Area Forecast Discussion
Issued by NWS Blacksburg, VA

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727
FXUS61 KRNK 260604
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
204 AM EDT Sat May 26 2018

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TODAY/...
As of 800 PM EDT Friday...

A quick update to reduce pops, cloud cover, and bring
temperatures into line with current readings. No major changes
though. Convective activity, just showers so far, with outer
fringes of tropical moisture very widely scattered so far and
confined to areas west of the Blue Ridge. HIRES HRRR and NAMNest
suggest this activity will dissipate quickly after sunset, but
showers may drift back into the area later in the night. Cloud
cover is also quite scattered at this point, so reduced the
percentages about 20% across the board at this time.

As of 230 PM EDT Friday...

Seeing small clusters of convection develop within southeast flow along
the southern Blue Ridge and foothills as well as across the far western
ridges where an axis of higher instability off to the west prevails.
Latest short term guidance continues to focus most convergence across
the far western/southwest counties through sunset with added
clusters/bands of at least shallow convection espcly along the I-77
corridor. Otherwise expect only isolated coverage at best elsewhere
over the southern/western tier and just some leftover cumulus across
the northeast where residual ridging lingers.

Appears will see most coverage fade with loss of heating this evening
given lack of support with the boundary well to the south, so trimmed
back pops to isolated or low chance mainly west which may be generous
into the overnight. However combination of increasing southwest flow
and deeper moisture may lead to added showers espcly south before
daybreak where forecast soundings show a rather saturated column late.
Should also see some fog around in the valleys and where earlier rain
occurred but likely limited via cloud cover so keeping coverage patchy
at this point. Lows again mainly in the 60s with some cooler 50s
western valleys.

Upper heights continue to slowly decrease on Saturday as the surface
high slides farther offshore. This in conjunction with increasing
southwest flow and a surge in moisture, per PWATs rising to above 1.5
inches, should allow for more widespread convective coverage by
afternoon. Appears initial coverage along the southern Blue Ridge and
points west by midday per forecast 85h theta-e axis/southwest flow,
with showers/storms spilling east into better forecast instability east
of the ridges in the afternoon as weak mid level wave also tracks east.
This along with slow movement given forecast steering of around 10
knots or less likely to result in a heavy rain concern with even some
stronger pulse storms possible within bands. Therefore expecting a
quick diurnal increase in convection from chance pops west early to
likelys most locations in the afternoon with even categorical in spots
along the eastern slopes of the Blue Ridge. Otherwise still warm and
quite muggy with highs low/mid 80s east and mostly 70s mountains.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
As of 300 PM EDT Friday...

Northern stream trof will move east through New England this holiday
weekend as Subtropical Storm Alberto slowly moves up the eastern
Gulf and into the Southeast.  Please refer to the latest advisory or
statements from the NHC on Alberto.

Unsettled weather is expected during the period with a flow of deep
moisture into the Appalachians. A series of weak shortwaves will
rotate up from the south and spark good coverage of diurnally
showers and thunderstorms for the weekend. It will not be raining
the whole time, and most should be able to work in a holiday picnic.
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.

SPC keep our forecast area in general thunderstorms on the
convective outlook. However, the instability looks healthy but deep
shear is lacking. The combination of recent rains and high PWATs
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.

Saturday evening convection will taper off to isolated to scattered
showers Saturday night. Low temperatures Saturday night will range
from the upper 50s in the mountains to the mid 60s in the piedmont.

The best chances of thunderstorms on Sunday will be along and west
of the Blue Ridge mountains. High temperatures will vary from the
lower 70s in the mountains to the mid 80s in the piedmont.

On Sunday night, Alberto lifts northward along the Gulf coast as the
upper trof over the northeast pulls out. This may stretch dynamic
forcing out and may keep the highest precipitation in the south.
Low temperatures Sunday night will generally be from the lower 60s
in the west to the upper 60s in the east. Unfortunately, there a
good to likely chance of showers and thunderstorms for Monday. Highs
will vary from the lower 70s in the mountains to around 80 degrees
in the piedmont. Kept scattered showers and isolated thunderstorms
in for Monday night with low temperatures from the lower 60s to the
upper 60s.

Will continue 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 FRIDAY/...
As of 300 PM EDT Friday

There is the potential for periods of heavy rain during the medium
range with Alberto and its track. Please refer to the latest
advisory from the NHC on Alberto. By mid to late week, remnants of
the tropical system could bring tropical moisture and heavy rains to
our region. Flooding potential will depend on the track of the
system and how much rainfall is accumulated from the showers and
thunderstorms earlier in the week.

The latest NHC track places Alberto in southern Mississippi by
Tuesday morning, then its lifts northward into the Tennessee valley
on Wednesday. The timing of the ECMWF was quicker and further north
and west (Ohio Valley) compared to the GFS which was slower and more
compacted (along the Appalachians. By Thursday and Friday, the low
will open up and weaken as it moves northeast. 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 in the week
with river flooding possibly by the end of the week depending on
actual rainfall totals.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
As of 200 AM EDT Saturday...

Increasing moisture from the south will bring increasing
cloudiness to the Mid-Atlantic Region with finger of MVFR Cigs
creeping north along spine of Appalachians. This moisture will
combine with the heating of the day Saturday to produce numerous
showers and embedded thunderstorms...esp during the afternoon.
Other than convergence from the mountains, showers/storms will
lack any sort of organization and are expected to dissipate
after sunset. Mean steering wnd aloft is fm 240 deg at 12 kts.
Low level wnds will be out of the SSE at less than 10 kt.

.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.


&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...JH
NEAR TERM...JH/RAB
SHORT TERM...KK
LONG TERM...KK
AVIATION...PM



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