Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 200735 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 335 AM EDT SUN JUL 20 2014 .SYNOPSIS... WEAK SURFACE FEATURES AND A SLOW-MOVING UPPER LEVEL TROUGH OVER THE EASTERN U.S. WILL ALLOW A CHANCE FOR SHOWERS TODAY AND INTO THE EARLY PART OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 330 AM EDT SUNDAY... UPPER LEVEL TROUGH OVER THE EASTERN U.S. WILL REMAIN IN PLACE TODAY AND TONIGHT WITH WEAK RIDGING FROM NEW ENGLAND CONTINUING TO MAINTAIN A WEAK EASTERLY LOW-LEVEL WIND COMPONENT INTO THE MID- ATLANTIC AND CENTRAL APPALACHIANS PRODUCING SUBTLE COOL-AIR DAMMING. WITH VERY LITTLE FORCING EXPECTED AT THE SURFACE AND ALOFT THERE SEEMS TO BE LITTLE OBVIOUS TRIGGER FOR SHOWER ACTIVITY BUT THE AIR MASS THE OVERHEAD WILL REMAIN QUITE MOIST WITH PWATS HOLDING NEAR 1.5 INCHES ACROSS MOST OF THE CWA...00Z/20 RAOB FROM KRNK HAD 1.48 INCHES WHICH IS ABOUT THE 75TH PERCENTILE FOR DATE IN JULY...ALSO RIGHT AT THE CLIMATOGICAL MAXIMA FOR THE YEAR. THAT SAID THE QUESTION REMAINS WHETHER WE CAN DEVELOP ANY CONVECTION AT ALL TODAY AND THAT MAY DEPEND ON SOME BREAKS IN THE PERSISTENT OVERCAST. BEST CHANCES FOR ANY SHOWERS OR EVEN A THUNDERSTORM TO DEVELOP WILL BE IN FAR WEST WHICH WILL BE LESS UNDER THE INFLUENCE OF THE WEDGE. MODEL CAPES FROM ARW_RNK REACH 1000 J/KG BY LATE AFTERNOON AT BLUEFIELD SO PUT ISOLATED THUNDER CHANCES IN THE WEST ALONG WITH CHANCE POPS GENERALLY FROM BLUE RIDGE WESTWARD AND ONLY SLIGHT CHANCE EAST. BEST SYNOPTIC FORCING FOR PRECIPITATION WILL BE WELL SOUTH OF OUR CWA IN ASSOCIATION WITH SHORT-WAVE AND WEAK LOW DOWN ALONG THE GULF COAST. SOME OF THIS ACTIVITY MAY REACH OUR SOUTHERN COUNTIES BUT AMOUNTS SHOULD BE QUITE MODEST...GENERALLY UNDER 0.25 INCHES ON A MEAN AREAL BASIS. TEMPS TRICKY AS WELL TODAY WITH CLOUDS/JULY SUN GAME IN FULL SWING. USED MODEL BLEND BUT A FEW HOURS OF EXTRA HEATING COULD PLAY HAVOC WITH CURRENT MID-70S WEST TO LOW 80S EAST FORECAST.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 330 PM EDT SATURDAY... UPPER TROUGH OVER THE AREA WILL WEAKEN AS WE TRANSITION INTO THE UPCOMING WEEK. MEANWHILE A MAMMOTH 600DM RIDGE WILL BEGIN BUILDING ACROSS THE WESTERN U.S. AND LARGELY CONTROL THE STEERING CURRENTS OVER THE CONUS FOR THE UPCOMING WEEK. IN SPITE OF THE BUILDING HEIGHTS...A DEFINITE AND PERSISTENT WEAKNESS WILL REMAIN LEFT BEHIND FROM THE BASE OF THE EASTERN U.S. TROUGH ACROSS THE SOUTHEAST CONUS AND EVENTUALLY APPEARS TO EVOLVE INTO A PSEUDO TROPICAL LOW ALONG THE GA/SC COAST. MODELS ARE IN FAIR AGREEMENT THIS FEATURE WILL REMAIN PRIMARILY INLAND...AND WITH THE BUILDING RIDGE...THE MODELS RETROGRADE THIS FEATURE WESTWARD INTO THE LOWER MS VALLEY BY MID WEEK. THE FLOW OVER OUR LITTLE PIECE OF REAL ESTATE...AT LEAST THE FIRST HALF OF THE WEEK LOOKS PRETTY DEAD ALOFT...LACKING ANY SIGNIFICANT ADVECTION OF AIR EITHER NORTH OR SOUTH. AS SUCH...EXPECT THE OVERALL AIRMASS TO MODIFY WITH TIME...THE JULY SUN DOING ITS THING TO WARM US UP A FEW DEGREES EACH DAY...TEMPERATURES CLIMBING BACK TO THE SEASONAL NORM. THE SHOWER THREAT WILL BECOME DIURNALLY DRIVEN WITH WIDELY SCATTERED SHOWERS/STORMS DURING THE PEAK HEATING OF THE AFTERNOON AND EVENING ONLY...AND LITTLE OR NO PRECIP THREAT AT NIGHT. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 445 PM EDT SATURDAY... UPPER RIDGE IS FORECAST TO REMAIN OVER THE WESTERN CONUS THROUGH THE LONG TERM...WITH A PERSISTENT UPPER TROUGH OVER THE EASTERN CONUS. A STRONG SHORT WAVE TRACKS FROM SOUTH CENTRAL CANADA ATOP THE UPPER RIDGE TOWARD THE GREAT LAKES. THIS DRIVES A FRONTAL SYSTEM INTO THE EASTERN U.S. AND OUR REGION BY THURSDAY. THE 12Z GFS IS THE MOST AGGRESSIVE WITH THE FRONT COMPARED TO THE LESS AMPLIFIED ECMWF...IN PUSHING THIS FRONTAL SYSTEM THROUGH THE REGION THURSDAY...THEN S-SE OF THE AREA FRI. FOLLOWING THE GFS...THE GREATEST CHANCE FOR SHOWERS/STORMS WILL BE THURSDAY... FOLLOWED BY A DRY FRIDAY AND SATURDAY. THIS SCENARIO WILL ALSO YIELD WEDNESDAY BEING THE WARMEST DAY OF THE WEEK IN ADVANCE OF THE FRONTAL SYSTEM...850MB TEMPS APPROACHING +20C ACROSS MUCH OF THE REGION...WITH LOW 90S IN THE PIEDMONT AND 80S ELSEWHERE. THURSDAY WILL BE A TRANSITION DAY WITH THE FRONTAL PASSAGE...FOLLOWED BY 4 TO 7 DEGREE DOWNTICK IN TEMPERATURES FOR FRIDAY AND SATURDAY. IF THERE IS ANY CHANCE OF ORGANIZED STORMS THIS WEEK IT WOULD MOST LIKELY OCCUR WITH THE FRONTAL PASSAGE THURSDAY. ANYTHING BETWEEN NOW AND THEN WILL BE DIURNALLY DRIVEN WITH AND FOCUSED MAINLY OVER THE MTNS...WEAK FORCING NOT PROVIDING FOR MUCH SUPPORT FOR ANYTHING ORGANIZED. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... AS OF 135 AM EDT SUNDAY... VARIABLE CONDITIONS AGAIN EXPECTED TO BE THE RULE AT TAF SITES THE REST OF THE NIGHT WITH PATCHY REDUCTIONS IN VSBY AND PLENTY OF LOW TO MID-LEVEL CLOUDS. MAINLY MVFR AT WESTERN TAF SITES AND SOMEWHAT HIGHER CIGS/VSBYS AT EASTERN TAF SITES. EXPECT SOMEWHAT IMPROVING CONDITION BY MID-MORNING WITH INCREASE IN CIGS BUT ANOTHER WAVE OF ENERGY IS EXPECTED TO PROGRESS INTO THE REGION BETWEEN 18-00Z/2PM- 8PM TODAY. LOOK FOR INCREASE IN SCATTERED RAIN SHOWERS MAINLY IN THE MOUNTAINS...AND POSSIBLY AN ISOLATED THUNDERSTORM IN THE FAR WEST...TOWARD BLF. PREVIOUS VALID DISCUSSION... AS OF 125 PM EDT SATURDAY... EXTENDED AVIATION DISCUSSION... PRECIPITATION WILL BECOME MORE SCATTERED AND DIURNAL IN NATURE SUNDAY AFTERNOON THROUGH WEDNESDAY...WITH A BETTER POTENTIAL FOR AFTERNOON/EVENING THUNDERSTORMS...AS WELL WITH WARMER TEMPERATURES AND MORE UNSTABLE CONDITIONS. THIS WILL RESULT IN BRIEF PERIODS OF MVFR-IFR CIGS IN SHRA/TSRA AS WELL AS INCREASING POTENTIAL FOR LATE NIGHT/EARLY MORNING FOG AND LOCALIZED IFR-LIFR VSBYS WHERE RAIN OCCURS THE PREVIOUS AFTERNOON. && .CLIMATE... THE PERSISTENT LOW CLOUD COVER...DRIZZLE AND EASTERLY FLOW COMBINED TO PRODUCE THREE NEW RECORD LOW MAXIMA FOR THE DATE YESTERDAY JULY 19 2014. BLACKSBURG...LEWISBURG AND BLUEFIELD ALL SET NEW DATE RECORDS...BY 6 DEGREES F IN THE CASE OF BLACKSBURG. SEE WBCRERRNK FOR DETAILS. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PC NEAR TERM...PC SHORT TERM...PM LONG TERM...PM/RAB AVIATION...DS/PC CLIMATE...PC

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