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000
FXUS61 KRNK 211834
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
234 PM EDT Tue Aug 21 2018

.SYNOPSIS...
Low pressure moving into the Great Lakes will push a slow moving
cold front through the region late tonight and tomorrow, and
bring strong thunderstorms to the Appalachians and central mid
Atlantic region. High pressure will then build in from the
midwest and bring much more pleasant weather to the region for
the end of the workweek and into the weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 230 PM EDT Tuesday...

Robust thunderstorms have developed west of the Blue Ridge.
Meso guidance has been handling this situation fairly well and
expect storms to continue to develop and strengthen through the
afternoon. Instability has exceeded expectations and will
continue to fuel storms while short but well curved hodographs
show a good amount of low level shear to aid organization. Expect
scattered clusters/line segments with shallow rotation capable
of producing damaging winds to affect the region through this
evening before moving off to our east early tonight.

The cold front will ever so slowly work its way eastward across
the region late tonight and tomorrow, shifting winds around to
the northwest. With deep synoptic moisture this will develop
upslope clouds and some sprinkles/drizzle overnight along and
west of the Blue Ridge with some downsloping improvement to the
east.

Conditions will trend upward after daybreak tomorrow. The low
level wind field will amplify and start some gusty conditions
along the hilltops overnight. The winds will mix down to lower
elevations as steep low level lapse rates develop tomorrow
morning, making conditions a bit gusty through the afternoon.
Instability appears tall and skinny on model soundings tomorrow
but lapse rates are steepening and will make for some isolated
showers/thunder tomorrow afternoon, especially east of the
Ridge.

Temperatures tonight will generally be in the upper 60s/around
70 east of the Ridge with low/mid 60s to the west. Highs
Wednesday will be in the mid 80s east to mid/upper 70s west.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 230 PM EDT Tuesday...

A much quieter and pleasant end to the workweek as a large high
pressure builds into the northern mid-Atlantic region and by Friday
into southern New England. The main highlight in this period is the
much more comfortable humidity levels and period of cooler than
normal temperatures.

Each day should feature sizable diurnal ranges given dry air both
surface (dewpoints in the 40s to mid 50s) and aloft as well as
largely clear skies. Our western counties may see some high-altitude
haziness to skies as northwest flow aloft may transport the eastern
extent of Canadian/western CONUS wildfire smoke well aloft. There
should still be enough of a northwesterly gradient wind to preclude
overnight radiation fog development Wednesday night, but this
gradient will slacken early Thursday allowing for lighter northwest
winds during the day. Prospect for nighttime radiation fog may be
greater Thursday and Friday nights. With 850 mb temperatures around
the upper single digits to low teens Celsius supporting highs in the
70s and lows in the mid 40s to 50s, conditions late this week may
draw some comparison to early fall. Indeed, forecast 850 mb
temperatures are more ordinarily observed around early October per
the SPC sounding climatology. Only small change expected Friday is
that the winds should shift to an easterly component.

Overall forecast confidence is high, though is moderate on
nighttime fog potential.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
As of 230 PM EDT Tuesday...

Our stretch of cooler than normal temperatures and low humidity
levels is short-lived, as a large heat ridge builds eastward for the
weekend. 850 mb temperatures rise to around +18C by the weekend with
humidity levels also on the rise. Thus look for a return to more
summerlike weather by the weekend and into early next week. Saturday
looks dry but a northern-stream upper-level trough may provide
enough of a weakness in subsidence to produce a greater coverage of
thunderstorms on Sunday. While possible, it`s still early to say
with any level of certainty if any may become strong on Sunday.

Temperatures should trend more typical of midsummer in this period,
trending above normal by early next week.

Overall forecast confidence is moderate in this period.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
As of 230 PM EDT Tuesday...

Showers and thunderstorms have developed well ahead of a cold
front approaching from the west. Expect this convective
activity will affect the region until it moves off to the east
later this evening/early tonight. Will generally use VCTS and
amend when convection appears imminent at an airfield. Cigs will
generally be VFR outside of thunderstorms, though conditions
down to IFR due to cig/vsby along with heavy rain and gusty wind
will likely accompany any storms.

The cold front will ever so slowly work its way eastward across
the region late tonight and tomorrow, shifting winds around to
the northwest. This will develop upslope MVFR/IFR conditions
west of the Blue Ridge with a trend to VFR conditions east.
Expect enough wind flow to keep fog formation in check but low
level moisture is abundant and cigs west of the Ridge will
likely be lower than typical upslope and expect some
sprinkles/drizzle as well, especially at KBLF. Any subtle
changes in timing will complicate fog/stratus forecast tonight
so this will be monitored closely and confidence is medium to
low.

Conditions will trend upward after daybreak tomorrow. The low
level wind field will amplify and start some gusty conditions
along the hilltops overnight. Expect steep low level lapse
rates to yield a well mixed boundary layer and allow low level
winds to mix down and make for some gusty conditions all
locations through Wednesday afternoon. Instability appears tall
and skinny on model soundings tomorrow but lapse rates are
steepening and will make for some isolated showers/thunder
tomorrow afternoon, especially east of the Ridge. Expecting
sparse coverage so will go with vicinity in TAFs.

Extended Discussion...

High pressure will be overhead by Thursday. VFR conditions are
expected with this cooler and drier air mass through Friday.
MVFR to IFR fog is possible for a few hours each night along and
near the typical river valleys, especially west of the Blue
Ridge.

&&

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

&&

$$
SYNOPSIS...MBS
NEAR TERM...MBS
SHORT TERM...AL
LONG TERM...AL
AVIATION...MBS/RAB