Scientific Forecaster Discussion
fxus61 krnk 221803
Area forecast discussion
National Weather Service Blacksburg Virginia
103 PM EST Fri Nov 22 2019
a cold front will pass across the appalachian chain today,
bringing widespread showers across the mountains that will break
up as they pass east of the Blue Ridge. The front will stall
across North Carolina tonight, before a wave of low pressure
moves along the boundary on Saturday, bringing another round of
widespread rain. This system will exit the region Saturday
night, with high pressure and drier conditions returning for the
beginning of next week.
Near term /through tonight/...
as of 1025 am EST Friday...
Initial wave of rain will move through and out of Piedmont area
by noon, but additional areas of rain with upslope will continue
to impact western slopes through much of the afternoon. With
rather strong westerly flow at ridge top level, this will help
dissipate any rain into downslope areas through remainder of the
day so look for a decreasing trend overall in rainfall
coverage, with the exception of far western slopes. Adjusted
pops downward accordingly for this afternoon for most locations,
using near term model blends as guidance. May need to make
further downward adjustments by early afternoon as well.
Surface cold front to move into western part of forecast area
by about noon and push through Piedmont during the afternoon,
but air mass is only slight cooler behind it and there will only
be a minor wind shift from west-southwest to west-northwest and if anything winds
will slowly weaken somewhat behind it. Ridge tops have been
getting gusts in the 30-40mph range but that is expected to
diminish into the 15-25mph range later this afternoon behind the
Previous discussion as of 639 am EST Friday...
Made some minor adjustments in temperatures for this morning.
Also modified pops and weather to capture latest radar trends.
More changes later this morning.
As of 310 am EST Friday...
A cold front to our west in the Ohio Valley early this morning will
move east today and stall tonight across North Carolina. The main
areas of rain associated with the frontal boundary was to our west
across Kentucky and Tennessee. However, regional WSR-88D images
showed a few prefrontal showers ahead of the main rain area. The
front will move into the mountains this morning. This should result
in winds shifting to a westerly direction. The downslope wind
direction will cause shower activity to gradually weaken as it
passes east across the Piedmont. The highest qpf expected range
from 0.25"- 0.60" across southeast West Virginia/western
Virginia and will taper off sharply as one heads eastward. The
rain and its coverage will diminish this afternoon as drier air
works in from the northwest. High temperatures this afternoon
will range from the low 40s in the northwest mountains
Greenbrier West Virginia to the lower 60s in the Piedmont.
The cold front will continue east before stalling this evening into
tonight across northern North Carolina. Moisture will slowly advance
northeast tonight into Saturday morning as low pressure forms
along the frontal boundary in the lower Mississippi River
valley. Slowed the advance of rain tonight utilizing the nbm for
pops. For low temperatures tonight blended in consall to
capture the colder air pushing in from the north. Low
temperatures tonight into Saturday morning will vary from the
upper 20s in the northern mountains to the low 40s in the
Medium confidence in the near term period.
Short term /Saturday through Sunday night/...
as of 200 am EST Friday...
Guidance remains fairly consistent in handling evolution of weather
systems for the weekend. The northern and southern streams of the split
upper level pattern will begin to phase and drive development of a low
pressure system that will move across the region Saturday. Big Warm
nose evident in BUFKIT and in-situ wedge will make for a cold rain.
The latest guidance is showing surface temps remaining above freezing
so anticipating all liquid until deeper cold air gets pulled in behind
the departing low Saturday night generating upslope rain-to-snow
showers in the mountains. Could be a wet coating of snow for the higher
elevations before daybreak Sunday morning. Some locations mainly form
the southern Blue Ridge into the mountains of NC may see enough
enhancement of rainfall to create some localized flooding but
widepspread Hydro issues do not appear likely.
Snow showers will linger west of the ridge on Sunday with a slushy
coating possible at the higher elevations, though expect insolation
will help limit any accumulations and keep roads clear.
Winds will become quite blustery with strong gusts developing late
Saturday night and continuing Sunday. Gusts over 45mph may be possible
along and west of the Blue Ridge, mainly at the higher elevations.
High pressure eventually builds in Sunday night with fair weather to
start off next week.
Saturday continues to look quite chilly in The Wedge with a cold rain.
Temperatures will be a bit below normal on Sunday behind the front with
low/mid 50s east to low/mid 40s west, then warm a bit for Monday to
more seasonal readings of mid/upper 50s east, low/mid 50s west.
Long term /Monday through Friday/...
as of 330 PM EST Thursday...
By Tuesday, high pressure should head offshore and open the door for a
developing low pressure system to reach the Appalachian Mountains by
Tuesday night and Wednesday. The exact timing of this system still
remains uncertain, but there is enough confidence to have a chance of
rain showers reaching the mountains by Tuesday night. However, the
dynamical energy appears to be far displaced to the north with its
associated shortwave trough passing over the Great Lakes, so any quantitative precipitation forecast
appears considerably light. As the low pressure system exits on
Wednesday, another round of northwest flow and upslope rain/snow
showers seems possible for the higher elevations in southeast West
Virginia. High pressure should return to provide dry weather for
Aviation /18z Friday through Wednesday/...
as of 1005 PM EST Friday...
Areas of light rain dissipating quickly early this afternoon
and conditions are generally VFR except for kblf and klwb where
MVFR ceilings will linger for a while as the cold front moves
through, but then should lift to VFR later this evening with
partial clearing at least temporarily. West winds remaining
below 10 kts except for on higher ridges, so there may be some
turbulence but not enough to consider low level wind shear mention in tafs for
remainder of the day.
Front expected to stall just east of the area tonight and
another upper wave will bring moisture back into the region on
Saturday with lowering ceilings again by Saturday morning, and
rain moving back during late morning to early afternoon. May see
MVFR ceilings again by end of taf period...18z...but then will
continue to lowering later in day with IFR likely with more
moderate rain. Cannot rule out some brief IFR conditions at
klyh early Sat morning with fog, but low confidence given higher
clouds may be moving back in toward morning so cooling may not
be enough to produce much fog. Even less chance for any fog at
other sites. Will take a closer look with future updates.
Winds will remain rather light and variable or southeasterly
tonight into Saturday.
Confidence is average on ceilings/vsbys and high on the winds.
Extended aviation discussion...
Winds will become gusty from the northwest as the low pressure
system exits the region on Saturday night and Sunday. Showers
and snow showers will linger into Sunday morning for western
slopes including kblf and possibly klwb with IFR conditions
likely there. Otherwise VFR and dry conditions are expected by
late Sunday. Dry weather is expected for Monday into Tuesday so