Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 121156 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 756 AM 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 LOCAL REGION. A WAVE OF LOW PRESSURE WILL RIPPLE EAST ALONG THE FRONT TONIGHT AND SATURDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 530 AM EDT FRIDAY... SURFACE FRONT IS WORKING ITS WAY THROUGH THE CWA THIS MORNING. AT 500 AM THE FRONT BISECTED THE FORECAST AREA FROM EAST TO WEST...GENERALLY ALONG THE HIGHWAY 460 CORRIDOR. DEWPOINTS ACROSS THE SOUTHERN HALF OF THE CWA...SOUTH OF THE FRONT WERE STILL IN THE U60S/L70S. DEWPOINTS NORTH OF THE FRONT...WERE IN THE M-U50S. THE AIRMASS CHANGE LOOKS LIKE IT HAS JUST ENTERED OUR NORTHERN CWA...THE DEWPOINT AT LYH AND FVX STILL FIDDLING WITH 70...WHEREAS THE DEWPOINT IN CHO AND HSP HAD FALLEN INTO THE U50S. THIS CHANGE IN AIRMASS WILL GRADUALLY WORK ITS WAY FROM NORTH TO SOUTH ACROSS THE CWA THIS MORNING...AREAS IN OUR FAR SOUTHWESTERN CWA...NW NC...HOLDING OUT UNTIL LATE IN THE DAY TO SEE ANY APPRECIABLE DROP IN DEWPOINT. THAT BEING SAID...OUR SOUTHWESTERN CWA WILL BE THE AREA TO WATCH FOR ANOTHER DAY OF INSTABILITY DRIVEN SHOWERS...CAPES INCREASING INTO THE 500-800 J/KG RANGE AND SUPPORTING RENEWED SHOWER AND THUNDERSTORM ACTIVITY FOR THE AFTERNOON. HIGHEST POPS WILL BE PLACED OVER THE SOUTHWESTERN CWA TO ACCOUNT FOR THIS CAPE. 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 DISTICT 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 ALTANTIC 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 TEMEPRATURES 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. FOR TEMPERATURES TODAY...SKEWED THE READINGS TOWARD THE WARMER GUIDANCE VALUES ACROSS THE SOUTHERN CWA WHERE ANY SORT OF COOLING BEHIND THE FRONT WILL LAG. THE NORTHERN CWA LOOKS OK...ALTHOUGH ANY SUNSHINE WILL NEGATE THE EFFECTS OF THE CAA BEHIND THE FRONT. CLOUDS EAST OF THE MOUNTAINS MAY HAVE A TENDANCY TO BREAK UP IN THE WAKE OF THIS MORNINGS FROPA AIDED BY THE DRIER DEPOINTS COMING INTO THE ARE FROM THE NORTHEAST. 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 /10Z FRIDAY THROUGH TUESDAY/...
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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.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...NF LONG TERM...NF AVIATION...PM

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