Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 231933 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 330 PM EDT TUE SEP 23 2014 .SYNOPSIS.. UPPER LEVEL LOW OVER THE CAROLINAS TONIGHT WILL SLOWLY WEAKEN OVER THE AREA THROUGH MID-WEEK. MEANWHILE...AT THE SURFACE...AN AREA OF LOW PRESSURE WILL FORM AND TRACK NORTH ALONG A STALLED COASTAL FRONT WEDNESDAY AND WEDNESDAY NIGHT AS HIGH PRESSURE REMAINS WEDGED ACROSS THE PIEDMONT THROUGH LATE WEEK. && .NEAR TERM /TONIGHT/... AS OF 330 PM TUESDAY... OVERVIEW: UPPER LEVEL LOW WILL CONTINUE TO DRIFT NORTHWARD OVER WESTERN NC TONIGHT. SHORTWAVE ENERGY ROTATING AROUND THE UPPER LOW AND STRENGTHENING DIVERGENCE ALOFT UNDERNEATH AN UPPER JETLET ON THE EAST SIDE OF THE MID/UPPER LEVEL CIRCULATION CENTER WILL AID IN CYCLOGENESIS ALONG A COASTAL FRONT/INVERTED SFC TROUGH AS HIGH PRESSURE OVER THE MID-ATLANTIC WEDGES SOUTHWARD THROUGH CENTRAL AND WESTERN PORTIONS OF THE CAROLINAS. THE REMAINDER OF THE AFTERNOON: LIGHT PRECIP/SPRINKLES CONTINUE TO STEADILY FAN NORTH ACROSS CENTRAL NC THE NICE UPPER DIFFLUENCE PATTERN SHOWING UP ON WV IMAGERY. THIS PRECIP SHOULD REMAIN LIGHT THROUGH THE AFTERNOON/EARLY EVENING...WITH A TENDENCY TO DRY UP/DISSIPATE AS IT ADVANCES NORTHWARD INTO THE PIEDMONT AS IT ENCOUNTER DRIER AIR TO THE NORTH WHILE BECOMING FARTHER REMOVED FROM THE LOW-LEVEL EASTERLY ONSHORE FLOW. WILL CARRY LOW-END LIKELY POPS ACROSS THE SANDHILLS/SOUTHERN COASTAL PLAIN...DECREASING TO SLIGHT CHANCE INTO THE WESTERN PIEDMONT WHERE PRECIP WILL LIKELY BE OF THE NON-MEASURABLE VARIETY. PRECIP AMOUNTS WILL REMAIN LIGHT. TONIGHT: PRECIP/LIFT WILL START TO CRANK UP LATE TONIGHT/TUESDAY MORNING WITH INITIAL SHARPENING OF THE INVERTED COASTAL TROUGH AND LOW PRESSURE WAVE DEVELOPMENT. RESULTANT ENHANCED ATLANTIC TRANSPORT/ISENTROPIC LIFT INLAND WILL YIELD INCREASING POPS AFTER MIDNIGHT WITH MOTORISTS EAST OF THE TRIANGLE EXPECTED TO CONTEND WITH A WET MORNING COMMUTE INTO WORK. EXPECT A SHARP CUT-OFF IN POPS AND QPF WEST OF THE TRIANGLE WITH RAINFALL AMOUNTS WEDNESDAY MORNING RANGING FROM A THIRD OF AN INCH OVER THE SOUTHEAST TO NEAR A TENTH ACROSS EASTERN PORTIONS OF THE TRIANGLE. LOWS TONIGHT IN THE MID 50S NORTHWEST TO NEAR 60 EAST. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 330 PM TUESDAY... OVERVIEW: UPPER LOW OVER WESTERN NC WILL UNDERGO GRADUAL FILLING WEDNESDAY-WEDNESDAY NIGHT AS THE MAIN CIRCULATION CENTER LIFTS NORTH UP THE LEE-SIDE OF THE APPALACHIANS TO NEAR THE MASON-DIXON LINE BY DAYBREAK THURSDAY. THE COASTAL LOW WILL FOLLOW SUITE...TRACKING INLAND ACROSS NC COASTAL AREAS DURING THE DAY ON WEDNESDAY... REACHING THE DELMARVA COAST THURSDAY MORNING. THERE STILL REMAINS SOME CONSIDERABLE SPREAD WITH RESPECT TO THE DETAILS SURROUNDING THIS SYSTEM. FORECASTER CONFIDENCE IS WELL BELOW AVERAGE...ESPECIALLY WRT TO QPF AMOUNTS. THE ECMWF HAS BEEN THE MOST CONSISTENT SOLUTION OVER THE GFS AND NAM...AND THUS WILL BE THE MODEL OF CHOICE. MODERATE TO HEAVY RAIN WILL SPREAD NORTH ACROSS THE NC COASTAL COUNTIES THROUGH THE DAY WITH A SHARP EAST-WEST GRADIENT IN QPF...THOUGH HOW FAR INLAND THAT GRADIENT WILL SETUP IS UNCLEAR AT THIS TIME. FOR NOW WILL HAVE QPF AMOUNTS RANGING FROM THREE- QUARTERS OF AN INCH ACROSS THE COASTAL PLAIN...A QUARTER OF AN INCH IN THE TRIANGLE...TO ONLY A FEW HUNDREDTHS IN THE TRIAD. OF NOTE...IF THE HI-RES CAM MODELS VERIFY...RAINFALL AMOUNTS ACROSS CENTRAL AND EASTERN PORTIONS OF THE FORECAST AREA COULD EASILY BE CUT IN HALF. PRECIPITATION CHANCES SHOULD DECREASE FROM SW-NE WEDNESDAY EVENING/NIGHT AS THE COAST LOW LIFTS NORTH OF THE AREA. TEMPERATURES: SIMILAR TO TODAY...EXPECT LITTLE DIURNAL VARIATION IN TEMPS. HIGHS IN THE LOWER TO MID 60S. LOWS IN THE 57 TO 61. -CBL FOR THU/THU NIGHT: THE COASTAL LOW IS EXPECTED TO BE TO OUR NORTHEAST OVER SRN DELMARVA BY THU MORNING. THE SURFACE HIGH CENTERED WELL NORTH OF THE LOW... OUT OVER THE NW ATLANTIC... WILL CONTINUE TO RIDGE WEST AND SOUTH INTO THE INTERIOR MIDATLANTIC... EVENTUALLY CLOSING OFF A WEAKER HIGH OVER THE GREAT LAKES BY LATE THU NIGHT. HEIGHTS ALOFT OVER NC WILL STEADILY RISE AS THE REMNANT TROUGH LEFTOVER FROM THE UPPER LOW CONTINUES TO SLOWLY DAMPEN AND LIFT OUT... SUPPLANTED BY A WESTWARD-EASING RIDGE ALOFT OFF THE SOUTHEAST COAST. WE EXPECT SOME DAYBREAK FOG/STRATUS... BUT THE LIMITED MOISTURE DEPTH... MILD MID-LEVELS... LOW PW... AND ONLY WEAK DYNAMIC LIFT SHOULD SUPPORT MORE CLOUDS THAN SUN DURING THE DAY... AND JUST SMALL POPS. A LINGERING 850-700 MB SHEAR AXIS RUNNING FROM SW TO NE INTO CENTRAL NC COULD BRING ABOUT ENOUGH UPSLOPE-DIRECTED LOW LEVEL FLOW FOR ENHANCED STRATOCU THU NIGHT OVER THE NW PIEDMONT. BUT MAINLY DRY WEATHER IS ANTICIPATED DRY WEATHER GIVEN THE OVERALL DEFICIENCY OF MOISTURE. THE NAM IS QUITE WET THU NIGHT OVER SC INTO THE SWRN PIEDMONT/FOOTHILLS OF NC... IN CONTRAST TO THE MUCH DRIER GFS/ECMWF... AND THIS DRIER SOLUTION IS SUPPORTED BY THE SREF WHICH DEPICTS VERY LOW PROBABILITIES OF MEASURABLE RAIN OVER CENTRAL/WRN NC... HOLDING THESE HIGHER CHANCES AT THE COAST WHERE UPPER DIVERGENCE WILL BE GREATEST (YET STILL MODEST). THICKNESSES THU ARE PROJECTED TO BE CLOSE TO NORMAL... SO WITH AT LEAST PARTIAL SUNSHINE THROUGH THE DAY... HAVE BUMPED UP HIGHS SLIGHTLY TO 74-79. LOWS 56- 62 UNDER PARTLY CLOUDY SKIES... A BIT GREATER SKY COVER SOUTH AND SE THAN NORTH. -GIH && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 230 PM TUESDAY... FOR FRI/FRI NIGHT: THE WEAKENING MID LEVEL PATTERN OVER THE EASTERN CONUS LEADS TO GREATER MODEL DIFFERENCES AND REDUCED CONFIDENCE IN THE DETAILS LATER IN THE WEEK. HIGH LEVEL FLOW SPEEDS UP A BIT... SOURCED FROM NRN MEXICO AND THE NW GULF... WHICH SHOULD MEAN A CONTINUATION OF SOME MID-HIGH CLOUDINESS STREAMING OVER CENTRAL NC. BUT GIVEN THE WEAK STEERING FLOW... LACK OF DYNAMICS... AND MARGINAL MOISTURE FLUX INTO THE AREA... THE DRIER GFS REMAINS FAVORED OVER THE WET NAM... AS THE FORMER HAS SOME SUPPORT FROM BOTH THE ECMWF AND THE SREF MEMBERS. WILL KEEP THE FORECAST DRY. STILL EXPECT A VEIL OF CLOUDS THROUGH THE DAY... BUT THICKNESSES HOLD NEAR OR JUST A TAD BELOW NORMAL... SO HAVE BROUGHT HIGHS UP SLIGHTLY TO 74-77. LOWS 56-62. FOR SAT THROUGH TUE: LOOKS LIKE A MOSTLY DRY PERIOD WITH TEMPS NOT FAR FROM NORMAL... BUT NOTABLE MODEL DIFFERENCES WITH THE OVERALL PATTERN WILL LEAD TO LOWER-THAN-USUAL CONFIDENCE IN THE DAILY DETAILS OF CLOUD COVER AND TEMPS. SURFACE HIGH PRESSURE LOOKS TO SIT OVER THE INTERIOR MIDATLANTIC/OH VALLEY OVER THE WEEKEND... WITH BOTH THE GFS AND ECMWF SHOWING LITTLE TO NO PRECIP OVER CENTRAL NC AS WE REMAIN CUT OFF FROM ANY SUBSTANTIAL MOISTURE SOURCE. LOOKING ALOFT DURING THIS TIME FRAME... A BAGGY NORTH-SOUTH ELONGATED MID LEVEL LOW EXTENDS OVER THE CENTRAL CONUS... WHILE WEAK TROUGHING HOLDS JUST OFF THE EAST COAST... LEAVING A WEAK PSEUDO-BLOCKING HIGH OVER THE EASTERN CONUS. THE GFS BREAKS THIS DOWN BY MON VIA A POSITIVELY-TILTED POLAR TROUGH DIGGING OVER NEW ENGLAND AND DOWN THROUGH THE EASTERN STATES... WHEREAS THE ECMWF MAINTAINS THIS RIDGE AXIS OVERHEAD. IN EITHER CASE... MODELS SHOW CENTRAL NC REMAINING DRY WITH NO GOOD SOURCE OF MOISTURE INTO THE AREA AND LITTLE TO NO DYNAMIC FORCING FOR ASCENT. IF THE POLAR STREAM DOES DIP ENOUGH SOUTHWARD MON/TUE... WE MAY SEE A BACKDOOR FRONT DROPPING INTO THE VICINITY... HOWEVER IT LOOKS LIKE THE MUCH CHILLIER AIR MASS WILL ALMOST CERTAINLY HOLD TO OUR NORTH THROUGH TUE. -GIH && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 230 PM TUESDAY... 24-HR TAF PERIOD: DESPITE LIGHT RAIN OVERSPREADING THE AREA...VFR CONDITIONS WILL CONTINUE THROUGH THE EVENING AND INTO THE FIRST HALF OF THE OVERNIGHT HOURS. CONDITIONS ARE EXPECTED TO RAPIDLY DETERIORATE EAST TO WEST BETWEEN 06 TO 15Z WEDNESDAY...VIA STRONG EASTERLY ATLANTIC MOISTURE TRANSPORT IN ADVANCE OF A WAVE OF LOW PRESSURE TRACKING NE ALONG A COASTAL FRONT. AS THE STEADIER PRECIP PUSHES INLAND...EXPECT AT LEAST IFR AT EAST TERMINALS(KFAY/KRWI)WITH AT LEAST MVFR ACROSS THE PIEDMONT(KRDU/KGSO/KINT). ADDITIONALLY...EXPECT BREEZY NELY WIND OF 20KTS BY THE LATE MORNING AND INTO THE AFTERNOON HOURS AS PRESSURE GRADIENT TIGHTENS IN RESPONSE TO SHARPENING COASTAL FRONT AND LOW PRESSURE DEVELOPMENT. LOOKING AHEAD: SUB-VFR CONDITIONS WILL PERSIST WEDNESDAY NIGHT WITH A RETURN TO VFR CONDITIONS ON THURSDAY AS THE SURFACE LOW TRACKS NORTH AWAY FROM THE AREA. OTHERWISE...EXPECT VFR CONDITIONS TO PREVAIL THROUGH THE REMAINDER OF THE WEEK AS HIGH PRESSURE EXTENDS INTO THE CAROLINAS FROM THE NORTH. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...CBL/HARTFIELD LONG TERM...HARTFIELD AVIATION...CBL

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