Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201349 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 949 AM EDT Sun Aug 20 2017 .SYNOPSIS... High pressure across the mid-Atlantic will maintain overall warm and dry weather through this afternoon. This high will gradually drift east tonight and Monday, allowing winds to shift southerly and return deeper moisture into the area. Another cold front will approach the area by the middle of the week, bringing with it another chance for showers and storms. && .NEAR TERM /THROUGH TONIGHT/... As of 940 AM EDT Sunday... Morning soundings again show limited moisture across the region with a strong mid level warm layer/cap around 600 mb within a rather deep westerly flow regime. However short term guidance still showing as the high starts to slide east this afternoon, that a weak low level southeast trajectory will develop espcly over the mountains. This will also help develop weak convergence, per latest Cam ensemble, mainly along and west of the Blue Ridge. HRRR also hinting at shallow convection popping along the ridge tops mid/late afternoon beneath the inversion aloft. Still appears most of this to remain quite isolated and mainly showers given dry air aloft and weak lapses. Therefore only included a few more locations within isolated pop coverage out to the Blue Ridge this afternoon, with perhaps a shower or two sliding east off outflow. Otherwise should be mostly sunny, except for a more clouds developing mountains this afternoon. Will be a bit more muggy as well with dewpoints up a little more than yesterday, and highs again generally 84-91 from west to east per latest thickness. Previous discussion as of 745 AM EDT Sunday... Main concern this morning is river valley fog across the mountains, which is locally reducing visibility to a few hundred feet in spots. Clear skies otherwise and strong heating will cause this fog to burn off quickly after 9 AM. Strong heating will support the development of scattered clouds during late morning/early afternoon, more so across the mountains. Models continue to hint at a few showers developing along the Blue Ridge during mid afternoon, possibly a thunderstorm, however instability appears quite limited due to warm mid level temperatures, and believe that any rainfall will be isolated and short-lived. With winds gradually shifting more southeasterly through the day, afternoon high temperatures are expected to top out a degree or two above those for yesterday, ranging from the mid 80s to the low 90s. Any shower activity is expected to fizzle quickly toward sunset as daytime heating ends. Winds will continue to shift more southerly ahead of another approaching cold front, allowing dewpoint temperatures to gradually notch upward. As such, believe river valley fog will be a little more widespread on Sunday night. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 AM EDT Sunday... High pressure will push east of the Virginia coast Monday into Monday night. With some weak southerly upslope flow, solar heating and marine moisture, scattered showers and thunderstorms are possible along the Blue Ridge Monday afternoon. Any afternoon storms will then drift east in zonal flow and fade over the foothills Monday evening into Monday night. Cloud cover Monday afternoon should not hinder viewing of the solar eclipse. The eclipse, coming over the region during peak heating, may hamper afternoon convection to isolated coverage. Temperatures during the eclipse may drop 3F to 5F, especially south of a line from Richlands VA to Mount Airy NC. Temperatures will rebound following the solar eclipse with daytime highs ranging from the upper 70s in the mountains to near 90F across Southside. Any convection should end before Midnight, leaving clear to partly cloudy conditions. Low temperatures Monday night will range from the lower 60s in the mountains to the lower 70s in the Piedmont. On Tuesday, high pressure will move further out into the Atlantic ocean and lose its hold on the region as a cold front approaches from the west. Isolated to scattered diurnal convection may be possible Tuesday afternoon into Tuesday night. High temperatures Tuesday will be above normal with readings from around 80 degrees in the west to the lower 90s in the east. Along and ahead of the cold front, some showers may push into the mountains Tuesday night. Low temperatures Tuesday night will generally be from around 60 degrees in the west to the lower 70s in the east. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 300 AM EDT Sunday... A cold front will travel east across the region Wednesday. This boundary will enter the mountains Wednesday morning and cross the Piedmont Wednesday afternoon. This may leave a minimum or shadow of rainfall along the Blue Ridge and foothills. The best low level jet is north towards DC and with the winds coming around to the west quickly, the severe threat will be limited. The exception to the rule will be across NW NC piedmont and Southside VA late in the afternoon and into the evening, where instabilities will be high. Best LI values were around minus 2 to minus 6 in the east. Following the front Wednesday night, cooler drier air will move into the region and remain into next weekend. The GFS is hinting at a shortwave rotating around the upper trough and generating some convection in the mountains Friday afternoon. As the high shifts east from the Great Lakes Sunday into Monday, some moisture may return to the mountains. Temperatures will likely be cooler than normal by 5F or 10F. Humidity levels will also be comfortable as dew points drop into the 50s. && .AVIATION /13Z SUNDAY THROUGH THURSDAY/... As of 745 AM EDT Sunday... Main concern this morning is river valley fog across the mountains, which is locally reducing visibility to IFR/LIFR, including LWB and BCB. Clear skies otherwise and strong heating will cause this fog to burn off quickly after after 20/13Z. Scattered CU will develop during early afternoon, with bases between 4 to 6 kft. Models hinting at isolated to widely scattered, short-lived showers developing along the Blue Ridge during the 20/18Z to 20/23Z timeframe, but not enough coverage to mention in TAFS. Expect to enter Sunday evening under mostly clear skies as CU/convection fizzles with the loss of daytime heating. With winds shifting southerly on Sunday evening, expect dewpoints to be on a gradual rebound. Another night of mostly clear skies and light winds are expected to support increased coverage of river valley fog. Extended Aviation Discussion... Moisture will increase Monday and Tuesday as high pressure weakens and moves offshore ahead of another cold front that will arrive from the northwest around midweek. However still appears it should remain mainly VFR Monday into Tuesday with localized MVFR under isolated to widely scattered convection. Late night/early morning fog will also be possible each day. Better potential for sub-VFR will come Wednesday when possibly more widespread showers and storms arrive with the next cold front. && .EQUIPMENT... As of 400 AM EDT Sunday Aug 20th... KFCX doppler radar expected to be down for the rest of the month due to a failing bull gear. Technicians are working on the radar through this week and the radar will most likely stay down completely as the repairs are being made. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...NF NEAR TERM...JH/NF SHORT TERM...KK LONG TERM...RCS AVIATION...NF EQUIPMENT...RAB/WERT/WP

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