Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Blacksburg Virginia
707 PM EST Thu Dec 5 2019
high pressure will provide dry weather through tonight. A weak
low pressure system should bring light precipitation on Friday.
Dry weather will resume for this weekend, but a low pressure
system should provide wet weather to start the next work week.
Near term /through Friday/...
as of 250 PM EST Thursday...
High pressure continues to build overhead, which has allowed the
winds to somewhat diminish and the skies to clear. It should be
a sunny and dry afternoon as the flow aloft becomes more zonal.
The west-northwest breeze will provide downsloping across the
Piedmont that should aid in warming the air mass there. It will
take until this evening for the breeze to fully subside.
Temperatures were bumped upward a little more across the
Piedmont due to recent observational trends and the persistent
downsloping that will continue through the remainder of the day.
The center of the high should cross overhead early tonight to
provide a good start to radiational cooling. After midnight,
the synoptic picture changes as the high moves toward the North
Carolina coast and a shortwave upper level trough approaches
from the Southern Plains. This trough will allow a small low
pressure system to form across the lower Mississippi River
valley that should pick up some Gulf moisture. That moisture
will spread to our area in the form of increasing clouds, which
should halt the fall of temperatures and may even cause them to
rise a little before sunrise west of the Blue Ridge.
By Friday, the developing but still weak low pressure system
will cross over the southeast. The high-resolution models
reveal that the quantitative precipitation forecast amounts and moisture coverage are
unimpressive. Confidence is fairly high that it will be a
cloudy day with light rain showers along and west of the Blue
Ridge. Locations in the Piedmont may just become cloudy but not
even see a drop. There is a low possibility that the moisture
could briefly start as snow showers during the morning in
western Greenbrier County before quickly turning over to rain
for most of the day. By late evening, that rain may turn back
to snow showers as temperatures fall in the higher elevations of
southeast West Virginia. Although there will be warm air
advection during most of the day due to a southwest breeze, the
extensive cloud cover warrants staying on the cooler side of
guidance for highs on Friday.
Short term /Friday night through Sunday night/...
as of 250 PM EST Thursday...
High pressure will settle down from the north as a shortwave
quickly makes its way offshore during Friday night into
Saturday morning. Over the weekend the center of the high will
slowly creep towards New England. This feature will keep the
weekend weather settled and seasonable with clouds but nothing
to speak of in terms of rain. High temps in the 40s west of the
Blue Ridge, 50s east, with lows in the 20s and 30s. On Sunday
night, synoptic scale southerly flow will begin advecting Gulf
moisture over much of the eastern Continental U.S. Ahead of a surface low
and its associated front that approach from the Southern Plains
Long term /Monday through Thursday/...
as of 250 PM EST Thursday...
Widespread rainfall should spread over the region starting
early Monday and continuing on through the end of this period.
We will be a bit warmer than the weekend ahead of the front,
with temps staying above freezing Sunday and Monday night.The
timing of the frontal passage on Tuesday is not totally certain,
but the precip should persist through much of Tuesday. Windy
conditions will also accompany the front as it passes. As the
colder air behind the boundary chases the Gulf moisture, there
is a chance for some snow west of the Blue Ridge Tuesday night
Wednesday and Thursday will see the upper atmosphere will assume
a mostly zonal pattern as high pressure builds in to keep the
weather quiet and relatively cool. Another upper trough will be
moving across the conus, but its arrival is inconsistent in the
guidance. Some models have it entering our County Warning Area with
precipitation as early as Friday morning, others hold it off
until Saturday. There is consensus, however, that precipitation
will be on its way late next week or early in the weekend.
Aviation /00z Friday through Tuesday/...
as of 700 PM EST Thursday...
The forecast for the upcoming taf period did not stray much
from the previous forecast this afternoon. With the inbound
pressure system Friday, cloud heights are going to gradually
drop starting in the morning. Once we move into Friday
afternoon, blf, lwb, and bcb with their location to the slopes
will drop to MVFR conditions with lowering cloud heights. With
limited precipitation, visibility through the period remains
unaffected. With blf's location and the west to east progression
of this system, a tempo group was included for IFR conditions
in the afternoon/evening.
As of 105 PM EST Thursday...
High pressure builds over the mid Atlantic and passes overhead
tonight. As it departs offshore, clouds will begin to increase
from the west ahead of a developing but weak low pressure system
in the lower Mississippi River valley.
Although ceilings will steadily lower through Friday, confidence
is fairly high that all sites will remain at VFR through this
valid taf period. After 18z on Friday, light rain showers and
lowering ceilings could drop blf, lwb, and maybe bcb to MVFR.
Lyh and Dan are not expected to receive any showers as the
moisture will mainly be confined to along and west of the Blue
Ridge, so these locations should stay VFR throughout the day.
Extended aviation discussion...
As the low pressure system exits on Friday night, lingering
clouds and moisture will take a while to clear along the
Appalachian Mountains. High pressure should return to provide
good flying weather for this weekend. However, the next low
pressure system should arrive by Sunday night to bring
widespread rain along with MVFR and possibly IFR ceilings and
visibilities through Monday.