Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 220046 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 846 PM EDT Sat Jul 21 2018 .SYNOPSIS... A wedge of high pressure east of the Appalachians will gradually weaken tonight in advance of low pressure approaching from the northwest. This system will cross the region Sunday before spilling to the south by early next week. Scattered showers and storms will accompany this system today before rainfall becomes more widespread Sunday and through the first part of next week. && .NEAR TERM /THROUGH SUNDAY/... As of 800 PM EDT Saturday... Convergence between easterly low level flow on the east side of the mountains and westerly flow associated with approaching upper level trough is resulting in scattered showers/storms across the mountains this evening. Upper level winds are out of the west, so this activity will drift east into the foothills and piedmont before dissipating during the overnight. Once the precipitation wanes after midnight, fog formation will be possible, particularly in areas which receive rain. Low level stratus is also possible late tonight and early Sunday. Upper level closed low will continue to sink south toward the gulf tomorrow, providing plenty of moisture ahead of the front before it finally stalls out to the east of the region by the end of the period. A short wave rotating around the upper level low could get get showers and thunderstorms started earlier than in a typical diurnal pattern which would reduce heating during the day and also the severe threat. Shower and thunderstorm coverage will peak during the afternoon into evening hours and will be more widespread than on Saturday. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 300 PM EDT Saturday... Blocky pattern remains in place with an upper ridge over the Atlantic and stacked closed low sinking south toward the Gulf coast with a distinct wedge signature in place through the period. This will gradually establish very deep moisture transport into the region with a well developed conveyor of southeasterly low level winds. This moisture will ride up over the top of the wedge and generate a good amount of isentropic lift along and east of the Appalachians. The end result will be persistent and occasionally heavy rain developing over the region, especially along and east of the Blue Ridge with some local enhancement from orographic effects possible. Rainfall totals of 1 to 3 inches by daybreak Wednesday appear quite attainable. However, this wet period is arriving after a couple of weeks of hot and relatively dry conditions, so soils will be eager to absorb a good amount of water and this will help temper runoff. Local hydro issues will be possible if rain rates become excessive, but at this time larger scale flooding problems do not look likely through Tuesday night. Given the wedge and expected cloud cover high temperatures will be running a bit below normal through the first part of next week, though mins will be around normal. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 300 PM EDT Saturday... Once the closed low reaches the Gulf coast, it will open up and become assimilated into the mean flow as another closed low moves across southern Canada to near Hudson Bay by the end of next week. However, the net result will keep us in a wet pattern as a stalled frontal boundary develops over the Appalachians and central mid Atlantic region on the periphery of high pressure over the Atlantic. This is a more typical summertime pattern and will yield ample amounts of instability with lower amounts of shear in southwesterly low level flow. Expect daily rounds of thunderstorms with locally heavy rain and a severe threat generally dependent on storms that can organize into lines and/or clusters. Will have to see where the heaviest rain occurs early in the week to get a handle on where a flood threat may materialize later in the week. Temperatures will warm steadily through the middle of next week with highs by Friday in the upper 80s/near 90 east of the Blue Ridge and in the low/mid 80s to the west. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/... As of 800 PM EDT Saturday... An upper level trough over the Ohio Valley will result in scattered to numerous showers and thunderstorm the next several days with greatest coverage during the afternoon and evening hours. This will result in highly variable flight conditions. In addition, shallow easterly low level winds may allow for the formation of fog/stratus along the Blue Ridge late tonight and early Sunday. Extended Aviation: Wet weather pattern is forecast for most of the upcoming week with a nearly stationary upper level trough of low pressure remaining over the eastern CONUS. As such, forecast will reflect Scattered to numerous showers and thunderstorms, but mainly during the afternoon hours coinciding with peak heating and instability. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...MBS NEAR TERM...JR/PM SHORT TERM...MBS LONG TERM...MBS AVIATION...PM

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