Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 211158 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 758 AM EDT MON JUL 21 2014 .SYNOPSIS... A WEAK WEDGE OF HIGH PRESSURE WILL CONTINUE TO PUSH OFFSHORE TODAY. EAST TO SOUTHEASTERLY WIND FLOW AROUND THE DEPARTING HIGH WILL FEED MOISTURE INTO THE REGION...WHILE AN UPPER LEVEL TROUGH STALLED ACROSS THE EAST WILL PROVIDE INSTABILITY TO SUPPORT SPOTTY SHOWERS AND THUNDERSTORMS THROUGH THE EARLY HALF OF THE WEEK. A COLD FRONT WILL ARRIVE TOWARD THE END OF THE WORKWEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 400 AM EDT MONDAY... WILL START THE DAY WITH A BROAD UPPER LEVEL TROUGH SITUATED OVER THE OHIO RIVER VALLEY...WHILE WEAK HIGH PRESSURE REMAINS IN PLACE ACROSS NEW ENGLAND INTO THE MID ATLANTIC. DEWPOINT TEMPERATURES ARE NOTICEABLY HIGHER THIS MORNING THANKS TO THE EASTERLY WIND FLOW AROUND THE HIGH CARRYING ATLANTIC MOISTURE INTO OUR AREA. ALSO KEEPING AN EYE ON WEAK UPPER LEVEL DISTURBANCES PUSHING INTO OUR AREA FROM THE SOUTH...RESULTING IN SHOWERS AND OCCASIONAL THUNDERSTORM ACTIVITY ACROSS THE SOUTHSIDE AND NORTHERN NORTH CAROLINA. CLOUDS WILL BE SLOW TO SCATTER TODAY DUE TO THE UPPER LEVEL TROUGHING...AND EXPECT MOSTLY CLOUDY SKIES WITH OCCASIONAL BREAKS OF SUNSHINE FOR MUCH OF OUR AREA. SHOWER AND THUNDERSTORM ACTIVITY WILL REMAIN CONFINED MAINLY ACROSS OUR SOUTHEAST THROUGH LATE MORNING... BUT EXPECT SHOWER ACTIVITY TO INCREASE AREAWIDE BY EARLY AFTERNOON IN SPOTTY...HIT AND MISS FASHION...WITH SOME OF THE SHOWERS INTENSIFYING INTO THUNDERSTORMS BY LATE AFTERNOON. DESPITE THE INCREASED INSTABILITY...BELIEVE THE WEAKENING HIGH PRESSURE WEDGE WILL STILL HAVE ENOUGH INFLUENCE TO PREVENT STORMS FROM BECOMING SEVERE. RATHER...THE BIGGER CONCERN WILL BE SLOW MOVING AND LOCALLY HEAVY RAINFALL DUE TO WEAK WINDS ALOFT. BELIEVE THE THREAT OF ANY SORT OF FLOODING IS VERY REMOTE...BUT ONE THAT CANNOT BE RULED OUT. SHOWER AND THUNDERSTORM ACTIVITY WILL DIMINISH DURING THE EVENING... BUT STILL EXPECT A FEW AREAS OF RAINFALL TO LINGER INTO EARLY TUESDAY. AFTERNOON HIGHS FOR TODAY WILL BE A FEW DEGREES WARMER THAN SUNDAY...BUT STILL SEVERAL DEGREES BELOW AVERAGE FOR THE SECOND HALF OF JULY...WITH MID 70S TO LOW 80S AREAWIDE. THE RETURN OF SUBTROPICAL AIR WILL MAKE FOR WARM AND MUGGY CONDITIONS TONIGHT... WITH PATCHES OF FOG AS LOWS BOTTOM OUT IN THE MID 60S TO THE LOW 70S. && .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... AS OF 415 AM EDT MONDAY... MODELS IN GOOD AGREEMENT ON THE OVERALL SYNOPTIC PATTERN WITH A MAMMOTH NEAR 600DM RIDGE BUILDING ACROSS THE INTERMOUNTAIN WESTERN U.S....A SIMILAR RIDGE BUILDING ACROSS THE WESTERN ATLANTIC... AND AN UPPER TROUGH LINGERING ACROSS THE SOUTHEASTERN U.S. STUCK BETWEEN THE TWO AFOREMENTIONED UPPER RIDGES. THIS PATTERN WILL KEEP THE HOT WEATHER WELL TO OUR WEST. THE PERSISTENT SE U.S. UPPER TROUGH WILL DRIFT/RETROGRADE TO THE NW WITH TIME IN RESPONSE TO THE BUILDING WESTERN ATLANTIC UPPER RIDGE. THIS SYSTEM HAS SOME PSEUDO TROPICAL CHARACTERISTICS WITH PWS NEARING 2.0 INCHES IN THE ASSOCIATED AIR MASS. AS THIS SPREADS NORTHWEST TUE-WED...EXPECT AN INCREASE IN DIURNALLY DRIVEN CONVECTION...ESPECIALLY ALONG THE EAST FACING SLOPES OF THE BLUE RIDGE FROM NW NC NORTHEASTWARD INTO SOUTHWEST/SOUTH CENTRAL VA. WITH SUCH HIGH PWS AND WEAK STEERING CURRENTS ALOFT...THE THUNDERSTORMS WILL BE VERY EFFICIENT RAIN PRODUCERS AND AS SUCH COULD RESULT IN LOCALIZED FLOODING. FORTUNATELY...MUCH OF THE CWA IS IN A MILD DROUGHT...SO THE RAINFALL WILL BE WELCOME. BUT IN MOUNTAINOUS TERRAIN...AN INCH OR TWO IN AN HOUR CAN BECOME PROBLEMATIC RATHER QUICKLY. HOWEVER...CERTAINLY NOT ENOUGH CONCERN FOR ANY FLOOD/FLASH FLOOD WATCH AT THIS POINT DUE TO THE LOCALIZED NATURE OF THE EXPECTED THUNDERSTORMS. HOWEVER...A MENTION OF LOCALIZED HEAVY RAIN IN THE HWO ACROSS MAINLY THE NC COUNTIES IN COLLABORATION WITH OUR NEIGHBORS IS WARRANTED. MEANWHILE...THE SEVERE THREAT SHOULD BE NEAR NIL WITH AN INCREASING TROPICAL AIR MASS...HENCE MOIST ADIABATIC SOUNDING...AND VERY WEAK WINDS ALOFT. NEVER CAN TOTALLY RULE OUT AN ISOLD WET DOWNBURST...BUT NOT ENOUGH CONFIDENCE TO EVEN MENTION IN THE HWO AT THIS POINT. THE BEST FOCUS FOR CONVECTION TODAY SHOULD BE ACROSS NORTHWEST/NORTH CENTRAL NC INTO THE ADJACENT COUNTIES OF SOUTHWEST/SOUTH CENTRAL VA...SHIFTING MORE TOWARD SW VA/SE WV ON THU. FOR THU...MODELS GENERALLY IN GOOD AGREEMENT IN BRINGING A FRONT INTO THE REGION FROM THE NORTHWEST AS A STRONG UPPER DISTURBANCE TRACKS ATOP THE WESTERN/CENTRAL U.S. UPPER RIDGE TOWARD THE GREAT LAKES. THE LINGERING DISTURBANCE ACROSS THE SOUTHERN/CENTRAL APPALACHIANS WILL SHEAR OUT IN ADVANCE OF THIS FEATURE...BUT LEAVE AMPLE MOISTURE FOR THE FRONTAL SYSTEM TO ACT UPON. FOR A CHANGE...THE ECMWF IS ACTUALLY SLIGHTLY FASTER THAN THE GFS IN BRINGING THIS SYSTEM THROUGH THE CWA...WITH MOST FAVORED TIMING TO ENTER THE WESTERN SECTIONS WED NIGHT/EARLY THU...TRACKING ACROSS THE CWA THU...SHIFTING TO THE SOUTH OF THE AREA FRI. AGAIN...THE MAIN CONCERN WITH THIS FRONT WILL BE LOCALIZED HEAVY RAINFALL AS IT INTERACTS WITH THE VERY MOIST AIR MASS IN PLACE ACROSS THE REGION. OVERALL PROGGED INSTABILITY AND SHEAR SUGGEST THAT THE SEVERE THREAT IS MINIMAL AND CURRENTLY SPC DOES NOT HAVE ANY AREAS OUTLOOKED. EVEN SO...USUALLY THE DYNAMICS/BETTER FORCING EVIDENT ALONG A FRONT OFFER AT LEAST A SLIGHT INCREASE IN THE SEVERE THREAT. WITH RESPECT TO TEMPERATURES...850MB TEMPS WILL CREEP UP SLIGHTLY INTO THE +18C RANGE AS 500MB HEIGHTS RISE TOWARD 590DM. HOWEVER...INCREASING MOISTURE CONTENT...ABUNDANT CLOUD COVER...AND SCT-NMRS SHRA/TSRA EACH AFTERNOON SHOULD KEEP TEMPERATURES FROM BECOMING OPPRESSIVELY HOT. HOWEVER...HUMIDITY LEVELS WILL BE NOTABLY HIGHER THAN RECENT DAYS...SO EVEN WITH HIGHS MOSTLY IN THE 80S WEST TO NEAR 90 PIEDMONT...DEWPOINTS 65 TO 70 WILL YIELD SOME RATHER UNCOMFORTABLE AFTERNOONS COMPARED TO RECENT DAYS WITH RECORD LOW HIGHS IN THE 60S. WEDNESDAY SHOULD BRING THE WARMEST TEMPERATURES TO THE REGION IN ADVANCE OF THE FRONT...ESPECIALLY ACROSS THE PIEDMONT...WHICH SHOULD SEE A SLIGHT DECREASE IN CONVECTION AT THAT TIME...THUS POTENTIALLY SEEING MAX TEMPS IN THE LOW 90S LYH-DAN AND VICINITY. && .LONG TERM /FRIDAY THROUGH SUNDAY/...
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AS OF 445 AM EDT TUESDAY... FRONTAL SYSTEM SHOULD SHIFT JUST SOUTH OF THE REGION FRI...ALTHOUGH ALWAYS UNCERTAINTY IN MID-SUMMER REGARDING AS TO HOW FAR SOUTH THE FRONT WILL GO BEFORE STALLING. WITH STRONG UPPER RIDGE TO THE WEST AND STRONG NW FLOW ALOFT ACROSS OUR REGION AS A RESULT...FEEL IT WILL AT LEAST GET FAR ENOUGH SOUTH OF THE CWA TO ENSURE ONE MOSTLY DRY DAY. HAVE HELD ONTO SLIGHT CHC POPS ACROSS THE FAR SE COUNTIES...MAINLY THE NC COUNTIES...TO ACCOUNT FOR THE SLIGHTLY LESS SOUTHWARD MOVEMENT ADVERTISED BY THE ECMWF. DRYING AND COOLING BEHIND THE FRONT COMPARED TO THE PAST TWO SUCH EVENTS IS MINOR AND WE SHOULD STILL SEE HIGHS IN THE 80S...70S MOUNTAINS. HUMIDITY LEVELS/DEWPOINTS WILL DROP SLIGHTLY...BUT WITH PWS STILL NEAR 1.5 INCHES...SIGNIFICANT DRYING IS NOT EXPECTED WITH THIS FRONTAL PASSAGE. FOR THE WEEKEND AND INTO EARLY NEXT WEEK...THE AREA REMAINS VULNERABLE TO NW FLOW DISTURBANCES TRACKING AROUND THE LARGE WESTERN/CENTRAL U.S. UPPER RIDGE. THERE ARE SEVERAL SUCH STRONG DISTURBANCES NOTED IN THE MODELS DURING THIS TIME FRAME...THE MOST NOTABLE ON SUN...THAT COULD BRING THUNDERSTORMS BACK INTO THE AREA. HAVE RETAINED EXISTING CHC POPS THAT WERE ADVERTISED WITH EARLIER FORECAST PACKAGES...BUT CLEARLY THESE COULD POTENTIALLY BECOME LIKELY AT SOME POINT AS THE DEVELOPMENT OF AN UPSTREAM MCS BECOMES MORE APPARENT. BY EARLY THE FOLLOWING WEEK...MODELS IN GOOD AGREEMENT ON THE UPPER TROUGH REAMPLIFYING ACROSS THE EASTERN U.S...WHICH SHOULD KEEP CONDITIONS UNSETTLED WITH NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES WHILE THE EXTREME HEAT REMAINS WELL TO OUR WEST AND WELL AWAY FROM OUR PART OF THE COUNTY...FORTUNATELY.
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&& .AVIATION /12Z MONDAY THROUGH FRIDAY/...
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AS OF 745 AM EDT MONDAY... UPPER DISTURBANCE ACROSS SOUTHEAST STATES SPREADING VERY MOIST AIR NORTHWARD INTO THE REGION. ALREADY SEEING CONSIDERABLE SHOWER ACTIVITY ACROSS EASTERN PIEDMONT COUNTIES IN RESPONSE TO THIS AND WEAK SFC WIND CONVERGENCE NOTED ACROSS THAT REGION. CONSEQUENTLY...WIDESPREAD MVFR TO OCCASIONALLY IFR CIGS NOTED ACROSS REGION...ESPECIALLY EAST OF THE BLUE RIDGE. IMPROVEMENT TO CIGS WILL BE SLOW AS A RESULT. WITH DAYTIME HEATING...EXPECT SCT- NMRS SHRA/TSRA TO DEVELOP THROUGHOUT THE DAY...WITH THE BEST CHANCE ACROSS EAST OF THE BLUE RIDGE. ACTIVITY SHOULD BE DIURNAL AND DISSIPATE AFTER SUNSET...BUT LEAVE WIDESPREAD MVFR CIGS TRENDING TOWARD IFR AFT 06Z WITH POCKETS OF -DZ BR. WINDS SOUTHEAST THROUGH THE TAF VALID PERIOD AT SPEEDS OF 5-7KTS...LESS AT NIGHT. MEDIUM CONFIDENCE IN CIGS/VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN WIND SPD/DIR THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN TSRA POTENTIAL THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... UPPER SYSTEM IN THE BASE OF THE FADING SE TROUGH WILL WEAKEN AND LIFT NORTH TUESDAY INTO WEDNESDAY IN ADVANCE OF AN APPROACHING COLD FRONT FOR THURSDAY. THIS WILL RESULT IN MORE WIDESPREAD DIURNAL CONVECTION EACH DAY WITH EARLY FOG IN SPOTS GIVING WAY TO BRIEF VFR...THEN PERIODIC MVFR IN CLOUDS/SHRA EACH AFTERNOON/EVENING. A COLD FRONT LOOKS TO PUSH THROUGH ON THURSDAY WITH BETTER COVERAGE OF MVFR/IFR PRODUCING SHOWERS AND STORMS. IMPROVED AVIATION CONDITIONS ARE EXPECTED FRIDAY BEHIND THE FRONT WITH CLEARING SKIES AND LITTLE TO NO PRECIPITATION...EXPECT POSSIBLY KDAN.
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&& .EQUIPMENT... AS OF 940 PM EDT SUNDAY... KFCX RADAR IS DOWN. TECHNICIANS HAVE BEEN NOTIFIED AND WILL INVESTIGATE ON MONDAY. NO ESTIMATED TIME FOR RETURN TO SERVICE. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...CF/NF SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...NF/RAB EQUIPMENT...CF

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