Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KRAH 010720 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 320 AM EDT FRI AUG 1 2014 .SYNOPSIS...A PROLONGED PERIOD OF UNSETTLED WEATHER CAN BE EXPECTED THROUGH EARLY NEXT WEEK AS AN UPPER LEVEL TROUGH SLOWLY APPROACHES FROM THE WEST. && .NEAR TERM /OVERNIGHT/... AS OF 830 PM THURSDAY... CYCLONIC FLOW ALOFT WILL PREVAIL OVER THE REGION THROUGH TONIGHT. UPPER LEVEL FORCING WILL BE PRESENT IN THE FORM OF CYCLONIC SHEAR VORTICITY IN ADDITION TO POCKETS OF MORE CONCENTRATED DPVA ATTENDANT TRANSIENT SMALL AMPLITUDE DISTURBANCES IN CYCLONIC FLOW ALOFT. AT THE SAME TIME...SOUTHEASTERLY RETURN FLOW WILL ADVECT RICH LOW-LEVEL MOISTURE INTO THE REGION...WITH 925 MB DEWPOINTS OF 18-19C IN COASTAL SC (23Z SPC MESO) ADVECTING INTO UPSTATE SC AND WESTERN NC OVERNIGHT. ALTHOUGH WEAK MID-LEVEL LAPSE RATES (5.0-5.5 C/KM) WILL PERSIST OVER THE REGION...RICH LOW-LEVEL MOISTURE/WARM ADVECTION WILL MAINTAIN 500-1000 J/KG OF MUCAPE OVERNIGHT...IN THE FORM OF ELEVATED INSTABILITY ATOP A SHALLOW RAIN-COOLED AIRMASS IN THE LOWEST 25-50 MB. WITH THE ABOVE IN MIND...EXPECT STRATIFORM RAIN WITH EMBEDDED ELEVATED CONVECTION TO PERSIST ALONG/WEST OF HWY 1 OVERNIGHT...PERHAPS INCREASING IN COVERAGE AND INTENSITY OVER THE FAR WESTERN PIEDMONT AND FOOTHILLS AFTER MIDNIGHT VIA LOW-LEVEL MOISTURE POOLING ALONG/EAST THE CREST OF THE APPALACHIANS AND OROGRAPHIC ASCENT IN PROXIMITY THEREOF. EXPECT LOWS DRIVEN LARGELY BY CLOUDS/PRECIP (EVAP COOLING)...IN THE MID/UPPER 60S. GIVEN THE PRESENCE OF LOWER/UPPER LEVEL FORCING...AS MUCH AS 500- 1000 J/KG MUCAPE...AND ~40 KNOTS OF DEEP LAYER SHEAR...IT IS POSSIBLE THAT ISOLATED UPDRAFTS COULD ACQUIRE MID-LEVEL ROTATION AND BRIEFLY EXHIBIT SUPERCELLULAR CHARACTERISTICS (I.E. SPLITTING/ DEVIANT MOTION) IN THE FAR WESTERN PIEDMONT/FOOTHILLS. GIVEN THE ELEVATED NATURE OF ANY CONVECTION AND THE PRESENCE OF EXTREMELY MARGINAL MID-LEVEL LAPSE RATES...DO NOT ANTICIPATE A POTENTIAL FOR SEVERE WEATHER. -VINCENT && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
-- Changed Discussion --
AS OF 300 PM THURSDAY... ON FRIDAY THE UPPER TROUGH WILL CONTINUE TO HOVER WEST OF THE AREA. AT THE SURFACE...THERE WILL BE STRONG SURFACE CONVERGENCE OVER CENTRAL NC AS DISTURBANCES MOVE THROUGH THE TROUGH ACROSS THE WESTERN PIEDMONT AND AT THE SAME TIME A SEPARATE PLUME OF MOISTURE WILL APPROACH CENTRAL NC FROM THE SSE. THE ONSLAUGHT OF MOISTURE WILL BEGIN IN EARNEST AS PRECIPITABLE WATER VALUES CLIMB OVER 2 INCHES ACROSS THE AREA. MODEL FORECAST SOUNDINGS AS SEEN IN BUFKIT ARE VERY WET FROM TOP TO BOTTOM BUT THERE STILL REMAINS A QUESTION OF HOW MUCH INSTABILITY WILL BE PRESENT. THE NAM IS VERY BULLISH AND THE GFS NOT AS MUCH BUT THEY BOTH AGREE THAT THE SOUTHEAST WILL CARRY THE MOST CAPE. PLENTY OF FORCING WILL BE PRESENT WITH 30-40 KTS OF BULK SHEAR ACROSS THE EAST AND POTENTIALLY SOME DECENT 0-3 KM HELICITY VALUES. SPC OUTLOOK NOT CALLING FOR A SLIGHT RISK AT THIS POINT BUT WOULD NOT BE SURPRISED TO SEE A FEW STRONGER OR ROTATING CELLS IN THE SOUTHEAST FRIDAY AFTERNOON. ALL THIS ASIDE THE MAIN STORY WILL STILL BE THE RAINFALL WITH A HALF OF AN INCH TO AN INCH (LOCALLY HIGHER) EXPECTED ACROSS THE AREA WITH HEAVIER TOTALS IN MORE CONVECTIVE CELLS IN THE EAST. MAX TEMPS IN THE UPPER 70S TO LOWER 80S NW TO SE. CHANCES FOR RAIN WILL CONTINUE THROUGH FRIDAY NIGHT WITH THE EAST EXPECTED TO SEE MORE OF THE ACTIVITY MAINLY IN THE FORM OF SHOWERS AS CONDITIONS BECOME SLIGHTLY MORE STABLE OVERNIGHT. FOG AND/OR LOW STRATUS SHOULD BE PREVALENT ACROSS THE AREA BEFORE DAYBREAK ON SATURDAY. LOWS 65-70 DEGREES. GUIDANCE SUGGESTS THAT ONE SHORT WAVE TROUGH WILL BE DEPARTING THE REGION EARLY SATURDAY MORNING WITH ANOTHER WAVE POISED TO MOVE ACROSS THE AREA SATURDAY NIGHT...BUT TRYING TO TIME THESE FEATURES TOO PRECISELY IS FOOLHARDY. IN ADDITION... GUIDANCE VARIES WITH THE INLAND PROGRESSION OF THE COASTAL TROUGH. THE END RESULT THOUGH SHOULD BE A FAIRLY ACTIVE CONVECTIVE PATTERN SATURDAY WITH THE BULK OF THE SHOWERS AND THUNDERSTORMS OCCURRING DURING THE AFTERNOON THROUGH THE EVENING INTO THE EARLY OVERNIGHT HOURS. THE NAM GENERATES A LOT MORE PRECIPITATION THAN THE GFS/ECMWF DURING THE DAY AND IS ACCORDINGLY COOLER AND MORE STABLE THAN THE GFS WHICH GENERATES MLCAPE VALUES UP TO 1000-1500 J/KG ACROSS THE EASTERN PIEDMONT AND COASTAL PLAIN. IT WILL BE DIFFICULT GETTING A BETTER READ ON THE INSTABILITY UNTIL A BETTER UNDERSTANDING OF THE EVOLUTION OF THE DIURNAL CONVECTIVE CYCLE ON FRIDAY IS COMPLETE. GREATER CONFIDENCE IS IN THE AMOUNT OF SHEAR WITH THE GFS NOTING STRONGER DEEP LAYER FLOW WITH BULK SHEAR VALUES OF 20-30KTS WHICH WOULD SUPPORT SOME STORM ORGANIZATION. THE NAM HAS WEAKER FLOW...AROUND 20KTS OR SO WITH THE SREF ENSEMBLE DISTRIBUTION SPREAD FROM 20-30 KTS. THE GREATEST SHEAR SHOULD BE LOCATED FROM THE TRIAD NORTH AND WEST WITH THE GREAT INSTABILITY TO THE SOUTHEAST. STILL ANY STORM ELEMENTS THAT DEVELOP NEAR THE SURFACE BOUNDARY WILL NEED TO BE MONITORED. FOR NOW THE MOST LIKELY THREAT IS FROM EFFICIENT RAIN MAKING STORMS THAT REPEATEDLY TRACK OVER THE SAME LOCATION RESULTING IN POTENTIAL FLOODING ISSUES.
-- End Changed Discussion --
&& .LONG TERM /SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
AS OF 315 AM FRIDAY... THOUGH NWP GUIDANCE INDICATES THE PARENT VORTEX NEAR THE SOUTHERN TIP OF HUDSON BAY WILL GRADUALLY FILL AND LIFT OUT DURING THE NEXT COUPLE OF DAYS...A POSITIVELY-TILTED TROUGH ALOFT WILL LINGER FROM THE FROM THE NE US TO THE LOWER MS VALLEY THROUGH TUE. SOUTHWESTERLY AND PERTURBED MID LEVEL FLOW WILL CONSEQUENTLY MAINTAIN AN AXIS OF DEEP MOISTURE CHARACTERIZED PRECIPITABLE WATER VALUES AOA TWO INCHES OVER THE EASTERN THIRD OF NC (INCLUDING THE RAH COASTAL PLAIN) SUN- MON...WITH PROGRESSIVELY LOWER VALUES TO AROUND 1.5 INCHES OVER THE WESTERN PIEDMONT. THE DEEP MOIST AXIS WILL THEN BE SHUNTED OFFSHORE DURING THE MIDDLE OF THE WEEK...WHEN GUIDANCE SUGGESTS A SUCCESSION OF SHORTWAVE TROUGHS WILL FORCE THE NORTHERN STREAM PORTION OF THE TROUGH OFF THE NE AND MID ATLANTIC COAST. THE MOVEMENT OF THE NORTHERN PORTION OF THE TROUGH SHOULD THEN LEAVE BEHIND TROUGHINESS/ A WEAK UPPER LOW OVER THE GULF COAST STATES THROUGH THE END OF THE WEEK. MEANWHILE...IN THE LOW LEVELS AND AT THE SURFACE...THE FRONTAL ZONE/INVERTED TROUGH WILL LINGER OVER EAST-CENTRAL NC THROUGH MON...THEN DRIFT EAST AND OFFSHORE IN RESPONSE TO THE EASTWARD PROGRESSION OF THE NORTHERN PORTION OF THE TROUGH ALOFT. THE RESULT OF THE EVOLVING PATTERN DESCRIBED ABOVE WILL BE CONTINUED UNSETTLED CONDITIONS OVER ESPECIALLY THE EASTERN HALF OF THE RAH FORECAST AREA THROUGH EARLY WEEK. SPECIFICALLY...A CONTINUED LIKELY PROBABILITY OF SHOWERS AND STORMS ROUGHLY EAST OF US HWY 1 ARE WARRANTED ON SUN...TAPERING TO CHANCE OVER THE WESTERN PIEDMONT (AND PERHAPS NOT MUCH OF ANY COVERAGE INVOF AND WEST OF THE YADKIN RIVER). THAT POP DISTRIBUTION WILL THEN EDGE EASTWARD ON MON...WITH COVERAGE FOCUSED OVER THE RAH COASTAL PLAIN AND ESPECIALLY POINTS EASTWARD. MID LEVEL FLOW WILL BE MODEST...15-25 KTS AND RELATIVELY STRONGEST ON SUN...SUPPORTIVE OF MAINLY MULTI-CELL ORGANIZATION. IN THE ABSENCE OF STRONGER FLOW AND/OR STEEPER LAPSE RATES ALOFT... LOCALLY HEAVY RAIN...AMIDST THE CONTINUED HIGH MOISTURE CONTENT AIR...WILL POSE A PRIMARY HAZARD. THE DEVELOPMENT OF DRYING WESTERLY FLOW AS THE NORTHERN STREAM MOVES OFFSHORE BY THE MIDDLE OF THE WEEK WILL FAVOR A RETURN TO MORE TYPICAL SUMMERTIME CONDITIONS OVER THE CAROLINAS...CHARACTERIZED BY WARMING TEMPERATURES INTO THE 80S TO NEAR 90 DEGREES - AFTER SUN-MON TEMPERATURES TRANSITIONING THROUGH THE LOWER TO MIDDLE 80S - AND ISOLATED TO WIDELY SCATTERED DIURNAL CONVECTION.
-- End Changed Discussion --
&& .AVIATION /06Z FRIDAY THROUGH TUESDAY/... AS OF 115 AM FRIDAY... HIGH CONFIDENCE OF A PROLONGED PERIOD OF SUB VFR CONDITIONS ACROSS CENTRAL NC...STARTING TODAY AND PERSISTING THROUGH THE WEEKEND. A MOIST EAST-SOUTHEAST FLOW NEAR THE SURFACE COUPLED WITH A MOIST SW FLOW ALOFT WILL MAINTAIN A NEARLY SATURATED AIR MASS THROUGH SUNDAY. THIS WILL RESULT IN WIDESPREAD MVFR CEILINGS WITH PERIODS OF IFR/LIFR CEILINGS. THE IFR/LIFR SHOULD MAINLY OCCUR IN THE LATE NIGHT-EARLY MORNING HOURS. A SERIES OF UPPER LEVEL DISTURBANCES IN THE FLOW ALOFT WILL TRIGGER AREAS OF SHOWERS AND A FEW THUNDERSTORMS. THE MOST WIDESPREAD COVERAGE ANTICIPATED TODAY WITH THE PASSAGE OF A POTENT UPPER LEVEL SYSTEM...AND AGAIN SATURDAY AFTERNOON-SATURDAY NIGHT WITH THE APPROACH/PASSAGE OF ANOTHER DISTURBANCE. A FEW STRONG STORMS MAY OCCUR IN THE VICINITY OF KFAY AND KRWI THIS AFTERNOON AND AGAIN SATURDAY AFTERNOON AS LOW LEVEL INSTABILITY WILL BE BETTER IN THE SANDHILLS AND COASTAL PLAIN COMPARED TO THE PIEDMONT. AVIATION CONDITIONS ARE EXPECTED TO SLOWLY IMPROVE MONDAY INTO TUESDAY AS THE AIR MASS SLOWLY DRIES OUT AND THE BETTER LIFT FOR SHOWERS AND THUNDERSTORMS DRIFTS EAST TOWARD THE IMMEDIATE COASTLINE. STILL...THERE WILL BE PERIODS OF MVFR/IFR CEILINGS DUE TO RESIDUAL MOISTURE...MAINLY IN THE LATE NIGHT-EARLY MORNINGS HOURS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...ELLIS/BLAES LONG TERM...MWS AVIATION...WSS

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.