Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Blacksburg Virginia
305 am EDT Mon Sep 16 2019
a cold front will drop southeast from the Ohio Valley today,
with a backdoor cold front pushing through from the north on
Tuesday and Tuesday night. High pressure will cover the region
Wednesday through Friday.
Near term /through tonight/...
as of 300 am EDT Monday...
Starting out with surface high pressure over the central
Appalachians this morning. Low pressure over the Ohio Valley will
move southeast, bringing a weak front toward the mountains. Isolated
to scattered thunderstorms will approach southwest Virginia and
southern West Virginia this afternoon and evening. The better
instability and low level convergence remain over the Tennessee
Valley, just to the southwest of Bluefield and Boone.
Full sunshine is expected today after morning fog Burns off and low
clouds over south central Virginia and north central North Carolina
dissipate. Expect low clouds to be mainly southeast of Lynchburg and
Danville this morning. Will stay close to a nbm/European model (ecmwf) blend for
maximum temperatures. No major changes to minimum temperatures
needed. Clouds increase from the north late tonight.
Short term /Tuesday through Thursday/...
as of 150 am EDT Monday...
A sharp upper level ridge centered across the Mississippi Valley at
the outset of this forecast period is perhaps the most noticeable
large scale feature across the Continental U.S. With troughs located over the
interior northwest and the Canadian Maritimes. Also of course there
is Hurricane Humberto off the Carolina coast but it is expected to
have no effects on our region as it tracks further out to sea. The
upper ridge nudges only slightly eastward from Tuesday into
Wednesday but a sprawling surface high over New England will wedge
southward into the mid-Atlantic.
Clouds and cooler air will push into the region from the
northeast during the day Tuesday which should see highs 5f to
10f lower than Monday along with more clouds. Several models
produce light precipitation mainly across the western County Warning Area during
this period mainly due to orographic lift. Rain amounts will be
generally less then a tenth of an inch except in widely
scattered or isolated shower or thunderstorms most likely
occurring over the southwestern mountains, if at all. Rain will
not be nearly enough to begin to alleviate the increasingly dry
conditions across most of the County Warning Area.
Lows Tuesday night generally in the 50s. Wednesday will see
fewer clouds as the high strengthens over New England pushing
the boundary further south. Despite more sun it will at least
remain somewhat cool with highs mainly in the 70s. Not much
change expected Thursday as the upper ridge builds even further
north and shifts closer to the southern/central appalachian
region. But rain chances will be essentially non-existent as
much drier air is advected into the region from the northeast,
with precipitable waters dropping to as low as 0.35 inches by Thursday
afternoon per the GFS.
Long term /Thursday night through Sunday/...
as of 340 PM EDT Sunday...
The upper ridge to our west, hovering around 590 dm, will drift
over the eastern U.S. And linger through the entire period.
Tropical cyclone Humberto will be steered rapidly away from the
East Coast by the western Atlantic trough. Deep troughing in the
western U.S. Will progress into The Rockies very slowly with the
high amplitude ridge across the eastern U.S.
This period will lead to dry conditions with mean troposphere relative humidity
values in the 10-20% range through the period and a dry
northeast flow much of the time frame with surface high
pressure anchored over the northeast/New England area. Diurnal
temperatures swings should be fairly significant with the dry
air mass and notably dry ground across the area as well. Look
for cool nights with low temperatures in the 40s and 50s, but
daytime highs should warm well into the 70s and 80s through the
period. Past Wednesday, precipitation probabilities are near
zero through this entire period, exacerbating what is already a
low end drought in at least the western part of the forecast
/Confidence in forecast parameters/
temperatures - moderate to high,
precipitation probabilities - low,
thunderstorm threat - low.
Aviation /07z Monday through Friday/...
as of 140 am EDT Monday...
Expect MVFR-LIFR visibility due to fog within the typical fog
prone mountain valleys, developing about 08z/4am. Nighttime
microphysics images showing the first patches of MVFR- IFR
stratus over southeast Virginia. These clouds are expected to
expand in coverage early this morning, potentially as far west
as klyh and kdan. Higher confidence is at kdan so have added a
period of MVFR ceilings from 09z/5am to 14z/10am.
Clouds and fog will erode by mid to late morning,then conditions
will be VFR for the rest of the day.
Confidence is average for ceilings and above average for visibilities
Extended aviation discussion...
VFR conditions are expected Monday night through Tuesday.
Isolated to scattered MVFR storms are possible in the mountains
of the central Appalachians late Tuesday into Wednesday. VFR
conditions are expected Thursday and Friday.