Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 250729

Area Forecast Discussion
National Weather Service Blacksburg VA
329 AM EDT Fri May 25 2018

High pressure moves offshore this afternoon. A tropical low
moving into the Gulf of Mexico Saturday will move ashore and
wobble over the lower Mississippi by Memorial Day. Tropical
moisture will stream northward into the region with a return of
shower and storms especially during the afternoons and evenings.


s 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

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.


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

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


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


As of 125 AM EDT Friday...

Not too much change in the forecast as will see some scattered
to broken mainly VFR cigs along/south of a BLF-ROA-LYH line this
morning, but cannot rule out some lower cigs approaching BCB
toward dawn. Fog still possible as dewpoint depressions are zero
to 2 degrees and winds are light, plus wet ground, but
confidence is low to medium on how low vsbys could go. Leaning
toward fog at all sites, except ROA/BLF for now.

Any fog and lower cigs will scatter out to a scatter to broken
deck of VFR cigs after 14z. Isolated to scattered showers/few
tsra in the afternoon, but coverage so low that no mention in
tafs at this point, but models indicate best threat would be
LWB-BLF-TRI corridor.

.Extended Aviation Discussion...

VFR Friday night.

Fairy active over the weekend into next week with tropical
moisture streaming back in. Not a complete washout, but periods
of sub-VFR likely with heavier showers/storms at times, with
worse conditions heading south to the Gulf Coast states.




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