Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 220543
Area Forecast Discussion
National Weather Service Blacksburg VA
143 AM EDT Thu Sep 22 2016
An upper low will meander across the eastern Carolinas through
Thursday before finally weakening and shifting offshore by the end
of the week. High pressure will gradually build in from the west
Friday into Saturday. A backdoor cold front drops south through
the area late Saturday into Saturday night followed by cooler
high pressure Sunday into early next week.
.NEAR TERM /THROUGH TODAY/...
As of 245 PM EDT Wednesday...
Closed low over the Southeast Coast will continue to interact with
the Post tropical remnants of Julia during the period. As been the
case for a couple of runs, the ECMWF and NAM remain slightly west
of the GFS. One of the forecast challenges is the western edge of
the moisture and the sharp gradient in showers. The HiResw-arw-east,
wrf-arw-rnk, RAP and HRRR support the mention of isolated to
scattered showers in southeast portions of forecast area this
afternoon into tonight.
The upper low remains fixed across the coastal Carolinas tonight
into Thursday morning. believe that shower coverage may wrap
tighter towards the coast tonight with drier air pushing into
northwest portions of forecast area. Cloud cover tonight will vary
from clear in the northwest to cloudy in the southeast. Lows tonight
will range from the mid 50s in the northwest mountains to the
mid 60s in the east.
The closed upper low will slowly weaken and lift northeast on
Thursday. The result of this transition will be even less coverage
of isolated showers across the south and southeastern portion of the
region. High temperatures Thursday will vary from the mid 70s in the
mountains to the lower 80s in the Piedmont.
.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
As of 230 PM EDT Wednesday...
Persistent upper low will finally open up and shift northeast
Thursday night in response to ridging nudging east from the
Midwest. However may still be enough moisture around with the
deformation axis on the back of the coastal system to produce a
few added showers far southeast so left in an isolated mention
Otherwise expecting a drier northerly flow to take shape under weak
high pressure later Thursday night into early Saturday. This should
bring clearing/sunny skies for late week into the weekend. However
passing 500 mb trough well to the north by Saturday will propel a
backdoor cold front toward the area Saturday afternoon and into parts
of the region Saturday night. This a bit slower than previous given
strong upper ridging overhead and warmth ahead of the front that should
slow it down until Saturday night. Other than perhaps some developing
post frontal low level cloudiness by late Saturday per the GFS, deep
moisture to remain limited so not including any pops with the boundary
for now. Given gradual 850 mb warming Friday and weak compression
ahead of the front Saturday, looks like will return to above
normal highs with mostly low/mid 80s both days with most surface
based cool advection holding off until Saturday night at this
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 130 PM EDT Wednesday...
High amplitude blocky pattern looks to evolve later in the weekend into
next week as potential cut off upper lows develop off New England and
across the upper Midwest. This could basically sandwich the area within
a sharp shortwave ridge axis between these two features pending exactly
where the upper block develops. Differences between models continue in
regards to strength of the upper systems and subsequent speed of
surface features in this setup. However still appears will see a rather
significant backdoor cold front drop south into the region by Saturday
night/early Sunday before the boundary fades crossing into the
Carolinas. Guidance still suggests some spotty shower potential Sunday
with the front aloft nearby and developing onshore flow. Thus thinking
more clouds and spotty shower pops Sunday and southern sections Sunday
night with a shallow moisture axis lingering but iffy.
Lots of uncertainty to take shape early next week as model spread
remains large in just how fast a second cold front to the west will be
able to slide east given eastern ridging in place. Latest 12Z GFS
has continued to make a shift toward the slower ECMWF from
overnight in keeping this slow moving front west of the mountains
through midweek. However these solutions remain much slower and
stronger than the GEFS which looks too weak/fast in lifting
support out to to the north, while spilling the front quickly
east. Overall the slower scenario would keep the area in more or
less a more stable low level wedge formation per high pressure to
the north under ridging aloft. Tendency in this setup likely to
lead to more clouds and spotty showers/drizzle including much
cooler temperatures into midweek. Therefore have trended in this
direction with highs below Mos, but still mostly 70s and lows 50s-
mid 60s, although highs by early week could be only in the 60s if
more widespread low clouds do materialize.
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --As of 135 AM EDT Thursday...
Surface low is east of the GA/FL coast early this morning with the
upper low/trough still situated across the coastal Carolinas. We
are seeing a bkn/ovc deck of MVFR to at times IFR ceilings pushing
toward DAN/LYH. Spotty showers also exists near DAN. Pattern
favors in and out periods of lower ceilings at DAN/LYH through the
morning and added tempo for -ra at DAN as well. Question will be
how far west the sub-VFR ceilings reach. The models hint at
potential for BCB/ROA to get a small window of MVFR ceilings this
morning so added a tempo group at Roanoke from 09-11z. Am not
forecasting it for BCB but should see scattered at 2-4kft with
broken cirrostratus. However, fog should form some at BCB with
MVFR vsbys while LWB drops to LIFR at times toward 09-12z.
Will notice more subsidence in the west today with upper trough
weakening. Should be VFR in the west after fog burns off with
LYH becoming VFR by mid morning/14z. Danville is forecast to stay
socked in a little longer but should go VFR in the afternoon.
Precip should be more to our southeast today.
Extended aviation discussion...
VFR conditions will prevail Thursday night outside of late
night/early morning fog/low clouds mainly BCB/LWB. GFS/ECMWF have
been consistent in filling and lifting out the low to the
northeast on Friday. VFR conditions will prevail on Friday.
A back-door cold front will come through the Mid-Atlantic region
on Saturday. High pressure will build in for Sunday. The chance of
precipitation or any sub VFR conditions will increase through the
day Sunday and into Sunday night into Monday as wedge sets up with
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