Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 281900 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 300 PM EDT SUN JUL 28 2014 .SYNOPSIS...A STRONG COLD FRONT WILL MOVE OFF THE NC COAST THIS EVENING...THEN STALL OFFSHORE TUESDAY. CANADIAN HIGH PRESSURE WILL OTHERWISE EXPAND ACROSS THE CAROLINAS AND MIDDLE ATLANTIC THROUGH MID-WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1120 AM MONDAY... HARD TO IMAGINE THAT SUCH STRONG DYNAMICS AND THE PASSAGE OF A SURFACE FRONT IN LATE JULY WOULD RESULT IN SO LITTLE RAINFALL FOR CENTRAL NC...AND THAT WHAT LITTLE RAIN THAT DID OCCUR RESULTED FROM AN MCV WELL DOWNSTREAM OF THE STRONGEST FORCING FOR ASCENT WITH THE UPPER TROUGH AND ACCOMPANYING LOW LEVEL FRONTAL ZONE. OVERWHELMING NOCTURNAL CINH FOLLOWED THIS MORNING BY DOWNSLOPE FLOW HAS SIMPLY PROVEN TOO GREAT TO OVERCOME. MOISTURE CHANNEL AND BLENDED TPW IMAGERY INDICATE DEEP DRYNESS...AND CAPPING/STABILITY PER PROXIMITY RAOBS AWAY FROM COASTAL AREAS...HAS ENVELOPED ALL BUT SE NC THIS MORNING. PRECIPITATION CHANCES FOR THE REMAINDER OF TODAY WILL CONSEQUENTLY NOW BE CONFINED TO THE SOUTHERN SANDHILLS AND SOUTHERN AND CENTRAL COASTAL PLAIN...INVOF AND AHEAD OF A SFC TROUGH/FRONT THAT WILL BECOME BETTER DEFINED FROM NEAR THE NC OUTER BANKS TO THE SANDHILLS TO THE SC UPSTATE...AS DRY AIR IN THE 850-925 MB LAYER IS IMPARTED ON THE SFC WITH HEATING/MIXING. THESE AREAS WILL BE ON THE NW EDGE OF MODERATE INSTABILITY FORECAST TO DEVELOP OVER COASTAL AREAS...FUELED BY KMHX 12Z-OBSERVED MID LEVEL LAPSE RATES IN EXCESS OF 7 C/KM. IN ADDITION...A BELT OF STRONG (40-50 KT) MID LEVEL FLOW OBSERVED FROM THE NORTHERN PLAINS- TN VALLEY-NC COAST WILL PROVIDE AMPLE DEEP LAYER SHEAR... CHARACTERIZED BY LONG AND STRAIGHT FORECAST HODOGRAPHS AT KFAY AND KILM THROUGH 00Z - SUPPORTIVE OF A CONDITIONAL SVR RISK OF DAMAGING WIND GUSTS AND LARGE HAIL (LIKELY FROM SPLITTING SUPERCELLS PROVIDED STORMS CAN BOTH DEVELOP AND NOT SUCCUMB TO ENTRAINMENT OF THE AFOREMENTIONED DRY AIR ALOFT). HOWEVER...THIS PROBABILITY OF STORMS FORMING AND THRIVING IN THE RAH CWFA IS RELATIVELY LOW - ONLY AROUND 20 PERCENT. OTHERWISE...A RELATIVELY TIGHT MSL PRESSURE GRADIENT ABOUT THE SFC FRONT WILL GENERATE A BREEZY GENERALLY WESTERLY SFC WIND (WNW OVER THE PIEDMONT TO WSW OVER THE SANDHILLS AND COASTAL PLAIN)...WITH GUSTS UP TO 20-25 MPH. LOW LEVEL THICKNESS VALUES AROUND 1425 METERS SUPPORT HIGH TEMPERATURES IN THE MID-UPPER 80S NW TO LOWER-MID 90S SE. LOWS GENERALLY WITHIN A FEW DEGREES EITHER SIDE OF 65. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 255 PM MONDAY... BENEATH AND WEST OF CYCLONIC FLOW ALOFT WITHIN A MID-UPPER TROUGH AXIS NEAR 85W...CANADIAN HIGH PRESSURE WILL EXTEND SOUTHEASTWARD INTO THE MIDDLE ATLANTIC AND CAROLINAS TUE AND TUE NIGHT. COOLER AIR CHARACTERIZED BY H85 TEMPERATURES AROUND 13C...WHICH WAS ALREADY ON THE DOORSTEP OF THE RAH CWFA/AT KRNK AND KBNA AT 12Z MON...WILL HAVE FULLY OVERSPREAD CENTRAL NC THIS PERIOD - SUPPORTIVE OF HIGH TEMPERATURES IN THE LOWER TO MIDDLE 80S. WITH DEWPOINTS EXPECTED IN THE 50S BASED ON UPSTREAM OBSERVATIONS OVER THE OH VALLEY...THE COMBINATION OF LOW RH AND MILD TEMPERATURES WILL FEEL FAR FROM LATE JULY. LOW LEVEL THICKNESS VALUES OF AROUND 1380 METERS OR SO AT 12Z WED FAVORS LOWS IN THE UPPER 50S TO AROUND 60 DEGREES ON AVG. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... AS OF 300 PM MONDAY... WEDNESDAY AND WEDNESDAY NIGHT... A STABLE LONGWAVE PATTERN WILL KEEP THE EAST/WEST COAST UPEPR TROUGH/RIDGE SETUP IN PLACE FOR THE REMAINDER OF THIS WEEK AND POTENTIALLY INTO NEXT WEEK. THE UNSEASONABLY DEEP TROUGH OVER THE EASTERN CONUS WILL LEAD TO THICKNESSES AS MUCH AS 20-25 DEGREES BELOW NORMAL WEDNESDAY...WITH ONLY A SLOW MODERATION THROUGH THE END OF THE WEEK. PW FALLS WELL BELOW ONE INCH WEDNESDAY...ABOUT 50 PERCENT OF NORMAL...WITH DEWPOINTS WILL INTO THE 50S ACROSS THE PIEDMONT. THE ECMWF PRODUCES A LITTLE QPF OVER THE SOUTHERN COASTAL PLAIN AS A SPEED MAX ON THE BACK SIDE OF THE UPEPR TROUGH NOSES ACROSS THE SOUTHERN APPALACHIANS. HOWEVER... PW FALLS WELL BELOW ONE INCH WEDNESDAY...ABOUT 50 PERCENT OF NORMAL...WITH DEWPOINTS WELL INTO THE 50S. THIS RESULTS IN ONLY A SHALLOW LAYER OF INSTABILITY AND LIKELY JUST A DECENT CU FIELD OVER THE COASTAL PLAIN. HIGHS 82-86. LOWS WEDNESDAY NIGHT IN THE LOW TO MID 60S. THURSDAY THROUGH MONDAY... MODELS SHOW SOME ADDITIONAL ENERGY DIVING INTO THE BACKSIDE OF THE TROUGH ON THURSDAY...WHILE THE TROUGH AXIS SHIFTS SLIGHTLY WESTWARD AND HEIGHTS BUILD OVER THE WESTERN ATLANTIC. THIS SHOULD LEAD INCREASING PRECIP CHANCES...MAINLY DIURNAL...AS 1) PW BEGINS TO INCREASE BACK TOWARD NORMAL...2)AN INVERTED COASTAL TROUGH POTENTIALLY SHIFTS WESTWARD AND INLAND...AND 3) AN UPPER JET BECOMES POSITIONED ALONG THE SPINE OF THE APPALACHIANS. GIVEN THAT FORCING SHOULD MAINLY COME FROM AFTERNOON DIFFERENTIAL HEATING AND/OR THE SEABREEZE...CHANCE POPS AROUND CLIMATOLOGY SEEM MOST REASONABLE THROUGH THE WEEKEND. THERE IS ALSO THE POTENTIAL FOR WEAK COLD AIR DAMMING AS THE UPPER LEVEL FLOW BECOMES MORE CONFLUENT OVER NEW ENGLAND AND A WEAK RIDGE OF HIGH PRESSURE EXTENDS THROUGH THE MID-ATLANTIC STATES. NOT SURPRISINGLY...FORECAST SOUNDINGS SHOW NOW SIGN OF LOW CLOUDS AT THIS POINT...AND ITS HARD TO TELL HOW MUCH IMPACT THERE WOULD BE. GIVEN THIS AND A GENERAL INCREASE IN CLOUD COVER...HIGHS WILL REMAIN ONE OR TWO CATEGORIES BELOW NORMAL. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... AS OF 150 PM MONDAY... A COLD FRONT NEAR KFAY WILL SETTLE SOUTHEASTWARD AND OUT OF THE RAH FORECAST AREA THROUGH SUNSET. WHILE THERE REMAINS A VERY SLIGHT CHANCE OF A SHOWER OR STORM AT KFAY WITH THE PASSAGE OF THE FRONT DURING THE NEXT FEW HOURS...IT IS MORE LIKELY THAT ANY SUCH STORM DEVELOPMENT WILL OCCUR ALONG COASTAL/SE NC WHERE LOW AND DEEP LAYER MOISTURE IS (MARGINALLY) MORE SUPPORTIVE. OTHERWISE...A BREEZY WESTERLY WIND WILL GRADUALLY VEER TO NW...AND SUBSIDE AROUND SUNSET...WITH LIGHT NW WINDS EXPECTED OVERNIGHT. DIURNAL CUMULUS SHOULD LIKEWISE DIMINISH AROUND SUNSET...THOUGH THE PASSAGE OF A TRAILING MID LEVEL TROUGH OVERNIGHT COULD PRODUCE A FEW PATCHES OF HIGH STRATOCUMULUS OR LOW ALTOCUMULUS PER UPSTREAM/OH VALLEY OBSERVATIONS...AND NWP GUIDANCE. PREDOMINATELY VFR CONDITIONS SHOULD OTHERWISE PREVAIL THROUGH MOST OF THE FORECAST PERIOD...AS CANADIAN HIGH PRESSURE BECOMES CENTERED OVER THE TN VALLEY AND CENTRAL APPALACHIANS THROUGH MID-WEEK...THEN YIELDS TO AN INVERTED SURFACE TROUGH AND SMALL CHANCE OF A SHOWER OR STORM BY FRI-SAT. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...BLS AVIATION...MWS

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