Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 211200
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
700 AM EST Wed Feb 21 2018

.SYNOPSIS...
A strong ridge of high pressure will remain off the southeast
coast providing much above normal temperatures through the
remainder of the week. Chances for rain increase late Wednesday
into Thursday with a cold front, followed by a better chance of
showers with another front by later in the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 430 AM EST Wednesday...

High pressure along the southeast Atlantic coast will provide
for another unseasonably warm day across the Mid-Atlantic
courtesy of southerly winds transporting warm moist air
northward from the Gulf of Mexico and northern Caribbean.
Dewpoints have risen into the lower 60s across the Carolinas,
and this air is flowing north around the periphery of the high.
Actual baroclinic zone resides west of our region from East
Texas up through the MS Valley and into the Great Lakes. This
will be the boundary for repetitive rains the next few days
while we bask in the warmth from the subtropical connection. The
only fly in the ointment as we bridge into Thursday will be for
a backdoor surge of somewhat cooler air to intrude from the
northeast, impacting Lynchburg and into NoVA. For the near term,
even Lynchburg and NoVA will partake in the near record
breaking warmth.

Fog this morning is not nearly as extensive as yesterday
morning, in part due to cloud cover. The rising boundary layer
dewpoints and deepening moisture is allowing for more cloud
cover thus limiting the radiational effects. As we transition
into the afternoon, surface heating will combine with this
moisture to provide for more cumulus, some of which will develop
into showers along and west of the Blue Ridge. Have maintained
an isolated threat for thunder across far western VA west of
I-77 and from the VA Highlands west into WV, where lifted
indices drop below zero for a few hours this afternoon and CAPE
values approach 500 j/kg.

Tonight will be another mild night, dewpoints above 50 deg F and
cloud cover helping to maintain boundary layer warmth.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
As of 400 AM EST Wednesday...

Large-scale mid-level features remain essentially unchanged in this
period, governed by an anomalous 594-dm ridge centered just west of
Bermuda and mean downstream troughing across the Intermountain
West/Desert Southwest. A quasi-stationary front, likely focusing
repetitive rain events across the Ohio, Tennessee and Mississippi
Valleys will make slow eastward progress. A colder high pressure
area north of New England will force northerly flow and cooler
temperatures into the northern mid-Atlantic region early in the
period, forcing a backdoor front southward/southwestward against the
Blue Ridge/northern Piedmont areas Thursday. 00z NWP guidance
continues to show large variability in the southward push of this
boundary. This results in a great deal of uncertainty and potential
for large temperature busts Thursday and possibly Friday, especially
from the Blue Ridge foothills eastward. The quasi-stationary front
then gains more eastward momentum very late in the period as
powerful shortwave energy ejects across the Plains.

Overall, period will continue to be ruled by well above normal temps
with generally limited but non-zero chances for rain. Those rain
chances increase as we move into the latter part of Saturday.

At least modest diabatic warming should take place through the
morning on Thursday, but the NAM and GFS each show northeast flow
and vestiges of the backdoor front into the northern/central
Piedmont late Thursday. The NAM is somewhat further south than the
GFS is. Areas of light rain falling on the cold side of the boundary
will likely reinforce the air on the cold side, while at least
modest diabatic heating will bolster the southwestern milder side of
the frontal zone. Expect some push southward at least as far as
route 460 east of the Ridge Thursday, but its progress may be halted
some until diabatic cooling can occur Thursday night. One only needs
to look at the MAV and MET guidance highs temps for Danville to get
a better sense of the uncertainty in high temps here - with a 21
degree difference in forecast highs (MAV shows mid 70s while MET is
mid 50s). Sided closer to the milder MAV under the idea the boundary
may slow as it pushes south. Overall temps should run into the 60s,
but utilized raw guidance to show an early high in the VA Piedmont
before hovering then falling. Best chance at rain Thursday is in
northern sections either more closely tied to the stationary front
to our west or from the backdoor boundary, with a minimum toward
evening. May see a fair amount of drizzle, mist or fog in the cooler
eastern sections Thursday night but will leave for later shifts to
further diagnose. Lows should run in the 50s, except mid/upper 40s
from Bath County southeast to Appomattox/Buckingham.

Still likely to have mild southwest flow west of the Ridge on
Friday, while also still dealing with remnants of the backdoor front
at least early in the day. This latter feature either washes out in
southerly flow and/or lifts northeast during the day with
temperatures recovering as it lifts out. With uncertainty with when
this happens, sided toward cooler side of guidance - an earlier
surge would result in even warmer temps than shown. Kept temps in
the 60s, mildest along and southwest of the New River.

Into Saturday, quasi-stationary front well to our west begins to
pick up more steam. This should result in an increase in clouds and
a west to east increase in PoPs to Chance levels in the far west,
and slight chance in the Piedmont/foothills. Still looks like the
best chance of rain is later into Saturday night. A bit more cloud
cover will keep temperatures in the 60s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
As of 300 PM EST Tuesday...

A low pressure system will organize over the lower Mississippi
River Valley on Saturday and track eastward toward the Mid
Atlantic by Sunday. Model solutions continue to slow the timing
of this frontal passage for our area, which appears to be during
Sunday afternoon based on the GFS. Chances of rain were lowered
a little on Saturday but increased a fair amount for Sunday. It
is worth noting that the ECMWF solution is a little slower with
the cold front than the GFS as it displays a Sunday evening
frontal passage. Therefore, some questions remain on how much
the moisture could linger into Sunday night and Monday morning,
especially in northwest North Carolina. Eventually, high
pressure should build overhead toward Monday afternoon. The
upper level pattern turns more zonal by Tuesday, which looks dry
with plentiful sunshine at this point. Temperatures still will
reside well above normal throughout this period although it
should turn a little cooler by early next week.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
As of 700 AM EST Wednesday...

Warm moist southerly flow will result in widespread low
clouds...flight category primarily MVFR. Somewhat lower cigs
will be found right along the Blue Ridge with potential for IFR
conditions farther south along the eastern slopes of the Blue
Ridge into NC. Little change is expected in this weather pattern
as strong subtropical ridge of high pressure remains anchored
just off the southeast U.S. coast, and very active baroclinic
zone with showers and thunderstorms across the Midwest/Ohio
Valley.

Showers are possible over the mountains today where daytime
heating results in cloud build-ups. Drizzle is possible along
the eastern slopes of the Blue Ridge south of Roanoke into North
Carolina which may result in lower visibility over the ridge
crests.


Extended Aviation Discussion...

Sub-VFR cloud bases will be widespread again tonight and
Thursday. A cold front will move into the area from the north
Thursday, potentially resulting in a wind shift to the northeast
for areas east of the Blue Ridge in Virginia. This backdoor
front will bring lowering cigs and potential for more showers
and drizzle. This front lifts back north Friday, although there
will be a continued threat of showers and potential low clouds.
The front will make another push to the south and east over the
weekend promoting a better chance for wetting showers and sub-
VFR conditions.

&&

.CLIMATE...
As of 330 AM EST Wednesday...

Today will again feature well-above normal temperatures that
may approach or eclipse daily record highs and daily record high
minimum temperatures. It`s also possible that all-time warmest
February minimum temperatures could be approached or broken in
this period.

Following are daily records, as well as the all-time warmest minimum
temperatures recorded in the month of February, for our five
climate sites with long-established periods of record:

Wednesday 2/21/2018
Site    MaxT Year   HiMin Year
BLF       65 1996      54 1997
DAN       75 2011      55 1953
LYH       75 1930      50 1981
ROA       73 1930      48 1997
RNK       71 1986      49 1953

Warmest HiMin - February:
Site   HiMin Date
BLF       57 Feb  5 2008
DAN       60 Feb 18 2008
LYH       59 Feb 20 1939
ROA       57 Feb 12 1932
RNK       52 Feb 16 1990

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...JH
NEAR TERM...PM
SHORT TERM...AL
LONG TERM...PW
AVIATION...PM
CLIMATE...AL



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