Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 251652 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1252 PM EDT Fri May 25 2018 .SYNOPSIS...
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High pressure offshore will maintain a moist southerly flow of air across the region into the weekend. Subtropical Storm Alberto moving into the Gulf of Mexico this weekend will move ashore and wobble over the lower Mississippi Valley early next week. Tropical moisture will stream northward into the region with a return of showers and storms especially during the afternoons and evenings over the next few days.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 955 AM EDT Friday... Morning soundings show low level moisture returning beneath the subsidence inversion with lingering dry air aloft above 7h where ridging prevails. Latest guidance slowly breaks down the lingering subsidence/dry air as higher PWATs return on deepening southwest flow aloft around departing high pressure offshore, and north of a weak wave to the south. Short term models also indicate increasing instability espcly south and west this afternoon after ongoing strato-cu along the Blue Ridge erodes. This could spark showers/storms as moisture depth increases but still overall isolated to widely scattered given lack of overall forcing per the latest HREF model ensemble. Therefore keeping mainly chance pops west and little northeast where moisture will be slower to return. Weak steering could also lead to slow moving cells but not thinking widespread enough for water issues this afternoon espcly after drying the last couple of days. Otherwise lowered highs slightly over the south/west where have early clouds while staying well into the 80s east-northeast where insolation will be greatest. Previous discussion of 300 AM EDT Friday... Very light returns noted on radar this morning along the Blue Ridge, but overall just lower stratocu. Fog somewhat limited at the moment and think the stratocu will maintain patchy nature to fog through the morning rush, with visibilities mainly above a mile. For today, not too much change from previous forecast as southeast flow continues to advect higher pwats our way, reaching 1.5" in the afternoon. Overall models favor more along and west of the Blue Ridge threat for better coverage of showers/storms today, but not too impressed with overall threat, so keeping it mainly in the scattered/chance range, with maybe 50-60 pops across the NC High county. In the east, with high pressure and weak subsidence keeping things fairly dry, with isolated to no coverage east of Roanoke to Martinsville. Having more moisture in the air will allow for more buildup of cumulus. Model sky cover forecast are showing more sunshine but think skies will become more broken in coverage, but still enough of sun today to get temps into the upper 70s to lower 80s most locations, with cooler/cloudier expected in the NC mountains north to the Grayson Highlands with upper 60s to lower 70s. Tonight, not seeing a dry forecast as models confident in showing more moisture advecting along backside of the high offshore, while tropical low moves northward toward the Gulf of Mexico near Cuba. The flow in the low levels becomes more southerly and should see scattered showers/storms stick around mainly in the mountains through the night, though thunder threat diminishes by midnight. Not enough coverage yet to have any flood watches, but not out of the question to have some localized issues in the NC mountains late today into this evening. Low temperatures will be stickier/muggy as dewpoints climb into the 60s, which will lead to lows in the 60s. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... As of 300 AM EDT Friday... A shallow northern stream trof will swing through New England this weekend as a tropical low slowly moves up the eastern Gulf and into the southeastern US. This will establish a flow of deep moisture into the Appalachians and central mid Atlantic region for the next several days. A series of weak short waves will move up from the south and bring good coverage of diurnally biased showers and thunderstorms for the weekend. While instability will be substantial, hodographs/deep shear are not impressive but precipitable water values are expected to be in the top percentiles. These factors will generate stout updrafts that will support heavy rainfall and set up the possibility of flooding with training convection, along with some degree of severe threat with the most vigorous storms. The threat appears to be across the entire area on Saturday but Sunday may be more confined to locations west of the Blue Ridge. By Sunday night the tropical low will start to retrograde along the Gulf coast as the upper trof over the northeast pulls out. This will stretch dynamic forcing out and may help suppress heavy precipitation to the lower half of the area, perhaps from route 460 southward, but confidence in specifics is not high in this pattern. We have had a few days with little rainfall to allow the ground to dry out but it will not take much to recharge. While there is considerable spread in ensemble guidance, there is enough clustering of hefty multiday QPF totals to warrant concern. Will start to highlight the region for potential hydro issues in the HWO and wait for a more specific region to declare itself in time before considering any watches. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 115 PM EDT Thursday Tuesday will have upslope southeast wind and precipitable water values around 1.5 inches so all that moisture will mean the potential for heavy rain. Potential tropical system will remain near the Gulf Coast Monday through Wednesday between upper ridge over the southwest then central United States and the off the southeast coast. Thursday the low opens and fills and moves northeast. Models have come into better agreement taking this feature into the Tennessee Valley by Thursday morning. ECMWF has the deeper moisture over Virginia and North Carolina again Wednesday and Thursday. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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As of 1250 PM EDT Friday... MVFR conditions across southern/western sections will continue to slowly improve to VFR as cigs scatter out and lift this afternoon. However sub-VFR cigs likely to remain along the Blue Ridge southwest of KROA where a few showers appear likely along the KHLX-KMWK-KUKF corridor. A few storms will also be close enough to KBLF, mainly along and west of the Interstate 77 corridor this afternoon to warrant a VCTS or TEMPO group, while keeping out mention elsewhere except for perhaps a VCSH at KBCB for now. Still looks like showers possible mainly southwest of a BLF- BCB line this evening, with broken deck of mainly high end MVFR to low end VFR cigs. Potential for fog is there, but only putting in where its typical and where it may rain. Cloud cover will limit the fog coverage outside of where rainfall occurred. Any fog or low cigs will slowly improve on Saturday but likely to see at least periods of MVFR cigs persist with deeper moisture in place. This should also lead to more in the way of showers/storms espcly over the mountains by midday, and across much of the region during the afternoon. This supports a VCSH mention at most locations outside of KLYH. .Extended Aviation Discussion... Wet pattern with periods of at least diurnally driven sub-VFR conditions in convection will take place into the middle of next week. Fog at night is possible if we clear enough due to wet ground conditions and rain. Worse conditions heading south to the Gulf Coast states, as a tropical system moves into the that area Monday or Tuesday.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/WP NEAR TERM...JH/WP SHORT TERM...MBS LONG TERM...AMS AVIATION...JH/JR/RCS/WP

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