Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 211935

Area Forecast Discussion
National Weather Service Blacksburg VA
235 PM EST Wed Feb 21 2018

High pressure will remain off the Southeast coast, which will
keep well above normal temperatures through the remainder of
this week. Chances of rain should increase as a cold front
approaches from the west. This front should cross overhead later
in the weekend.


As of 230 PM EST Wednesday...

An anomalous upper level ridge remains off the Southeast coast,
which is providing quite a warm day for February with near
record high temperatures expected. See the climate section for
more details. Cloud cover has been thinning over most of the
area during the day, but a copious amount remains over the
southern Blue Ridge. It will likely not break up until late
afternoon. The latest mesoscale models are not impressive with
the development of a few showers or thunderstorms along and west
of the Blue Ridge, but only a slight trim to coverage and POPs
was made as enough warming is taking place to provide some weak
instability. For this evening and beyond in this period due to
what happens tomorrow, this forecast steered away from the GFS
solution and in more agreement with the NAM and higher-
resolution models.

It will remain unseasonably mild overnight, but a cold front
will approach from the west to possibly bring a few showers.
Coverage appears highest over the southern Blue Ridge and parts
of the Alleghany Highlands of Virginia. Meanwhile, high pressure
will head east of the Great Lakes and begin to wedge southward
along the eastern slopes of the Appalachian Mountains. As a
result, a backdoor cold front should slide southward east of the
Blue Ridge toward Thursday morning. Several adjustments were
made for Thursday such as shaping temperatures to fall
throughout the day in the Piedmont along with adding areas of
fog and drizzle. POPs were also increased near Lynchburg to
accommodate the likelihood of rain developing along the
backdoor cold front. Temperatures were also shoved well below
guidance, and the timing of the wedge was also sped up a few
hours based on the latest high-resolution model solutions.


As of 200 PM EST Wednesday...

Surface front will continue to bow south through much of the region
Thursday night per the favored colder Nam before slowly lifting back
north Friday ahead of another stronger wave lifting by well to
northwest. This would support higher pops over the north closer to the
baroclinic zone aloft and perhaps spotty light rain/drizzle behind the
boundary into early Friday. Models suggest only weak support for added
measurable rainfall Friday afternoon as the main lift passes well west
and the wedge lingers for much of the day. Will keep some low pops
going mainly north/west with perhaps lingering drizzle elsewhere
Friday. Temps into Friday very tricky pending exactly where the
backdoor front ends up as latest Mos showing a 10-15 degree difference
in values from the colder Nam to the warmer GFS. For now will lean more
toward the Nam but stay above its coldest values at this point.

Front should lift back to the north Friday night into Saturday ahead of
stronger shortwave energy heading northeast out of the central states.
This will gradually push the area back into the warm sector Saturday
into Saturday night. However lift and deeper moisture will remain north
and west of the area until the moisture ahead of the front arrives west
late Saturday night. Appears could be some scattering of showers mainly
north and west, but overall chance to slight pops which may be overdone
until very late Saturday night. Lows Friday night remain iffy with lows
mostly 40s to mid 50s with values steadying/rising late. Highs Saturday
look to be mostly late day within the residual eastern wedge while
perhaps jumping to around 70 west espcly if more sunshine occurs. Thus
stayed below guidance given the likely slower trend of Cad erosion at
this point.


As of 145 PM EST Wednesday...

Strong upper ridge off the southeast coast looks to weaken during the
period allowing more in the way of zonal flow to take shape next week.
This will initially occur as stronger shortwave energy passes well
north late in the weekend with a trailing cold front crossing the area
from the west on Sunday per model consensus. Swath of weakening showers
along the boundary should affect the region during the day although
some solutions remain slower and have much of the rain behind the front
which would suggest best pops west at this this point. Showers may also
linger far southern sections Sunday evening as the boundary folds over
otherwise drier later Sunday night across the region. Should be the
last day of much above normal highs with another round of 60s to lower

Drier/cooler air follows the front for early next week as high pressure
builds in Monday and wedges in from the north on Tuesday. This likely
to return some clouds to the region by later Tuesday with the wedge
holding into Wednesday. May see another weak shortwave pass along the
boundary just to our south Monday night per 00z Euro which could bring
more rain back to southern sections but iffy. Otherwise next impulse
dropping out of the Rockies may tag with the front to bring another
area of organized rainfall into the region by later Wednesday. Temps
cooler into next week, but still above normal with highs 50s to lower


As of 230 PM EST Wednesday...

VFR conditions should hold for most locations through the
afternoon, but some MVFR clouds and showers will be possible
along the southern Blue Ridge and parts of southeast West
Virginia. Increasing moisture during the evening and tonight in
the boundary layer should allow for ceilings to deteriorate
overnight. Confidence is high that IFR should arrive at all TAF
sites between 06Z and 12Z on Thursday.

The most problematic aspect of this forecast is the timing of a
backdoor cold front sagging southward over the Piedmont
courtesy of high pressure wedging against the eastern slopes of
the Blue Ridge. Flying conditions should worsen during the
morning as ceilings and visibilities fall toward IFR. The
frontal passage will bring cooler east winds along with areas of
fog and drizzle. LYH has the highest confidence of IFR
throughout the day, but confidence is lower for ROA/DAN/BCB due
to how far south the backdoor cold front advances. Cloud cover
alone will likely keep it MVFR/IFR throughout the area into the

Extended Aviation Discussion...

High pressure will continue to wedge southward against the
eastern slopes of the Blue Ridge, which will keep areas of fog
and drizzle through tonight into Friday. Conditions will likely
plummet to IFR by Friday morning. Eventually, the backdoor cold
front will stall along the Virginia and North Carolina line and
retreat northward as a warm front toward Friday evening. VFR
conditions should return for most locations during Friday night
and Saturday aside from any typical low clouds along the Blue
Ridge on Saturday morning. By Saturday afternoon, shower
coverage should increase as a cold front arrives from the west
that could bring MVFR/IFR conditions toward Sunday. Better
flying weather should return later on Monday.


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 is 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




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