Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/27/20

Area Forecast Discussion

National Weather Service Blacksburg VA

 949 PM EDT Tue May 26 2020

.SYNOPSIS...
A wave of low pressure will move up from the south and bring widespread
rainfall to the Appalachians and central mid Atlantic region
Wednesday into Wednesday night. Unsettled conditions will then
prevail with showers and thunderstorms possible through the end
of the week. A cold front will moves through on Saturday,
followed by direr and cooler conditions as a large area of high
pressure builds down from the upper midwest on Sunday and
through the first part of next week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 949 PM EDT Tuesday...

Made some minor adjustments to pops and weather tonight into
Wednesday. Tonight will turn out similar to the past several
nights with clouds and some patchy drizzle and fog especially
along the Blue Ridge mountains. Low temperatures overnight will
range from the lower 50s in the mountains to the lower 60s in
the piedmont. Low pressure will lift northward from the
southeast Wednesday into Wednesday night. Southeast upslope flow
will amplify ahead of the approaching low and combine with an
upper closed low moving slowly through the Southern Plains to
result in deep moisture being push into the Appalachians. Strong
lift will become established Wednesday afternoon into Wednesday
night as the moist air runs over the top of the wedge. This
will result in periods of rain, heavy at times. This rainfall
Wednesday into Wednesday over a wet ground will create the
potential for flooding and flash flooding. With some uncertainty
with placement of heavier bands, will hold off on any flood
watch at this time. More later tonight...


As of 525 PM EDT Tuesday...

Made some minor adjustments in temperatures for this evening
into tonight utilizing the latest surface obs, their trends and
blended in NBM. Increased cloud cover a little this evening into
tonight. Anticipate that tonight will be similar to the past
several nights with clouds and some patchy drizzle and fog
especially along the Blue Ridge mountains. Low pressure will
lift northward from the southeast Wednesday with periods of
rain. More later tonight...


As of 140 PM EDT Tuesday...

High pressure remains wedged down east of the mountains this afternoon
while moisture is starting to stream up form the south. Expect some
showers may brush northwest North Carolina this afternoon into this
evening but generally dry wit just a sprinkle elsewhere and some more
persistent clouds/fog/patchy drizzle along the Blue Ridge. Anticipate
tonight will be much the same as the past several with a good amount of
cloud cover redeveloping along with patchy fog/drizzle.

The weather will then start to get more active on Wednesday as a weak
wave of low pressure moves up from the southeast. The low level wind
field out of the southeast will start to amplify ahead of the
approaching low and combine with an upper closed low moving slowly
through the southern plains to create an abundant supply of deep
moisture into the area. Strong isentropic lift will become established
as the moist air runs over the top of the wedge in place east of the
mountains, resulting in widespread rainfall pushing up form the south
tomorrow afternoon. Periods of heavy rain are expected later Wednesday
afternoon and there will also be orographic enhancement of the
precipitation along the Blue Ridge. Many locations are still dealing
soil that remains quite wet from heavy rains last week, so the expected
rainfall tomorrow will create renewed concerns for flooding and flash
flooding. However, there is still some uncertainty as to exactly where
the wave of low pressure will track and in turn where the heaviest rain
will fall. Believe it best to wait to see if later guidance can narrow
the area of concern before issuing a watch.

Not a lot of spread in the temperatures as lows tonight reach the upper
50s/around 60 west of the Blue Ridge with lower 60s to the east. Highs
tomorrow will generally be in the mid 60s/around 70 west, lower 70s
east.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 220 PM EDT Tuesday...

Looking to Wednesday night, a weak tropical disturbance will
continue to drift north across the Carolinas, bringing with it a
plume of deep tropical moisture. Weather forecast models
indicate precipitable water values climbing into the 1.75" to 2+"
range across the Piedmont as this disturbance approaches.  Combine
this moisture with a steady easterly upslope windflow across the mid-
Atlantic, and we are set for another round of heavy rain along the
Blue Ridge Wednesday night through dawn Thursday. While this system
does pass through our area quickly - within 12 hours - rainfall
amounts ranging from 1.5 to locally 3 inches along the Blue Ridge
appear reasonable, with widespread 1" to 1.5" amounts across much of
the Piedmont. Given this rain will fall across areas where soils
already remain moist from heavy rain during the previous week, the
potential for flash flooding will be elevated across the Piedmont
Wednesday night. We can also expect rises on the Yadkin, Roanoke
(Staunton) and (most notably) the Dan Rivers on Thursday.

After the tropical disturbance exits on Thursday morning, enough
residual moisture will remain across the mid-Atlantic to support
spotty showers and thunderstorm which develop with daytime heating
Thursday afternoon and gradually fizzle after sunset.

Expect showers and thunderstorms to increase in coverage on Friday
as deeper moisture pools ahead of an approaching cold front. Weather
forecast models indicate enough instability developing with
afternoon heating to support a few severe thunderstorms, capable of
producing locally damaging winds and some hail. Storms will weaken
after sunset with the loss of daytime heating.

Temperatures through the period will be near normal for late May,
with afternoon highs in the mid 70s to low 80s, while overnight lows
will generally be in the 60s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 220 PM EDT Tuesday...

A strong cold front will pass across the central Appalachians on
Saturday. Timing of the frontal passage remains uncertain at this
point as some weather forecast models indicate the front passing
through early in the day. Other models favor delaying the frontal
passage until evening, which would allow for the development of
additional showers and thunderstorms, mainly east of the Blue Ridge.

Regardless, frontal passage will bring with it significantly drier
air and cooler temperatures for Sunday and Monday.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
As of 730 PM EDT Tuesday...

VFR and MVFR conditions this evening will lower to MVFR/IFR
conditions tonight into Wednesday morning. As the boundary
layer cools expect a return to MVFR/IFR in low clouds with
patchy fog/drizzle overnight into Wednesday morning. Expect a
slight improvement into the lower end of MVFR later Wednesday
morning before rain starts spreading up from the south Wednesday
afternoon.

Winds will generally be light with some low end gusts, but little
impact to aircraft operations is expected through tonight.
However, east to northeast flow will be steadily increasing on
Wednesday ahead of a wave of low pressure pushing up from the
south.

High confidence in ceilings,visibilities and winds during the taf
period.

Extended Aviation Discussion...

Overall poor aviation conditions will continue through the week.
At night and early morning, look for widespread low clouds, fog, and
drizzle with IFR-LIFR visibilities likely prevailing much of the period
in the 08Z-15Z time frame, with MVFR-VFR outside of convection and rain
during the afternoons. Winds are expected to remain variable and on the
light side throughout the week.

A cold front comes through the area on Friday and Saturday bringing a
more widespread chance of precipitation and MVFR or lower flight
conditions. Drier weather is forecast for Sunday.

&&

.HYDROLOGY...
As of 730 PM EDT Tuesday...

Another round of heavy rainfall could impact the region beginning
Wednesday, lasting through into Thursday morning, leading to
heightened flash flooding and flooding risks.

A tropical disturbance is currently located along the east coast of
Florida this evening. This feature will eventually move off shore
into the Atlantic and continue northward, straddling the coastline.
Meanwhile, a closed low over the Arklatex region will begin to turn
our flow southeasterly. This closed low will "capture" the tropical
disturbance and bring it northward across the area.

The main concern with this will be the increased flash flooding
threat Wednesday night and into early Thursday morning. WPC has
placed much the the CWA in an excessive rainfall threat, with the
highest threat along the Blue Ridge and just to the east. Rightfully
so, as the antecedent soil conditions are completely saturated, and
rainfall amounts will not need to be that impressive to exceed the
already lowered flash flood guidance (FFG). Some areas of
particularly higher concern will be right along and just east of the
Blue Ridge where thunderstorms this past Sunday already dropped 3-4"
of rain in Franklin and Henry Counties, on top of a widespread 4-8"
from last week`s rain event. Rises on area rivers are also expected,
especially along the Yadkin, Roanoke, and Dan Rivers.

With continual deep moisture being advected in from the east, PWAT
values will be on the rise. Model guidance is advertising PWAT
values maxing out overnight Wed/Thu morning, with some indication
that they they could approach 2". Per the SPC sounding climatology,
this would be approaching, if not exceeding observed PWAT values for
this time of year. This indicates plenty of ambient moisture around
and rainfall will be very efficient if these PWAT values are
realized.

&&

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

&&

$$
SYNOPSIS...MBS
NEAR TERM...KK/MBS
SHORT TERM...NF
LONG TERM...NF
AVIATION...KK/MBS
HYDROLOGY...BMG