Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 151841

Area Forecast Discussion
National Weather Service Blacksburg VA
241 PM EDT Mon May 15 2017

A weak stationary front will remain across southern sections
into Tuesday before dissipating. Meanwhile, high pressure will
build in over the region tonight before exiting offshore Tuesday
afternoon. This will allow for a summery southwest flow of
warmer and moist air to develop for mid and late week.

As of 218 PM EDT Monday...

Weak surface front remains across extreme southern sections late this
afternoon with MSAS showing a bit higher dewpoint air pooling just off
the Blue Ridge near the VA/NC border. This where also seeing a more
extensive cumulus field but without any convection so far given the cap
aloft. May need to add in an isolated shower mention before release as
a weak mid level wave slides across but leaving out for now per trends
and lingering dry air aloft.

Otherwise upper heights should continue to slowly build through the
next 24 hours with the ridge axis aloft overhead on Tuesday. This will
also allow surface high pressure to build across the region from the
north tonight before slipping offshore by Tuesday afternoon. Expect may
see some of the cumulus field evolve into trapped strato-cu for a while
this evening over the southwest per latest Nam before giving way to
subsidence overnight. Light winds and clear skies should allow for good
radiational cooling espcly north half where dewpoints remain low.
Therefore expecting some 40s in the valleys, with 50-55 elsewhere,
except perhaps a bit milder ridges and far southern sections. Appears
fog to be limited to near the rivers and deeper valleys so trimming
back coverage a bit.

Low level flow to gradually turn southwest in the wake of the departing
surface high on Tuesday but remain rather weak overall. This should
start to bring higher dewpoints back north in the afternoon as well as
warming aloft with 850 mb temps progged to around +19C west by late in
the day. Latest forecast soundings also show the mid level cap fading
as guidance indicates some weak convergence Blue Ridge along with
progged 1000 J/KG CAPE over the southwest. This may be enough to spark
isolated convection so leaving in a mention for a few hours across
parts of the ridges. Otherwise should be turning quite warm per ample
insolation with highs 80s including some increase in late afternoon
humidity from southwest to northeast.

As of 215 PM EDT Monday...

Summer-like weather will continue through Thursday night. Upper
ridge will remain over the East keeping our area in an increasingly
warm and humid airmass through late in the week.

Any late day isolated shower or thunderstorm along the Blue Ridge
will fade quickly Tuesday evening. With mostly clear skies and light
winds expected overnight, low temperatures Tuesday night into
Wednesday morning will vary from the lower 50s in the mountains to
the lower 60s in the Piedmont.

Wednesday will be sunny to partly cloudy with a southwest breeze and
a very warm afternoon. While instability will also be increasing,
the lack of a good convective trigger and CIN evident on model
soundings should be enough to limit our chances for showers and
thunderstorms to a few isolated orographically forced cells mainly
along the Blue Ridge. High temperatures Wednesday will range from
the the mid 70s in the mountains to around 90 degrees in the

Under partly cloudy conditions, low temperatures Wednesday night
will generally be in the 60s. By Thursday, the upper ridge axis will
be flattening a bit as it moves to our east. This will allow upper
level shortwave to stream in our direction in the southwesterly flow
aloft as a cold front slowly approaches from the northwest. This
will gradually build our chances for showers and thunderstorms as we
go through Thursday afternoon and Thursday night. High temperatures
on Thursday will warm to the upper 70s in the mountains to around 90
degrees in the Piedmont. Low temperatures Thursday night into Friday
morning will mainly be from 60 to 65 degrees.

As of 230 PM EDT Monday...

The upper ridge will flatten across the eastern CONUS, while a
trough will transition into the central part of the country by the
weekend. There remains some differences between the GFS/ECMWF
regarding the evolution of the synoptic pattern for this weekend
into early next week. The GFS suggests that a persistent upper level
trough over the Rockies will become progressive over the weekend,
with strengthening Southwest flow aloft and a cold front approaching
from the west early Monday. GFS supports cooler temperatures and
increased chances for convection. The 00z ECMWF maintains troughing
over the west through the weekend, re-amplifying the upper level
ridge along/east of the Appalachians through Sunday, then gradually
transitions to a more zonal pattern early next week. The ECMWF has a
slower cold front passage from west-east Monday and Tuesday. The 12z
run of the ECMWF continued the slower timing of the frontal
boundary. Used the Superblend for pops from Friday to Monday which
was a nice compromise.

In general, temperatures will remain warm headed into the weekend
with increasing dewpoints preventing temperatures from falling below
60 degrees in most areas. Daytime highs in the 80s will be common,
and 90 is not out of the question for areas east of the Blue Ridge
on Friday. High temperatures will cool early next week with
increased convective chances and additional cloud cover. The details
will become more clearer as we head closer in time.

As of 1250 PM EDT Monday...

Overall VFR conditions will prevail this afternoon with more
widespread scattered to broken cumulus fields south and west of
a KBLF-KBCB-KDAN line. May also see a shower develop across
southwest sections through early this evening but without any
impact on the terminals.

High pressure overhead tonight should ensure a continuation of
VFR although some river valley fog may develop late espcly over
southern and western sections where low level moisture lingers.
This combined with a light west wind could push some fog into
KBCB late although quite iffy so adjusting to more of a MVFR for
vsby at this point. Otherwise appears any added fog should
remain away from the TAF locations with much drier air lingering
around KLWB/KLYH for now.

More good flying weather expected on Tuesday with the flow
turning light southwest during the afternoon. This likely to
lead to a bit more afternoon cumulus buildup across the
mountains with perhaps an isolated shower or storm possible.
Otherwise expecting any cigs to remain VFR with convection too
spotty to mention.

Extended Aviation Discussion...

Dry and becoming summerlike by Wednesday under deepening
southwest flow. VFR conditions are anticipated for most of the
time, outside any late night valley fog.

Some isolated MVFR convection may develop Wednesday and
Thursday across the higher terrain, with a better threat for
afternoon sub-VFR Friday everywhere as a frontal boundary slips
across the Central Appalachians. Front stalled across the region
likely to lead to more convection by Saturday afternoon with
periodic MVFR possible.




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