Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 190032 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 832 PM EDT Sun Jun 18 2017 .SYNOPSIS... High pressure offshore will maintain a warm and humid airmass across the region, continuing our chances for scattered showers and thunderstorms through tonight. A weak cold front will approach the area from the northwest by Monday with a better chance for strong thunderstorms and heavy rainfall. Behind the front, a bit drier weather is expected through the middle of next week, along with a warming trend to above normal temperatures. && .NEAR TERM /THROUGH MONDAY/... As of 645 PM EDT Sunday... Latest radar trends indicate only isolated showers and showers and thunderstorms this evening, focused across the mountains. Regardless, instability continues to diminish as daytime heating is coming to an end, and believe we will see remaining showers and storms fade after sunset. Given low coverage of rainfall, have lowered rain chances with the early evening forecast update. Expect a relatively quiet night before things ramp up again as the front draws near tomorrow morning. Guidance varies a bit with timing but expect showers/storms to slowly spread across the region from the west and spill east of the Blue Ridge by the afternoon. Heavy rain is definitely a concern as precipitable water values approach 2.0 inches, but rather than issue a blanket flash flood watch for the entire region, believe it better to hold off and wait to see if later model runs zero in on a particular area of concern. While the best dynamics with the front will be pulling off to the northeast as the front moves through, there looks to be ample shear with the boundary coupled with pooling instability to maintain some vigorous updrafts and a severe threat. Expect storm clusters in the west to possibly form a broken line as the front moves east of the Ridge and reaches the best instability tomorrow afternoon, also bearing in mind that extent and magnitude of any convection upstream can influence how the situation unfolds tomorrow. Warm and muggy conditions will continue tonight and tomorrow before some cooler and slightly drier air moves in on Tuesday. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... As of 325 PM EDT Sunday... Monday night into Tuesday, the cold front will progress through the area and stall just to our southeast. Coincident to the passage of the front, anticipate heavy rain producing showers and storms across the eastern sections of the area during the evening. Lingering isolated to scattered showers are anticipated behind the front across central and western sections through the evening. By daybreak Tuesday, the last of the showers will still be across the far southeastern sections. As Tuesday progresses, look for a redevelopment of isolated to scattered showers across the far southern and southeastern parts of the area given the close proximity of the front, with late afternoon isolated thunderstorms near and south of the VA/NC state line. Western and northern parts of the region will experience mostly sunny skies. Tuesday night the stalled front is expected to buckle a bit eastward and northward. This progression will allow for isolated showers to work their way at little farther north into parts of Southside Virginia. Temperatures during this part of the forecast will average around or slightly cooler than normal for this time of year. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 325 PM EDT Sunday... What is interesting is there is less uncertainty in the details of the forecast Wednesday night through roughly Friday, as compared to better certainty next weekend. The fly in the ointment is the progression of what likely will be remnants of a tropical system. Model guidance offers a huge variety of solutions, some of which offer a relatively dry solution for our area, others offer solutions with a more wet scenario. For now, until there greater clarity, will opt to follow the output of the superblend of models which averages the solutions into a ramping up of precipitation chances Wednesday night into Friday. Even without the potential for tropical remnants, this trend makes sense as moisture pools and instability increases in advance of what will be an approaching cold front for the weekend. That is why the weekend has higher clarity than the days immediately prior. Models are in decent agreement of bringing a cold front through the area Saturday into Sunday. Temperatures during this portion of the forecast will average a few degrees above normal through Saturday, but then be a few degrees below normal on Sunday. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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As of 815 PM EDT Sunday... Radar indicates only isolated showers and thunderstorms passing across the mountains this evening, with instability gradually waning with the loss of daytime heating. Cannot rule out a stray shower/storm at LWB/BLF before 19/03Z, but unlikely enough that will not mention in the TAFs. With a cold front approaching, believe scattered clouds will linger across the central Appalachians through the night, which will limit the development of fog and widespread stratus compared to previous nights. Have made mention of sub-VFR ceilings toward dawn in some of the TAFs, but believe these low ceilings will only be spotty as well as in and out. Latest rapid update models indicate only widely scattered showers developing after sunrise through about 19/14Z, with rain chances significantly increasing thereafter from west to east as the cold front makes its approach. Storms tomorrow, particularly east of the Blue Ridge, have the potential to become severe with gusty winds, hail, and locally heavy downpours which will limit visibilities to less than one quarter mile at times. Extended Aviation Discussion... Appears will see more in the way of widespread VFR conditions develop by midweek given arrival of post frontal dry air with only brief periods of fog resulting in brief sub-VFR during the late night/early morning hours. However given uncertainty in just how far south the deeper moisture may or may not make it, the threat for isolated showers could still linger Tuesday through Thursday at this point.
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&& .HYDROLOGY... As of 420 AM EDT Sunday... While there have been localized issues of flooding and flash flooding over the past 3-4 days, mainly across Southside VA, the Roanoke area, NC Piedmont, as well as a few other spots, there are other areas that have had very little rainfall during the past two weeks. If any hydro watch were issued, a flash flood watch would probably be more appropriate given the localized nature of summertime convective thunderstorms and past localized rainfall. A flood watch would be more appropriate for widespread rainfall and runoff into area rivers when evapotransporation is low, which is certainly not the case as we near the summer solstice. Problems can be handled via localized flood advisories, warnings, or flash flood warnings in the worst case scenarios, just as have been done during the past week. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH NEAR TERM...MBS/NF SHORT TERM...DS LONG TERM...DS AVIATION...MBS/NF HYDROLOGY...RAB is the U.S. government's official web portal to all federal, state and local government web resources and services.