Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 270855 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 455 AM EDT MON JUL 27 2015 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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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.
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&& .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
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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.
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&& .LONG TERM /FRIDAY THROUGH SUNDAY/...
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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.
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&& .AVIATION /08Z MONDAY THROUGH FRIDAY/... AS OF 0145 AM EDT MONDAY... TAF SITES ARE CURRENTLY VFR...BUT EXPECTING SOME THIN FOG BY DAYBREAK AT MOST SITES. KLWB IS A TRICKY FOG FORECAST SINCE SATELLITE IMAGES SHOW A GOOD AMOUNT OF MID/HIGH CLOUDS STREAMING IN FROM THE NORTHWEST. THIS IS USUALLY ENOUGH TO INHIBIT RADIATION FOG BUT INCREASING AMOUNTS OF LOW LEVEL MOISTURE MAY TIP THE SCALES BACK IN FAVOR OF FOG FORMATION. WILL DEFER TO THE CLOUDS AND KEEP FOG ON THE UPPER END OF IFR. WILL MONITOR THIS CLOSELY AND AMEND TO LIFR IF IT LOOKS LIKE VSBYS WILL BE BOTTOMING OUT. AREA RADARS SHOW SOME LIGHT SHOWERS SKIRTING BY TO OUR NORTH ALONG A DIFFUSE FRONTAL BOUNDARY. MESO MODEL GUIDANCE INDICATE TAF SITES SHOULD REMAIN DRY UNTIL LATER THIS AFTERNOON WHEN FORCING AHEAD OF THE APPROACHING FRONT COMBINES WITH DIURNAL INSTABILITY TO GENERATE SHOWERS AND THUNDERSTORMS. ALL 00Z SYNOPTIC AND MESO MODEL RUNS ARE QUITE BULLISH ON DEVELOPING CONVECTION WITH MUCH MORE SPATIAL COVERAGE THAN WE HAVE SEEN RECENTLY...BUT THERE IS STILL NOT ENOUGH CONFIDENCE IN LOCATION AND TIMING TO PINPOINT WHEN IT WILL BE AFFECTING TAF SITES...SO WILL USE VCTS AND ALLOW LATER TAFS TO BETTER ADDRESS THE SPECIFICS AS THEY COME INTO FOCUS. GIVEN THE CONTINUATION OF A WEAK DYNAMIC ENVIRONMENT AND HIGH PRECIPITABLE WATER VALUES WE SHOULD BE DEALING WITH HEAVY RAINERS WITH LITTLE IN THE WAY OF A SEVERE THREAT...AND ACTIVITY WILL BE WANING WITH LOSS OF HEATING AFTER SUNSET. CONDITIONS SHOULD REMAIN VFR OUTSIDE OF CONVECTION THROUGH THE AFTERNOON. WITH HIGHER THETA/E AIR MOVING TO SUPPLY A MOIST BOUNDARY LAYER EXPECT TO SEE SOME FOG DEVELOPMENT TOWARD THE END OF THE TAF PERIOD. EXPECT LIGHT WINDS THROUGH THE TAF PERIOD. EXTENDED AVIATION FORECAST... MODELS APPEAR IN DECENT AGREEMENT THAT THE COLD FRONT WILL STALL JUST NORTH OF THE FORECAST AREA...BEFORE RETREATING BACK TO THE NORTH ON TUESDAY. EXPECT MAINLY VFR CONDITIONS THROUGH THE WORKWEEK OUTSIDE OF SPOTTY CONVECTION EACH AFTERNOON/ EVENING...AND LOCALIZED FOG/STRATUS EARLY EACH MORNING. SHOWER AND THUNDERSTORM CHANCES INCREASE TOWARD THE END OF THE WEEK AS ANOTHER COLD FRONT APPROACHES. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...RAB NEAR TERM...MBS SHORT TERM...RAB LONG TERM...RAB/WP AVIATION...MBS/NF

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