Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 121632 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1232 PM EDT FRI SEP 12 2014 .SYNOPSIS... A COLD FRONT EXTENDS FROM THE MID ATLANTIC COAST...WEST THROUGH THE LOWER TENNESSEE VALLEY AND INTO EAST TEXAS. THIS FRONT WILL DRIFT A LITTLE FARTHER SOUTH TODAY...BECOMING NEARLY STATIONARY JUST SOUTH OF OUR REGION. A WAVE OF LOW PRESSURE WILL RIPPLE EAST ALONG THE FRONT TONIGHT AND SATURDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1225 PM EDT FRIDAY... WEDGE HAS ADVANCED THROUGH THE EASTERN COUNTY WARNING AREA WITH LOWER DEW POINTS AND MORE STABLE AIR AS SEEN ON THE MSAS LIFTED INDEX ANALYSIS AT 16Z/NOON. MOST LIKELY LOCATION FOR SCATTERED THUNDERSTORMS THIS AFTERNOON REMAIN IN THE NORTH CAROLINA MOUNTAINS AND FOOTHILLS WERE THERE HAS BEEN SOME HEATING AND CAPES WERE UP CLOSE TO 900 J/KG. LOCAL WRF AND HRRR RUNS HAVE STORMS DEVELOPING BETWEEN 17Z/1PM AND 19Z/3PM. MODELS ALSO BRING LOW LEVEL WINDS AROUND TO THE NORTHEAST THEN EAST BY 20Z/4PM WHICH WILL ALSO INCREASE THE CONVERGENCE ALONG THE SOUTHERN BLUE RIDGE DURING THIS TIME FRAME. HAVE ADJUSTED THE MAXIMUM TEMPERATURES A COUPLE OF DEGREES DOWN IN THE NORTHEAST UNDER THE WEDGE...AND A FEW DEGREES WARMER IN THE SOUTHWEST WHERE THERE HAS BEEN MORE SUN. BY TONIGHT ALL AREAS WILL BE UNDER THE GUN FOR NUMEROUS SHOWERS...AND OR A MUCH LARGER SCALE RAIN EVENT. MODELS ARE IN AGREEMENT THAT A WAVE OF LOW PRESSURE WILL RIPPLE EAST ALONG THE FRONT TONIGHT...WIDESPREAD RAIN/DRIZZLE DEVELOPING OVER THE AREA...CONTINUING SATURDAY. THERE IS A VERY DISTINCT UPPER LEVEL TROUGH THAT WILL BE MOVING OUT OF THE CENTRAL PLAINS TODAY...CROSSING THE OHIO VALLEY TONIGHT. STRONG DYNAMIC LIFT ASSOCIATED WITH THIS FEATURE WILL RESULT IN A BAND OF RAIN THAT WILL MOVE EAST ACROSS THE OHIO VALLEY...APPROACHING OUR AREA FROM THE WEST. MORE IMPORTANTLY...BACKING FLOW AHEAD OF THIS TROF WILL CAUSE LOW LEVEL WINDS OVER THE MID ATLANTIC REGION TO BECOME SOUTHEASTERLY. THIS SOUTHEAST WIND WILL THEN MOVE UPSLOPE INTO THE BLUE RIDGE...THIS INCREASING OROGRAPHIC LIFT RESULTING IN RAIN/DRIZZLE/FOG. GENERAL RAINFALL ACROSS THE CWA THROUGH TONIGHT IS EXPECTED TO BE AROUND A QUARTER OF AN INCH. HOWEVER...AN ENHANCED AREA OF RAINFALL IS LIKELY TO OCCUR OVER THE NORTH CAROLINA MOUNTAINS WHERE UPWARDS OF AN INCH OF RAIN MAY OCCUR. A SIMILAR SITUATION OCCURRED LAST WEEKEND WHEN THE NC HIGH COUNTRY ENDED UP WITH 1-3 INCHES OF RAIN...THE FRONT AT THAT TIME LAGGING. THE NET RESULT WAS WARMER TEMPERATURES DURING THE DAY PRIOR TO THE RAINFALL (6 DEG ABOVE GUIDANCE) AND CAPES OF ABOUT 1000 J/KG. BUFKIT SOUNDING AT BOONE TODAY IS SUGGESTING THE CAPE WILL REACH 750 J/KG. COMBINE THIS WITH A PWAT THAT IS CLOSE TO 200% ABOVE NORMAL AND THE NET EFFECT MAY BE THE SAME AS LAST SUNDAYS HIGH COUNTRY DELUGE. CLOUDS WILL EVENTUALLY FILL BACK IN PER THE APPROACHING UPPER LEVEL TROUGH AND BACKING LOW LEVEL FLOW. TEMPERATURES TONIGHT SHOULD LEVEL OFF CLOSE TO THE DEWPOINT VALUES...THE RAIN COOLED AIR RESULTING IN TMINS IN THE U50S/L60S. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... AS OF 430 AM EDT FRIDAY... BY SATURDAY MORNING...AN UPPER LEVEL TROUGH WILL PASS RAPIDLY EASTWARD ACROSS THE GREAT LAKES...WHILE UPPER LEVEL RIDGING WILL REMAIN STEADFAST ACROSS THE SOUTHEAST. DEEPENING SURFACE LOW PRESSURE ASSOCIATED WITH THE UPPER TROUGH WILL BE RACING NORTHEAST OF OUR AREA INTO QUEBEC...DRAGGING A COLD FRONT TOWARD THE APPALACHIAN CHAIN. WITH WINDS HAVING SHIFTED SOUTHWESTERLY AHEAD OF THE APPROACHING COLD FRONT...ATLANTIC MOISTURE WILL POOL ACROSS OUR AREA...PUSHING PRECIPITABLE WATER VALUES INTO THE 1.6 TO 1.9 INCH RANGE. INSTABILITY ASSOCIATED WITH THE UPPER TROUGH...COMBINED WITH LOW LEVEL CONVERGENCE AHEAD OF THE FRONT...WILL SUPPORT RAIN FOR MUCH OF OUR AREA...SOME OF WHICH WILL BE LOCALLY HEAVY. BELIEVE RAINFALL WILL BE ON AND OFF BUT NEARLY EVERYWHERE WILL OBSERVE MEASURABLE RAINFALL AT SOME POINT DURING THE MORNING. THE COLD FRONT WILL ENTER OUR SOUTHEAST WEST VIRGINIA COUNTIES BY LATE MORNING...WITH DRIER COOLER CANADIAN AIR BUILDING FROM BEHIND. AS SUCH...EXPECT DECREASING RAIN CHANCES FROM NORTHWEST TO SOUTHEAST DURING THE AFTERNOON AS THE FRONT PASSES THROUGH. EXPECT ONLY SPOTTY SHOWERS REMAINING ACROSS THE PIEDMONT DURING EARLY EVENING...AS WELL AS IN THE NORTHWEST WIND UPSLOPE AREAS ACROSS THE MOUNTAINS. THE FRONT WILL BEGIN TO STALL ACROSS THE CAROLINAS SATURDAY NIGHT AS UPPER RIDGING ACROSS THE AREA HALTS ITS SOUTHWARD ADVANCE. HIGH PRESSURE WILL SHIFT ACROSS THE GREAT LAKES SATURDAY NIGHT INTO NEW ENGLAND...WHERE IT WILL THEN BUILD SOUTHWARD...HUGGING THE EASTERN FACE OF THE APPALACHIANS. NORTHEAST WINDS FLOWING AROUND THE HIGH WILL DRAW COOL MARITIME AIR INTO OUR AREA...FORCING IT UP THE BLUE RIDGE. AS SUCH...EXPECT MOSTLY CLOUDY SKIES WITH AREAS OF DRIZZLE OR LIGHT RAIN AND PATCHES OF FOG IN THE MOUNTAINS. HAVE UNDERCUT MAV/MET GUIDANCE FOR AFTERNOON TEMPERATURES ON SUNDAY... HOLDING MOST LOCATIONS IN THE 60S FOR HIGHS. THE EXCEPTION MAY BE IN PORTIONS OF THE MOUNTAIN EMPIRE ON THE WESTERN SIDE OF THE HIGHER RIDGELINES...WHICH MAY WARM INTO THE MID 70S IF THE SUN BREAKS OUT OF THE CLOUDS. ON MONDAY...HIGH PRESSURE WILL MOVE OFFSHORE...ALLOWING WINDS TO GRADUALLY SHIFT MORE SOUTHERLY AS ANOTHER COLD FRONT APPROACHES FROM THE WEST. AS SUCH...EXPECT WARMER TEMPERATURES...WITH AFTERNOON HIGHS CLIMBING INTO THE LOW TO MID 70S. RAIN CHANCES WILL INCREASE DURING THE EVENING...WITH THE COLD FRONT ENTERING THE AREA MONDAY NIGHT. && .LONG TERM /TUESDAY THROUGH THURSDAY/... AS OF 330 AM EDT FRIDAY... UNSETTLED WEATHER CONTINUES TUESDAY AS SEVERAL UPPER LEVEL DISTURBANCES WILL SHIFT EAST ACROSS OUR AREA. SOME DRIER AIR WILL TRY TO PUSH ACROSS THE REGION TUESDAY NIGHT INTO WEDNESDAY. HOWEVER...SOME ISOLATED CONVECTION MAY FORM ACROSS THE SOUTHWESTERN HIGH TERRAIN CLOSER TO THE FRONTAL BOUNDARY WITH BETTER INSTABILITY. WEDNESDAY NIGHT INTO FRIDAY...THE HIGH CENTER OVER NEW ENGLAND WILL SLOWLY MOVE EAST TOWARDS THE ATLANTIC OCEAN. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... AS OF 800 AM EDT FRIDAY... EXTENDED PERIOD OF MVFR OR WORSE CIGS/VSBYS EXPECTED ACROSS THE CWA. COLD FRONT WILL BECOME NEARLY STATIONARY AND ORIENTED EAST-WEST JUST SOUTH OF THE REGION TODAY. THIS BOUNDARY WILL BECOME THE FOCUS FOR OVERRUNNING MOISTURE WHICH WILL RESULT IN PERIODS OF -RA/DZ THROUGH MUCH OF THE UPCOMING WEEKEND. NORTH TO NORTHEAST WINDS TODAY WILL BECOME EASTERLY TONIGHT. THIS EASTERLY UPSLOPE FLOW WILL LIKELY RESULT IN LOWERING CLOUD BASES THAT WILL OBSCURE THE RIDGES TONIGHT...A PERSISTENT DRIZZLE DEVELOPING OVER MOST OF THE FORECAST AREA IN ADDITION TO PERIODS OF RAIN...CONDITIONS LOWERING TO IFR. EXTENDED AVIATION DISCUSSION... NOT EXPECTING MUCH IF ANY IMPROVEMENT THROUGH THE WEEKEND...EVEN AFTER THE -RA ENDS SUNDAY...LOW LEVEL CLOUDINESS WILL REMAIN. BEYOND SUNDAY...LOW CONFIDENCE. MODELS SHOWING OVERALL MVFR TO PERSIST INTO MONDAY BEFORE SOUTHWEST WINDS ALOFT BEGIN TO RESULT IN IMPROVING CONDITIONS. EVEN THOUGH LOW CLOUDS ERODE ON MONDAY...LINGERING MOISTURE EXPECTING POTENTIAL FOR MVFR AT TIMES IN SPOTTY SHOWERS MONDAY AFTERNOON AS ANOTHER UPPER TROUGH APPROACHES THE REGION FROM THE WEST. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PM NEAR TERM...AMS/PM SHORT TERM...NF LONG TERM...NF AVIATION...PM

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