Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 030850 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 450 AM EDT FRI JUL 3 2015 .SYNOPSIS...
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A LOW PRESSURE SYSTEM WILL MOVE OUT OF THE OHIO VALLEY AND INTO THE MIDDLE ATLANTIC REGION. THIS WILL BRING SHOWERS AND THUNDERSTORMS TO THE AREA...ALONG WITH CONTINUED COOL TEMPERATURES...AS WE CLOSE OUT THE WORKWEEK. UNFORTUNATELY OUR WEATHER WILL REMAIN UNSETTLED...WITH A SERIES OF UPPER LEVEL DISTURBANCES BRINGING A CHANCE FOR SHOWERS AND THUNDERSTORMS THE REGION THROUGHOUT THE HOLIDAY WEEKEND.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 400 AM EDT FRIDAY... SHORT WAVE ENERGY ENTERING THE MEAN UPPER TROF OVER THE EASTERN US WILL DRIVE A WAVE OF LOW PRESSURE AT THE SURFACE FROM THE OHIO VALLEY TO THE MID ATLANTIC REGION. THIS WILL TAKE THE FRONTAL BOUNDARY THAT PUSHED SOUTH OF OUR AREA YESTERDAY AND DRAG IT BACK NORTHWARD AS A WARM FRONT WITH WEAK HIGH PRESSURE WEDGING DOWN THE EAST SIDE OF THE APPALACHIANS. EARLY MORNING SATELLITE AND RADAR LOOPS SHOW THAT THINGS ARE BEGINNING TO COME TOGETHER AS THE VIGOROUS CONVECTION OVER TENNESSEE IS BEGINNING TO MOVE MORE TOWARD THE EAST/NORTHEAST...WHICH IS HEADING IN OUR DIRECTION. THIS SYSTEM HAS A LOT GOING FOR IT WITH GOOD DYNAMIC ENERGY AND A VERY MOIST AIRMASS IN PLACE. HODOGRAPHS ARE SMALL BUT SHOW A SIGNIFICANT AMOUNT OF SHEAR AS WOULD BE EXPECTED IN THE VICINITY OF A FRONTAL BOUNDARY. THE MISSING INGREDIENT FOR SEVERE WEATHER TODAY IS INSTABILITY. ABUNDANT CLOUD COVER COMBINED WITH THE SOMEWHAT EARLY ONSET TIME WILL LIMIT DAYTIME HEATING AND MODEL SOUNDINGS IN BUFKIT ARE SHOWING A LONG AND SKINNY CAPE PRESENTATION WHICH DOES NOT FAVOR VIGOROUS UPDRAFTS. BASED ON THESE FACTORS...CURRENTLY ANTICIPATE A SEASONABLE WITH UPPER 60S EAST TO LOWER 60S WEST.EALTHY AREA OF SHOWERS WITH EMBEDDED THUNDER WILL MOVE ACROSS THE AREA FROM WEST TO EAST TODAY WITH ACTIVITY MOVING OUT AND WINDING DOWN THIS EVENING/EARLY TONIGHT. THIS SITUATION WILL BE MONITORED VERY CLOSELY SINCE IF THE CLOUD COVER IS LESS THAN CURRENTLY ANTICIPATED AND WE CAN GENERATE GREATER AMOUNTS OF INSTABILITY...ESPECIALLY ACROSS THE SOUTHERN AND EASTERN PORTIONS OF THE AREA...THE SEVERE THREAT WILL INCREASE. WITH PRECIPITABLE WATER VALUES RUNNING WELL ABOVE NORMAL HEAVY DOWNPOURS CAN BE EXPECTED...BUT THE LACK OF WIDESPREAD SIGNIFICANT RAINFALL ON THURSDAY HAS EASED CONCERN FOR FLOODING A BIT SO WILL NOT BE ISSUING A FLOOD WATCH WITH THIS PACKAGE. WILL CONTINUE TO HIGHLIGHT THE POTENTIAL FOR HEAVY RAIN AND POSSIBLE HYDRO ISSUES IN THE HWO. AS THE LOW MOVES OFF TO OUR NORTHEAST TONIGHT THE FRONTAL BOUNDARY WILL SWING BACK THROUGH THE REGION AS A COLD FRONT. THIS WILL YIELD SOME LINGERING SHOWERS WEST OF THE BLUE RIDGE WITH SOME IMPROVEMENT TO THE EAST HIGH TEMPERATURES TODAY WILL CONTINUE ON THE COOL SIDE WITH READINGS IN THE LOWER 80S EAST OF THE RIDGE TO THE LOWER 70S WEST...AND LOWS TONIGHT RANGE FROM THE UPPER 60S EAST TO LOWER 60S WEST.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
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AS OF 415 AM EDT FRIDAY... THE BROAD UPPER TROUGH PLAUGING THE EASTERN U.S. WILL UNDERGO SOME SUBTLE MODIFICATIONS DURING THIS PERIOD. SAT-SUN...THE UPPER TROUGH WILL TAKE ON A POSITIVE TILT AS A SHORT WAVE RIDGE BUILDS INTO THE GREAT LAKES/PA REGION. MEANWHILE...THE SOUTHERN END BECOMES CUTOFF ACROSS THE CAROLINAS AND LINGERS ACROSS THAT REGION SUN...THEN GRADUALLY DRIFTS BACK NORTHWARD INTO EASTERN VA MON AND NORTHERN VA TUE. THUS...THE AREA REMAINS UNSETTLED AND WET...BUT WITH A GRADUAL SHIFT OF THE BETTER COVERAGE OF SHOWERS AND THUNDERSTORMS TOWARD THE EASTERN PART OF THE CWA WITH TIME. FOR SATURDAY...YET AGAIN...POTENTIAL FOR WIDESPREAD SHOWERS AND EMBEDDED THUNDERSTORMS TO START OFF THE DAY...JUST AS HAS BEEN THE CASE THE PAST TWO DAYS. HOWEVER...CONFIDENCE IN THIS IS LOW AT THIS POINT AS IT WILL LARGELY BE BASED ON UPSTREAM CONVECTIVE COMPLEXES...TRACK...AND INTENSITY. HOWEVER...FEEL THAT CONFIDENCE IN ONGOING PRECIPITATION AT 12Z IS SLIGHTLY GREATER THAN THE PAST TWO DAYS AS THE UPPER TROUGH SHIFTS EAST MOVING THE CURRENT CORRIDOR OF PRECIPITATION ACROSS THE TN VALLEY EASTWARD INTO OUR REGION. THE EXTENT OF CLOUDS AND PRECIPITATION IN THE MORNING WILL DETERMINE THE DEGREE OF INSTABILITY AND HENCE CONVECTIVE COVERAGE LATER IN THE DAY. UPPER FLOW TENDS TO BECOME MORE SOUTHWEST INSTEAD OF NORTHWEST DURING THIS PERIOD GIVEN THE TRANSITION OF THE WEAK UPPER LOW TO THE SOUTH OF THE REGION. THIS SHOULD BE ENOUGH TO SUPPORT HIGH CHANCE TO LIKELY POPS INTO THE AFTERNOON/EVENING. SPC CURRENTLY ONLY HAS GENERAL THUNDER ACROSS THE REGION GIVEN THE LACK OF INSTABILITY. WITH FAIRLY WET ANTECEDENT CONDITIONS...THE MAIN CONCERN WILL BE HEAVY RAINFALL AND LOCALIZED FLOODING. HOWEVER...IT APPEARS UNLIKELY THAT FFG WILL BE EXCEEDED AS RAINFALL AMOUNTS WOULD NEED TO EXCEED 2-2.5 INCHES IN 1-3 HRS MOST LOCATIONS FOR THIS TO OCCUR. PROJECTED RAINFALL FOR THE THREE DAY PERIOD TODAY THROUGH SUNDAY IS MOSTLY 1.5 TO 2.5 INCHES. FOR SUNDAY...THE WEAK UPPER LOW DRIFTS BACK NORTH INTO THE CWA. WIDESPREAD SHOWERS AND THUNDERSTORMS APPEAR LIKELY...BUT THE EXTENSIVE CLOUD COVER WILL AGAIN LIMIT INSTABILITY. ONCE AGAIN...LOCALIZED HEAVY RAINFALL WILL BE THE MAIN CONCERN...BUT GIVEN THAT THE HEAVIEST RAINFALL SHOULD REMAIN MOSTLY EAST OF THE MOUNTAINS...THIS FURTHER REDUCES CONCERNS OF FLOODING. HOWEVER...THE PATTERN DOES ONCE AGAIN SUPPORT LIKELY POPS ACROSS MUCH OF THE CWA...ESPECIALLY EASTERN SECTIONS. MONDAY PROMISES TO BE YET ANOTHER WET DAY AS THE REMNANT UPPER LOW DRIFTS INTO NORTHERN VA. ONCE AGAIN...THE BEST COVERAGE OF PRECIPITATION SHOULD BE ACROSS THE EASTERN SECTIONS...BUT DIFFERENTIAL HEATING ACROSS THE MOUNTAINS SHOULD RESULT IN AN UPTICK OF AFTERNOON CONVECTION THERE AND FURTHER NORTH COMPARED TO SUN. AGAIN...HIGH CHANCE TO LIKELY POPS APPEAR IN ORDER. INSTABILITY ONCE AGAIN APPEARS MARGINAL AND THE MAIN CONCERN WILL REMAIN THAT OF LOCALIZED HEAVY RAINFALL. MAX TEMPS SHOULD REMAIN WELL BELOW NORMAL THROUGH THE PERIOD THANKS TO CLOUD COVER AND PRECIPITATION...WITH HIGHS MOSTLY IN THE 70S...TO LOWER 80S EAST IF A FEW BREAKS IN THE OVC CAN OCCUR. ON THE OTHER HAND...LOW TEMPERATURES WILL REMAIN ABOVE NORMAL THANKS TO HIGH PWATS/DEWPOINTS AND CONSIDERABLE CLOUD COVER.
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&& .LONG TERM /TUESDAY THROUGH THURSDAY/...
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AS OF 430 AM EDT FRIDAY... BY TUESDAY...THERE IS FAIRLY GOOD AGREEMENT AMONG THE MODELS THAT THE CUT OFF UPPER LOW LINGERING ACROSS THE REGION WILL SPLIT IN TWO...WITH THE PART ACROSS NORTHERN VA LIFTING NORTHEAST TOWARD NY/NEW ENGLAND...AS THE PARENT UPPER LOW SINKS SOUTHWARD TOWARD THE FL PANHANDLE/SOUTH GA. MEANWHILE...A SHORT WAVE AND ASSOCIATED FRONT WILL APPROACH FROM THE NORTHWEST BY TUESDAY...THEN DRIFT INTO THE REGION AND STALL WED-THU. AT THIS POINT...TUE SHOULD BE THE DAY WITH THE LOWEST POPS OVERALL...AND LIKELY LOWER THAN ANY PRIOR DAYS OR SUCCEEDING DAYS. ONCE THE FRONT DRIFTS INTO THE REGION WED AND STALLS...WAVES OF LOW PRESSURE WILL RIDE ALONG THE FRONT AND KEEP GOOD CHANCES OF SHOWERS/THUNDERSTORMS ACROSS THE REGION. HOWEVER...COMPARED TO THE CURRENT WEEK WITH NORTHWEST FLOW...UPPER FLOW WILL BE MORE WEST-SOUTHWEST AS BROAD UPPER RIDGING IS NOTED ACROSS THE SOUTHERN STATES. PRECIPITATION OVERALL SHOULD BE SLIGHTLY MORE DIURNAL IN NATURE...I.E...LESS NOCTURNAL...AS A RESULT AND TEMPERATURES WILL CERTAINLY BE TRENDING WARMER...BUT REMAIN MOSTLY 70S MOUNTAINS AND 80S PIEDMONT AS 850MB TEMPS TOP OUT IN THE +16C TO +18C RANGE.
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&& .AVIATION /08Z 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 NEAR TERM...MBS SHORT TERM...RAB LONG TERM...RAB/RCS AVIATION...MBS/NF

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