Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 10/11/20

Area Forecast Discussion

National Weather Service Blacksburg VA

 912 PM EDT Sat Oct 10 2020

.SYNOPSIS...
The remnants of Delta will track slowly through the Tennessee
Valley tonight and Sunday bringing widespread rain to the Mid
Atlantic region through Sunday night. A cold front crosses
through the East on Tuesday with high pressure and dry weather
for Wednesday and Thursday. Another front arrives in the area at
the end of the week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 910 PM EDT Wednesday...

The remnant circulation of Delta is still a good ways off to the
southwest on the AL/MS border. However, southerly flow ahead of
the system is pushing deep moisture over an in-situ wedge and
generating good coverage of showers/rainfall. Thus far guidance
seems to have a decent handle on the situation and continues to
show some hefty rainfall totals piling up through Sunday night,
especially from the NC mountains up through the southern Blue
Ridge. Dry antecedent conditions will help manage expected
runoff to a degree but anticipate there is still a good
possibility of flooding where rainfall is maximized. The current
flood watch delineates the area well and see no compelling
reason for adjustments.

Previous discussion...

By late Sunday at upper levels the tropical depression has
weakened into an open wave with rising 500 mb heights and the
trough axis over the Ohio Valley. Best upper diffluence is
tonight. Will have enhanced low-level convergence tonight and
Sunday as well as southeast upslope winds Sunday so enough lift
to continue rain.

In general, surface pressure will be falling as the remnant low
moves into the Tennessee Valley and then the Mid Atlantic but still
seeing some signs in the models of in-situ wedging on Sunday.
Surface winds may be lighter and variable direction but just above
southeast low-level jet will move from southwest to northeast along
the Blue Ridge. Similar to today, little rise or fall in
temperatures tonight and Sunday.

Dry slot and any clearing and potential heating and instability look
to stay in central North Carolina so have left thunder out of the
Sunday forecast.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 120 PM EDT Saturday...

The moderate to heavy rain axis will begin to lift north of the area
by early Monday morning as the upper level trough pivots over the
region. Most models have up to three-quarters of an inch of rain
coming across the mountains/foothills and around a third-of an inch
over the piedmont Sunday evening. After midnight, rainfall intensity
and amounts begin to taper from south to north. So Sunday night`s
rainfall amounts will generally range around an inch for the area
and possible up to an inch and a half along the Blue Ridge.

On Monday, the trough moves east of the area with ridging increasing
aloft. PWATS lower from 1.50-1.70 inches in the morning to around
1.00-1.25 inches in the afternoon. With some lingering tropical
moisture in the area, a few instability showers are possible in the
afternoon and early evening. Rainfall totals Monday will be less
than a tenth of an inch, most of that falling in the morning.

Winds become westerly behind the departing remnants of Delta and
ahead of an approaching cold front Monday afternoon and Monday
night. A few mountain showers are expected with the frontal passage
with any measurable rainfall concentrating along western slopes.
With a westerly wind establish ahead of the front, we are not
expected any showers to advance east of the Blue Ridge. Behind the
front, dry high pressure will build over the area Tuesday and
Tuesday night. PWATS will then dip below half of an inch. Weak
pressure rises may bring breezy/gusty conditions into the area, but
will not reach advisory criteria. However, trash cans and Halloween
lawn decorations may be at risk.

Temperature will run warmer than normal Monday and Tuesday with
highs ranging from the upper 60s to low 70s west of the Blue Ridge
to mid and upper 70s east.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 115 PM EDT Saturday...

Zonal flow pattern as high pressure builds overhead Wednesday and
Thursday keeping us dry and fairly mild. High temperatures on both
days should range from the upper 60s and low 70s out west to mid 70s
out east. The high slides east late Thursday afternoon and evening
as a surface low over the Upper Great Lakes pushes east dragging a
cold front through. The front, albeit weak, looks to arrive
late Thursday into the day Friday.

Most of the model consensus shows limited moisture with the
exception of the 00z European and earlier run of the GEM. These
two models remain aggressive with precipitation as the front
passes along with an area of low pressure that looks to ride
close to the coast as the boundary pushes east. Opted to stick
with the 12z GFS and Canadian solution. Both show rain showers
over the mountains Friday morning quickly spreading east by
Friday afternoon. Behind the front brings slightly below
average temperatures and dry conditions with high pressure
settling in for the weekend.

&&

.AVIATION /01Z SUNDAY THROUGH THURSDAY/...
As of 738 PM EDT Saturday...

Skies have been chaotic this evening with cigs alternating
between IFR and VFR at numerous locations as periods of rain
move across the region. Believe the near surface boundary layer
is saturated but a pocket of drier air aloft continues to mix
down from time to time to disrupt the formation of a continuous
low cig. Expect this will be the case through the first part of
the valid period until the entire column gradually saturates and
CIGS settle to IFR later tonight and heavier rainfall sets in.
Believe the best course of action will be to favor the lower
flight categories and amend as needed for trends that are
supported by persistent changes upstream. IFR conditions are
expected to dominate at all sites through the latter half of the
valid period.

Winds are generally expected to be light with little impact to
aircraft operations.

.Extended Aviation Discussion...

Conditions will improve Monday morning, with only the remnant
moisture and the better lift off to the northeast of the area
and further weakening.

A cold front crosses the area on Tuesday, with a chance of MVFR
clouds and showers on the western slopes of the central
Appalachians. Breezy winds and drier air arrive behind the
front. Wednesday and Thursday are expected to be dry and VFR.

&&

.HYDROLOGY...
As of 315 PM EDT Saturday...

Flood Watch has been expanded up the Blue Ridge to include
Roanoke, Floyd and Franklin Counties.

Expecting periods of rainfall through Sunday night with the
heaviest amounts along the spine of the southern Blue Ridge, the
High Country and foothills of northwest NC. These areas will
likely see between 2-4" of rain with locally higher amounts.
Given dry antecedent conditions, flash flood guidance (FFG)
values were quite high making flash flooding unlikely, as there
is little to no support for heavy rainfall rates, which will
generally stay under 0.5" per hour.

The threat for river flooding is also low because of the
recent dry conditions. Minor rises are expected on the James, Dan,
Roanoke and New Rivers, but no flooding is expected at this
time. The current forecast had the Dan River at South Boston
reaching Action Stage Monday night.

There may be areal flooding in the mountains and foothills. Small
creeks, streams, and locations with poor drainage may be subject
to flooding. Leaf clogged drains in urban areas may produce
flooding or ponding as rain amounts accumulate. The risk for
flooding of small creeks and streams is also enhanced in
locations with steeper terrain.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Flood Watch from 4 AM EDT Sunday through Monday morning for
     VAZ015>017-022-032-033-043.
NC...Flood Watch from 4 AM EDT Sunday through Monday morning for
     NCZ001>005-018>020.
WV...None.

&&

$$
SYNOPSIS...AMS
NEAR TERM...MBS/AMS
SHORT TERM...RCS
LONG TERM...ET
AVIATION...MBS/AMS
HYDROLOGY...AMS/VFJ