Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 211936

Area Forecast Discussion
National Weather Service Blacksburg VA
336 PM EDT Thu Jul 21 2016

A Bermuda high will keep pushing warmer and more humid air into the
region throughout the weekend and into the first part of next week. The
combination of high air temperatures and humidity will create
dangerously high heat index values, especially east of the  Blue Ridge,
with readings around 105 at times through the weekend. The heat and
humidity will also create an unstable airmass, and a series of weak
fronts moving through the region will help keep a chance for showers
and thunderstorms in our forecast for the next several days.


As of 330 PM EDT Thursday...

Satellite/radar indicate essentially nothing in the way of shower
activity across the region this afternoon, and only noted one or two
isolated showers earlier across the piedmont which quickly dissipated.
However the cumulus field still shows orographic forcing along the Blue
Ridge with a pool of instability just to the east. this will keep some
slight chance pops for a stray shower across the southern Blue
Ridge/foothills from VA into NC into this evening, then dry everywhere
for the rest of the overnight period. There will be a little cirrus
blowoff from convective activity well upstream in the Great Lakes/Ohio
valley heading in our direction, but the overall synoptic pattern with
light winds and no significant coverage of lower clouds will result in
good radiational cooling once again tonight with lows just a degree or
two warmer than last night. Also expect some valley fog to develop west
of the Blue Ridge.

Any fog/stratus will burn off Friday morning, then we can expect some
more isolated showers/thunder to develop thanks to diurnal heating and
orographic effects primarily be along and west of the Blue Ridge.
However convection will get a bit of a boost late in the day thanks to
a weak front approaching from the northwest and this may increase
coverage in the west late in the day.

With high pressure off the coast and front upstream, southerly winds
will allow temperatures will begin their upward surge tomorrow and we
can expect highs in the middle 90s east of the Ridge with mid/upper 80s


As of 330 PM EDT Thursday...

The heat is on is the main weather story for this period. The strong
upper ridge over the central U.S. will gradually shift west during
the weekend. This will result in a better for a better opportunity
for a cold front to move into the area and then stall over the
region by Sunday night.

Any isolated diurnal convection sparked by orographical influences
along and near the crest of the Blue Ridge will dissipate quickly
with the loss of solar heating Friday evening. There is a small
chance that some of the convection associated with the cold front to
our north may sag south into our area late Friday night into
Saturday morning. In any case, it is going to be another night for
the AC with readings from the mid 60s in the mountains to around 70

Coverage of showers and thunderstorms will increase Saturday ahead
of the cold front. High temperatures on Saturday will climb into the
mid 80s in the mountains to the mid 90s in the Piedmont. Heat index
values will top the century mark across portion of the Piedmont.

Another humid night expected Saturday night into Sunday morning, low
temperatures will vary from the mid 60s in the west to the lower 70s
in the east.

Hazy, hot and humid weather anticipated for Sunday as 850mb
temperatures climb to around 22 C by Sunday afternoon. A few
mountains locations may see cooling showers or thunderstorms.
High temperatures will range from the the mid and upper 80s in the
mountains to the low to mid 90s across the Piedmont. Heat index
values will once again top the century mark Sunday afternoon across
the southeastern portion of our forecast area. Will mention the heat
in the HWO for the weekend.


As of 330 PM EDT Thursday...

The large upper ridge will extend from the West coast to the East
coast through Wednesday. In the northern stream, a shortwave
will drop southeast out of eastern Canada and crosses through New
England on Tuesday. A frontal boundary will settle across the Mid-
Atlantic and Southeast Wednesday into Thursday. Moisture will slowly
increase Monday and Tuesday ahead of the front. Afternoon and
evening showers and thunderstorms are possible Monday into Midweek.
There remain disagreement in model solutions with just how far south
the front will make it. This makes it harder to place the best time
convection. Temperatures will be above normal for the start of the
week and return to normal by end of the week.


As of 220 PM EDT Thursday...

Fairly high confidence in conditions this period with little
change in the pattern since yesterday and essentially going with
a persistence forecast for this TAF package. Do not expect any
isolated showers to affect airstrips during the next 6 hours, and
any showers at all will fade this evening with loss of heating.
We should see another night of good radiational cooling with some
fog development in the typical spots. Expect LIFR at KLWB with a
tempo to MVFR primarily at KBCB and also see a possibility for
KLYH and KDAN as well. Believe elevation of KBLF will keep them
out of any fog and KROA is not a favored location for radiational
fog. Any fog/stratus will burn off Friday morning and leave
SCT/BKN cirrus but will not clutter TAFs with another line for
high clouds.

Any diurnal convection will likely hold off until after this TAF
period, and expect any isolated showers/thunder to primarily be
along and west of the Blue Ridge thanks to orographic forcing and
a weak front approaching late in the day.

Winds will be light through the period.

Extended aviation discussion...

Strong high pressure aloft centered across the Midwest will
attempt to build eastward into the weekend, then retreat back to
the west early next week. Our region will remain on the eastern
periphery of the upper high and thus subject to weak disturbances
in northwest flow aloft tracking around the Great Lakes and into
the Mid-Atlantic. Moisture and instability will be sufficient for
isolated pop up thunderstorms, but a slightly better coverage will
be possible by late Friday into Saturday with a weak front/short
wave moving into the Mid-Atlantic with a better threat for
convection early next week as another front moves into the area,
stalls, and lingers over the region for several days. Hot and
humid conditions east of the Blue Ridge this weekend which may
impact density altitude. Late night and early morning fog will be
possible at the usual sites almost every day.




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