Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 200435
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1135 PM EST Fri Jan 19 2018

.SYNOPSIS...
High pressure will provide for mainly dry and mild weather
through the weekend. A cold front and its associated
precipitation will cross the region Monday into early Tuesday.
High pressure quickly returns to the area by Wednesday, along
with a return to drier weather.
&&

.NEAR TERM /THROUGH SATURDAY/...
As of 915 PM EST Friday...

Main concern again with forecast low temps given ongoing wide
range between ridgetops and valleys with some spots still in the
40s and others in the 20s. Since winds aloft look to increase
again late tonight, appears this trend to persist, so bumped up
lows a little more at elevation and reduced in the valleys
including outlying spots out east. Evening soundings show a
very arid airmass still over the region which should cause the
low deck now approaching from the TN valley to initially fade
before perhaps things moisten enough for some clouds to make it
into the far west around daybreak. Thus kept late night clouds
in along the western perimeter similar to the previous update.
Models again show the westerly 85h jet increasing to around 40
kts espcly over the north/west after midnight but appears much
of this only to clip the higher ridges until better mixing
develops on Saturday.


Previous update as of 654 PM EST Friday...

Current satellite imagery depicts clear skies across the
Blacksburg forecast area with high pressure still in control. RH
profile resembling desert-like conditions. Even as of 600 PM,
RH values were still ranging from the 15 to 35 percent range.
Dewpoints will only be slow to recover, with a more substantial
increase expected Saturday. Expect gradual recovery in RH as
temperatures plummet in good radiational cooling conditions as
boundary layer decouples. Less decoupling anticipated along the
Blue Ridge Mountains, and in a strong radiational regime at
night these areas are often notably warmer than lower-lying
valleys.

More noticeable changes to the forecast were then made to sky
cover west of the Blue Ridge into the central Appalachians and
extreme eastern Tennessee Valley for late overnight into
Saturday. METARs and GOES East satellite RGBs confirm a well
defined stratus deck near or just west of Nashville, TN in
regime of west- southwest warm advection. 18z/19 NAM and RAP-
based BUFKIT profiles depict saturated RH below 875 mb for the
areas where sky cover was increased, so they may be better
depicting this stratus layer perhaps better than the GFS is.
Extrapolation of the western TN stratus layer brings it into
Smyth and Tazewell County around 09z, which is about when I
start to increase clouds. Opted toward partly/mostly cloudy
conditions after 09z in these areas, while maintaining clear
skies for the foothills/Piedmont.

Previous discussion issued at 200 PM follows...

High pressure was centered over southern Alabama. Its associated
ridge axis extended north into the Upper Ohio Valley. Plenty of
sunshine has helped to melt snow today, with some areas in the west
having little or no snow remaining on grassy surfaces. After
coordination with GSP/RAH, there will be no Winter Weather Advisory
for black ice tonight across our North Carolina Counties due to
limited expected coverage. In its place will be a Special Weather
Statement that will highlight isolated coverage from roughly Wilkes
County and points eastward. This statement will also include most of
our Virginia counties east of the crest of the Blue Ridge.

High pressure at the surface will continue to build into the region.
Concurrently, zonal flow aloft will increase with 850 mb winds
expected to be around 45 kts by daybreak Saturday. The result will
be decouple valleys and the Piedmont overnight with ridge tops
staying mixed, thus milder. On Saturday, these stronger winds aloft
will start mixing the surface, and provide for a gusty day.

Temperatures will trend milder through tomorrow as heights build and
850mb temps increase. Anticipate lows tonight in the the mid 20s for
much of the region. The exception will be the higher ridge tops where
lows closer to 30 degrees are forecast. Also, the area of Southside
Virginia and neighboring sections of north central North Carolina
will be closer to 20 degrees thanks to the greater snow pack there.

On Saturday, anticipate high temperatures milder than those realized
today. The upper 40s to the lower 50s are expected across the
mountains with mid 50s to around 60 forecast across the Piedmont.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 315 PM EST Friday...

Keeping close to previous forecast and it appears warm frontal
precip with weak isentropic lift may move across the mountains of
WV/far SW VA Sat night-early Sunday mainly as light rain/possibly
drizzle. Cannot rule out some ice pellets north of Lewisburg WV Sat
night.

As warm front heads further north we will see southwest flow
increase but with a dry period Sunday night-early Monday before cold
frontal showers move in from the west, with a consensus on most of
this occurring Monday night. Appears to be a good rain with one
quarter to one half inch expected.

Winds along and ahead of this front will be strong in the low levels
but instability appear weak. Still could see some gusty showers,
especially in the mountains Monday afternoon/evening.

Temps modifying with lows in the lower to mid 30s Sat night, then
upper 30s Sunday night to upper 30s to lower 40s Monday night.

Highs Sunday will be mild with 50s west, to lower 60s east, similar
again Monday.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 200 PM EDT Friday...

Timing of front per models showing it moving east of the mountains
Tuesday morning and into the piedmont by midday. Will see falling
temperatures mainly in the mountains with any rain showers turning
to snow showers in the higher elevations. However, overall airmass
behind this front is not that cold as its Pacific in origin, so not
arctic blasts. Beyond this temperature start to rebound as we dry
out with surface high building in from the TN Valley midweek, and off
the VA coast by Friday.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
As of 1115 PM EST Friday...

VFR SKC conditions projected for most of the TAFs through late
tonight as high pressure continues to govern the region. Only
significant aviation operational weather impact in this period
will be from low-level wind shear w/ westerly low-level jet of
35-40 kts as winds decouple. This could lead to areas of
turbulence especially along or west of the western
mountains/Blue Ridge.

Toward daybreak, the ceiling forecast becomes less certain
along or west of the Blue Ridge. Current low cloud layer
entering eastern TN may reach the far western sections very late
tonight. Latest Nam continues to depict some of this cloud cover
making it through the very dry air but iffy at this point. Thus
will show ceilings lowering to at least a SCT deck by 12z/7am
for KBLF/KBCB, then trend closer to BKN/OVC VFR/MVFR (025-040
bases) at KBLF during the morning. Confidence in ceilings lower
than VFR is low to medium for these locations, but given recent
trends expect there to be at least VFR strato-cu around. Would
expect VFR SKC conditions elsewhere. Though west winds should
increase to 10-20 kts, with gusts to 25-30 kts tomorrow, there
may still be pockets of low-level wind shear at Bluefield and
Blacksburg with low- level jet increasing to 40-45 kts.

Extended Discussion...

Generally VFR for the TAFs through Sunday, with exception being
lingering SCT-BKN MVFR stratus Saturday night west of the Blue
Ridge.

Sub-VFR conditions will start to return to the area Sunday night
into and through Tuesday night as a cold front and its
associated precipitation moves through the region.

Very gusty northwest winds return to the area Tuesday night
into Wednesday on the backside of the departing system.
Lingering sub-VFR conditions possible across SE WV thanks to
strong upslope flow and residual low level moisture.

&&

.EQUIPMENT...
As of 325 PM EST Friday...

NOAA Weather Radio, WXL60 (Roanoke Transmitter) which
broadcasts at 162.475 MHz remains off the air. The phone company
reported that the circuit line had been cut and will take until
Monday January 22nd to fix it.

&&

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

&&

$$
SYNOPSIS...DS
NEAR TERM...AL/DS/JH
SHORT TERM...WP
LONG TERM...DS/WP
AVIATION...DS/JH
EQUIPMENT...WP


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