Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 131756
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1256 PM EST Tue Nov 13 2018

.SYNOPSIS...
Low pressure off the Mid Atlantic cost will deepen and move
northeast today bringing a cold front through the eastern United
States. High pressure over the central United States will move
northeast Wednesday and Thursday. Low pressure will develop in the
southeast United States and will track along the East Coast Friday
and Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1230 PM EST Tuesday...

The front is currently moving across the foothills and will soon
pass over the piedmont counties. Light rain continues to fall
in the vicinity of the front. Behind the front, cooler air is
filtering in with increasing northwest winds. Rain chances will
be on a sharp decline come the evening commute.

As of 1000 AM EST Tuesday...

A second front is coming across the mountains this morning with
light rain ending west to east by mid afternoon. The upper level
portion of this system will bring light precipitation back
across the mountains, moreso along western slopes later this
afternoon and evening. Colder air will also work into the area
with higher elevations seeing rain changing over to snow. any
accumulations through this evening will remain light and under
an inch.


As of 450 AM EST Tuesday...

Cold front will cross through southwest Virginia, northwest North
Carolina and southeast West Virginia this today. Areal coverage of
rain will gradually diminish from west to east especially once
surface and low level winds come around to the northwest and
downsloping begins east of the Blue Ridge. Upper trough in the
northern stream moves east into New England today leaving the Mid
Atlantic region briefly under an upper ridge ahead of the closed low
moving toward the Tennessee Valley. Upslope showers will continue
in southeast West Virginia down to Tazewell County today but with
very light precipitation amounts. As temperatures drop this
afternoon behind the cold front, rain may mix with or change to
snow/sleet, but again, only trace amounts expected.

Winds turn from the northwest to the north tonight as the northern
edge off the deep moisture moves into central North Carolina as high
pressure builds in from the Ohio Valley. Went on the cool side of
guidance today, closer to the HiRes NMM/ARW models with the
precipitation and all the cloud cover and with a small drop in
temperatures tonight.

Downslope wind will help erode fog after sunrise in the east but
reduced visibilities may linger in the mountains, especially at
higher elevations through most of the morning.

Confidence is average for all elements.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 400 AM EST Monday...

High pressure over the Great lakes Wednesday will build south into
our area. This high center will quickly move east Wednesday
afternoon into Wednesday night. A deep upper cutoff low over the
ArkLaTex region, and diffluent Southwest flow downstream over the
Southeast will advect moisture into our region.  By Wednesday
afternoon, light precipitation will start to overspread this high
pressure from the south. Light rain will impact southwest portion of
forecast area. High temperatures Wednesday will range from the upper
30s in the northwest mountains to the upper 40s in the Piedmont.

There is a potential for a winter event of freezing rain Wednesday
night into Thursday.  Deep upper low will drift northeast from the
Mississippi Valley into the Mid-Atlantic. At the surface, cold high
pressure to our north will before retreating slowly to the northeast
into Thursday. Isentropic lift will increase steadily atop the
surface high as mid-level flow remains from the southwest leading to
precipitation overspreading the area from the south. The surface
high wedging down the mountains will result in cold surface
temperatures. Low temperatures Wednesday night will generally be in
the mid 20s to the lower 30s. However, above the surface, a warm
nose will rapidly lift northward across the area. Forecast profiles
depict an extended period of freezing rain about 18 hours as surface
temperatures remain below freezing despite warming 850-700mb
temperatures. QPF forecast are a challenge, but now highlight the
potential of heavy QPF. The highest accretion amounts are expected to
be along and near the crest of the Blue Ridge thanks to enhanced
precipitation totals here where the effect of a southeast upslope
flow will maximize precipitation totals. WPC probabilities are
increasing for significant icing around 0.25 inches.

For PTYPE used the top down method with as blend of GFS/NAM for
temperatures profiles and WPC QPF totals.  Thursday morning will
features freezing rain, rain and some sleet. Any sleet will lower
ice accretion totals. By Thursday afternoon, the entire region looks
warm enough for plain rain, albeit a cold rain. High temperatures
Thursday afternoon will vary from the the mid 30s in the north to
around 40 degrees in the south and far west.

Thursday night, the parent upper low will move northeast along the
Mason Dixon line, bring its associated trough axis and cold front
through our region. This transition will shunt the warm nose to our
east as cold air advection streams into the area on progressively
gusty northwest winds. This will result in a transition to scattered
rain and snow showers across mainly across the mountains. Light snow
accumulations up to an inch or so are possible in the northwest
mountains. Low temperatures Thursday night will range from the upper
20s in the west to the mid 30s in the east.

There is still some uncertainty in the models in how thermal
profiles will evolve and placement of the highest QPF. Ground
temperatures are relatively warm. Because of this uncertainty, have
decided to wait for another set of model runs before decisions are
made about any winter headlines and surrounding NWS offices agree
with this assessment.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 1230 PM EST Monday...

Friday morning an upper low will be making headway eastward
through the Upper Ohio River Valley with its associated trough
axis extending southward into a portion of our forecast area. A
timing challenge within the models exists to pinpoint just where
this axis will be at the start of the day. However, the general
trend of the day will be for any lingering precipitation in the
east from the Thursday/Thursday Night system to be exiting the
region, or to dissipate thanks to increasing northwest,
downsloping, winds across the eastern parts of the area. Across
the west, these same gusty northwest winds will allow for a
period of upslope scattered snow/rain showers across portions of
southeast West Virginia.

Heading into and through the weekend, a general northwest flow
pattern will continue across the area, but but with notably
weaker speeds. Very isolated lingering rain/snow showers will be
possible across parts of southeast West Virginia Friday night
through Sunday.

Sunday night into Monday models vary as to the degree which a
cold front will impact our region. Our latest forecast will
reflect a consensus of the guidance which yields isolated
rain/snow showers from roughly the Blue Ridge and points west
Sunday night and isolated rain showers across the southeastern
sections of the area on Monday.

Temperatures during this portion of the forecast are not
expected to show a lot of variation, although there will be a
slightly trend lower by the second half of the weekend post-cold
front. Readings on average will be just a few degrees below
normal.

Forecast confidence is highest on Friday, at moderate
confidence, and trends downhill heading into Monday.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
As of 1245 PM EST Tuesday...

A second cold front is passing over the area early this
afternoon. Light rain and MVFR will remain in the vicinity of
the front. Higher elevations, especially western slopes will
continue with IFR or lower restrictions through at least
midnight, when drier air works into the area. Widespread VFR
conditions are expected through the day Wednesday.

Forecast confidence is high for ceilings and average for
visibilities.


Extended Discussion...

Another area of low pressure develops in the southeast United
States on Wednesday night with a wedge on the east slopes of the
Appalachians and fairly good consensus in the long range models.
Widespread rain and freezing rain are increasingly likely
Wednesday night and Thursday espcly across the mountains.

This storm system is expected to exit the region by Friday with
conditions returning to VFR with the exception of residual
upslope snow showers on the western slopes of the central
Appalachians.

Forecast confidence above average into Thursday night and
average Friday and Saturday.

&&

.HYDROLOGY...
As of 450 AM EST Tuesday...

Radar and gage estimated through 3AM today showed a range of
rainfall amounts from around one half inch southeast West Virginia
and parts of the New River Valley to nearly three inches in the
North Carolina piedmont. This has resulted in a sharp rise in river
levels along the Dan River and lower reaches of the Roanoke River.
The latest forecast from the River Forecast Center accounts for all
the rainfall through 1AM and had moderate flooding along the parts
of the Dan River and minor flooding at Randolph on the Roanoke
River. These forecasts will be updated again before noon.

&&

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

&&

$$
SYNOPSIS...AMS
NEAR TERM...AMS/RCS
SHORT TERM...KK
LONG TERM...DS/KK
AVIATION...RCS
HYDROLOGY...AMS


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