Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 031412 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1012 AM EDT Mon Aug 3 2020 .SYNOPSIS... Tropical Storm Isaias will track northward along the East Coast during today and Tuesday to bring bands of showers and thunderstorms to the Mid Atlantic. A cold front should cross overhead by Tuesday night but stall along the coast for the remainder of this week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... As of 345 AM EDT Monday... Bands of showers and thunderstorms are moving northward toward the Mid Atlantic. Some of the stronger storms have produced frequent lightning, heavy rainfall, and gusty winds. Patchy fog has been added for the remainder of the overnight hours given the moist boundary layer and recent rainfall. Meanwhile, Tropical Storm Isaias will churn northward along the Florida and Georgia shoreline today. An approaching cold front will enter the Ohio River Valley by this afternoon. The resulting moisture convergence will result in increasing coverage of showers and thunderstorms. The showers and thunderstorms present several hazards with the potential for severe due to damaging winds and flooding due to heavy rainfall. As a result, no changes have been made to the Flash Flood Watch due to an anticipated predecessor rain event, or PRE, that typically occurs well away from landfalling tropical cyclones when moisture interacts with some kind of frontal boundary. There is the potential for isolated amounts of one to two inches of rain along parts of the Blue Ridge before the day is done. High temperatures should reach the 70s in the mountains and the low to mid 80s in the Piedmont. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/... As of 330 AM EDT Monday... Heading into Monday evening, the axis of heaviest rainfall associated with the wave of energy (PRE) passing across the lower Mid-Atlantic is expected to be situated across the Piedmont and foothills of the Blue Ridge, lifting gradually northeast. Meanwhile, Isaias will make landfall near the North Carolina/South Carolina border and advance quickly northward toward the mouth of Chesapeake Bay. Isaias is a rather compact and fast-moving storm, with its greatest impacts expected to remain confined east of a Danville to Lynchburg line. After a brief lull in rain in the wake of the departing wave of energy, the main bands of Isaias will enter Halifax County shortly before dawn Tuesday. Northerly windflow on the western half of the storm will draw drier air across the Piedmont to counteract the moisture radiating outward from the core of Isaias. The result will be a tight gradient in rainfall accumulations as the storm passes, with 4+ inch amounts expected across portions of Buckingham and Charlotte Counties, with accumulations diminishing by about an inch roughly every 30 miles to the west. The wind threat associated with the storm is expected to be marginal at best, 25 to occasional 35 mph gusts across Buckingham and Charlotte Counties during the morning. By noon Tuesday, the center of Isaias is expected to be near the Chesapeake Bay, with dry air quickly working its way in from the northwest in the wake of the storm as a trailing cold front passes across the Appalachains chain. Clearing skies can be expected across the Piedmont during the afternoon as winds shift northwesterly and downslope. Cannot rule out a few showers developing across the mountains during the afternoon, but believe this activity will be spotty and disorganized, and will fade toward sunset with the loss of afternoon heating. Widely-scattered showers and thunderstorms will return for Wednesday as the frontal boundary stalls across the Piedmont, serving as the focus for afternoon convection. May see a few of these storms become severe for brief periods of time, capable of producing localized damaging wind gusts. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 300 PM EDT Sunday... Weather pattern returns to more typical for summer time. Will again be repetitive forecast of daily chances for afternoon and evening thunderstorms, along with heat and humidity typical of summer. No major deviation from long range synoptic scale guidance. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... As of 210 AM EDT Monday... Outside of periods of heavy rainfall/storms, conditions will be VFR. This AM`s band of showers and storms have eroded and are being replaced by a new line of thunderstorms stretching from western TN, into SWVA through far east WV. These storms will obviously produce sub VFR conditions when over TAF sites through today and into this evening. As the day progresses, this line of convection will traverse eastward while another band of storms makes there way northward from central NC. These two bands will ultimately provide a prolonged period of storm chances for all TAF sites along and east of the Blue Ridge. Eventually the storm move out of the region, ushering in the next focus of the forecast, Isaias. Due to its proximity moving up the coast, light to moderate rainfall will spread over the eastern part of the region, bringing rainfall for LYH and DAN. This also places BCB and ROA on the edge between light rainfall/BR producing low ceilings, or gusty conditions as downslope occurs with the wind shift associated with the system, resulting in better flight ceilings. For now, leaning toward the low ceilings lighter winds. Sites in WV will drop tonight, but terrain influences combined with winds will determine whether BLF and LWB drop sub VFR, or remain VFR with windy conditions. Extended Aviation Discussion... Poor flying conditions are expected into Tuesday due to Tropical Storm Isaias passing over eastern Virginia. Showers and thunderstorms will continue through this time until a cold front sweeps the moisture away by Tuesday night. Conditions should improve to VFR on Wednesday and generally remain this way through Friday, but some early morning patchy fog and scattered afternoon showers and thunderstorms could temporarily restrict flight conditions during this time. && .HYDROLOGY... A frontal boundary stalled near the spine of the Blue Ridge will support bands of showers and thunderstorms that will pass across the region through the day. Moisture will continue to increase as Tropical Storm Isaias continues its approach, which will cause some storms to produce 2 to 3 inch per hour rainfall rates this afternoon and evening. In addition, training of storms across the same locations is probable, leading to prolonged periods of heavy rain and possibly localized flash flooding. A few locations could receive 3 to 4 inches locally. Just as this system exits to the northeast late this evening, Tropical Storm Isaias is expected to make landfall near the border of North Carolina and South Carolina tonight, and pass rapidly northward to near the mouth of Chesapeake Bay by early Tuesday afternoon. This will bring the potential of 3 to 5 inches of rain to areas east of a Danville to Lynchburg line. Rainfall associated with Isaias will exit during early afternoon, with rapidly clearing conditions expected thereafter. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Flash Flood Watch from 2 PM EDT this afternoon through Tuesday evening for VAZ022>024-033>035-043>047-058-059. Flash Flood Watch through Tuesday evening for VAZ015>017-032. NC...Flash Flood Watch from 2 PM EDT this afternoon through Tuesday evening for NCZ004>006-020. Flash Flood Watch through Tuesday evening for NCZ001>003-018- 019. WV...None. && $$ SYNOPSIS...PW NEAR TERM...PW SHORT TERM...NF LONG TERM...AMS AVIATION...PW/RR HYDROLOGY...NF is the U.S. government's official web portal to all federal, state and local government web resources and services.