Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 241741 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 141 PM EDT FRI APR 24 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD ACROSS THE APPALACHIAN CHAIN THIS AFTERNOON... MAINTAINING DRY CONDITIONS WITH ABUNDANT SUNSHINE. LOW PRESSURE WILL TRACK EAST FROM THE SOUTHERN AND CENTRAL PLAINS TONIGHT...AND WILL PASS ACROSS OUR AREA ON SATURDAY...MAKING FOR A WET WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 125 PM EDT FRIDAY... VERY DRY THIS AFTERNOON WITH A NW BREEZE UNDER PLENTY OF SUNSHINE. SOME THIN CIRRUS SHOULD NOT AFFECT TEMPS...AS THEY RISE INTO MID TO UPPER 50S ACROSS THE MOUNTAINS TO 60S ELSEWHERE. PREVIOUS VALID DISCUSSION... AS MENTIONED...CLOUDS WILL INCREASE LATE THIS EVENING AS ANOTHER LOW PRESSURE SYSTEM PASSES ACROSS THE CENTRAL PLAINS. TONIGHT WILL BE ONE OF THOSE NIGHTS WHERE TEMPERATURES COOL QUICKLY AROUND SUNSET... BUT THEN COOLING SLOWS OR STOPS ALTOGETHER AFTER MIDNIGHT AS CLOUDS THICKEN AND LOWER AS THEY BUILD IN FROM THE SOUTHWEST. WILL SEE A FEW SHOWERS ENTER THE AREA TOWARD DAWN SATURDAY...HOWEVER BELIEVE IT WILL TAKE TIME FOR MOISTURE TO OVERCOME THE DRY AIR IN PLACE...SO EXPECT THE MORE CONTINUOUS RAINFALL TO HOLD OUTSIDE OUR AREA UNTIL AFTER SUNRISE SATURDAY. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... AS OF 415 AM EDT FRIDAY... SURFACE HIGH PRESSURE AND DRY AIR WILL QUICKLY GIVE WAY TO A STRONG AND HIGHLY KINEMATIC UPPER TROUGH MOVING ESE FROM THE CENTRAL PLAINS. THIS SYSTEM WILL BE THE WEATHER FOCUS FOR THIS PERIOD AS IT MOVES EAST INITIALLY...THEN BECOMES CAUGHT IN THE CIRCULATION ON THE BACK SIDE OF THE PERSISTENT NORTHEAST U.S. UPPER LOW EARLY SUN...SLIDING EAST-SOUTHEAST TO OFF THE VA/NC COAST BY SUNDAY NIGHT. AN EXTENDED PERIOD OF WET WEATHER WILL RESULT. STRONG ISENTROPIC LIFT WILL ALLOW PRECIPITATION TO SPREAD QUICKLY INTO THE DRY...COOL ANTECEDENT AIR MASS AFTER DAYBREAK SATURDAY. HOWEVER...MODELS ARE A TAD SLOWER BRINGING PRECIPITATION INTO THE CWA AT 12Z SATURDAY THAN NOTED YESTERDAY. AS THE PRECIPITATION FALLS INTO THE INITIALLY COOL/DRY SFC AIR MASS...AN INSITU WEDGE WILL QUICKLY EVOLVE AND PERSIST SATURDAY WITH MAX TEMPS STRUGGLING TO RISE INTO THE 50S. EVEN SOME AREAS ONLY IN THE UPPER 40S...SUCH AS PARTS OF THE NEW/ROANOKE/AND SHENANDOAH VALLEYS. A PERIOD OF LIGHT TO MODERATE RAINFALL IS LIKELY FROM WEST TO EAST THROUGH THE DAY. ANY CONVECTION SHOULD BE CONFINED TO FAR SOUTHWEST VA...LIKELY HITTING A WALL AS IT NEARS OUR CWA BORDER AND THE WEDGE. THERE IS A SHARP GRADIENT IN INSTABILITY/SHEAR AS YOU SHIFT WEST INTO EASTERN TN...WHERE SEVERE THUNDERSTORMS APPEAR LIKELY SATURDAY AFTERNOON. SPC HAS OUTLOOKED MUCH OF TN INTO A ENHANCED RISK AREA...WITH THE SLIGHT RISK AREA CREEPING TO NEAR OUR WESTERN CWA BORDER...AND THE MARGINAL RISK INTO THE NEW RIVER VALLEY. SPC THINKING IS THAT DEEP WESTERLY FLOW ACROSS THE TN VALLEY MAY ALLOW SOME OF THE TN STRONGER CONVECTION TO DRIFT INTO WESTERN VA BEFORE DIMINISHING IN THE STABLE WEDGE AIR MASS. FOR NOW...HAVE JUST INDICATED A SLIGHT CHC OF THUNDER IN THE FAR WEST VA COUNTIES...WEST OF I-77. OF BIGGER CONCERN...IS RAINFALL ON THE SATURATED GROUND WHICH HAS JUST BARELY RECOVERED FROM HEAVY RAINFALL EARLIER THIS WEEK. A GOOD SOAKING 3/4 TO 1 INCH OF RAIN APPEARS LIKELY IN THE WEST...1/2 TO 3/4 INCH EAST FROM THE FIRST ROUND. AS THE UPPER/SFC LOW DRIFTS EAST- SOUTHEAST INTO SUN...ADDITIONAL RAINFALL IS EXPECTED WITH INPUT FROM ATLANTIC MOISTURE. THIS COULD BRING ANOTHER 1/4 TO 1/2 INCH OF RAINFALL TO THE REGION. WPC HAS OUTLOOKED PARTS OF THE NEW RIVER/GREENBRIER/CLINCH RIVER BASIN IN OUR WESTERN COUNTIES FOR EXCESSIVE RAINFALL. GIVEN THAT RAINFALL AMOUNTS OVERALL SHOULD BE 1 INCH OR LESS...WILL NOT ISSUE ANY FLOOD WATCH HEADLINES YET...BUT SUCH HEADLINES MAY BE FORTHCOMING WITH LATER FORECAST PACKAGES. I DO NOT FEEL THAT THIS EVENT COMES ANYWHERE CLOSE TO THIS PAST SUN-MON EVENT...BUT THE CONCERN IS THAT THIS RAIN WILL BE FALLING ON SATURATED SOILS AND RIVER LEVELS ARE STILL ABOVE NORMAL IN SOME AREAS...SO RISES COULD BE QUICKER THAN NORMAL...EVEN WITH MODEST RAINFALL AMOUNTS. THE UPPER-LEVEL DISTURBANCE WILL MOVE EAST-SOUTHEAST OF THE CWA BY EARLY MON. HOWEVER...DEEP LOW PRESSURE REMAINS ANCHORED OVER THE NORTHEAST U.S. AND IS PROGGED TO SLIDE ALMOST DUE SOUTH ALONG THE MID-ATLANTIC COAST. THIS WILL KEEP OUR AREA UNSETTLED AND COOL INTO MONDAY...BUT PRECIPITATION SHOULD BECOME MORE SHOWERY AND GENERALLY CONFINED TO THE MOUNTAINS. BELOW NORMAL TEMPERATURES ARE EXPECTED THROUGH THE ENTIRE PERIOD...A GOOD 10-15 DEGREES ON MAX TEMPS SAT AND SUN...WITH LOW TEMPS CLOSER TO NORMAL. && .LONG TERM /TUESDAY THROUGH THURSDAY/... AS OF 430 AM EDT FRIDAY... THE UPPER LOW OFF THE NORTHERN MID-ATLANTIC COAST WILL BEGIN TO DRIFT EAST...BUT DEEP LOW PRESSURE ALOFT IS SLATED TO QUICKLY FILL IN BEHIND IT ACROSS THE GREAT LAKES. MEANWHILE...A CLOSED AREA OF LOW PRESSURE ALOFT IN THE CENTRAL/SOUTHERN U.S. WILL BEGIN TO DRIFT EASTWARD. GENERALLY A SPLIT FLOW IN PLACE. CONFIDENCE IN THIS PERIOD IS LOW WITH THE GFS TRENDING SOUTHWARD NOW WITH THE MID-LATE WEEK SYSTEM...AND THE ECMWF SHOWING WHAT THE GFS HAD YESTERDAY. ANOTHER PERIOD OF AT LEAST MODERATE RAINFALL APPEARS LIKELY MID TO LATE WEEK...BUT PERHAPS NOT AS HEAVY AS THOUGHT YESTERDAY. THEREAFTER...LOW PRESSURE REMAINS IN PLACE ACROSS THE GREAT LAKES/NORTHEAST WITH DEEP NORTHWEST FLOW IN PLACE ACROSS OUR REGION NORTHWARD. THIS WILL KEEP VARIABLE CLOUDINESS AND MUCH BELOW NORMAL TEMPERATURES IN PLACE AS WE GO INTO EARLY MAY WITH VERY LIMITED THREAT OF NORMAL SPRING CONVECTION. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... AS OF 135 PM EDT FRIDAY... YOU CAN EXPECT VFR CONDITIONS THROUGH THE NEXT 12-15 HRS...BUT THEN CIGS WILL DROP UNDER VFR AFTER 12Z SAT AS STORM SYSTEM AND WARM FRONT IMPACT THE AREA. THIS LOW WILL BRING LIGHT THEN MODERATE RAIN TO EVERYONE BY MIDDAY/EARLY AFTERNOON SATURDAY. THE WORSE CONDITIONS WHERE SUB MVFR TO LIFR IS GOING TO HOLD OFF UNTIL AFTER THIS PERIOD...WITH THE BLUE RIDGE AND NEARBY AIRPORTS EXPECTED TO SEE SUB 1KFT CIGS THANKS TO IN SITU WEDGE...WITH ROA/BCB THE WORST. CIGS ACTUALLY MAY RISE IN BLF LATE SATURDAY AFTERNOON AS A SOUTHERLY WIND INCREASES WITH DRY SLOT BEHIND ONE AREA OF RAIN ARRIVES. MAY SEE SOME VFR RETURNING SAT NIGHT AS WARM FRONT LIFTS NORTH AND WEDGE BREAKS...BUT EXPECT MORE SCATTERED TO NUMEROUS SHOWERS IN SUNDAY...WITH SUB VFR AT TIMES. EXTENDED AVIATION DISCUSSION... FLYING CONDITIONS SHOULD START TO IMPROVE SOME BY MONDAY AS THE LOW PULLS FARTHER OFFSHORE AND WEAK HIGH PRESSURE BUILDS IN FROM THE NORTHWEST. HOWEVER CONTINUED CYCLONIC FLOW LIKELY TO KEEP MORE MVFR CIGS OVER THE MOUNTAINS WITH IMPROVEMENT TO VFR ACROSS THE EAST ON MONDAY. BREEZY CONDITIONS MONDAY-TUESDAY WITH HIGH PRESSURE STARTING TO BUILD IN FROM THE NORTHWEST...SO VFR CONTINUES. BY WEDNESDAY A SOUTHERN STREAM SYSTEM APPEARS TO MAINLY AFFECT THE GULF COAST TO CAROLINAS BUT COULD SEE SEND RAIN OR SUB VFR CIGS INTO THE DAN-BCB-BLF AREA...BUT CONFIDENCE IS LOW. && .FIRE WEATHER... AS OF 1000 AM EDT FRIDAY... VERY LOW RH IN THE AFTERNOON WITH DRIER FUELS WILL BE A CONCERN MAINLY OVER OUR DISTRICTS NORTH OF BLACKSBURG TO BEDFORD...AS WIND SHOULD STAY IN THE 10 TO 15 MPH RANGE...WITH SOME GUSTS TO 20-23 MPH...ESPECIALLY IN THE HIGHLANDS OF BATH/ALLEGHANY. AFTER COORDINATING WITH USFS HAVE ISSUED A FIRE DANGER STATEMENT FROM CRAIG-ROANOKE-BEDFORD NORTH ALONG AND WEST OF THE BLUE RIDGE. OTHER AREAS WILL NOT HAVE AS HIGH A WIND BUT WILL BE VERY DRY WITH HUMIDITY DROPPING INTO THE TEENS TO LOWER 20S. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...RAB/WP SHORT TERM...RAB LONG TERM...RAB AVIATION...RAB/WP FIRE WEATHER...

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