A LINGERING CHANCE OF SHOWERS WILL ALSO REMAIN...MAINLY OVER THE COASTAL WHERE A DEPARTING H85 WAVE/TROUGH WILL AUGMENT WEAK FORCING ALOFT ATTENDING A PAIR OF SHORTWAVE TROUGHS FORECAST TO CROSS THE CAROLINAS AND MIDDLE ATLANTIC THROUGH MID-LATE THU AFTERNOON. UNDER ASSOCIATED VARIABLY CLOUDY SKY COVER...WITH RELATIVE GREATEST COVERAGE EAST...TEMPERATURES SHOULD FALL ABOUT A CATEGORY OR SO SHY OF WHAT FULL SUN THICKNESSES OF AROUND 1385 METERS WOULD OTHERWISE SUPPORT. COOL AGAIN OVERNIGHT WITH DEEP LAYER DRYING/FALLING PRECIPITABLE WATER VALUES TO AROUND AN INCH...AS THE AFOREMENTIONED MID LEVEL RIDGE EXPANDS EASTWARD AND CAUSES - LOWS MIDDLE 50S TO AROUND 60. OTHERWISE...THE INCREASING INFLUENCE OF THE RIDGING AT THE SFC AND ALOFT SHOULD PROMOTE DRY CONDITIONS FRI-SUN...THOUGH WITH TEMPERATURES MODERATING ONLY SLOWLY THROUGH THE 70S...TO AROUND 80 DEGREES BY SUN. THE PASSAGE OF THE SFC COLD FRONT EARLY NEXT WEEK SHOULD THEN SUPPORT A CHANCE OF SHOWERS IN CENTRAL NC ON MON. ONCE THE INHERENT D7 TIMING DIFFERENCES ARE IRONED OUT...A SLIGHT CHANCE OF THUNDER MAY BE INTRODUCED WITH LATER FORECASTS IF IT APPEARS FAVORABLE DIURNAL TIMING OF THE FRONTAL PASSAGE WILL OCCUR. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 150 PM TUESDAY... EARLIER SUB-VFR CONDITIONS HAVE IMPROVED TO VFR AREAWIDE. THESE VFR CONDITIONS ARE EXPECTED TO DOMINATE THROUGH THIS EVENING... BUT WILL BE FOLLOWED BY A TREND TO MVFR CIGS/VSBYS (AND POTENTIALLY SLIPPING TO IFR AT TIMES) GRADUALLY STARTING AFTER 05Z TONIGHT. A WEAK SURFACE TROUGH EXTENDS THROUGH ERN NC... WITH LIGHT AND VARIABLE WINDS OVER CENTRAL NC. A COLD FRONT LOCATED NW OF NC WILL CONTINUE MOVING TOWARD THE SE THEN SOUTH THROUGH THE STATE TONIGHT. FRONTAL PASSAGE IS EXPECTED AT INT/GSO SOON AFTER 05Z... AT RDU/RWI SOON AFTER 07Z... AND AT FAY SOON AFTER 10Z TONIGHT. LIGHT/VARIABLE WINDS WILL SWING AROUND TO NW THEN NE... AND REMAIN FROM THE NE AT 7- 10 KTS AFTER SUNRISE WED AT ALL SITES. AFTER FRONTAL PASSAGE... WITH THE EXCEPTION OF FAY WHICH HAS A LOWER CHANCE OF SUB-VFR CONDITIONS... THE REST OF CENTRAL NC TAFS WILL SEE MVFR CLOUDS DEVELOP OVERNIGHT... SUCH THAT BY SUNRISE... INT/GSO/RDU/RWI SHOULD ALL HAVE CIGS AROUND 1000-1500 FT AGL... POSSIBLY FALLING LOWER WED MORNING. LOOKING BEYOND 18Z WED... SUB-VFR CONDITIONS AT INT/GSO/RDU/RWI ARE EXPECTED TO LAST THROUGH WED NIGHT... LIFTING AND MIXING OUT TO VFR DURING THU MORNING. PATCHY DRIZZLE WILL BE POSSIBLE WED EVENING/NIGHT. AFTER MIDDAY THU... EXPECT QUIET WEATHER AS HIGH PRESSURE BUILDS IN FROM THE NORTH. THIS HIGH PRESSURE AREA WILL SLIDE OFFSHORE YET CONTINUE TO EXTEND SOUTHEASTWARD OVER CENTRAL NC HEADING THROUGH THE WEEKEND... BRINGING GENERALLY DRY WEATHER AND VFR CONDITIONS THROUGH SUNDAY. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD/WSS SHORT TERM...WSS LONG TERM...MWS AVIATION...HARTFIELD

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