Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 171408 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1008 AM EDT FRI APR 17 2015 .SYNOPSIS... A WEDGE OF COOL HIGH PRESSURE WILL REMAIN OVER THE REGION INTO THIS MORNING BEFORE WEAKENING AS A WEAK TROUGH OF LOW PRESSURE CROSSES THE AREA FROM THE WEST DURING THE AFTERNOON. HIGH PRESSURE FOLLOWS THIS SYSTEM TONIGHT INTO SATURDAY BRINGING DRIER AND WARMER WEATHER TO START THE WEEKEND. A COMPLEX STORM SYSTEM PASSING TO THE WEST WILL RESULT IN MORE WIDESPREAD RAIN SUNDAY INTO SUNDAY NIGHT BEFORE A COLD FRONT CROSSES THE REGION WITH A CHANCE OF SHOWERS AND STORMS ON MONDAY. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1005 AM EDT FRIDAY... A MOIST AIRMASS REMAINS IN PLACE THIS MORNING WITH PW VALUES AT 0.80 AT RNK AND 1.23 IN AT GSO. VISIBLE SATELLITE PHOTOS SHOW PLENTY OF BREAKS IN THE CLOUD COVER AND TEMPS HAVE JUMPED ABOVE GUIDANCE VALUES IN SOME AREAS IN RESPONSE TO THIS CLEARING. AS A RESULT...REDUCED THE CLOUD COVER THE FORECAST AND PUSHED UP HIGHS A DEGREE OR TWO. A SUBTLE UPPER LEVEL DISTURBANCE ACROSS OHIO THIS MORNING WILL MOVE ACROSS THE NORTHEAST PORTION OF OUR FORECAST AREA AND SPARK A FEW PASSING SHOWERS OR ISOLATED STORMS AS DCAPES ARE FORECAST TO REACH AROUND 500 J/KG. ISOLATED STORMS ALSO POSSIBLE LATER THIS AFTERNOON ALONG THE EDGE OF THE CLOUDINESS SOUTH OF HIGHWAY 460. HOWEVER...KEPT HIGHEST POPS CLOSER TO THE WEAK UPPER LEVEL SUPPORT IN THE NORTHEAST. WEAK SURFACE HIGH SLIDES IN FROM THE WEST OVERNIGHT AS 5H HEIGHTS BUILD AND LEFTOVER DEEP MOISTURE HEADS TO THE SE. THIS SHOULD ALLOW CLEARING AFTER ANY EARLY EVENING SHOWERS EXIT THE EAST MAKING FOR A TRANQUIL OVERNIGHT. HOWEVER RESIDUAL WET GROUND AND LIGHT WINDS UNDER STILL RATHER MOIST DEWPOINTS SUPPORT SOME FOG FORMATION VALLEYS AND ESPCLY SOUTH/EAST WHERE MOISTURE WILL BE HIGHER AND WINDS LIGHTER. OTRW MILD LOWS IN THE 50S OVERALL WITH A FEW 40S IN THE VALLEYS.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY/... AS OF 330 AM EDT FRIDAY... A LARGE AREA OF HIGH PRESSURE MOVING THROUGH SOUTHERN CANADA AND INTO NEW ENGLAND WILL BUILD SOUTHWARD INTO THE REGION AND BRING A PLEASANT SPRING DAY TO THE REGION AS WE START THE WEEKEND ON SATURDAY. HOWEVER...THIS RESPITE OF TRANQUIL WEATHER WILL BE SHORT LIVED AS THE HIGH WEDGES DOWN THE EAST SIDE OF THE APPALACHIANS AND COMBINES WITH A LOW MOVING UP THE MISSISSIPPI VALLEY TO BRING A SIGNIFICANT INFLUX OF MOISTURE ALONG WITH ENHANCED LIFT TO THE REGION WITH A WARM FRONT ON SUNDAY. THIS WILL PRODUCE COPIOUS AMOUNTS OF RAINFALL. PRECIPITATION WILL ARRIVE IN THE WEST AS EARLY AS DAYBREAK SUNDAY BUT THE HEAVIEST RAIN WILL BE LATER ON SUNDAY AND INTO SUNDAY NIGHT. DEEP SOUTHEASTERLY FLOW WILL BE FAVORABLE FOR OROGRAPHIC ENHANCEMENT ALONG THE EAST FACE OF THE BLUE RIDGE WHERE RAINFALL TOTALS THROUGH MONDAY MAY TOP THE TWO INCH MARK. IF MODEL GUIDANCE CONTINUES TO INDICATE SUCH PROLIFIC RAINFALL AMOUNTS IN LATER RUNS A FLOOD WATCH WILL BE NEEDED FOR PORTIONS OF THE AREA FOR LATE SUNDAY AND SUNDAY NIGHT. LOW LEVEL WINDS WILL ALSO BECOME SQUEEZED BETWEEN THE LOW PRESSURE TO THE EAST AND HIGH PRESSURE TO THE WEST WHICH WILL ACCELERATE THE SOUTHEASTERLY FLOW. HIGHER ELEVATIONS FROM THE BLUE RIDGE WEST MAY SEE GUSTY CONDITIONS BY SUNDAY AFTERNOON... ESPECIALLY ACROSS THE MOUNTAIN EMPIRE REGION WHERE SOUTHEAST FLOW FAVORS DOWNSLOPING AND ENHANCED WINDS. WE WILL BE IN THE WARM SECTOR ON MONDAY AS A COLD FRONT APPROACHES FROM THE WEST. UNSTABLE CONDITIONS WILL FAVOR THE DEVELOPMENT OF THUNDERSTORMS AHEAD OF THE FRONT. PARAMETERS INDICATE THE POSSIBILITY FOR SOME STORMS TO APPROACH SEVERE LEVELS SO THIS SITUATION WILL BE WATCHED CLOSELY AS IT DEVELOPS. TEMPERATURES THROUGHOUT THE PERIOD WILL BE ABOVE NORMAL EXCEPT FOR SUNDAY WHEN THE WEDGE OF HIGH PRESSURE AND COOLING AFFECTS OF RAINFALL WILL KEEP TEMPERATURES ON THE COOL SIDE. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... AS OF 345 PM EDT THURSDAY... A TRANSITION TO A PATTERN MORE REMINISCENT OF WINTER APPEARS TO EVOLVE THROUGH THE MID AND LATER PART OF NEXT WEEK AS A DEEP UPPER TROUGH BUILDS INTO THE CENTRAL/EASTERN U.S. IN THE WAKE OF THE STRONG UPPER SHORT WAVE ON SATURDAY. BY TUESDAY...500MB HEIGHTS DROP INTO THE 560DM RANGE AND 850MB TEMPS PLUNGE TOWARD THE 0C MARK ACROSS THE NORTH BY MIDWEEK. ANTICYCLONIC FLOW WILL KEEP VARIABLE CLOUDINESS AND POTENTIALLY UPSLOPE SHOWERS IN PLACE ACROSS THE MOUNTAINS. THE CLOUDS AND CYCLONIC FLOW WILL HOLD MAX TEMPS INTO THE 50S ACROSS THE MOUNTAINS THROUGH MUCH OF THE LATER HALF OF NEXT WEEK...WHILE 60S TO 70S PREVAIL TO THE EAST WITH DOWNSLOPE NORTHWEST FLOW AND SIGNIFICANTLY GREATER AMOUNTS OF SUNSHINE. EMBEDDED SHORT WAVES ROTATING THROUGH THE UPPER TROUGH MAY ENHANCE CLOUD AND RAIN SHOWERS AT TIMES...ESPECIALLY ACROSS THE MOUNTAINS...BUT NO SIGNIFICANT RAINFALL EVENTS APPEAR THROUGH THIS PERIOD WITH DEEP CYCLONIC NORTHWEST FLOW IN PLACE. BY THE END OF THE WEEK...THE UPPER FLOW DEAMPLIFIES AND BECOMES MORE ZONAL. AN EMBEDDED SHORT WAVE MAY BRING A MORE SIGNIFICANT THREAT OF RAIN TO THE REGION THU NIGHT/FRI...SO HAVE RETAINED CHC POPS TOWARD DAY 8 AS A RESULT. INSTABILITY MAY SUPPORT ISOLD THUNDER...BUT HAVE NOT INTRODUCED JUST YET. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... AS OF 1253 AM EDT FRIDAY... MVFR TO OCNL IFR/LIFR CIGS CONTINUE ACROSS THE REGION EARLY THIS MORNING WITH AREAS OF -DZ/FOG MAKING FOR PERIODS OF MVFR TO IFR/LIFR VSBYS AS WELL ESPCLY ACROSS THE MOUNTAIN LOCATIONS. INCREASING WARM ADVECTION OVER THE SLOWLY ERODING LOW LEVEL COLD POOL SHOULD CONTINUE TO MAKE FOR POOR FLYING CONDITIONS THROUGH MID MORNING. LOW LEVEL FLOW TURNS TO THE SOUTHWEST THIS AFTERNOON IN ADVANCE OF A TROUGH OF LOW PRESSURE APPROACHING FROM THE NW. THIS SHOULD ALLOW CEILINGS TO RISE AND EVEN BRING SOME CLEARING TO VFR...ESPECIALLY BY AFTERNOON. HOWEVER TIMING OF WHEN THIS STUCK LOW LEVEL MOISTURE EXITS STILL IN QUESTION GIVEN LATEST BUFKIT SOUNDINGS SHOWING A BIT SLOWER EROSION LATER TODAY. THUS DELAYED THE RETURN TO VFR A COUPLE HOURS ESPCLY BLUE RIDGE SITES AND POINTS EAST. ONCE MORE CLEARING/HEATING DEVELOPS...A MORE UNSTABLE AIRMASS WILL SPAWN WIDELY SCATTERED SHOWERS AND STORMS. HOWEVER THE COVERAGE IS NOT EXPECTED TO BE GREAT ENOUGH TO ADD PRECIP AT ANY TAF SITES WITH MAINLY A PERIOD OF BKN VFR CIGS AS A WEAK TROUGH CROSSES THE REGION LATER IN THE DAY. DRIER HIGH PRESSURE WILL BUILD IN BEHIND THIS FEATURE FRIDAY NIGHT AND SATURDAY WITH A RETURN TO VFR EXPECTED TO START THE WEEKEND. EXTENDED AVIATION... A COMPLEX STORM SYSTEM WILL BEGIN TO AFFECT THE REGION LATER IN THE WEEKEND WITH A WARM FRONT BRINGING WIDESPREAD MVFR/IFR CONDITIONS IN RAIN SUNDAY/SUNDAY NIGHT FOLLOWED BY ANOTHER COLD FRONTAL PASSAGE MONDAY. THIS LIKELY TO KEEP PERIODS OF MVFR IN PLACE UNTIL THE FRONT POSSIBLY CLEARS THE REGION LATER MONDAY. VFR RETURNS LATER MONDAY NIGHT AND TUESDAY WITH HIGH PRESSURE BUILDING IN BEHIND THE FRONT WITH GOOD DRYING EXPECTED. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...JH/PH SHORT TERM...MBS LONG TERM...RAB AVIATION...JH/PM/RCS

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