Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 030557 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 157 AM EDT FRI JUL 3 2015 .SYNOPSIS... A FRONTAL BOUNDARY WILL REMAIN DRAPED ACROSS THE AREA FOR THE NEXT SEVERAL DAYS. THERE WILL BE SEVERAL WAVES OF LOW PRESSURE PASSING ACROSS THE BOUNDARY KEEPING THE THREAT OF SHOWERS AND THUNDERSTORMS IN OUR FORECAST THROUGH THE WEEKEND. && .NEAR TERM /THROUGH TODAY/... AS OF 822 PM EDT THURSDAY... SHOWERS QUITE ISOLATED AT BEST ACROSS THE REGION THIS EVENING IN WAKE OF THE PASSING MID LEVEL WAVE FROM EARLIER WHICH BASICALLY PUT A CAP ON DEEP INSTABILITY GIVEN LACK OF INSOLATION. EVENING SOUNDINGS ALSO SHOW MORE DRIER AIR ALOFT AS WE REMAIN IN BETWEEN DEEP CONVECTION THAT PASSED TO THE SOUTH AND AHEAD OF THE NEXT IMPULSE OFF TO THE WEST. THUS FOCUS AND LIFTING MECHANISMS REMAIN LIMITED THROUGH THE REST OF THE EVENING WITH ONLY A FEW SHOWERS BANDS POSSIBLE ALONG THE EAST-WEST SURFACE FRONT ACROSS THE WEST WHERE SOME WEAK INSTABILITY DEVELOPED BEFORE SUNSET. THIS SUPPORTED BY MOST SHORT TERM MODELS INCLUDING THE HRRR SO CUT BACK ON POPS TO LOWER CHANCE AT BEST THROUGH MIDNIGHT...WITH THEN SOME POSSIBLE SLOW INCREASE IN COVERAGE MAINLY MOUNTAINS AFTER MIDNIGHT AS THE NEXT WAVE APPROACHES BUT IFFY. MOIST ENVIRONMENT UNDER SOME BREAKS IN THE CLOUD CANOPY LIKELY TO RESULT IN A BIT MORE FOG ESPCLY EAST WHERE CLOUDS SHOULD BE LESS LONGER. LEFT LOW TEMPS MAINLY IN THE 60S WITH ONLY ANOTHER CATEGORY OR TWO FALL IN VALUES EXPECTED UNDER THE SOUPY CONDITIONS THROUGH MORNING. FOR FRIDAY...THE MODELS KEEP THE CLOUDS AROUND SO NOT REALLY EXPECTING SOLAR INSOLATION TO DESTABILIZE THE AIRMASS. YET ANOTHER SHORTWAVE PUSHES ACROSS KY/OHIO INTO WV/NRN VA BY AFTERNOON WHILE ANOTHER WAVE MOVES ACROSS SRN TN. MODELS ARE VARYING ON WHO GETS THE HEAVIER RAIN BUT THE OVERALL SOLUTION SUGGESTS THE ENTIRE FORECAST WILL LIKELY SEE MEASURABLE RAINFALL FRIDAY. OUR FORECAST RAINFALL TOTAL FROM THIS AFTERNOON THROUGH FRIDAY AFTERNOON SHOWS AN INCH OR LESS. SINCE WE HAVE LOWER CONFIDENCE ON EXACT TRACK OF ANY HEAVIER BANDS OF DEEP CONVECTION...THE THREAT OF FLOODING WILL BE ISOLATED...AND WILL HOLD OFF ON ANY FLASH FLOOD WATCHES. WILL CONTINUE TO MENTION HEAVY RAIN THREAT IN THE HAZARDOUS WEATHER OUTLOOK. THE AIRMASS WILL NOT CHANGE MUCH...SO LOWS TONIGHT WILL ONLY BE ABOUT 5-10 DEGREES COOLER THAN CURRENT TEMPS...AND WILL SEE SIMILAR RESULTS FOR HIGHS FRIDAY...RANGING FROM THE LOW TO MID 70S WEST TO UPPER 70S TO AROUND 80. && .SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... A BROAD UPPER LEVEL TROUGH OVER THE GREAT LAKES AND OHIO VALLEY WILL MAKE FOR A COMPLICATED LOW CONFIDENT FORECAST THROUGH THE WEEKEND. ADDING TO THE DIFFICULT FORECAST ARE TWO AREAS OF WEAK LOW PRESSURES...ONE OVER THE OHIO VALLEY AND ANOTHER ACROSS VA/NC PIEDMONT. MODELS ARE UNSURE WHICH SURFACE LOW BECOMES THE DOMINATE ONE. THE ONE THAT DOES WILL HAVE THE STRONGER STORMS...EITHER ALONG THE WESTERN SLOPES OF APPALACHIANS OR ALONG THE COAST. FOR THIS FORECAST PACKAGE...WILL HAVE THE HIGHEST POPS ACROSS THE MOUNTAINS WITH THE UPPER LEVEL TROUGH REMAINING TO THE WEST AND A SERIES OF SHORT WAVES APPROACHING THE REGION THROUGH THE WEEKEND. WILL ALSO OPT FOR MORE SHOWERS THAN THUNDERSTORMS AS CLOUD COVER SHOULD BE THICK AND PREVAIL THROUGH MOST OF THE PERIOD. FOR OVERALL COVERAGE...SATURDAY LOOKS LIKE THE BETTER DAY. ON SUNDAY...THE OHIO VALLEY LOW MAY SHIFT EAST AND MERGER WITH THE MID ATLANTIC LOW. THIS MAY PUSH A BOUNDARY SOUTH ACROSS THE AREA...KEEPING THE SOUTHERN HALF WET WHILE BECOMING RAIN-FREE AND MOST CLOUDY NORTH. WITH RAIN AND THICK CLOUDS OVER THE REGION...TEMPERATURES WILL BE SLIGHTLY COOLER THAN NORMAL THIS HOLIDAY WEEKEND. && .LONG TERM /MONDAY THROUGH THURSDAY/... AS OF 305 PM EDT THURSDAY... MODELS ARE CONVERTING THE UPPER LEVEL TROUGH TO A CUT-OFF LOW OVER VIRGINIA-NORTH CAROLINA ON MONDAY. MEANWHILE AT THE SURFACE...HIGH PRESSURE OVER NEW ENGLAND WILL WEDGE DOWN THE MID ATLANTIC COAST...LIKELY TO HANG AROUND UNTIL TUESDAY. WITH A SURFACE LOW OVERHEAD...CLOUDY SKIES AND LIGHT RAIN IS A GOOD BET...ESPECIALLY ALONG AND EAST OF THE BLUE RIDGE. THE WEDGE SHOULD ERODE BY WEDNESDAY WITH THE CLOSED LOW OPENING TO A TROUGH AND LIFTING NORTH AS A COLD FRONT APPROACHES FROM THE WEST. BASED ON THE SLOWER TIMING OF THE MODELS...SHOWERS WITH THE FRONT COULD ARRIVE WEDNESDAY NIGHT OR POSSIBLY WAITING UNTIL THURSDAY. TEMPERATURES WILL BE COOLER THAN NORMAL MONDAY AND TUESDAY WITH THE WEDGE IN PLAY...THEN WARM TO NEAR NORMAL BEFORE THE FRONT MOVES THROUGH THURSDAY. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... AS OF 155 AM EDT FRIDAY... NOT A HIGH CONFIDENCE FORECAST AS THE SYNOPTIC REGIME IS MAKING IT DIFFICULT TO PIN DOWN DETAILS AND TAF SITES WILL EXPERIENCE A GOOD DEAL OF VARIABILITY IN CONDITIONS. CURRENT RADAR SHOWS LIMITED SHOWER ACTIVITY THAT CAN BE HANDLED WITH VCSH AT ALL SITES EXCEPT KLYH WHERE THEY SHOULD BE DRY THROUGH DAYBREAK. FOG HAS BEEN IN AND OUT AT SEVERAL SITES AND BELIEVE THIS WILL CONTINUE TO BE THE CASE AS CLOUD COVER WILL LIMIT RADIATIONAL COOLING AND PROHIBIT THICK RADIATIONAL FOG FROM FORMING. AT THE SAME TIME LOW LEVEL MOISTURE WILL BE STREAMING IN FROM THE SOUTHWEST SO CIGS WILL BE COMING DOWN AND KBLF MAY WELL BE IN CLOUD FROM TIME TO TIME WITH LIFR VSBY. THE FRONTAL BOUNDARY THAT HAS BEEN WAVERING OVER THE AREA FOR THE PAST FEW DAYS PUSHED TO THE SOUTH AND HAS LEFT THE REGION WITH A DEVELOPING WEDGE. AS THE UPPER TROF SHARPENS TODAY AND SHORT WAVE ENERGY COMES AT US FROM THE SOUTHWEST...A SURFACE LOW WILL MOVE INTO THE OHIO VALLEY AND DRAG THE FRONT BACK TO THE NORTH. THIS SCENARIO WILL KEEP A GOOD AMOUNT OF CLOUD COVER OVER THE AREA AND HELP LIMIT INSTABILITY. BELIEVE THE NET RESULT WILL BE FOR A LARGE AREA OF SHOWERS WITH EMBEDDED THUNDER MOVING ACROSS FROM WEST TO EAST THIS AFTERNOON INTO THIS EVENING. AS THE LOW CONTINUES TO MOVE INTO THE MID ATLANTIC REGION THE BOUNDARY WILL COME BACK SOUTHWARD AS A COLD FRONT. THIS SHOULD ALLOW FOR SOME IMPROVEMENT IN CONDITIONS TOWARD THE END OF THE TAF PERIOD EAST OF THE BLUE RIDGE WITH A LIGHT DOWNSLOPE WIND...WHILE KBCB/KBLF/KLWB SEE LIGHT UPSLOPE AND DETERIORATING CONDITIONS. EXTENDED AVIATION DISCUSSION... THE REGION WILL REMAIN IN A GENERAL NORTHWEST FLOW PATTERN ON SATURDAY...AND AGAIN EXPECT ANOTHER ROUND OF SHOWERS AND STORMS AS ANOTHER UPPER LEVEL DISTURBANCE PASSES ACROSS THE FORECAST AREA. VFR CONDITIONS ARE EXPECTED FOR THE MOST PART. THE EXCEPTIONS WILL COME AS TEMPORARY DECREASES WITHIN ANY HEAVIER RAIN SHOWERS OR THUNDERSTORMS...AND THEN LATE AT NIGHT AND EARLY MORNING DUE TO RIVER OR MOUNTAIN VALLEY FOG...ESPECIALLY IN AREAS THAT RECEIVED PRECIPITATION THE DAY BEFORE. SUNDAY INTO MONDAY...WHILE UPPER LEVEL HEIGHTS RISE DURING THE PERIOD...THERE REMAINS AN UPPER TROUGH MOVING OVER THE MID ATLANTIC DURING THIS TIME...SO STORMS ARE NEVER OUT OF THE FORECAST. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...MBS/WP NEAR TERM...JH/WP SHORT TERM...RCS LONG TERM...RCS AVIATION...MBS/NF

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