FXUS61 KRNK 270825

Area Forecast Discussion
National Weather Service Blacksburg VA
425 AM EDT Sun May 27 2018

High pressure centered offshore will maintain a moist southerly
flow of air into the region for the next several days. Subtropical
Storm Alberto moving into the Gulf of Mexico this weekend will
move ashore and into the lower Mississippi Valley early in the
week. Tropical moisture will stream north into the region
making for very rain efficient showers and thunderstorms.


As of 400 AM EDT Sunday...

Relatively quiet but moist Sunday morning. Considerable
cloudiness most areas this morning along with patchy fog,
temperatures AOA 60.

For today, moisture laden airmass will quickly yield to
thermally driven showers with convergence along the mountains
providing the focus for deep convection. Squeeze play will also
be ongoing between upper trough over the northern Mid-Atlantic
and tropical moisture streaming north from the Gulf of Mexico...
convergence axis along or north of our CWA border. Similar to
yesterday showers/storms will be very rain efficient with PWATs
2 standard deviations above normal. For our CWA, HiRes models
focus the greatest shower concentration along the VA/WV border
from Tazewell northeast into Greenbrier and Bath. Tazewell got
hit pretty hard yesterday with some gages reporting 2-3 inch

Attm will hold off on a Flash Flood Watch. Prefer to see where
convergence boundaries will line-up and target those as opposed
to blanketing a larger piece of real estate. The Weather
Prediction Center has painted a pretty wide swath with respect
to rainfall exceeding flash flood guidance today...the greatest
threat right along the spine of the Appalachian crest where the
low level convergent flow will be the greatest.

Temperatures today will be very similar to Saturday, the clouds
and showers keeping the numbers confined to the 70s to lower 80s
for highs this afternoon, and low temperatures in the 60s.


As of 330 AM EDT Sunday...

Our weather through the first part of next week will be dominated by
the nuances associated with Alberto as the tropical circulation moves
through the southeast then accelerates as it heads toward the Great
Lakes. Expect a wet few days with an increasing threat for flooding.

Alberto will start to push a band of tropical rainfall up from the
south early Monday but this initial surge will become sheared and have
trouble making significant northward progress past the NC/VA border.
However, as Al starts moving north with more enthusiasm on Tuesday,
better transport of deep tropical moisture will become established
across the Appalachians and central mid Atlantic region with NAEFS
precipitable water anomalies of 2 to 3 standard deviations. Diurnally
biased pattern to convection should yield widespread coverage of
showers/thunderstorms with heavy rainfall and an as yet ill defined
area wide hydro threat as ensemble precipitation plumes still exhibit a
great deal of spread through the period. Wednesday may offer the most
coverage of heavy rainfall and greatest hydro threat this period on the
heels of several days of heavy rainfall as Al moves into the Great
Lakes with a trailing convergence zone through our area. Additionally,
instability and the synoptic wind regime are on the light side but
shallow shear profiles with a small looping hodograph in the boundary
layer become more pronounced and indicate a potential severe threat
lurking Tuesday and Wednesday. Expectation is that threats will declare
themselves as the situation evolves and flood watches will be issued
once specific areas to be impacted can be identified.


As of 300 PM EDT Saturday

By mid to late week, flooding potential will depend on how much
rainfall is accumulated from several days of locally heavy tropical

Alberto is expected to be in the Ohio Valley Thursday morning. Thursday
night into Friday, the low will open up and weaken as it moves
northeast into the weekend. There is a continued threat for showers and
thunderstorms into the end of the week. Urban and small stream flooding
risk will be highest early with river flooding possibly by the end of
the week depending on actual rainfall totals. High temperatures will
generally be around normal, climbing to above normal at the end of the
week, with overnight lows remaining fairly mild mainly around 60
degrees to about 70 degrees.


As of 200 AM EDT Sunday...

Very moist boundary layer will promote areas of fog and stratus
through daybreak with potential for IFR/LIFR until the sun comes
up and promotes mixing. Confidence low with respect to how
widespread the cigs/lower visibilities will be. Confidence
medium to high that once mixing begins that vsbys will improve
back to VFR until showers/storms develop for the afternoon.

Focus for showers/storms today will reside along weak
trough/boundary which extends from central OH valley into
northern VA. Best coverage for showers/storms will be along this
boundary. Convergence along the spine of the Appalachians will
favor scattered to numerous clustering of showers and storms
from NE-SW along the Appalachian divide. These showers will be
very rain efficient due to the high moisture content of the air.
Areas of IFR/MVFR cigs will prevail across the mountains today
with partial ridge obscurations from stratofractus associated
with the rain showers.

Winds will generally be light and variable or calm through the
24 hour forecast period.

.Extended Aviation Discussion...

Wet pattern anticipated through the upcoming week with periods
of at least diurnally driven sub-VFR conditions associated with
deep convection. Moist low level southerly winds will also favor
lower layers of cloudiness at night, especially along the spine
of the Appalachians with potential for both MVFR Cigs and early
morning MVFR visibilities from mist/haze. The tropical system
over the Gulf of Mexico may begin to impact the region mid-week.


NOAA Weather Radio, All Hazards, WZ2500 at Wytheville, VA,
broadcasting on a frequency of 162.45 mHz, will be off the air
until further notice. Technicians are aware of the problem, and
corrective action will be attempted on Sunday.

Until repairs are complete, you may be able to receive
broadcasts from neighboring transmitters if you are located
close enough to them. These include WXL60 in Roanoke, VA,
broadcasting at 162.475 mHz, WZ2543 in Richlands, VA,
broadcasting at 162.425 mHz, or WNG588 in Mount Jefferson, NC,
broadcasting at 162.500 mHz.




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