Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 210510 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 110 AM EDT THU AUG 21 2014 .SYNOPSIS...A SERIES OF UPPER LEVEL DISTURBANCES IN NORTHWEST FLOW ALOFT WILL CROSS THE REGION THROUGH LATE WEEK. A BACK DOOR COLD FRONT IS FORECAST TO SLIP INTO THE AREA OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 930 PM WEDNESDAY... EARLIER ISOLATED STRONG TO SEVERE STORMS HAVE LONG SINCE DIED OFF OVER WAKE/JOHNSTON COUNTIES. TO THE WEST... STRONG CONVECTION IS RAPIDLY WEAKENING AS IT MOVES FROM TENNESSEE/KENTUCKY INTO THE WESTERN NORTH CAROLINA MOUNTAINS THIS EVENING. TO THE NORTH... A CLUSTER OF STRONG STORMS WAS MOVING SOUTH THROUGH THE CHARLOTTESVILLE TO RICHMOND AREAS. HOWEVER... THE LATEST STABILITY INDICES INDICATE A GRADUAL STABILIZING OF OUR BOUNDARY LAYER WITH DEVELOPING CINH SINCE SUNSET. THIS ALONG WITH THE LATEST HI-RES CONVECTION ALLOWING MODELS SUGGEST THAT THE STORMS WILL WEAKEN BEFORE APPROACHING THE NC/VA BORDER JUST BEFORE 1200 AM. THIS WILL HAVE TO BE WATCHED AS THE CONVECTION WAS MOVING TO THE SOUTH AT NEARLY 30 MPH INTO A BOUNDARY LAYER WITH LINGERING... BUT WEAKENING INSTABILITY. WE WILL MAINTAIN THE SLIGHT CHANCE POP FOR THE NORTHERN TIER THROUGH 200 AM. OTHERWISE... PARTLY CLOUDY BECOMING MOSTLY CLEAR. PATCHY LATE NIGHT FOG. LOWS 68-73. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 305 PM WEDNESDAY... MID-LEVEL RIDGING BUILDS OVER THE DEEP SOUTH ON THURSDAY...LEADING TO WEAK HEIGHT RISES OVER THE CAROLINAS AND H85 TEMPS SURPASSING 20C. FORECAST SOUNDINGS SHOW DEEP MIXING WITH WESTERLY FLOW...AND DRY ADIABATIC MIXING YIELDS HIGHS WILL INTO THE 90S...WITH A CONSENSUS OF 93-97. MIXING SHOULD ALSO HELP KNOCK DEWPOINTS BACK A FEW DEGREES...HELPING KEEP HEAT INDICES AT 100F OR LESS. MLCAPE OF AROUND 1000 J/KG IS FORECAST...BUT FORCING APPEARS TO BE LIMITED TO THE RESIDUAL/THERMAL TROUGH WHICH SETS UP OVER THE EASTERN PIEDMONT. WILL KEEP POPS AS ISOLATED UNLESS. LOWS THURSDAY NIGHT IN THE LOWER 70S. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 145 PM WEDNESDAY... THE INITIAL LONG TERM PERIOD REMAINS CHARACTERIZED BY A BUILDING UPPER RIDGE ACROSS THE MISSISSIPPI RIVER VALLEY WITH AN UPPER TROUGH/CLOSED LOW OFF THE NORTHEAST COAST...LEAVING CENTRAL NC UNDER NORTHWEST UPPER FLOW INTO EARLY NEXT WEEK. A BACKDOOR FRONT WILL MOVE ACROSS THE AREA LATE FRIDAY THROUGH SATURDAY...WHICH WILL PRODUCE OUR BEST CHANCE OF PRECIPITATION DUE TO LOW LEVEL LIFT FROM THE COOL AIR ADVECTION POTENTIALLY AIDED BY MODEST UPPER LEVEL SUPPORT. OUTSIDE OF THE SLIGHTLY INCREASED CONFIDENCE IN THIS EARLY WEEKEND PERIOD... PRECIP CHANCES HINGE ON MESOSCALE DISTURBANCES ALOFT WITHIN THE NORTHWEST FLOW...WHICH ARE JUST ABOUT IMPOSSIBLE TO FORECAST THIS FAR IN ADVANCE. AS SUCH...WILL MAINTAIN SMALL CHANCE POPS THROUGH MONDAY...AFTER WHICH THE UPPER RIDGE AXIS SHIFTS EAST ENOUGH TO DAMPEN PRECIP CHANCES. HEIGHTS AND LOW LEVEL THICKNESSES PEAKING FRIDAY ARE INDICATIVE OF HIGHS REACHING THE MID 90S OVER MUCH OF THE AREA. THESE HEIGHTS FALL AS THE UPPER TROF DEEPENS ALONG THE EAST COAST CONCURRENT WITH COOL AIR ADVECTION BY LATER SATURDAY IN UNIFORM LOW LEVEL NORTHEAST FLOW. HIGHS WILL BE IN TRANSITION SATURDAY...FROM MID 80S NORTH TO 90 SOUTH...AND BOTTOMING OUT IN THE UPPER 70S TO LOWER 80S SUNDAY AND MONDAY AS DAMMING SETTLES DOWN THE EAST COAST. MORNING LOWS INITIALLY IN THE LOWER 70S SATURDAY MORNING WILL GRADUALLY FALL INTO THE LOW TO MID 60S BY TUESDAY MORNING. THE UPPER RIDGE AXIS WILL SHIFT EAST ON TUESDAY...WITH DRIER AIR AND GRADUAL MODIFICATION OF THE AIR MASS IN PLACE. HIGHS TUESDAY WILL BE MOSTLY IN THE LOW TO MID 80S...WARMING TO MOSTLY MID 80S ON WEDNESDAY. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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AS OF 110 AM THURSDAY... SHORTWAVE VORT DISTURBANCE RESPONSIBLE FOR ONGOING AREA OF STORMS SURGING SOUTHWARD FROM SOUTHERN VA/NE NC IS IN THE PROCESS OF MOVING EAST AND OUT OF THE AREA. IF THESE STORMS HOLD TOGETHER...KRDU AND KRWI STAND THE BEST CHANCE OF SEEING SOME BRIEF RESTRICTIONS BETWEEN 06 TO 08Z. OTHERWISE...THE REMAINDER OF THE OVERNIGHT/EARLY MORNING HOURS ARE EXPECTED TO BE DRY WITH THE CHANCE FOR ALL TAF SITES TO SEE SOME VISIBILITY RESTRICTIONS FROM FOG DURING THE PRE-DAWN HOURS. FOG PRONE KRWI AND KRDU WHO SAW SIGNIFICANT/HEAVY RAINFALL THIS PAST EVENING COULD ONCE AGAIN SEE LIFR TO IFR RESTRICTIONS. ELSEWHERE MVFR VISBYS WILL BE FAVORED....UNLESS MORE PRECIP AFFECTS A GIVEN SITE. ANY SUB-VFR CONDITIONS WILL AGAIN LIFT TO VFR BY MID TO LATE MORNING AT THE LATEST... WITH THE PROSPECTS OF VFR CONDITIONS BY 13-15Z AT ALL TAF SITES FOR THURSDAY MORNING. ISOLATED TO WIDELY SCATTERED SHOWERS AND STORMS WILL BE POSSIBLE AGAIN ON THURSDAY ACROSS ALL OF CENTRAL NC. HOWEVER... THE PROBABILITY AT A GIVEN SITE IS TOO LOW TO INCLUDE IN THE TAFS AT THIS TIME. OUTLOOK... EARLY MORNING STRATUS/FOG...ALONG WITH AFTERNOON SHOWERS AND STORMS WILL BE POSSIBLE EACH DAY THIS WEEK. A BACKDOOR COLD FRONT WILL MOVE INTO THE AREA OVER THE WEEKEND...WHICH MAY BRING ANOTHER PERIOD UNSETTLED WEATHER FOR PORTIONS OF THE AREA.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...PWB NEAR TERM...PWB SHORT TERM...BLS LONG TERM...MLM AVIATION...CBL/BLS

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