National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 261001
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
501 AM EST Fri Feb 26 2021

.SYNOPSIS...
Canadian high pressure will drift eastward from the Ohio Vally
and Pennsylvania today toward New England tonight allowing
colder air to spread southwest down the east side of the
Appalachians. Meanwhile, a series of vigorous weather systems
will track northeastward from the south central U.S. bringing
moisture and precipitation to the area. This precipitation will
occur in the form of a wintry mix today and tonight for the
mountains and rain elsewhere. Additional widespread rainfall
and periods of heavy rainfall possibly leading to flooding are
expected through the weekend and into early next week.

&&

.NEAR TERM /THROUGH TODAY/...
As of 445 AM EST Friday...

...Minimal Winter Weather Event Expected Today Impacting Mainly
the Higher Terrain of the Western Mountains...

A difficult and complex forecast in place today from the
standpoint of winter precipitation. After unseasonably warm
temperatures the past couple of days and lots of sunshine, we
return to the winter weather problems today at least in a
minimal fashion. The complexity is that confidence is low in
winter precipitation type, supporting temperatures, and
accumulations. Certainly this event does not rival any of the
high impact events we have had in recent weeks this February.
Feeling is that this is a minimal impact event at best and
almost entirely confined to higher terrain, mostly above 3000
ft.

Temperatures this morning are still well above freezing in most
areas this morning, generally in the upper 30s to mid 40s with
dewpoints in the 20s, so clearly some room for evaporative
cooling as the precipitation arrives later this morning,
currently moving northeast from Middle TN and northern AL/GA.
However, the timing of this precipitation into the area mid to
late morning allows for some additional warming this morning.
Current advertised temperatures grids do not even show
temperatures throughout the vast majority of the CWA, especially
elevations below 2500 ft., even reaching freezing today or
tonight. Even with the wedge, largely "in-situ" confidence in
temperatures dropping low enough to support accumulations of
snow/sleet/freezing rain across the majority of the area remains
low to very low as we proceed further into the day as the
precipitation spreads further northeast.

With these factors in mind and mainly a rain event with
temperatures above freezing, have tailored the Winter Weather
Advisory to include areas only along/west of the Blue Ridge and
emphasized higher elevations. Would have used elevation potion
in GFE, but unfortunately it failed within GFE here, so had to
include the entire county and specify the elevation in the
wording. Could clearly see the WSW being cancelled early if any
winter weather fails to materialize outside the highest terrain
mainly in western NC, Grayson county, and southeast WV,
specifically western Greenbrier county.

Rain amounts today should generally be 1/2 inch or less. While
this should not result in any flooding issues, it combined with
all of the recent and frequent rain/snow/sleet/freezing rain
events of the past month, sets the stage for a potentially
significant flooding threat going into the weekend and early
next week, including rivers, creeks, and streams, as FFG values
are low with very saturated ground and the potential for 2-4
inches of rainfall during the weekend and early next week.

/Confidence Levels in Forecast Elements/ Temperatures -
Moderate to High, Precipitation Probabilities - Moderate to
High, Winds - High, Winter Precipitation Threat - Low.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
As of 230 AM EST Friday...

...Heavy, potentially flooding rains possible for parts of the
area this weekend into early Monday...

February has been a wet month across the region with most of our
climate sites ranging from around 0.50 inch to 1.25 inches above
normal. Much of this precipitation fell in the form of freezing
rain, sleet or snow, that helped maintain wet soil conditions as the
collective snowpack gradually melted as days warmed.

This weekend, we are looking at a pattern where low pressure heads
eastward through the Great Lakes region all while a second low lifts
northeast out of the mid-Mississippi valley into the Lower Ohio
Valley. As this is transpiring, a warm front is expected to approach
the area from the south on Saturday, cross region on Sunday, and
stall just to our north Sunday night. As the Great Lakes low heads
eastward, its associated cold front then is expected to sweep
through the area Sunday night into early Monday.

Southwest flow south of the warm front will increase in velocity and
advect a generous amount of Gulf of Mexico moisture into the region.
A look at the NAEFS Standard Anomalies for precipitable water show
values reaching the 1.00 to 1.25 inch range, or plus two sigma, from
Saturday morning through Sunday night. The area with the most
prolonged period of plus two sigma is over the southwestern sections
of the region -- including parts of the Mountain Empire region and
New River Valley sections of southwest Virginia and the Northern
Mountains and Foothill region of North Carolina. Our latest forecast
will have around two to three inches of rain over the area during
the period of Saturday through Sunday night. We will need to watch
for potential flooding first in the short term, especially Sunday
night with heavier rain showers associated with the passage of the
cold front. In a somewhat later time period, mainstream river
flooding may be possible, especially within the more reactive
headwaters region of the Tennessee River, including the Clinch
and Holston Rivers.

Monday into Monday night, cooler and drier high pressure will build
into the region. Lingering scattered showers will be possible after
daybreak Monday across mainly southern and eastern sections of the
region.

Temperatures during this portion of the forecast will average around
five degrees above normal on Friday, around ten degrees above normal
on Saturday and Sunday.

Confidence in the above scenario is moderate to high on the general
synoptic pattern transition. Specifics on rainfall amounts and
location of the highest amounts are still a question mark, but signs
are pointing to our southwest sections for the highest totals.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 230 PM EST Thursday...

A cold front will move south into the Carolinas Monday morning.
From there, guidance still remains divided on an early week
system that could slip in from the southwest, bringing in an
opportunity of mixed precipitation whilst cold air lingers. On
the other hand, some guidance wants to park high pressure
overhead and keep us dry through mid-week. For now, opted with
blended guidance that reflects the first option with
precipitation moving in. Following that system, a weak frontal
passage is possible Thursday, but looks to lack deep moisture
with it.

Temperatures through the period will run warmer than normal.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
As of 100 AM EST Friday...

...Increasingly Poor Aviation Conditions Expected Today...

VFR conditions are expected to persist through most of the night
with increasing mid/high clouds in a BKN-OVC fashion, all
generally AOA 100.

Lower clouds will begin to develop and advect northward after
daybreak, mostly in the 025-050 range. Isentropic lift along a
developing baroclinic zone and southwest flow aloft will spread
light rain into the region by mid to late afternoon from the
southwest. At this point, temperatures and sounding profiles
support mostly rain at the TAF sites, with any winter
precipitation generally confined to the higher elevations. A
brief period of sleet is possible in the western higher terrain,
but mostly expecting just rain and fog going into the evening
and overnight hours. IFR ceilings and visibilities will develop
toward sunset.

The heavier rainfall moves out of the area after 03Z leaving
low clouds, drizzle, and fog with generally IFR to LIFR
conditions in place throughout much of the CWA.

Winds will veer to the northeast and east overnight as high
pressure slides eastward across OH/PA into the northeast,
setting up a favorable wedge pattern. Winds will become more
southeast west of the Blue Ridge by afternoon and increase in
speed with low end gusts developing across much of the area
during the afternoon/evening.

/Confidence in Forecast Elements/
Ceilings - Moderate to High,
Visibilities - Moderate to High,
Winds - Moderate to High,
Winter Precipitation Threat - Low.

Extended Aviation Discussion...

Prolonged periods of sub-VFR flight conditions will persist
through the weekend. A frontal boundary/baroclinic zone will
persist from southwest to northeast across the area with a moist
Pacific-based southwest flow aloft. Numerous waves of low
pressure moving along the front, bringing periods of
precipitation, mostly in the form of rain. The rain will persist
into early next week, with the heaviest rainfall expected Sunday
into Monday. Some improvement in conditions is possible by
Tuesday.

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Winter Weather Advisory from 1 PM this afternoon to 7 AM EST
     Saturday for VAZ011-014-018>020-023-024.
     Winter Weather Advisory until 10 PM EST this evening for
     VAZ007-009-010-012-013-015>017.
NC...Winter Weather Advisory until 10 PM EST this evening for
     NCZ001-002-018.
WV...Winter Weather Advisory from 1 PM this afternoon to 7 AM EST
     Saturday for WVZ042>044-507-508.

&&

$$

SYNOPSIS...RAB
NEAR TERM...RAB
SHORT TERM...DS
LONG TERM...DS/RCS
AVIATION...RAB