Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 051140 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 740 AM EDT THU MAY 5 2016 .SYNOPSIS... AN UPPER LEVEL LOW PRESSURE SYSTEM MOVES FROM KENTUCKY THIS MORNING TO ALONG THE NC/VA COAST BY FRIDAY MORNING....THEN TO THE MID ATLANTIC COAST OF PA/NY BY SATURDAY. THIS WILL KEEP UNSETTLED CONDITIONS THROUGH FRIDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 435 AM EDT THURSDAY... GETTING SOME CLOUD TO GROUND LIGHTNING STRIKES IN THE PIEDMONT...WITH SBCAPES OF 100-200 J/KG. PER HRRR ADDED ISOLATED THUNDER CHANCES THROUGH THE MORNING OVER THE PIEDMONT AREAS OF VA/NC. PREVIOUS MORNING DISCUSSION... VERY WET SCENARIO SHAPING UP TODAY INTO TONIGHT. ALREADY SEEING RAIN EXPANDING ACROSS THE NW NC PIEDMONT INTO THE FOOTHILLS/PIEDMONT OF VA AT 320 AM. QUESTION TODAY IS NOT IF IT IS GOING TO RAIN...IT IS WHERE WILL AXIS OF HEAVIER RAINS SET UP...AND HOW HEAVY WILL THE RAIN BE...IN TERMS OF AMOUNTS AND MOVEMENT. MODELS SEEM TO BE DECENT AGREEMENT THAT A CORRIDOR OF STRONG LOW LVL MOISTURE CONVERGENCE WITH PERIODS OF UPPER DIFLUENCE FAVOR A SE WV TO SOUTHSIDE VA REGION FOR STEADIER RAINS...HEAVY AT TIMES...ESPECIALLY NORTH OF A ROANOKE TO SOUTH BOSTON LINE. STILL IFFY AS TO HOW MUCH FALLS AND SPEED OF MOVEMENT. AT THE MOMENT WILL HOLD OFF ON ANY FLOOD WATCHES...THOUGH AM CONCERNED SINCE SOME OF THE RIVERS IN THE PIEDMONT HAVE BEEN RUNNING HIGH...WITH SOUTH BOSTON ALONG THE DAN RIVER STILL ABOVE FLOOD STAGE...THAT SOME MINOR FLOODING MAY OCCUR AGAIN LATER TODAY INTO FRIDAY. FOR NOW WILL HIT THIS IN THE HAZARDOUS WEATHER OUTLOOK FOR POTENTIAL STREAM OR RIVER FLOODING. FORECAST RAINFALL TODAY WILL RANGE FROM ONE HALF TO JUST OVER AN INCH FROM LEWISBURG WV SOUTHEAST TO DANVILLE AND POINTS NORTHEAST TO LESS THAN A QUARTER INCH OVER THE NC MTNS/FOOTHILLS. AS FAR AS CONVECTION/THUNDER GOES...IT APPEARS CLOUD COVER AND COOLER SFC TEMPS WILL LIMIT LOW LVL LAPSE RATES AND THERMODYNAMIC INSTABILITY...THOUGH MID LEVEL LAPSE RATES ARE THERE ALONG WITH COOLER AIR ALOFT THAT POTENTIAL FOR SMALL HAIL MAY EXIST WITH ISOLATED LIGHTNING. THE CONFIDENCE IN HAVING THIS IN THE FORECAST IS LOW...THINKING ANY THUNDER WILL BE ISOLATED AND ANY BREAKS IN THE CLOUD COVER WILL BE SOUTH AND WELL EAST OF OUR CWA THIS AFTERNOON. WE ARE GOING TO SEE SHOWERS/RAIN WORK IN A NW TO SE PATTERN THEN PIVOT TO AN EAST-WEST AXIS LATER TODAY INTO TONIGHT. AS THE UPPER LOW MOVES EAST OF US TONIGHT...THE SHOWERS SHOULD SPIN AROUND TO MORE A N-S AXIS WITH BANDS SETTING UP ALONG AND WEST OF A BUCKINGHAM TO BOONE LINE BY EVENING WHILE HEAVIER SHOWERS WORK EAST OF OUR FORECAST AREA. OVERNIGHT WILL KEEP POPS HIGH THOUGH QPF WILL BE LOW...GENERALLY UNDER ONE QUARTER INCH. NEEDLESS TO SAY IT WILL BE COOL TODAY WITH POTENTIAL RECORD COOL HIGH TEMPERATURES BEING BROKEN MAINLY AT BLUEFIELD...BLACKSBURG AND ROANOKE. SEE CLIMATE SECTION BELOW FOR DETAILS. HIGHS WILL RANGE FROM THE UPPER 40S TO LOWER 50S WEST...TO MID TO UPPER 50S EAST. WITH CLOUDS AROUND TONIGHT...TEMPS SHOULD BE SLOW TO FALL..WITH MIXING OCCURRING AS SFC LOW OFF THE COAST SHIFTS NORTH. LOWS WILL RANGE FROM THE UPPER 30S TO LOWER 40S IN THE NC MTNS/FAR SW VA INTO SE WV...TO MID TO UPPER 40S ELSEWHERE. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... AS OF 400 AM EDT THURSDAY... THE OMEGA BLOCK PATTERN OVER THE UNITED STATES SHOULD SHIFT EASTWARD AND WEAKEN DURING FRIDAY. AS A RESULT, THE UPPER LEVEL LOW OVERHEAD SHOULD DRIFT TOWARD THE EAST COAST. MOISTURE WRAPPING AROUND THE SURFACE LOW THAT IS VERTICALLY STACKED WITH THE UPPER LEVEL LOW WILL KEEP MAINLY OVERCAST SKIES AND SCATTERED SHOWERS FOR THE MID- ATLANTIC. BY FRIDAY NIGHT, 500 MB HEIGHTS BEGIN TO BUILD AS THE AFOREMENTIONED LOW DEPARTS AND THE UPPER LEVEL RIDGE OVER THE PLAINS HEADS EASTWARD. LINGERING SHOWER ACTIVITY SHOULD DIMINISH OVERNIGHT, BUT THE REPRIEVE WILL NOT LAST LONG IN THE MOUNTAINS. A WEAK COLD FRONT WILL APPROACH FROM THE GREAT LAKES ON SATURDAY, WHICH WILL INCREASE THE CHANCE OF SHOWERS. HIGHER POPS WERE INSERTED WEST OF THE BLUE RIDGE. MODELS ARE IN GOOD AGREEMENT WITH THE COLD FRONT STALLING OVERHEAD BY SUNDAY, BUT THE RAINFALL AMOUNTS REMAIN UNCERTAIN AS THE GFS CARRIES LOWER QPF THAN THE ECMWF. WHILE CLOUD COVER AND SCATTERED SHOWERS COULD LOWER THE HIGH TEMPERATURES, THE UPPER LEVEL RIDGE SHOULD TRUMP THESE VARIABLES TO ALLOW A WARMING TREND THROUGH THE WEEKEND. MODEL SOUNDINGS SHOW LITTLE CAPE, SO THUNDER WAS REMOVED FROM THIS PORTION OF THE FORECAST DUE TO CONSIDERABLE UNCERTAINTY. IF DIURNAL HEATING AND OROGRAPHICAL EFFECTS CAN OVERCOME THIS LACK OF INSTABILITY, THE NORTH CAROLINA MOUNTAINS MAY SEE A STRAY THUNDERSTORM DEVELOP ON SUNDAY AFTERNOON. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... AS OF 330 PM EDT WEDNESDAY... CUTOFF LOW OFF THE MID ATLANTIC COAST DRIFTS EAST IN THE ATLANTIC OCEAN AS FLOW ALOFT SLOWLY EVOLVES INTO A MORE PROGRESSIVE PATTERN FOR THE SECOND WEEK OF MAY. A COLD FRONT TO OUR NORTHWEST WILL DROP SOUTH SUNDAY INTO OUR AREA AND STALL SOUTH OF THE REGION SUNDAY NIGHT BEFORE RETURNING AS A WARM FRONT MONDAY INTO TUESDAY. MOISTURE CONVERGENCE ALONG THIS FRONT WILL RESULT IN A RISK FOR SHOWERS AND PERHAPS A FEW THUNDERSTORMS DURING THE PERIOD...BUT NOT CONFIDENT ON TIMING OR AMOUNTS ATTM. IT DOES LOOK LIKE THE BEST CHANCES WILL BE WEST OF INTERSTATE 77 EARLY NEXT WEEK. ON WEDNESDAY...OUR AREA IN THE WARM SECTOR WITH WARM FRONT TO THE NORTH AND COLD FRONT TO OUR WEST IN THE OHIO VALLEY. TEMPERATURES WILL BE NEAR NORMAL FOR SUNDAY...THEN MODERATE INTO MIDWEEK. BEHIND THE COLD FRONT...A COOL DOWN IS POSSIBLE FOR THE END OF THE WEEK. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... AS OF 735 AM EDT THURSDAY... LOOKING AT POOR FLYING WEATHER TODAY INTO TONIGHT AS UPPER LOW PIVOTS FROM ERN KY TO THE VA TIDEWATER THROUGH 12Z FRIDAY. EXPECT MVFR TO IFR CIGS/VSBYS WITH PERIODS OF MODERATE TO HEAVY RAINFALL...ESPECIALLY IN A CORRIDOR FROM LWB-DAN AND NORTHEAST TO LYH. CANNOT RULE OUT SOME THUNDER BUT OVERALL THREAT WILL STAY SOUTHEAST OF DANVILLE/LYH THROUGH THE AFTERNOON/EVENING. WITH ANY DRYING...RAINFALL ENDING TRENDS...EXPECT CIGS/VSBYS TO DROP BELOW 1KFT AND 3-4SM. THIS IS LIKELY AFTER MIDNIGHT AT BLF/LWB/BCB. CONFIDENCE IN SUB VFR CIGS/VSBYS THIS PERIOD IS HIGH. EXTENDED DISCUSSION... THE CLOSED UPPER LOW WILL REMAIN OVER THE MID ATLANTIC STATES THROUGH FRIDAY. MVFR OR LOWER CEILINGS AND REDUCED VISIBILITY WITH SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED INTO FRIDAY. SOME VFR IS POSSIBLE EAST OF THE BLUE RIDGE SATURDAY. CONDITIONS WILL BE BETTER ON SATURDAY AS THE UPPER LOW MOVES OFF THE COAST...BUT AS ANOTHER SHORT WAVE REACHES THE AREA FROM THE NORTHWEST ON SATURDAY NIGHT AND SUNDAY MORE SHOWERS AND SUB-VFR CONDITIONS ARE LIKELY. MONDAY WILL BE MAINLY VFR WITH SOUTHWEST FLOW IN PLACE THOUGH WARM FRONT MAY BRING SOME MVFR CIGS AND POSSIBLE SHOWERS TO THE MOUNTAINS. && .CLIMATE... A SEASONABLY COOL AIR MASS WILL IMPACT THE REGION THROUGH THE END OF THE WORK WEEK. HIGH TEMPERATURES TODAY MAY APPROACH BREAK THE RECORD FOR COOLEST HIGHS FOR MAY 5TH. BELOW ARE THE CURRENT RECORD COOL HIGH TEMPERATURES FOR MAY 5TH. THURSDAY 05/05/2016 SITE LOMAX YEAR KBLF 50 1988 KDAN 51 1994 KLYH 51 1908 KROA 52 1917 KRNK 48 1994 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...WP NEAR TERM...WP SHORT TERM...PW LONG TERM...KK AVIATION...AMS/WP CLIMATE...CF/WP

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