Area Forecast Discussion
Issued by NWS Blacksburg, VA

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944 FXUS61 KRNK 271336 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 936 AM EDT Sun May 27 2018 .SYNOPSIS... High pressure centered offshore will maintain a moist southerly flow of air into the region for the next several days. Subtropical Storm Alberto moving into the Gulf of Mexico this weekend will move ashore and into the lower Mississippi Valley early in the week. Tropical moisture will stream north into the region making for very rain efficient showers and thunderstorms. && .NEAR TERM /THROUGH TONIGHT/...
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As of 936 AM EDT Sunday... Made a quick update to adjust pops down for this morning as cloud desk and patchy fog are hindering convection. Regional radar image showed a few light showers in the western mountains. This is the peaceful moment before deep convection forms this afternoon especially along the mountains and in the east near linger boundary. Modified temperatures with latest surface obs and trend towards NBM for this afternoon. High temperatures will be from the 70s to around 80 degrees. Holding off on any flash flood watch at this time. Have a good Sunday. As of 400 AM EDT Sunday... Relatively quiet but moist Sunday morning. Considerable cloudiness most areas this morning along with patchy fog, temperatures AOA 60. For today, moisture laden airmass will quickly yield to thermally driven showers with convergence along the mountains providing the focus for deep convection. Squeeze play will also be ongoing between upper trough over the northern Mid-Atlantic and tropical moisture streaming north from the Gulf of Mexico... convergence axis along or north of our CWA border. Similar to yesterday showers/storms will be very rain efficient with PWATs 2 standard deviations above normal. For our CWA, HiRes models focus the greatest shower concentration along the VA/WV border from Tazewell northeast into Greenbrier and Bath. Tazewell got hit pretty hard yesterday with some gages reporting 2-3 inch amounts. Attm will hold off on a Flash Flood Watch. Prefer to see where convergence boundaries will line-up and target those as opposed to blanketing a larger piece of real estate. The Weather Prediction Center has painted a pretty wide swath with respect to rainfall exceeding flash flood guidance today...the greatest threat right along the spine of the Appalachian crest where the low level convergent flow will be the greatest. Temperatures today will be very similar to Saturday, the clouds and showers keeping the numbers confined to the 70s to lower 80s for highs this afternoon, and low temperatures in the 60s.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... As of 330 AM EDT Sunday... Our weather through the first part of next week will be dominated by the nuances associated with Alberto as the tropical circulation moves through the southeast then accelerates as it heads toward the Great Lakes. Expect a wet few days with an increasing threat for flooding. Alberto will start to push a band of tropical rainfall up from the south early Monday but this initial surge will become sheared and have trouble making significant northward progress past the NC/VA border. However, as Al starts moving north with more enthusiasm on Tuesday, better transport of deep tropical moisture will become established across the Appalachians and central mid Atlantic region with NAEFS precipitable water anomalies of 2 to 3 standard deviations. Diurnally biased pattern to convection should yield widespread coverage of showers/thunderstorms with heavy rainfall and an as yet ill defined area wide hydro threat as ensemble precipitation plumes still exhibit a great deal of spread through the period. Wednesday may offer the most coverage of heavy rainfall and greatest hydro threat this period on the heels of several days of heavy rainfall as Al moves into the Great Lakes with a trailing convergence zone through our area. Additionally, instability and the synoptic wind regime are on the light side but shallow shear profiles with a small looping hodograph in the boundary layer become more pronounced and indicate a potential severe threat lurking Tuesday and Wednesday. Expectation is that threats will declare themselves as the situation evolves and flood watches will be issued once specific areas to be impacted can be identified. && .LONG TERM /THURSDAY THROUGH SATURDAY/... As of 300 PM EDT Saturday By mid to late week, flooding potential will depend on how much rainfall is accumulated from several days of locally heavy tropical rainfall. Alberto is expected to be in the Ohio Valley Thursday morning. Thursday night into Friday, the low will open up and weaken as it moves northeast into the weekend. There is a continued threat for showers and thunderstorms into the end of the week. Urban and small stream flooding risk will be highest early with river flooding possibly by the end of the week depending on actual rainfall totals. High temperatures will generally be around normal, climbing to above normal at the end of the week, with overnight lows remaining fairly mild mainly around 60 degrees to about 70 degrees. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... As of 800 AM EDT Sunday... Very moist boundary layer will promote development of scattered to numerous showers/storms today. Primary focus is expected along a weak trough/boundary which extends from central OH valley into northern VA, and along the spine of the Appalachians. These showers will be very rain efficient due to the high moisture content of the air. Areas of MVFR cigs will prevail across the mountains today with partial ridge obscurations from stratofractus associated with the rain showers. Winds will generally be light and variable or calm through the 24 hour forecast period. .Extended Aviation Discussion... Wet pattern anticipated through the upcoming week with periods of at least diurnally driven sub-VFR conditions associated with deep convection. Moist low level southerly winds will also favor lower layers of cloudiness at night, especially along the spine of the Appalachians with potential for both MVFR Cigs and early morning MVFR visibilities from mist/haze. The tropical system over the Gulf of Mexico may begin to impact the region mid-week. && .EQUIPMENT... NOAA Weather Radio, All Hazards, WZ2500 at Wytheville, VA, broadcasting on a frequency of 162.45 mHz, will be off the air until further notice. Technicians are aware of the problem, and corrective action will be attempted on Sunday. Until repairs are complete, you may be able to receive broadcasts from neighboring transmitters if you are located close enough to them. These include WXL60 in Roanoke, VA, broadcasting at 162.475 mHz, WZ2543 in Richlands, VA, broadcasting at 162.425 mHz, or WNG588 in Mount Jefferson, NC, broadcasting at 162.500 mHz. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...KK/PM SHORT TERM...MBS LONG TERM...KK/MBS AVIATION...PM EQUIPMENT...DS is the U.S. government's official web portal to all federal, state and local government web resources and services.