Scientific Forecaster Discussion
fxus61 krnk 210552
Area forecast discussion
National Weather Service Blacksburg Virginia
152 am EDT Sat Sep 21 2019
high pressure will reside across our area through the weekend,
then shift offshore Sunday night. A weak cold front will drift
into the area from the northwest early next week.
Near term /through today/...
as of 930 PM EDT Friday...
High pressure remains in control of our weather tonight. Winds
have become calm and clouds are clearing which will lead to a
decent shot of radiational cooling overnight. However, winds are
westerly aloft which could send in some high clouds towards
sunrise. With this in mind and dew points in the 50s, overnight
lows will range in the mid to upper 50s across the area,
slightly warmer than previous forecast.
Expect increasing clouds Saturday morning as a weak impulse
moves across the Ohio Valley/central Appalachians. A few models
showing shower potential increasing with this feature but
overall system will be weak, so mainly going isolated/widely
scattered coverage across the mountains. Anticipate a mix of
clouds and sun in the mountains, with more sunshine in the
Piedmont, a little more cloud cover along the ridges.
Saturday will be mild/warm with upper 70s to lower 80s
mountains, though some lower 70s in the higher ridges. Should be
reaching the mid to upper 80s across the Piedmont and Roanoke
Short term /tonight through Monday night/...
as of 130 PM EDT Friday...
High pressure will be centered off the North Carolina coast during
Saturday night and Sunday. A large upper level ridge will also be
situated over the mid Atlantic. Although the GFS tries to show a
couple pop-up showers west of the Blue Ridge during Sunday, the NAM
and European model (ecmwf) models do not show anything developing over the County Warning Area. The
consensus of the NAM and European model (ecmwf) was preferred here as it should stay
dry throughout the day with the vertically stacked ridging in place.
High temperatures were bumped upward on Sunday by a few degrees to
accommodate the expected plentiful sunshine and light southwest flow
providing warm air advection.
By Sunday night, high pressure should head further out to sea, and a
weak cold front will arrive over the Appalachian Mountains during
Monday. The models continue to advertise a moisture-starved boundary
that will be lucky to provide any meaningful amounts of rain.
Sprinkles at the most may reach the I-81 corridor, and there is high
confidence that the Piedmont will remain dry throughout the frontal
passage. Thus, the unseasonably warm and dry trend from late Summer
should continue into the first day of autumn. Any moisture will
dissipate during Monday night as high pressure returns from the west.
Long term /Tuesday through Friday/...
as of 153 PM EDT Friday...
Very few changes in this period since the last update. An upper
level trough that moves over the Great Lakes region Monday and
Tuesday will begin to shift into New England and exit off the coast
of Nova Scotia by Wednesday. Some leftover showers may stick around
in the mountains of West Virginia Tuesday morning from the weak northwest
flow behind the front. A broad ridge then begins to build into
the southeast United States for Wednesday and especially Thursday.
There are still some model differences in regards to rainfall.
The GFS is finally advertising some rainfall due to a weak frontal
boundary draped west to east across the region and a generally
flatter flow at 500mb. However, the European model (ecmwf) is much faster in
building in the 500mb ridge and leaves our area with little to no
precip through this entire forecast period. Other than these
differences, the models tend to agree temperatures will likely be
above normal with 850mb temps reaching anywhere from +16 to +20.
Will likely side with the persistence of a dry pattern and go with
a blend of the European model (ecmwf) and nbm for this period.
Aviation /06z Saturday through Wednesday/...
as of 145 am EDT Saturday...
Surface high pressure, which has been northeast of the region,
now located over the forecast area. This high was moving slowly
east off the North Carolina coast which will allow low level
winds to become west to southwest Saturday morning while
remaining mostly calm overnight tonight. Concerned with good
radiational cooling and few clouds noted upstream, that some
patchy dense fog could develop in the mountain valleys and near
rivers later tonight, so have increased/added fog potential at
klwb and kbcb as a result, as well as a brief period of MVFR at
The remainder of the taf valid period will feature VFR
conditions with a persistent inversion in the lower atmosphere
and trapped marine moisture from several days of easterly flow
across the region yielding once again a fair amount of cloud
cover during daytime heating, especially in the west. A weak
upper-level disturbance will help in this regard as well. There
could even be a few sprinkles in the western mountains, but
overall feel atmosphere is try dry for much if anything, so am
not advertising it in any tafs at this time.
Winds becoming west-southwest-west 5-8kts after 13z, with low end gusts
possible around kblf.
/Confidence in forecast parameters/
ceilings - moderate to high,
visibility - moderate through 13z, then high,
winds - moderate,
thunderstorm threat - none.
Extended aviation discussion...
High pressure will keep conditions VFR into Sunday. Only
exceptions may be late night and early morning fog in the
mountain valleys which would impact the usual terminals (e.G.,
Klwb and kbcb).
A weak cold front may bring scattered MVFR showers on Monday,
mainly in the mountains. Otherwise VFR Tuesday and Wednesday.