Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 210115
Area Forecast Discussion
National Weather Service Blacksburg VA
915 PM EDT FRI MAY 20 2016
A complex area of low pressure will approach from the southwest
tonight and cross the region Saturday through Sunday. High
pressure will slowly build into the area on Monday, and remain in
place for much of the week, resulting in warmer and drier weather
for most of the workweek.
.NEAR TERM /THROUGH SATURDAY NIGHT/...
-- Changed Discussion --As of 840 pm EDT Friday...
Band of heavier rain along the leading edge of the upper trough now
crossing into the Interstate 77 corridor and should continue
northeast across the region overnight. However some of the latest
short term solutions a bit more progressive, including the HRRR,
which shifts this axis across the Blue Ridge around midnight, and
into eastern sections overnight before exiting around daybreak.
This along with a forecast weakening scenario upon precip moving
deeper in the wedge may result in a bit less QPF given less
prolonged nature to embedded heavy rainfall. However this trend
looks a bit too fast as well as underdone. Thus only trimmed back
QPF some over the far west and followed closer to the earlier
ECMWF that had higher totals across the nw closer to the upper
low, and over the southeast where more elevated convection
possible late as a secondary surface low takes shape. Still mainly
1-2 inches except less than an inch far west within the southeast
downslope shadow. Otherwise running with a period of categorical
pops from southwest to northeast overnight with some fog mixed in
as things saturate even more. Lowered temps a few degrees where
already near forecast lows due to cooling via rainfall resulting
in a few 40s mountains, while bumping up out east given current
warmer readings and latest LAV mos trends.
Previous discussion as of 350 pm EDT Friday...
An upper ridge of low pressure will approach the region overnight.
Plenty of moisture will ride north along the eastern side of this
trough and across a lee side wedge of high pressure. A surface low
pressure will start to develop over the region tonight, and then
strengthen off the coast Saturday afternoon. Patchy light rain will
spread northeast through the area this evening. A larger swath of
moderate to heavy rain will reach the area during the late evening,
and begin to exit the area late tonight. A generous amount of rain
is still expected in the one to two inch range. See the HYDROLOGY
section of this discussion for more details.
On Saturday the area will start to experience northwest flow on the
backside of the developing surface low pressure. This flow will help
to gradually erode the wedge. Instability will increase through the
day with showers still expected in the west with isolated to
scattered thunderstorms in the west and south by the afternoon.
Saturday night the main upper low will continue approach and then
cross the region. Anticipate additional scattered showers under the
increased lapse rate of its associated cold pool.
Temperatures during this portion of the forecast will be slightly
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.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 320 pm Friday...
A broad upper level trough, sitting over New England and the Mid
Atlantic region, is expected to become a closed low Sunday. This
closed low is forecasted to track south across the coastal piedmont
of Virginia and North Carolina Sunday night, then off Cape Hatteras
Monday. This low is then forecasted to track north to New England on
Tuesday. Since this low will remain inland, there is a good chance
for showers Sunday, especially east of the Blue Ridge. Also with a
cold pool pivoting over the piedmont during the afternoon, isolated
strong to severe storms are possible with hail being the primary
threat. Bulk of the stronger storms and heavy rain will remain with
the low and points east. With this in mind, the actual track of this
upper low will dictate our weather for Sunday. Stay tune.
The chance for showers will remain in the area Sunday night,
however, strong storm threat will decrease as the low jogs to the
east. As this low continues to move east, showers will taper off
from west to east with rain leaving the piedmont sometime Monday
evening. It is obvious with the change in this low`s track, PoPs
have been increased and durations has been stretched into Monday,
mainly across the piedmont.
While this low is in the vicinity, temperatures will remain cooler
than normal Sunday and Monday. Sunday afternoon temperatures will
range from the mid 60s to lower 70s. Slight warmer Monday with the
chance to see more sun. Highs Monday will be in the upper 60s to mid
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 330 pm Friday...
Finally, the upper level low is out of our hair and ridging begins
to build along the east coast Tuesday.
Temperatures will warm above normal Tuesday, then well above normal
Wednesday through Friday. With the warmer weather comes a better
chance for showers and thunderstorms each afternoon and evening.
Storms do not look organized but pulse-like, tracking slowly from
the southwest to the northeast.
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
As of 700 pm EDT Friday...
Flying conditions will continue to deteriorate this evening with
spotty light rain and drizzle resulting in cigs falling to MVFR
levels or worse over the next few hours. A more widespread area of
light to moderate rain will overspread the southern/western sections
by midnight, and the remainder of the region overnight.
Visibilities will trend to MVFR including ocnl IFR in heavier
rainfall with ceilings lowering to IFR at most locations.
Conditions will start to improve toward daybreak Saturday as the
heaviest rain moves northeast, out of the region.
Expecting widespread rainfall to exit the region early Saturday
morning with residual areas of fog/stratus keeping sub-VFR
conditions in place. Appears some improvement to MVFR or perhaps
brief VFR possible around midday Saturday as the region slides in
between exiting surface low pressure to the east and the upper
low to the nw. This may create enough low level west/nw flow to
help scour out low cigs along/east of the Blue Ridge pending how
deep the leftover wedge gets. Cigs will again lower over the west
later Saturday as the upper cold pool drops in from the north
resulting in scattered showers along with isolated thunderstorms.
However given uncertainty with the degree of instability will only
keep prevailing showers in from KBCB westward and VCSH at KROA
without any thunder mention for now. Otherwise mainly MVFR cigs
and vsbys west and possible VFR at KDAN/KLYH by late in the day.
Saturday night into Sunday night, cigs look to remain quite
variable under the passing upper low with periods of mainly MVFR
cloud bases during the daylight hours and VFR cigs at night.
Isolated to scattered showers will also occur, espcly over the
mountains Saturday evening and across the east Sunday into Sunday
evening making for MVFR vsbys or worse at times. Isolated thunder
will also be possible along with patchy sub-VFR vsbys overnight in
fog where earlier rainfall occurred. Northwest upslope flow may
maintain some IFR ceilings at times in the west espcly around
KBLF. Surface gusts of 20 to 25 kts will be possible across the
mountains during this time frame. 850 mb winds are progged to
increase to 25 to 35 kts, and gradually veer northwest to north.
On Monday, winds will start to decrease as the center of the upper
low continues to exit the region. Isolated showers will still be
possible, especially in the east, related to this feature.
Monday night through Wednesday, expect mainly VFR conditions as
high pressure settles offshore with southwest flow in place.
-- Changed Discussion --As of 900 pm EDT Friday...
Consistent forecast from the models and the Weather Prediction
Center with one to two inches of rain expected across the forecast
area tonight through late in the day Saturday. The bulk of this
precipitation will fall overnight into early Saturday morning.
There is still a potential that this longer duration rainfall will
lead to localized minor flooding along streams and creeks if rates
are higher, while elevating some mainstem rivers to near bankfull
pending total QPF into Saturday.
-- End Changed Discussion --