000 FXUS61 KRNK 291743 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 143 PM EDT THU JUL 29 2010 .SYNOPSIS... A COLD FRONT WILL MOVE THROUGH THE AREA BY THIS EVENING. HIGH PRESSURE WILL BRING DRIER AND COOLER WEATHER BY FRIDAY. A MOIST SOUTHEAST FLOW OVER THE WEEKEND WILL BRING WETTER WEATHER...WITH NEAR NORMAL TEMPERATURES. && .NEAR TERM /THROUGH TONIGHT/... SVR TSTM WATCH 548 IN EFFECT UNTIL 7 PM THIS EVENING FOR THE NE PIEDMONT. REGIONAL RADAR SHWOING CONVECTION FIRING UP ALONG THE MASON-DIXON ALONG THE FRONTAL BOUNDARY. EXPECTING THE MOVEMENT OF THESE STORMS TO GO SSE...WITH MLCAPES ALREADY AROUND 1500 J/KG. WILL SEE AN ENVIRONMENT CONDUCIVE FOR WIND DAMAGE. THIS WILL SKIRT THE NE CWA THIS AFTERNOON...THEREFORE THE WATCH. STILL LOOKS LIKE THE SW CWA WILL BE IN A LULL...WITH BETTER CHANCE ARRIVE IN THE NW TOWARD LATE AFTERNOON. PREV DISCUSSION... LOW LVL ANALYSIS SUGGEST SOME ANTICYCLONIC FLOW WHICH WOULD CAUSE LESS CONVERGENCE TO INITIATE CONVECTION THIS MORNING. MODIFIED 12Z RNK SOUNDING SHOWS A MODERATALY UNSTABLE AIRMASS FOR THIS AFTERNOON GIVEN HIGHS IN THE MID 80S. SBCAPES ARE IN THE 2500-3000 J/KG RANGE. THIS MAY NOT BE REACHED IF WE GET MORE CLOUDS IN HERE EARLY...AND LEANING THAT WAY. THE DECENT NW FLOW ALOFT ALLOWS FOR MORE SHEAR...BUT THE DOWNSLOPE EFFECTS WILL LIMIT SOME DEVELOPMENT. WITH THE FRONT APPROACHING THIS AFTERNOON FROM THE NORTH...APPEARS BEST THREAT OF CONVECTION MAY OCCUR OVER THE PIEDMONT AND ESPECIALLY NORTH AND EAST OF ROA/LYH. WILL KEEP POPS AS IS FOR THIS AFTERNOON BUT HAVE LOWERED CONSIDERABLY THIS MORNING. IF TRENDS GO THE WAY THAT I AM THINKING WILL HAVE TO UP POPS IN THE EAST...AND LOWER IN THE WEST/SW. STILL LOOKS LIKE THE NEW RIVER VALLEY SOUTHWEST MAY SEE LITTLE COVERAGE. BY 06Z TONIGHT SURFACE AND 850 MB FRONT WILL BE SOUTH OF THE FORECAST AREA. 850 MB TEMPERATURES DROP DOWN TO AROUND +16 BY FRIDAY MORNING AND MODELS BRING SURFACE DEW POINTS DOWN INTO THE MID 50S TO LOWER 60S. WILL STAY WITH A DRY FORECAST AFTER 06Z/2AM TONIGHT. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... HIGH PRESSURE PAYS A PASSING VISIT ON FRIDAY...WITH A TRANSIENT MORE COMFORTABLE AIR MASS IN PLACE THAT DAY. THE 0Z NAM SQUEEZES OUT SOME CONVECTION IN NW NC...BUT THINK THIS IS A FACTOR OF ITS OVERBLOWN SURFACE DEW POINTS/CAPE...WHICH IS ABSENT IN THE REST OF THE MODEL SUITE. SAT/SUN IS A BIT OF A CONUNDRUM. OLD SREF SUGGESTS ISOLATED COVERAGE ALONG THE RIDGES...WHEREAS OPERATIONAL SOLUTIONS OF THE GFS/NAM/ECMWF ARE SUGGESTING LIKELY POPS. WEAK SOUTHERLY FLOW WILL RETURN 60S TO LOWER 70S DEW POINTS WITH UPSLOPE FLOW...COMBINING WITH NUMEROUS WEAK DISTURBANCES IN THE WNW TO ESE UPPER FLOW. THE ECMWF AND TO A LESSER DEGREE..OTHER SOLUTIONS...MAINTAIN A SURFACE LOW ACROSS THE TN VALLEY AND INTO THE VA/NC BORDER BY 12Z SUNDAY. CONSIDERING THE TIME OF YEAR AND UPPER FLOW...THIS TRACK SEEMS A BIT ODD. THE SREF IS MUCH DRIER PROBABLY BECAUSE AS IT HAS A LESS AMPLIFIED UPPER FLOW RESULTING IN LITTLE IF ANY SURFACE LOW REFLECTION. TECHNICALLY...ENSEMBLE FORECASTS ARE MORE SMOOTHED...SO NOT SURE IF THE SREF IS CORRECT BY ACCIDENT OR BY SKILL. NONETHELESS...WILL KEEP THE FORECAST INTACT...WHICH IS BASICALLY THE MIDDLE GROUND WITH REGARDS TO POPS AND TEMPS THROUGH THE WEEKEND...WITH BELOW AVG CONFIDENCE. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... A FRONT WILL STALL SOUTH OF US FOR MON-WED WITH SFC HIGH PUSHING SWD INTO THE MID ATLANTIC. VICINITY OF FRONT AND NW FLOW ALOFT DESPITE BUILDING HEIGHTS WILL KEEP SLIGHT CHANCE POPS AROUND THROUGH WED WITH MORE SEASONABLE TEMPS. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... MAIN AVIATION IMPACTS THIS AFTERNOON WILL BE CONVECTION. AS OF 17Z...THE COLD FRONT LIES ALONG A LINE FROM KCVG-KPKB-KPIT. A BROKEN LINE OF SHRA/TSRA EXISTS AHEAD OF THIS FRONT FROM NE KY EAST INTO MD. AM LOOKING AT BEST THREAT FOR SHRA/TSRA TO EXIST AT KLWB EAST TO KLYH. HOWEVER...SOME DOWNSLOPING FLOW MAY LIMIT THIS OVER ROANOKE. FOR NOW...SINCE IT IS EARLY WILL KEEP CB IN THE TAFS AT ALL TAF SITES WITH VCSH AT LWB AND LYH AT 18Z...DAN/BLF AT 20Z...LEAVING VCSH OUT OF ROANOKE. THE FRONT AND SHOWERS/STORMS WILL SWING BY LYH/LWB AROUND 23Z...EXITING DANVILLE BY 01-02Z. THE MODELS KEEP SOME LINGERING LOW LVL MOISTURE AROUND OVERNIGHT SO ADDED SOME LOWER VSBYS TO BLF/LWB...BUT THINK DRIER AIR AND SOME LIGHT MIXING MAY KEEP LYH/DAN/ROA FROM GETTING ANY. VFR CONDITIONS ARE EXPECTED FRIDAY AS A DRIER AIR MASS MOVES INTO THE REGION. INCREASING MOISTURE AND MORE SHOWERS AND THUNDERSTORMS ARE POSSIBLE SATURDAY AND SUNDAY...WITH DRIER WEATHER AGAIN FOR MON- TUE. SO OUTSIDE OF STORMS AND ANY LATE NIGHT FOG...SHOULD BE VFR CONDITIONS. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS/JJ/WP NEAR TERM...AMS/WP SHORT TERM...KM LONG TERM...WP AVIATION...AMS/WP
NWS Office Area Forecast Discussion
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