Area Forecast Discussion
Issued by NWS Blacksburg, VA

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895
FXUS61 KRNK 190807
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
307 AM EST Thu Jan 19 2017

.SYNOPSIS...
High pressure overhead this morning shifts east to the coast
tonight as a warm front lifts north from the Gulf Coast states
into the southern Appalachians. The warm will swing north across
Virginia and into the mid-Atlantic Friday, before stalling.
Another storm system moving across the southern U.S. will impact
our region Sunday into Monday.


.NEAR TERM /THROUGH TONIGHT/...
As oF 230 AM EST Thursday...

Amplified 5h ridge over us today will give way to upper low/trough
moving across the midwest tonight. Will see a period of warm
advection high clouds today with increasing mid clouds starting to
roll into the southwest by dusk.

We will be staying warmer than normal again today with highs mainly
in the mid to upper 50s. Sunshine will be in and out, and expect to
see more sunshine east of the mountains.

Isentropic lift increases after sunset across the mountains of NC
and shift to the rest of the forecast area overnight. Models
advertise more rain in the mountains with lower threat in the
piedmont. Clouds will overspread the area. Will see the warm front
stay southwest of us into early Friday morning. Rainfall amounts
overall will be under a quarter inch with locally higher in the
mountains of NC to Southeast WV.

Lower dewpoints in the evening combined with increasing moisture
allows for temperature drop once the rain starts to fall, but since
more clouds and some steady rains, lows should stay mild for this
time of year with upper 30s in the Alleghanys/Greenbrier Valley to
upper 40s Mountain Empire.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
As of 230 AM EST Thursday...

During the day Friday a broad area of isentropic lift progresses
northeast through the region on the eastern side of a Upper
Mississippi Valley low, and on the west side of an upper level
shortwave ridge that will be positioned over the mid-Atlantic
region. By sunrise Friday, the bulk of the precipitation will be
oriented northwest to southeast across the central portions of the
region, heading northeast. Anticipate most of the precipitation to
have moved northeast of the region by the early to mid afternoon.

Friday night into early Saturday, another 500mb shortwave ridge
briefly takes up residency across the area, all while the 850mb flow
remains southwest, tapping Gulf of Mexico moisture. We expect a
break in the precipitation Friday evening into part of the overnight
hours Friday nights. Models differ on just how quickly the next wave
of precipitation enters the southern half of the region. A consensus
forecast allow for a slight chance by day break Saturday across our
North Carolina counties, and perhaps one tier north of Virginia
counties.

As Saturday progresses, a shortwave trough within the prevailing
southwest flow is progged to move toward the region and cross late
Saturday night and Sunday. Surface based lifted index values vary
from model to model during the Saturday through Sunday period. Some
have readings right around zero through the region, others are
slightly negative. Given this will favor showers as compared to
stratiform rain for Saturday. Will introduce isolated thunderstorms
across the far southern and southeastern sections of the area Sunday
afternoon. This corresponds the good agreement of guidance for
slightly negative LI values in this area along with some small
amount of surface based CAPE. There is also good spacial agreement
with neighboring offices to the south for its inclusion into the
forecast.

This wave moves north of the area by early Sunday evening. While
there may be a small break in the activity, it will be short lived.
Precipitation on the eastern and northern flank of the parent closed
upper low is expected to traverse the region Sunday night.

Temperatures will continue to be very mild during this portion of
the forecast, averaging some fifteen to twenty degrees above normal.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 315 PM EST Wednesday...

Guidance remains generally consistent with the big picture details
into the first part of next week with some variation in the
finer details. A large vertically stacked closed low will move
across the deep south and bring a strong and very moist flow of
air to the region. Several spokes of energy rotating around the
low will bring several surges of precipitation to the region
Monday before the system starts to pull away from the area by
Monday night. So while the main baroclinic zone is now expected
to be much closer to the coast, the overall scenario still
favors widespread precipitation with significant orographic
enhancement along the Blue Ridge. Will continue to keep a close
eye on how this situation evolves as the indicated QPF amounts
generally in the 1 to 3 inch range by Monday night may result in
some flooding. Instability to drive thunder will likely reside
closer to the baroclinic zone, though with enough forcing under
the cold core upper low some thunder is possible but confidence
not high enough at this point to include in the forecast. Will
keep ptype as all liquid though dynamic cooling under the deep
upper low may generate thickness values favorable for some
wintry mix, but confidence in this is low. Some wrap around
precipitation will linger west of the Blue Ridge through
Tuesday before we can get a brief break ahead of the next system
approaching later Wednesday night.

Temperatures will trend down through Tuesday as the cold core low moves
over the region, though readings will still remain above normal through
the first part of next week.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
As of 1200 AM EST Thursday...

The first of several negatively tilted upper systems will
approach the forecast area from the south Thursday night. High
clouds will overspread the area in advance of this system, and
are already doing so. Low clouds linger across eastern WV, but
the lack of a significant west wind field has resulted in
scattering out of the low clouds at KBLF, while they hold in at
KLWB. All indications are that these clouds will gradually
dissipate from the south through the night leaving both sites
KBLF. Otherwise, expect BKN-OVC high clouds throughout much of
the TAF valid period at all sites. Any further sub-VFR ceilings
and precipitation will be beyond the end of the TAF valid
period. No issues expected with visibility through the TAF valid
period. Winds diminishing and becoming light and variable
throughout the CWA. The winds will veer to the southeast through
the day Thursday, but speeds are expected to remain mostly 5kts
or less through the TAF valid period.

Medium to high confidence in ceilings throughout the TAF valid
period.
High confidence in visibilities throughout the TAF valid
period. Medium confidence in wind direction, high confidence in
wind speed throughout the TAF valid period.

Extended Aviation Discussion...

Conditions will begin to deteriorate Thursday night from
southwest to the northeast as a wave of low pressure track
across the Tennessee Valley. Expect periods of rain Thursday
night through Friday afternoon, then again Sunday into Monday.
During this time expect sub-VFR cigs and at times vsbys.

&&

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

&&

$$
SYNOPSIS...WP
NEAR TERM...WP
SHORT TERM...DS
LONG TERM...MBS
AVIATION...RAB/RCS



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