Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 181821 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 220 PM EDT THU SEP 18 2014 .SYNOPSIS...
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HIGH PRESSURE CENTERED NORTHEAST OF THE GREAT LAKES WILL EXTEND DOWN THROUGH VIRGINIA AND THE CAROLINAS THROUGH THE WEEKEND... AS IT SLIDES EAST. A COLD FRONT WILL APPROACH FROM THE NORTHWEST LATE SUNDAY... THEN MOVE SOUTHEAST THROUGH THE REGION MONDAY.
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&& .NEAR TERM /THROUGH FRIDAY NIGHT/...
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AS OF 220 PM THURSDAY... THROUGH TONIGHT: QUIET AND DRY NIGHT FOR MOST. SURFACE MAP SHOWS A WEAK MSLP PATTERN OVER NC WITH A WEAK INVERTED TROUGH OVER THE WRN PIEDMONT... HELPING TO FOCUS MOISTURE IN THE LOWEST 5-6 THOUSAND FT IN THIS AREA AND FOSTERING DEVELOPMENT OF VERY ISOLATED SHALLOW SHOWERS. THESE SHOULD PERSIST INTO THE EVENING HOURS... GIVEN THIS WEAK LOW LEVEL MASS CONVERGENCE IN CONJUNCTION WITH WEAK TERRAIN UPGLIDE... BUT WITH A CAPPING INVERSION EVIDENT AT 775-750 MB AND WARM/DRY/STABLE AIR ABOVE... EXPECT DEVELOPMENT TO BE STUNTED BOTH VERTICALLY AND IN COVERAGE... AS PW REMAINS BELOW NORMAL. THE LATEST SEVERAL HRRR RUNS SUPPORT THIS AS WELL. WILL KEEP AN ISOLATED SHOWER CHANCE IN THE WRN AND EXTREME SW CWA THROUGH THE EVENING. OTHERWISE... FORECAST SOUNDINGS SHOW THE LOW LEVEL MOISTURE GRADUALLY DISPERSING WITH TIME... STILL GREATER OVER THE WRN CWA THAN IN THE EAST... SO EXPECT MOSTLY CLEAR SKIES EAST AND PARTLY CLOUDY WEST. SLOWLY LOWERING SURFACE DEWPOINTS SHOULD LOWER THE RISK OF FOG... EXCEPT PERHAP IN THE WRN CWA NEAR THE SURFACE TROUGH. BASED ON LAST NIGHT`S LOWS AND STATISTICAL GUIDANCE... EXPECT LOWS OF 58-63. FOR FRI/FRI NIGHT: RAIN CHANCES WILL REMAIN LOW. THE MID LEVEL TROUGH AXIS IS EXPECTED TO BE SHIFTING TO OUR SE WITH RISING HEIGHTS ALOFT. LOW LEVEL MOISTURE TRANSPORT PERSISTS BUT IS CONFINED TO THE FAR SRN AND SE CWA... WHERE PW VALUES WILL HOVER NEAR 1.4-1.5". THE ONSHORE-DIRECTED LOW LEVEL STEERING FLOW COULD DRAW SHALLOW SEA BREEZE SHOWERS INLAND OVER THE FAR SE CWA. ISOLATED UPSLOPE- SUPPORTED SHOWERS REMAIN POSSIBLE IN THE FAR WRN CWA AS WELL. IN GENERAL HOWEVER... THE TRADITIONAL MODELS REMAIN TOO WET... SHOWING PRECIP COVERING THE MAJORITY OF THE CWA... WHICH APPEARS UNLIKELY GIVEN THE LACK OF FORCING AND INSTABILITY WITH LIMITED MOISTURE. WILL KEEP ISOLATED POPS ALONG THE WRN/SRN AND SE EDGES OF THE CWA FRI AFTERNOON INTO THE EVENING. THICKNESSES ARE EXPECTED TO DIP SLIGHTLY... INDICATING HIGHS OF 76-81. LOWS 56-61 WITH PARTLY CLOUDY SKIES WEST AND MOSTLY CLEAR EAST. -GIH
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&& .SHORT TERM / /...
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AS OF 310 AM THURSDAY... TO BE UPDATED.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 330 AM THURSDAY... A PORTION OF THE LONGWAVE TROUGH INITIALLY ALONG THE EAST COAST WILL BE LEFT BEHIND AND SUPPORT WEAK FRONTAL WAVE DEVELOPMENT OFFSHORE THE SE US COAST THIS WEEKEND...BUT THE OTHERWISE DEAMPLIFYING/LIFTING TROUGH WILL YIELD TO RISING HEIGHTS ALOFT OVER THE CAROLINAS...AS A FLAT MID LEVEL RIDGE RIDGE NOSES EASTWARD FROM THE SOUTHERN PLAINS AND LOWER MS VALLEY. THE RE-ESTABLISHMENT AND AMPLIFICATION OF A WESTERN NOAM RIDGE WILL THEN RESULT IN DOWNSTREAM TROUGH AMPLIFICATION FROM SOUTH-CENTRAL CANADA TO THE EAST-CENTRAL US THIS WEEKEND-EARLY NEXT WEEK. THE WESTERN RIDGE...IN PROGRESSIVE FLOW ALOFT...WILL BUILD EAST ACROSS THE MID-LATITUDES OF THE CENTRAL AND EASTERN STATES MID TO LATE NEXT WEEK. BENEATH THE CONTINUED RISING HEIGHTS ALOFT SAT...A CANADIAN SFC HIGH (AROUND 1030 MB) WILL BUILD FROM CENTRAL CANADA TO THE CANADIAN MARITIMES AND RIDGE SOUTH/SOUTHWESTWARD THROUGH THE EASTERN STATES THROUGH THE FIRST HALF OF THE WEEKEND...BEFORE YIELDING - AMIDST FALLING HEIGHTS DOWNSTREAM OF THE AFOREMENTIONED REDEVELOPING TROUGH ALOFT HEADED FOR THE EAST-CENTRAL US - TO APPALACHIAN-LEE SFC TROUGH DEVELOPMENT SUN...AND A PASSING COLD FRONT MON. ANOTHER STRONG CANADIAN HIGH WILL EXPAND AND STRENGTHEN ACROSS MUCH OF THE CENTRAL AND EASTERN CONUS IN THE WAKE OF THE PASSING COLD FRONT...WHICH GUIDANCE SUGGESTS WILL CLEAR ALL BUT PERHAPS SOUTHERN FL BY MID NEXT WEEK. WITH THE BRUNT OF THE COOLER AND DRIER AIR ASSOCIATED WITH THE LEAD HIGH LIKELY TO HOLD OVER THE NORTHERN MIDDLE ATLANTIC AND NORTHEAST STATES THIS WEEKEND...CENTRAL NC TEMPERATURES ARE APT TO WARM TO ABOVE AVG...IN THE LOWER TO MIDDLE 80S - WARMEST SUNDAY. ANY SIGNIFICANT LOW-MID LEVEL CLOUD COVER ATTENDING THE OFFSHORE FRONTAL WAVE IS FORECAST AT THIS TIME TO HOLD ALONG COASTAL AREAS...WITH MORE OF A NORTHWESTERLY FLOW COMPONENT OVER CENTRAL NC...INTO THE OFFSHORE LOW/FRONTAL ZONE. FRONTAL PASSAGE TIMING HAS SPED FOR MON...SUCH THAT A FEW LINGERING SHOWERS FROM UPSTREAM CONVECTION MAY DRIFT INTO THE NW PIEDMONT SUN NIGHT...AND LEAVE MAINLY THE FAR SOUTHEAST CWFA IN THE WARM SECTOR THROUGH EARLY AFTERNOON...WITH EARLIER/UNFAVORABLE DIURNAL FRONTAL TIMING ACROSS THE REMAINDER OF THE AREA. SHOWER CHANCES WILL BE RELATIVELY LOW...THROUGHOUT THIS PERIOD...HOWEVER...AS GULF MOISTURE RETURN WILL BE LIMITED. COOLER TUE-WED...WITH HIGHS IN THE 70S IN THE POST-FRONTAL CANADIAN HIGH...WITH SFC DEWPOINTS IN THE 40S-50S. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... AS OF 145 PM THURSDAY... VFR CONDITIONS ARE LIKELY TO HOLD THROUGH THE TAF FORECAST PERIOD. EARLIER MVFR CIGS AT INT/GSO HAVE MIXED OUT TO SCATTERED... ALTHOUGH THESE MAY STILL GO BROKEN BRIEFLY PRIOR TO 20Z. OTHERWISE... ANY CLOUDS THROUGH TONIGHT AND FRI MORNING SHOULD BE BASED ABOVE 3 000 FT AGL... MORE LIKELY TO BE BROKEN AT INT/GSO WITH LESS COVERAGE AT RDU/RWI/FAY. LIGHT AND VARIABLE WINDS MAINLY FROM THE NE WILL CONTINUE TONIGHT AT SPEEDS MAINLY UNDER 6 KTS... THEN SHOULD INCREASE TO 7-10 KTS FROM THE ENE AFTER 14Z FRI. LOOKING BEYOND 18Z FRI... VFR CONDITIONS SHOULD DOMINATE THROUGH AT LEAST SUNDAY... ALTHOUGH MVFR FOG IS POSSIBLE EARLY SAT MORNING AS THE LIGHT ONSHORE LOW LEVEL FLOW PERSISTS. A PERIOD OF MVFR CIGS IS POSSIBLE LATE SUN INTO SUN NIGHT AHEAD OF A COLD FRONT. VFR CONDITIONS SHOULD THEN RETURN FOR MON/TUE WITH HIGH PRESSURE BUILDING IN FROM THE NW. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...WSS LONG TERM...MWS AVIATION...HARTFIELD

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