Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 232336
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
736 PM EDT Tue May 23 2017

.SYNOPSIS...
A weak stalled front over northern North Carolina will remain in
place as ripples of low pressure slide northeast along the
boundary resulting in added rainfall into tonight. Yet another
area of low pressure will arrive Wednesday with added showers
likely thru Thursday. Weak high pressure will follow this
system for Friday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 730 PM EDT Tuesday...

Forecast still looks rainy though some breaks developing in the
piedmont though still drizzly/light rain. Shower more focused
over the mountains this evening, with high-res models shifting
this area northeast through midnight. Should see a drying trend
from southwest to northeast by late evening/midnight though not
completely dry, given depth of moisture. Will also have to watch
upstream convection over Al/northern GA as it moves toward the
NC mountains/foothills/piedmont after midnight. The high-res
models weaken it, but not so sure this will occur.

No changes to the flood watch, with minor flooding still
possible though focus looks to shift more toward the mountains.

Previous discussion from this afternoon...

Radar imagery shows that the shield of precipitation associated
with wave of low pressure sliding northward along the front
lingering in the east has spread across the piedmont, with a
secondary area of precipitation to the west advancing up the
mountains. Guidance seems to be handling the wave in the
piedmont fairly well, but not so much for the precipitation in
the west. Given very wet antecedent conditions in the mountains,
have expanded the flood watch to the western border. As dynamic
forcing pulls off to the northeast overnight we will see a
decrease in precipitation, though fully expect some degree of
shower activity to be around through the night.

The next wave will move out of the southern Appalachians as a
large closed low digs southward into the lower Mississippi
valley, with a trailing cold front not pushing through until
Wednesday night. These systems will be running into a solid
wedge east of the Appalachians, setting up another period of
rain with good isentropic lift over the wedge. However, there
are good dynamics in place and the wedge will be eroding,
allowing instability to creep in from the west and south in s a
highly sheared environment, opening a window for embedded
thunderstorms late tomorrow afternoon with possibly linear
organization to embedded convection heading into Wednesday
night. The current day 2 SPC outlook for a marginal risk of
severe across the south and west portions of our area looks
right on target and the situation will be watched closely.
Additionally, the expected precipitation tomorrow may warrant
another flood watch if later guidance continues to indicate
sufficient rainfall.

Expect temperatures to fall slowly tonight and remain well
below normal through Wednesday.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 330 PM EDT Tuesday...

A slow moving area of upper level low pressure will head eastward
through the Ohio Valley Wednesday night into Thursday.  A
substantial stream of moisture will be advecting into at least the
eastern portion of the area early Wednesday evening. As the evening
progresses, this moisture axis will shift eastward in concert with
the approaching upper level trough axis. Anticipate very good
coverage of moderate rain showers and scattered storms to give way
to decreasing coverage by late evening, and even less coverage after
midnight. The activity across the region after midnight will be
associated with cold pool lapse rate with the passage of the trough
axis.

On Thursday, this trough axis will still be passing overhead, have
daytime heating to help fuel additional showers and storms, all
while its associated surface front heads east of the region. Expect
good coverage of showers and storms during the day with west to
northwest wind becoming gusty by the afternoon.

Thursday night, northwest flow continues to increase on the backside
of the system. Precipitation will quickly decrease in coverage east
of the Blue Ridge thanks to increased subsidence. Upslope rain
scattered rain showers are forecast across parts of southeast West
Virginia during the overnight. Some of the gusts at the higher
elevations will be on the order of 30 to 40 mph.

On Friday, drier air will continue to work its way into the area,
but lingering upslope showers in the west will continue through at
least mid-day. Although, coverage will be on the decline.

By Friday night, the winds will have weakened as the pressure
gradient continues to weaken.  Just as conditions trend drier, we
will start to watch our next system developing in the mid-
Mississippi Valley by late Friday night, with associated leading
moisture reaching western parts of the area by sunrise Saturday
morning.

Temperatures during this portion of the forecast will start slightly
below normal but trend to readings near normal by Friday.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 330 AM EDT Tuesday...

Saturday into Sunday, our weather will turn wet again as low
pressure tracks through the Ohio Valley. In advance of this system,
a warm front will lift through the region on Saturday, followed by
an associated Sunday afternoon and evening.

Guidance differs on how promptly this front will exit the region,
along with any associated lingering showers. What is more uniform in
solution is the position of another closed upper low. Anticipate a
slow moving upper low just north of the Great Lakes region to linger
through at least Tuesday. Energy pinwheeling around this feature
will interact with the remnants of the cold front from the weekend.
Additionally, a cold front in association with this upper low will
be heading toward our area late in the day Tuesday.

The result will be a weekend that will have the potential to be on
the wet side, with Monday and Tuesday having scattered activity.

Temperatures during this portion of the forecast will average a
little over five degrees above normal.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 730 PM EDT Tuesday...

Expect poor flying conditions all TAF sites this period.

Confidence is high that most if not all sites will stay IFR or
worse through the period. Exceptions at times may be BLF/DAN Wed
afternoon as wedge/stable layer shifts east with thunderstorms
possible. At the moment will keep sites on the IFR side with
some MVFR this evening at times, but not a big window.

Looking at light-moderate rain especially mountains this
evening, then somewhat of a break late tonight mainly west, with
showers moving back in after 12z Wednesday.

Extended Aviation Discussion...

Rainfall should become a bit more showery by Thursday with
sub-VFR mainly associated with the showers while periods of
afternoon VFR possible outside of the convection. Friday will
be drier with a better chance of VFR ceilings and visibilities.
Another front reaches the area for Saturday with more showers
and thunderstorms including sub- VFR conditions into Sunday.

&&

.HYDROLOGY...
As of 330 PM EDT Tuesday...

Abundant rainfall has left the ground quite saturated.
Additional rainfall totals through early tonight will be around
one inch across Southside VA and the piedmont of NC, with
amounts of one half to locally one inch in the mountains. The
flood watch has been expanded to cover the most vulnerable
locations which may experience flooding even without
exceptionally high rain rates. The flood watch will expire at
2AM and the situation will be reevaluated to see if any
additional watches are needed for expected precipitation on
Wednesday.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch until 2 AM EDT Wednesday for VAZ007-009-010-012-
     015-016-032-043-044-058.
NC...Flood Watch until 2 AM EDT Wednesday for NCZ001>006-018>020.
WV...None.

&&

$$
SYNOPSIS...MBS
NEAR TERM...MBS/WP
SHORT TERM...DS
LONG TERM...DS
AVIATION...JH/MBS/WP
HYDROLOGY...JH/MBS


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