Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 210332 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1132 PM EDT Sat May 20 2017 .SYNOPSIS... A series of fronts will cross through the region tonight through Thursday and provide several periods of precipitation. The first will move across southwest Virginia and northern North Carolina from east to west tonight, followed by a stronger front moving from west to east on Monday. The next cold front comes through Wednesday night. && .NEAR TERM /THROUGH SUNDAY/...
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As of 1125 PM EDT Saturday... Storms lined up along deep moisture convergence zone and instability gradient from near High Point NC to Floyd, VA. High-res models and mesoanalysis suggest that the storms will drift to the north and east over the next couple of hours. Overall instability should fade so not much threat of svr, and should see lightning gradually drop off as well after 1am. PWATs running high in the 1.3 to 1.6" range suggest localized flooding possible as storms train at times. Will have to monitor areas near Danbury to Floyd and east to Stoneville to Rocky Mount. At the moment cells moving fast enough to keep flooding threat down. Previous forecast discussion from early evening... Storms starting to propagate south across the piedmont of Virginia, along old outflow and moving toward greater instability. Western CWA has subsided and stabilized, so mainly dealing with showers with embedded thunder. As we head thru the evening, storms will be mainly weakening after 8-9pm, but will still see overall scattered coverage of showers anywhere from the NC/VA piedmont, northwest to the Greenbrier Valley. Previous discussion from early afternoon... Backdoor cold front extended from around Hot Springs to South Boston. Air mass ahead of the front was unstable enough for scattered to numerous thunderstorms. Mean 850-300MB wind is fairly light crossing the axis of the synoptic scale ridge over Virginia and North Carolina so storm motion is less than 20 mph but outflow was also influencing motion and development of storms. Front will have little movement until after sunset then will have a better push southeast. Expect the boundary to reach Boone and Bluefield after midnight. Low clouds will fill in behind the front and showers and thunderstorms will diminish overnight as air mass becomes more stable. Models showed better convergence by Sunday morning along the backdoor front and with the approaching cold front from the west. Stayed at or just below guidance for lows tonight, and took a couple of degrees off the minimum temperatures in the piedmont of Virginia and North Carolina. Also went closer to cooler guidance for the maximum temperatures on Sunday with abundant clouds and numerous showers expected.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 330 PM EDT Saturday... Our weather will remain unsettled through the short term as the upper pattern transitions from an eastern ridge to a deepening broad trof pushing down from the Great Lakes. This will allow a broad surface low moving into southern Canada to slowly push a diffuse cold front through the region on Monday, keeping us in a good chance for showers and thunderstorms. The dynamic support looks rather lackluster in a muddy convective environment with a relatively low threat for widespread severe storms. However, a shallow lingering boundary associated with the retreating wedge and instability pooling ahead of the front seem capable or supporting some robust storm clusters and high precipitable water values indicate the potential for heavy rain and possibly flooding. The cold front will stall to our east and, after a brief break in precipitation Monday night into Tuesday, a wave to move up from the Gulf coast along the front and bring another period of rainfall to the region. Guidance differs in timing/location of rainfall so will have to wait for a consensus to develop in later runs to narrow down any potential hydro issues. Temperatures look to be cooling to levels a bit below normal for the first part of next week as we get on the cools side of the front and deal with considerable cloudiness and precipitation. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 330 PM EDT Saturday... The upper trof will develop into a closed low as it moves out of the Ohio valley and pushes through the Appalachians and central mid Atlantic region by the end of the week. This will swing another cold front through the region and bring more thunderstorms to the forecast for midweek. Dynamics look to be more supportive of a severe threat but instability is a bit limited so will watch later model runs closely for potential severe threat Wednesday. As the closed low moves over with a cold pool aloft to steepen lapse rates, there looks to be a good chance for thunderstorms with some graupel/small hail on Thursday, before the upper low slowly departs and we get into some upper ridging and improving conditions heading into the weekend. Temperatures will be running slightly below normal through the end of the week. && .AVIATION /04Z SUNDAY THROUGH THURSDAY/... As of 715 PM EDT Saturday... Looking at showers and some thunder in vicinity of LWB/ROA/LYH/DAN to wane this evening. As we head into the overnight expect cigs to drop as wedge front sinks southwest. At least low end MVFR to IFR cigs will occur by 12z Sunday. Showers overnight will be limited after the evening coverage dissipates, though some light shower/drizzle may occur in the BLF/LWB area late. Fog appears limited due to increasing low clouds, but still could see some vsbys around 3-5sm. Sunday will stay cloudy but shower will increase, with limited if any thunder. With some moderate to heavier showers possible cigs should come up to MVFR at all sites, while vsbys stay in the MVFR to low end VFR range. Extended Aviation Discussion... Wet weather will continue Sunday night and Monday with an opportunity for showers and thunderstorms and MVFR ceilings and visibility, especially along and ahead of a cold frontal passage Monday. Improvement is expected behind Monday`s front with dry weather returning Monday night into Tuesday. Another front may then bring the next round of showers and subsequent MVFR by Wednesday. Drier weather with VFR conditions is expected behind the front. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS/PM/WP NEAR TERM...AMS/PM/WP SHORT TERM...MBS LONG TERM...MBS AVIATION...AMS/PM/WP is the U.S. government's official web portal to all federal, state and local government web resources and services.