Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 220003

Area Forecast Discussion
National Weather Service Blacksburg VA
803 PM EDT Mon Oct 21 2019

A strong cold front will cross the Appalachians and central mid
Atlantic region on Tuesday, bringing another round of widespread
rainfall to the area. High pressure will build in behind the
front with fair weather through the middle of the workweek. Our
next chance for rain will arrive by Friday as Low Pressure
develops over the southeastern US.


As of 750 PM EDT Monday...

Adjusted the timing of the pops to reflect increasing patches of
light rain showing up along and west of the Blue Ridge. Timing
of the main area of precipitation appears to remain on track,
arriving late tonight/early Tuesday. Added drizzle to areas
along/west of the Blue Ridge given latest observation/radar
trends. T/Td readings so far are on track with no major changes
needed here. Pushed the thunder to start a bit later in the
morning and further east per neighboring offices thinking.

As of 300 PM EDT Monday...

Low clouds and fog are holding fast with the lingering wedge
banked up against the mountains, but clearing on the edges has
allowed for some improvement across portions of Southside and
the piedmont as well as in the Mountain Empire of VA. However
expect clouds will fill back in as the boundary layer saturates
after dark and a strong cold front approaches form the west.
Hilltops will be blustery as the low level wind field amplifies
ahead of the approaching cold front, and some orographically
forced light rain is possible from the southern Blue Ridge down
into he mountains of NC. The better precipitation chances
arrive as the front starts to push in from the west by daybreak.

The front will move across the region from the west on Tuesday
and looks to exit off to the east bu Tuesday afternoon. While
the best dynamics will be pulling off to our north and the best
instability Will reside off to our southeast, there is a good
amount of forcing with the front and shear will be considerable.
Any embedded convective elements will have the potential to mix
strong winds to the surface, particularly across portions of
Southside and the piedmont where a small degree of instability
may be able to pool ahead of the front. Will be watching trends
in the mesoscale guidance closely for any changes in the
expected evolution of the system.

Rainfall will be enhanced by a wave sliding up along the front.
Expect another good dousing for locations along/west of the
Blue Ridge with amounts of 0.5 to 1.0 inches, and greater
amounts at the higher elevations where totals may exceed 1.75
inches especially from the southern Blue Ridge into the
mountains of NC. Overall amounts east of the Ridge look to be
0.5 to 0.75 inches. Late summer drought conditions had water
levels running well below normal but recent widespread rainfall
is starting to add up. Do not anticipate any widespread hydro
problems but may see some localized runoff issues with higher
rainfall rates associated with the more vigorous showers.

Temperatures tonight will generally be in the 50s. Ahead of the
front on Tuesday temperatures will perk up into the middle 60s
west of the Blue Ridge with mid 60s/near 70 to the east.


As of 210 PM EDT Monday...

A cold front will move east Tuesday evening and exit offshore
Tuesday night. Some gusty northwest winds are possible due to the
pressure gradient from low pressure departing and high pressure
building eastward. However, the winds will remain below wind
advisory levels and provide some cold air advection into Wednesday
morning. Low temperatures Tuesday night will vary from the mid 30s
in the mountains to the lower 40s in the piedmont.

High pressure will build east Wednesday into our region and settle
over Mid-Atlantic region Wednesday night.  High temperatures on
Wednesday will range from the upper 40s in the mountains to the mid
60s in the piedmont under sunshine.

Winds should relax Wednesday evening into Wednesday night with high
pressure overhead. Clear skies, calm winds, and good radiational
cooling for Wednesday night could present another opportunity for
frost and freeze concerns west of the Blue Ridge by Thursday
morning. Low temperatures Wednesday night will range from the lower
30s in the deeper mountain valleys to around 40 degrees in the

High pressure will travel east on Thursday and push off the Atlantic
coast Thursday night. At the same time, an upper level trough will
dig southward through the plains. High temperatures Thursday will
climb into climb into the lower 50s in the west to the upper 60s to
around 70 degrees in the east. Low temperatures Thursday night will
drop into the upper 30s in the mountains to the mid 40s in the

Forecast confidence is high during the short term period.


As of 210 PM EDT Monday...

An active weather pattern is expected during the long term period.
Pattern evolution uncertainty result in low forecast confidence in
details of the forecast. The uncertainties stem from when the upper
trough approaches from the west, which will depend on whether or not
it remains attached to the larger scale westerly flow or developed a
cutoff low in the base of the trough.

On the ECMWF(similar on UKMET and CMC), the low becomes cutoff over
Texas and Oklahoma around Saturday and lifts northeast into early
next week, while the GFS holds an open trough that progresses east.
The new WPC prognostic charts showed a less prominent frontal wave
moving across the Southeast during the weekend compared with
previous progs. Utilized a blend of Hpcguide and NBM to capture
a progressive solution.

A cold front will move southeast across the region Friday and
be located to our south Friday night. A wave of low pressure will
develop along the boundary around Friday night and ride along the
boundary Saturday into Saturday night. A weak shortwave will rotate
east across the region Sunday morning. High pressure will build
across the region on Sunday afternoon into Sunday night. A cold
front will approach from the west on Monday. Details on the long
range will become clearer over time.


As of 750 PM EDT Tuesday...

Poor aviation conditions expected through roughly 18Z Tuesday
before conditions return to VFR by mid or late afternoon (in
most areas) Tue afternoon.

Strong upper-level negatively tilted upper trough will sweep
through the area early Tuesday morning. Isentropic lift will
support light rain/drizzle overnight until the main rain event,
most likely in the form of a QLCS, arrives toward daybreak in
the west. Not including thunder at that point due to lack of
instability, but brief heavy rainfall and gusty winds seem quite
plausible. As the activity moves further east into the Piedmont
during the late morning/early afternoon, a few thunderstorms
become possible. More intense and discrete activity will likely
wait until later afternoon/east of our area, before developing.

Overnight, look for widespread IFR-LIFR ceilings in place across
most of the area, but especially west of the Blue Ridge. Drizzle
and patches of light rain are likely as well, again especially
along/west of the Blue Ridge. Toward daybreak, the
aforementioned line of showers should arrive in the 10Z-14Z time
frame in the west to the 16Z-18Z time along the eastern border
of the CWA. A brief period of IFR-LIFR visibilities in rain/fog
possible, but not enough confidence to TEMPO that at this time.
Mostly looking at MVFR-IFR visibilities in light rain/fog.
Visibilities will quickly return to VFR after the front moves
through and the rain ends, but MVFR ceilings will likely persist
west of the Blue Ridge for a few hours behind the front, then
becoming VFR by 00Z (too close to TAF end time to advertise yet,
but that would be the plan in the next TAF issuance).

Winds will remain southeast overnight at speeds of 5-10kts, with
some gusts to around 20kts remaining possible for several more
hours in the usual southwest Virginia area of BLF-MKJ. Winds
will shift to the west with the frontal/trough passage around
daybreak in the west to late morning east.

/Confidence in Forecast Parameters/
Ceilings - Moderate,
Visibilities - Moderate,
Winds - Moderate to High,
Thunderstorm Potential - None to Low.

.Extended Aviation Discussion...

Dry weather and VFR conditions are expected by Wednesday.
Moisture is expected to return by Friday with another
opportunity for rain and sub-VFR as yet another strong upper low
pressure area approaches from the west.


The remnants of tropical storm Nestor provided a widespread
wetting rain over the past weekend (Oct 19-20th) with rainfall
amounts of 1 to 3 inches across the Hydrologic Service Area
(HSA). Additional rainfall is likely with a frontal passage
Tuesday, and more rain is forecast toward the end of the week.

The weather pattern supports the potential for rain every 4 to 7
days. This trend is expected to improve ground water conditions
and help mute fire concerns.




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