Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 271354 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 954 AM EDT MON JUL 27 2015 .SYNOPSIS... A WEAK COLD FRONT WILL DRIFT THROUGH THE REGION TODAY...THEN STALL JUST TO OUR SOUTH. THE FRONT WILL BE ACCOMPANIED BY SCATTERED SHOWERS AND THUNDERSTORMS. ANOTHER COLD FRONT WILL ARRIVE THURSDAY WITH THE NEXT BEST CHANCE FOR SHOWERS AND THUNDERSTORMS. WEAK HIGH PRESSURE AND MOSTLY DRY WEATHER IS EXPECTED BY THE WEEKEND. OTHERWISE...IT WILL REMAIN WARM AND HUMID FOR THE NEXT SEVERAL DAYS. && .NEAR TERM /THROUGH TONIGHT/... AS OF 940 AM EDT MONDAY... PREFRONTAL SHOWERS WILL CONTINUE TO TRACK EAST FROM THE BLUEFIELD AREA TOWARD THE NEW RIVER AND ROANOKE VALLEYS THIS MORNING. AS THEY ARE MOVING EAST...THEY ARE LOSING SOME INTENSITY. THIS AREA OF SHOWERS WILL MOVES EAST OF THE BLUE RIDGE THIS AFTERNOON. IF THE SUN CAN POKE OUT BEFORE THEN...RE-INTENSIFICATION COULD BRING SOME STRONG STORMS TO THE PIEDMONT. AT THIS TIME...STRONG STORMS ARE NOT FORECASTED DUE TO THICK CLOUDS OVER THE PIEDMONT. CONVECTION ASSOCIATED WITH THE FRONT IN THE OHIO VALLEY WILL ENTER THE MOUNTAINS THIS AFTERNOON. THIS MORNING`S SHOWERS HAVE MOSTLY STABILIZED THE ENVIRONMENT AND ARE EXPECTED NOT TO BECOME STRONG THIS AFTERNOON. HOWEVER...LIKE THE PIEDMONT...IF THE SUN CAN SHINE THROUGH...DESTABILIZATION CAN OCCUR. AS OF 750 AM EDT MONDAY... SHOWERS AND THUNDERSTORMS HAVE INCREASED FAIRLY RAPIDLY ACROSS SOUTHERN WV AND FAR SOUTHWEST VA. THESE ARE A MOVING INTO THE BLF AREA...AND WILL LIKELY IMPACT LWB AND BCB BEFORE THE MORNING IS OVER. EXPECT BETTER COVERAGE OF SHOWERS AND STORMS FURTHER EAST BY AFTERNOON. HAVE INCREASED POPS THROUGH THE NEAR TERM IN ACCORDANCE WITH HRRR TRENDS...WHICH SEEMS TO HAVE A GOOD HANDLE ON CURRENT SITUATION. ONLY MINOR TWEAKS TO TEMPS/DEWPOINTS/CLOUD/QPF GRIDS AT THIS TIME. AS OF 400 AM EDT MONDAY... DIFFUSE FRONTAL BOUNDARY REMAINS TO OUR NORTH EARLY THIS MORNING AND SHOWERS CONTINUE TO DEVELOP ALONG IT AND SKIRT THE REGION TO THE NORTH. THE FRONT WILL SINK INTO THE REGION TODAY AND SERVE AS A FOCUS FOR CONVECTIVE DEVELOPMENT THIS AFTERNOON...AIDED BY SHORT WAVE ENERGY STREAMING IN OUR DIRECTION IN NORTHWEST FLOW ALOFT FROM THE UPPER RIDGE OVER THE MIDSECTION OF THE COUNTRY. OVERALL DYNAMIC ENVIRONMENT REMAINS WEAK AND INSTABILITY IS MODEST AT BEST SO THE THREAT OF SEVERE STORMS CONTINUES TO BE LOW. THIS BEING SAID...ALL OF THE LATEST SYNOPTIC AND MESO MODEL GUIDANCE IS KEEN TO DEVELOPING SHOWERS AND THUNDERSTORMS THIS AFTERNOON WITH MORE EXPANSIVE SPATIAL COVERAGE THAN HAS OCCURRED IN RECENT DAYS. MOISTURE WILL ALSO BE INCREASING TODAY AS SEEN IN THE LOW LEVEL THETA/E FIELDS AND RISING PRECIPITABLE WATER VALUES. THIS WILL CONTINUE TO MAKE LOCALLY HEAVY DOWNPOURS A GOOD BET TO ACCOMPANY STORMS DURING THE AFTERNOON. EXPECTING A TYPICAL DIURNAL TREND TO CONVECTION SO ACTIVITY WILL BE DECLINING THIS EVENING WITH THE LOSS OF HEATING AFTER SUNSET. CURRENT SATELLITE IMAGES SHOW A GOOD DEAL OF MID CLOUDS MOVING OVER THE REGION. COMBINED WITH EXPECTED CONVECTIVE DEVELOPMENT AND ATTENDANT CLOUD COVER...WILL BUY INTO THE GUIDANCE TREND WHICH SHOWS READINGS A DEGREE OR TWO COOLER THAN WHAT OCCURRED ON SUNDAY...YIELDING READINGS AROUND 90 EAST OF THE BLUE RIDGE WITH LOW/MID 80S TO THE WEST. TONIGHT WILL BE MUGGY WITH SOME FOG DEVELOPING AND LOWS RANGING FROM THE LOWER 70S EAST TO MIDDLE 60S WEST. && .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... AS OF 415 AM EDT MONDAY... THE WEAK COLD FRONT OF TODAY WILL LIE SOMEWHERE ACROSS THE SOUTH- SOUTHWEST PART OF THE BY TUE MORNING...BUT BECOMING VERY WEAK AND DIFFUSE AND DIFFICULT TO FIND IN THE MODELS. HOWEVER...IT WILL LIKELY REMAIN AS ENOUGH OF A CONVERGENCE ZONE TO SERVE AS A FOCUSING MECHANISM FOR DIURNAL SHOWERS AND THUNDERSTORMS. A STRONG SUBTROPICAL RIDGE WILL REMAIN ANCHORED ACROSS THE CENTRAL U.S. THROUGH TUE...WITH 590DM+ HEIGHTS ALOFT AND WARM 500MB TEMPS. THIS WILL CONTINUE TO PUT A LID ON ANY WIDESPREAD CONVECTION. THE COMBINATION OF THE DIFFUSE FRONTAL BOUNDARY AND DIFFERENTIAL HEATING ACROSS THE MOUNTAINS SHOULD FOCUS THE BEST CHANCE OF CONVECTION ACROSS THE MOUNTAINS OF SOUTHWEST VA AND NORTHWEST NC INTO THE SOUTHERN PARTS OF THE PIEDMONT COUNTIES IN THE CWA. CONVECTION SHOULD DIMINISH QUICKLY AFTER SUNSET TUESDAY. FOR WED...THE FRONTAL BOUNDARY CONTINUES TO WASH OUT ACROSS THE REGION...PERHAPS LINGERING ACROSS SW VA/NW NC...WHICH MAY AGAIN SERVE AS A WEAK FOCUS FOR DIURNAL CONVECTION. THE STRONG SUBTROPICAL RIDGE IN THE CENTRAL U.S. BEINGS TO RETROGRADE INTO THE SOUTHWEST U.S. AS LOW PRESSURE ALOFT MOVES EASTWARD ALONG THE U.S./CANADIAN BORDER. THIS WILL DRIVE THE NEXT FRONT INTO OUR REGION FROM THE NORTHWEST WEDNESDAY NIGHT INTO THURSDAY. OVERALL...CONVECTION SHOULD BE AT A MINIMUM WEDNESDAY...BUT AS NOTED...THERE IS A SLIGHT CHANCE TO LOW END CHANCE ACROSS MUCH OF THE CWA...FAVORING AREAS WEST OF I-77. LATE WED NIGHT OR EARLY THU...DIMINISHING CONVECTION COULD REACH THE WESTERN BORDER OF THE CWA IF EXPECTED THUNDERSTORMS FROM THE OH VALLEY HOLD TOGETHER THAT LONG. THU SHOULD IN THEORY BRING THE BEST CHANCE FOR WIDESPREAD CONVECTION TO THE CWA ASSOCIATED WITH THE COLD FRONT. INSTABILITY WILL BE MAXIMIZED. HOWEVER...TIMING OF THE FRONTAL BOUNDARY INTO THE REGION THU MORNING AND THE POTENTIAL FOR MORNING CLOUD DEBRIS AND LIGHT SHOWERS COULD INHIBIT MORE ROBUST CONVECTION LATER IN THE DAY. LATEST MODEL TRENDS HAVE BEEN TO DECREASE THE THREAT FOR WIDESPREAD CONVECTION THURSDAY. WHAT THERE IS MAY BE FOCUSED MOSTLY EAST OF THE BLUE RIDGE DURING THE AFTERNOON WHERE HEATING WILL BE BETTER WITH LESS MORNING CLOUD COVER AND WHERE THE FRONT IS ALSO EXPECTED TO BE LOCATED BY AFTERNOON. FOR ALL THREE DAYS AT THIS POINT...NO MORE THAN CHANCE POPS WARRANTED AT THIS TIME. TEMPERATURES WILL REMAIN ABOVE NORMAL THROUGH THE PERIOD...ESPECIALLY LOW TEMPS WITH DEWPOINTS HOVERING IN THE 65 TO 70 RANGE ACROSS MOST OF THE CWA. WEDNESDAY SHOULD BE THE WARMEST DAY OVERALL BETWEEN WEATHER SYSTEMS...WITH 850MB TEMPS HOVERING AROUND +20C...SOUTHWEST SFC WINDS...AND PRE-FRONTAL CONDITIONS. && .LONG TERM /FRIDAY THROUGH SUNDAY/... AS OF 445 AM EDT MONDAY... MODELS HAVE TRENDED MUCH DRIER IN THE EXTENDED PERIODS THAN NOTED THE PAST FEW DAYS AND OVERALL ARE IN FAIRLY GOOD AGREEMENT ON THIS SCENARIO. THE UPPER TROUGH ACROSS THE NORTHEAST U.S. BECOMES DEEP ENOUGH AS THE SUBTROPICAL RIDGE SHIFTS WEST INTO THE CA/AZ REGION...TO PUSH THE FRONTAL BOUNDARY SOUTH INTO THE SOUTHEAST STATES BEFORE IT STALLS. CONSEQUENTLY...ANY SUBSEQUENT LOW PRESSURE OR TROPICAL LOW PRESSURE DEVELOPMENT WILL REMAIN WELL SOUTH OF THE REGION RIDING ALONG THE FRONTAL BOUNDARY. AT THIS TIME...IT DOES NOT APPEAR THAT THIS MOISTURE WILL TRACK FAR ENOUGH NORTH TO IMPACT ANY OF OUR REGION. IT WILL BE INTERESTING TO SEE IF THE MODELS STICK WITH THIS LATEST TREND. DEWPOINTS DROP INTO THE 50S ACROSS THE MOUNTAINS AND 60S PIEDMONT FRI- SUN...WITH INDICATED INSTABILITY AT A MINIMUM...ACTUALLY QUITE STABLE FOR LATE JULY INTO EARLY AUGUST. BY MONDAY...THE UPPER TROUGH ACROSS THE GREAT LAKES DEEPENS AS SHORT WAVE ENERGY TRACKS THROUGH THE BASE OF THE TROUGH. THIS WILL PUSH THE NEXT COLD FRONT INTO THE AREA AND ITS ASSOCIATED PRECIPITATION. MAX/MIN TEMPERATURES SHOULD TREND CLOSER TO NORMAL DURING THIS PERIOD AS DEWPOINTS DROP. WE SHOULD SEE HIGHS IN THE 70S ACROSS THE MOUNTAINS AND 80S ELSEWHERE...WITH LOWS MOSTLY IN THE 60S. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... AS OF 745 AM EDT MONDAY... AREA OF SHOWERS AND THUNDERSTORMS ALREADY MOVING INTO THE SOUTHWEST PART OF THE CWA AND WILL LIKELY IMPACT BLF...AND POSSIBLY LWB AND BCB WITHIN THE NEXT FEW HOURS. A FEW LIGHTNING STRIKES AND POCKETS OF VERY HEAVY RAINFALL. COULD BE A PERIOD OF MVFR CIGS/VSBYS AT BLF/LWB/BCB THROUGH 15Z AS A RESULT. MOST MODELS AGRESSIVE WITH CONVECTION THIS AFTERNOON...AND IF CURRENT TREND IS A SIGN OF THINGS TO COME...MODELS MAY BE ON THE RIGHT TRACK. FOCUS WILL BE ON A WEAK FRONTAL BOUNDARY AND A FAIRLY HEALTHY SHORT WAVE TRACKING ESE FROM THE OH VALLEY...SLATED TO ARRIVE DURING THE AFTERNOON. MORNING ACTIVITY MAY DICTATE WHERE AFTERNOON ACTIVITY FORMS...WHICH COULD AT THAT POINT BE MAINLY EAST OF THE BLUE RIDGE. HAVE RETAINED VCTS IN ALL TAFS AS IN THE 06Z SET...BUT HAVE NOT IDENTIFIED ANY TEMPO OR PROB30 GROUPS FOR SPECIFIC PERIODS OF MORE LIKELY TSRA AT THIS POINT. AGAIN...CONVECTION MAY BE ACCOMPANIED BY MVFR-IFR CIGS/VSBYS...BUT TIMING NOT CERTAIN. OUTSIDE CONVECTION...WHICH MAY LINGER INTO THE EVENING HOURS...BUT SHOULD BE DONE BY 04Z...MOIST GROUND AND LOWER ATMOSPHERE SHOULD ALLOW FOR BETTER DEVELOPMENT OF RADIATIONAL FOG. HOWEVER...PERSISTENT MID-LEVEL DECK MAY TEND TO INHIBIT FOG DEVELOPMENT. HAVE ADVERTISED MVFR-IFR BR AT MOST TAF SITES...WITH LIFR AT LWB WHERE WET GROUND AND CALM WINDS SHOULD ALLOW FOR BETTER FOG DEVELOPMENT IN THE GREENBRIER VALLEY. WINDS THROUGH THE TAF PERIOD WILL BE MOSTLY LIGHT AND VARIABLE...BUT WILL TEND TO LEAN TOWARD THE SSE EAST OF THE BLUE RIDGE...AND SSW WEST OF THE BLUE RIDGE. SPEEDS 5KTS OR LESS THROUGH THE TAF VALID PERIOD...EXCEPT IN AND NEAR THUNDERSTORMS. MEDIUM CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN WIND SPEED THROUGH THE TAF VALID PERIOD. LOW CONFIDENCE IN WIND DIRECTION THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN THUNDERSTORM POTENTIAL THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION FORECAST... MODELS APPEAR IN DECENT AGREEMENT THAT THE COLD FRONT WILL STALL JUST SOUTH OF THE FORECAST AREA...BEFORE RETREATING BACK TO THE NORTH ON TUESDAY. EXPECT MAINLY VFR CONDITIONS THROUGH THE WORKWEEK OUTSIDE OF SCATTERED CONVECTION EACH AFTERNOON/ EVENING...AND LOCALIZED FOG/STRATUS EARLY EACH MORNING. SHOWER AND THUNDERSTORM CHANCES THURSDAY AS A NEW COLD FRONT MOVES INTO THE REGION FROM THE NORTHWEST. THIS FRONT SHOULD PUSH SOUTH OF THE AREA AND ALLOW FOR DRIER AND MOSTLY VFR CONDITIONS FRI-SAT. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...RAB NEAR TERM...MBS/RCS SHORT TERM...RAB LONG TERM...RAB/WP AVIATION...MBS/NF/RAB

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