Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Blacksburg Virginia
540 am EST sun Feb 14 2016

Synopsis...
cold high pressure moves east and off the middle Atlantic coast by
tonight. A warm frontal boundary works toward the Tennessee Valley
by this evening with snow moving into the mountains. By
Monday...low pressure works from the lower Mississippi Valley to
the southern Appalachians. With cold air in place expect snow
changing to a wintry mix Monday into Monday night. This system
moves east by Tuesday afternoon.

&&

Near term /through tonight/...
as of 400 am EST Sunday...

Wind Chill Advisory cancelled early as winds have dropped for most
of the area to below 5 miles per hour. Only areas with near Wind Chill Advisory
levels are elevations above 3500 feet like Hot Springs...so majority
of the area will stay warmer...than -5f through the morning.

Now our eyes focus on the winter storm threat taking shape over the
middle part of the country early this morning. Models show decent
agreement in bringing light snow toward the mountain Empire of SW Virginia
into northwest NC by late afternoon...then shifting in bands east across
the New River valley into the Piedmont. Airmass will stay very cold
with thermal profile staying below zero through 12z Monday. Hence
will see snow through tonight. Question remains on how any mesoscale
bands will line up. Models favor a mountain Empire to Alleghany Highland
corridor for heavier snow band potential by midnight tonight.
Smaller band should slide east to the Piedmont through the night.
This Arctic airmass in place should start the snow to liquid ratios
pretty high in the 20:1 range...dropping toward 15:1 by 12z Monday.

Snowfall totals late this afternoon through tonight will range from
6 to 10 inches west of the Blue Ridge to 2 to 5 inches east.

We have gone with a Winter Storm Warning to account for snow in the
west...with mix of snow/sleet and freezing rain in the east. More
details on the wintry mix part of the storm will be mentioned in
the short term discussion below.

Look for increasing clouds today with highs in the lower to middle 20s
west to upper 20s east.

&&

Short term /Monday through Wednesday night/...
as of 400 am EST Sunday...

Starting the period in the middle of a winter storm. The band of
isentropic lift north of a warm front to our south should continue
into the afternoon. Most areas should still see snow at 12z Monday
as the entire column of the sounding is below freezing throughout
the County Warning Area. Leaning toward the colder NAM for temperatures and the
GFS for storm track and quantitative precipitation forecast...should see precipitation changing to
sleet across the Piedmont and Southside around midday or early
afternoon...gradually working its way north and west toward the
Blue Ridge as the day progresses. Still concerned given the
intensity of the antecedent Arctic cold air mass...that it will
not recover as quickly as the models indicate...especially the
GFS. Like the way the NAM holds onto the cold layer at the
surface...even across Southside...well into early Tuesday morning.

A decrease in precipitation appears likely Monday evening as the
best isentropic lift shifts north in response to increasing middle-
level warm advection as a southern stream short wave induces a
deepening area of low pressure across the Cumberland Plateau. A
dry slot is evident among most models...spreading into the region
from the NC foothills/Piedmont area during the evening. This will
result in a decrease in synoptic-scale induced
precipitation...resulting in much of the area seeing a change over
to freezing drizzle during the evening.

Overnight...into Tuesday morning...the main synoptic system lifts
through the region as the surface low moves north into the eastern
Ohio Valley. Quantitative precipitation forecast is highest during this time frame...averaging
around 1/2 inch for much of the County Warning Area. By this time...precipitation
should be mostly snow/sleet Greenbrier valley/I-64 area...sleet
New River valley...sleet/freezing rain/rain far SW Virginia...and
freezing rain/rain Piedmont/Southside. Will need to watch this
period very carefully if warming is not as advertised or greater
than expected...as this will result in substantial changes in
amounts of snow/sleet/ice.

Expecting all snow most areas through 18z Monday...then
snow/sleet/freezing rain encroaching from the S/se/SW remainder of
the period...have used top down procedure for 18z Monday
Onward...and generally snow amounts from quantitative precipitation forecast and thickness after
18z. Given consideration for sleet accumulations...have lowered
snow/liquid ratios to much less than 10/1 during the later half of
the event. All of this in consideration...have issued a Winter
Storm Warning for the entire County Warning Area as noted above as in areas where
the snow accumulations do not meet criteria...snow/sleet/ice
accumulations should.

Quickly on the heels of the main weather system is a strong
Alberta clipper that appears destined to bring additional snowfall
to the region...especially west of the Blue Ridge. As one would
typically expect from this type of system...the bulk of the
snowfall will be across the alleghanys down through the Cumberland
mountains of SW Virginia into the Blue Ridge mountains of northwest NC.
An additional 1-4 inches of snow appears possible as a result of
this clipper.

Temperatures will remain well below normal and mostly below
freezing Monday...closer to normal values for Tue-Wed. No
significant warming is expected through this period by any means.

&&

Long term /Thursday through Saturday/...
as of 530 am EST Sunday...

A quieter weather period...and potentially warmer. Northwest flow
aloft remains over the region...so am reluctant to indicate too
much warming. Main focus this morning was on the winter storm...so
no significant changes were made to the long term forecast at this
time.

Previous valid discussion...

Chilly high pressure builds overhead and to the north early
Thursday resulting in a cold but dry start with lows 20s to a few
teens valleys. Shortwave ridging builds in later Thursday and
lingers into Friday before the next trough and associated cold
front arrive for day 7. With gradual warming aloft on Thursday
should see temperatures return to more seasonal levels under sunshine
before much warmer air surges in Friday into Saturday ahead of the
front. This should finally push highs into the 40s and 50s under
increasing return SW flow Friday...and possibly 50s to near 60
Piedmont Saturday despite more clouds and perhaps a few mountain
rain showers.

&&

Aviation /12z Sunday through Thursday/...
as of 538 am EST Sunday...

VFR anticipated through late Sunday afternoon with high clouds
becoming middle deck by 12z then low end VFR by 18-22z.

Warm front and snow will move into the western areas by 22z...and
shift east by the end of this taf period. Look for visibilities/ceilings to
drop to MVFR and lower especially west of the Blue Ridge by
06z...with IFR ceilings/visibilities spreading east overnight.

Winds light or from the northwest swing to the east and southeast Sunday
afternoon...some gusts over blf to 20kts after 00z Monday.

Extended discussion...

Expect snow switching to sleet/freezing rain Monday with this mix
into Monday night and early Tuesday. MVFR to IFR ceilings/visibilities to
remain. Some rain is expected at least Dan/blf as warmer surge of
air rides in Tuesday.

This storm exits Tuesday afternoon...but is followed quickly by a clipper
system that may impact the area for Tuesday night-Wednesday...possibly
resulting in the continuation of poor flying conditions.

High pressure builds in Thursday with VFR returning.

&&

Climate...
coldest air of the season has settled over the middle Atlantic
region. Several record low maximum temperatures and low temperatures
are possible. Below are the current records for Sunday 2/14.
Looks like blf tied a record low for 2/13.

Sunday 02/14/2016
site mint year Lomax year
kblf 5 1971 16 1960
kdan 15 1986 32 1986
klyh 4 1899 24 1905
kroa 10 1943 26 1986
krnk -2 1969 24 1986

&&

Rnk watches/warnings/advisories...
Virginia...Winter Storm Warning from 4 PM this afternoon to noon EST
Tuesday for vaz007-009>020-022>024-032>035-043>047-058-
059.
NC...Winter Storm Warning from 4 PM this afternoon to noon EST
Tuesday for ncz001>006-018>020.
WV...Winter Storm Warning from 4 PM this afternoon to noon EST
Tuesday for wvz042>044-507-508.

&&

$$
Synopsis...jh/wp
near term...wp
short term...rab
long term...jh
aviation...PM/wp
climate...cf

National Weather Service Glossary of Abbreviations