Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 180755 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 355 AM EDT Fri May 18 2018 .SYNOPSIS... A frontal boundary extends from Tennessee eastward to coastal Virginia. Several waves of low pressure will ride north along the front. Warm and humid conditions will continue into the weekend with widespread and numerous showers and thunderstorms today becoming more scattered over the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 355 AM EDT Friday... Flash Flood Watch remains in effect through this evening. The heavy rain threat continues with deep southerly flow of moisture, quasi-stationary front and wet antecedent conditions. The frontal boundary will linger over the region today with a gradual drift to the north as weak impulses of shortwave energy aloft move up form the south in deep, moist tropical flow. This morning the frontal boundary combined with a weak shortwave is focusing low level convergences and instability mainly in the south and east. With pockets of light rain, drizzle and fog in the west. Later today an upper low will travel into our forecast area. This create favorable QG ascent, along with the persistent southerly upslope flow induced by the Bermuda High. Scattered showers and thunderstorms with rain heavy at times are expected this afternoon into tonight. Rainfall will continue to be very efficient and it will not take long for slow moving cells to produce excessive rainfall. The FFG is quite low in several places and widespread heavy rain fall Thursday night. High temperatures this afternoon will range from the mid 60s in the northwest mountains to the mid 70s in the piedmont. Rain chances will decrease tonight mainly in the west. Cloudy skies will persist with lingering showers along and east of the Blue Ridge. Low temperatures tonight will vary from the upper 50s in the mountains to the mid 60s in the piedmont. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 330 PM EDT Thursday... The item of focus for this portion of the forecast will be a slowly northward moving upper level low across the Lower Ohio/Tennessee River valleys and copious moisture that will be streaming north on its east side. This moisture will be impacting our region with moderate to heavy rain showers and some thunderstorms through Saturday night. A Flash Flood Watch is in effect for the first half of Friday night for entire region. As we progress into and through this part of the forecast, where, and how much, precipitation falls, and additional expected precipitation, will dictate where, and if, any additional watches may be needed through Saturday night. There will be a brief lull in the precipitation late Saturday night into early Sunday morning as the upper low washes out and gets caught up in the northern jet. In its wake will a brief period where a shortwave ridge will be over the area, all the while an area of low pressure begins to develop across the Central Plains states. This low will begin to head eastward Sunday night. A return of precipitation is expected as early as Sunday afternoon across western sections of the region where surface heating, and a beginnings of a return of low level moisture will coincide. Sunday night, with the loss of daytime heat, precipitation coverage will decline. However, scattered showers will still be possible in the west, within the region of best moisture return and dynamics aloft in advance of approaching low pressure. Temperatures during this part of the forecast will start around five degrees above normal for Saturday, but warm to around five to ten degrees above normal on Sunday. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 130 PM EDT Thursday... On Monday, an area of surface low pressure is expected to be heading east through Indiana along a stationary front that extends into Pennsylvania. The low`s associated cold front will trail southwest into eastern Texas, all while its parent upper low tracks through the western Great Lakes region. High pressure will still be anchored in the western Atlantic, east of the GA/FL. For our region, plenty of moisture streaming north between the cold front and the high pressure will be realized in form of at least a mostly cloudy sky and an abundance of showers and some thunderstorms. Monday night into Tuesday, the surface low is expected to have reached KY/OH/WV with the stationary front over PA sinking south as a backdoor cold front. The cold front associated with the surface low is progged to stall and take on warm front characteristics from roughly Missouri into Kansas. While there initially be a decrease in coverage of precipitation across the region Monday night, most of this decline will be due to loss of heating. Western sections of the area, closer to the approaching low, will be the most likely to continue to see some isolated to scattered showers, and few storms, through the night. On Tuesday, coverage is expected to increase again with the return of daytime heating, and increased dynamics as the system draws closer. Tuesday night night into Wednesday, look for the low to wash out, but the back door cold front will continue to inch south through, then south of the area, stalling over GA/SC by Thursday morning, and remaining there into Friday. Behind the front, high pressure will build into our region. The result for our region will be another decrease in coverage Tuesday night with the loss of heating. On Wednesday, scattered showers will be confined to primarily the southern third of the area. Wednesday night into Thursday, limited, if any, precipitation is forecast for the area with the push of high pressure into the area. Temperatures during this portion of the forecast will average about ten degrees above normal on Monday, and trend cooler each day. By Thursday, temperatures will average around five degrees above normal. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... As of 148 AM EDT Friday... Poor flight conditions will continue at TAF sites this period with low clouds and convection. Lingering frontal boundary combined with impulses of short wave energy in a tropical airmass will generate showers and thunderstorms with heavy rain. Adjusted timing of features with latest mesoscale models, and will amend as necessary with a preference to leave lower conditions prevailing when more activity is expected to move in. Light rain and drizzle expected early this morning with MVFR and IFR cigs to remain in place. Another wave of convective precipitation is expected to push in from the southeast toward daybreak and continue to affect TAF sites through the latter portion of the valid period as the frontal boundary starts to push back to the north. Medium confidence in ceilings, visibilities and winds during the taf period. .Extended Aviation Discussion... The pseudo-tropical low and the lingering frontal boundary will begin to drift north of the CWA later Friday and especially into the weekend. This should bring about a slight decrease in rain coverage with activity trending more scattered and diurnal in nature as we go into the weekend and high pressure ridging is noted across the southeast states. However, still feel that chances for showers/thunderstorms and associated aviation issues will be greater than normal for this time of the year, at least through Saturday with periods of sub-VFR possible. Fog and low clouds will be common during the late night and early morning hours as well. After more isolated storms on Sunday, appears another weak cold front may bring increasing coverage of showers and thunderstorms again on Monday. && .HYDROLOGY... A Flash Flood Watch is in effect for the entire CWA through Mid-Night Friday night. The main concern through Friday will be for localized flash flooding, as well as flooding on small creeks, streams, and smaller rivers as a result of heavy tropical rain showers and thunderstorms expected across the area. Rainfall during the past few days has been spotty and highly variable, but as low pressure passes overhead Friday, the coverage is expected to increase. Flood Guidance suggests 2 inches or more of rain in less than 3 hrs may lead to flooding, and if this sort of rainfall occurs in less than an hour, flash flooding would be possible. WPC is concerned about excessive rainfall, and especially for those areas along a stationary near the Interstate 64 corridor. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Flash Flood Watch through this evening for VAZ007-009>020- 022>024-032>035-043>047-058-059. NC...Flash Flood Watch through this evening for NCZ001>006-018>020. WV...Flash Flood Watch through this evening for WVZ042>044-507-508. && $$ SYNOPSIS...KK/PM NEAR TERM...KK SHORT TERM...DS LONG TERM...DS AVIATION...KK/MBS HYDROLOGY...PM is the U.S. government's official web portal to all federal, state and local government web resources and services.