Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 210110 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 910 PM EDT WED AUG 20 2014 .SYNOPSIS...A SERIES OF UPPER LEVEL DISTURBANCES IN NORTHWEST FLOW ALOFT WILL CROSS THE REGION THIS WEEK. A BACK DOOR COLD FRONT IS FORECAST TO SLIP INTO THE AREA OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 220 PM WEDNESDAY... THE OVER ALL WEATHER PATTERN STILL CONSISTS OF RELATIVELY WEAK NORTHWESTERLY FLOW ALOFT AND A BROAD TROUGH AT THE SURFACE. ONE UPPER DISTURBANCE...ATTENDANT TO A SHORTWAVE CROSSING THE APPALACHIANS...CLIPPED THE NORTHERN HALF OF THE AREA THIS MORNING...BUT THE ASSOCIATED CONVECTION DIED AS IT MOVED INTO THE TRIAD. A TRAILING DISTURBANCE IS EVIDENT IN WATER VAPOR AND RAP H5 ANALYSIS OVER SOUTHWEST VA AND NORTHEAST TN...AND IS PROGGED TO CROSS THE AREA THIS EVENING. THE BEST INSTABILITY HAS DEVELOPED FROM THE SANDHILLS TO THE WESTERN PIEDMONT WHERE HEATING WAS UNINHIBITED BY MORNING STRATUS. WITHIN THE INSTABILITY AXIS...A ZONE OF LOW-LEVEL CONVERGENCE ACROSS THE SANDHILLS HAS INITIATED SOME SLOW MOVING SHOWERS AND ISOLATED STORMS FROM RAEFORD TO THE SOUTHEAST. THE APPROACHING DISTURBANCE SHOULD HELP TO INITIATE SOME ADDITIONAL CONVECTION THIS AFTERNOON...THOUGH THE HRRR HAS YET TO LATCH ONTO ANY TREND IN THE NEAR TERM. EXPECT SHOWERS AND STORMS ARE MORE LIKELY FROM THE TRIAD DOWN TO FAYETTEVILLE...WITH JUST A SLIGHT CHANCE FROM THO TRIANGLE NORTHEAST. IF CONVECTION DOES FIRE...A RIBBON OF 30KT EFFECTIVE DEEP SHEAR AT THE BASE OF THE UPPER TROUGH WILL SUPPORT SOME STRONGER CLUSTERS OF STORMS CAPABLE OF PRODUCING SMALL HAIL AND ISOLATED DAMAGING WIND GUSTS. TONIGHT...FORECAST SOUNDINGS SHOW SOME STEEP L;APSE RATES ABOVE THE NOCTURNAL INVERSION...BUT THERE ISNT A CLEAR MECHANISM TO FORCE ANY PARCELS OVERNIGHT...SO WILL LEAVE POPS OUT OF THE FORECAST AFTER 03Z. FORECAST SOUNDINGS ALSO SHOW LESS LOW-LEVEL MOISTENING TONIGHT WITHOUT THE NORTHEASTERLY FLOW WE`VE SEEN THE LAST COUPLE OF NIGHT...AND THEREFORE LESS POTENTIAL FOR STRATUS. LOWS IN THE UPPER 60S AND LOWER 70S. && .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 /00Z THURSDAY THROUGH MONDAY/...
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AS OF 840 PM WEDNESDAY... ISOLATED TO WIDELY SCATTERED SHOWERS AND STORMS HAVE GENERALLY DISSIPATED ACROSS CENTRAL NC THIS EVENING. HOWEVER... A WEAKENING CLUSTER OF SHOWERS AND STORMS COULD MOVE INTO WESTERN PORTIONS OF CENTRAL NC... POSSIBLY AFFECTING KGSO/KINT VERY LATE THIS EVENING OR AFTER MIDNIGHT. ANOTHER AREA OF SHOWERS AND STORMS MOVING SOUTHWARD THROUGH VA MAY ALSO AFFECT PORTIONS OF THE AREA VERY LATE THIS EVENING AND/OR AFTER MIDNIGHT... WITH KRDU AND KRWI STANDING THE BEST CHANCE OF SEEING ANY OF THIS ACTIVITY. IN ADDITION TO THESE TWO AREAS OF POTENTIAL CONVECTION MOVING INTO THE CENTRAL NC WE COULD SEE AN ISOLATED SHOWER/STORM DEVELOP THIS EVENING INTO THE OVERNIGHT... AS THE BOUNDARY LAYER IS EXPECTED TO ONLY SLOWLY STABILIZE THIS EVENING/EARLY THURSDAY. OTHERWISE... EXPECT THE CHANCES FOR LOW STRATUS AND LIFR FOG WILL BE LOWER TONIGHT WITH THE LOW LEVEL FLOW BECOMING MORE WESTERLY TO NORTHWESTERLY. HOWEVER... EXPECT WE MAY STILL HAVE AT LEAST SOME IFR TO MVFR VISBYS DURING THE PRE-DAWN HOURS AT ALL SITES... WITH PERHAPS FOG PRONE KRWI AGAIN DROPPING INTO THE LIFR RANGE. KRDU... HAD SUBSTANTIAL PRECIP FROM THIS AFTERNOON... SO EXPECT WE WILL HAVE SOME IFR TO POSSIBLY LIFR CONDITIONS THERE. 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...BLS NEAR TERM...BLS SHORT TERM...BLS LONG TERM...MLM AVIATION...BSD/BLS

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