Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 180202
Area Forecast Discussion
National Weather Service Blacksburg VA
1002 PM EDT Mon Apr 17 2017
A cold front will move into eastern Virginia and North Caroline
this evening and off the southeast North Carolina coast by
Tuesday morning. In the wake of this front, a wedge of high
pressure will build over the Mid-Atlantic region bringing
noticeably cooler temperatures for Tuesday and Wednesday.
Overrunning moisture will bring a threat of rain back to the
southern part of the area on Tuesday and spread northward
Tuesday night into Wednesday.
.NEAR TERM /THROUGH TUESDAY/...
-- Changed Discussion --As of 950 PM EDT Monday...
Shower activity across the region continues to wane. The
greatest concentration is over parts of Southside Virginia and
neighboring sections of north-central North Carolina. We expect
this activity to continue to decrease in coverage as it exits
to the southeast.
Coverage is still expected to be on the increase again later
tonight across mainly portions of the Northern Mountains and
Foothills of North Carolina, as well as, neighboring sections of
the Mountain Empire region of southwest Virginia. This increase
will be thanks to an upper level disturbance, currently over
central Tennessee, moving eastward into the Carolinas.
The latest update will reflect a greater period of time with
limited coverage of showers across our area between the
departing activity in the southeast, and the arrival later
tonight across the southwest.
Have also made minor tweaks to reflect hourly temperature, dew
point, and wind based upon the latest observations and expected
trends into wee morning hours of Tuesday.
As of 704 PM EDT Monday...
Showers remain scattered about the region early this evening,
generally in the New River Valley and into the North Carolina
foothills and the Southside of Virginia. This activity generally
located on the northern side of a wavy, nearly stationary
frontal zone positioned to our south into the Tennessee Valley.
RAP analysis also depicting a vort max located over northern
Arkansas that may be encouraging the current area of showers and
thunderstorms over the Tennessee Valley as well. Through late
evening, coverage of showers should remain isolated to widely
scattered and mainly confined from Grayson County eastward and
southward. As this does so, will be watching for
A re-development/northward shift in the frontal zone and
accompanying rain showers as the upper wave approaches is
expected during the overnight hours, resulting in an increase
in PoPs in much of the North Carolina foothills and the High
Country after 07z. High- resolution guidance and the 18z runs of
the NAM and GFS are not particularly consistent with how far
northward the showers extend, perhaps as far north as the New
River Valley. Showers will also be fighting building ridge to
the north. Didn`t feel the need to extend isolated showers
overnight any further north than the Grayson Highlands at this
point, but that is something to monitor as the night progresses.
Otherwise, only changes made were to account for current
Previous near-term discussion issued at 415 PM follows...
Cold front has shifted to just east and south of the Blacksburg
forecast area this afternoon with a line of broken convection
near the boundary moving into southeastern Virginia and north-
central and northeast North Carolina. Scattered lingering
showers behind the front, closer to where the boundary likely
is at 850mb, are expected to fade through the late afternoon
into evening hours. Have moved out showers and storms much more
quickly next few hours so that the tonight forecast should have
no mention of thunder in for any locations, and even chances for
showers are fairly low.
Late tonight, an upper level wave currently over western KY will
approach and bring an increasing chance for light rain back into
the southwestern part of the forecast area, especially NW NC and
far SW VA. Light rain could continue at times into Tuesday
across parts of the far southwest and south overspreading the
wedge, but think this will have a hard time getting much past
the NC/VA border.
Only partial clearing expected across the far north well behind
the front, but most locations will remain overcast. Winds shift
northeast overnight as high pressure center moves east across
Great Lakes and noses southward through NY/PA and northern VA.
Temperatures will be cooler tonight behind the front and with
shallow wedge building in, but most noticeably tomorrow
compared to the highs today. However, even with wedge firmly in
place, the air advecting in from the northeast is fairly dry and
some sunshine is expected at times across the northeast. In
locations where is remains overcast, and additionally there is
rain continue into some of the day, temperatures will be well
below normal and went as much as 5 degree below coolest MAV
guidance. Might have trouble getting out of the 40s in places
like Boone, but most locations will remain in the 50s in the
mountains, with a few low 60s in Mountain Empire, perhaps toward
Bluefield, and then mid to upper 60s in the Piedmont of VA.
Tricky temperature forecast and suspect some areas across the
south we may need to go even cooler, while others may end up
being warmer farther north.
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.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 230 PM EDT Monday...
A strong surface wedge will be draped across the region and
stretching south into Georgia Tuesday night and Wednesday. A
short wave axis over the Tennessee Valley will push moisture
over this wedge starting from the southern Appalachian mountains
Tuesday, then northward over southwestern Virginia Tuesday
night. A surface reflection is expected to form off the North
Carolina coast late Tuesday night into Wednesday. This coastal
reflection and the short wave axis, moving over the southern
Appalachians, will nudge precipitation east off the Blue Ridge
Wednesday afternoon and east of the piedmont Wednesday evening.
The best isentropic lift and upslope flow is across all of the
North Carolina mountains into southwestern Virgina Blue Ridge
(Floyd and Patrick counties) Tuesday night into Wednesday
morning. This lift and moderate rain will track along the NC/VA
border Wednesday into Wednesday evening. Rainfall amounts,
especially along the eastern slopes of the Blue Ridge will range
from a half to one inch. Foothill and piedmont counties along
the VA/NC border should see up to half an inch. Rainfall amounts
north of 460 will range from a few hundredth towards the
Southern Shenandoah Valley to a quarter of an inch in the
Roanoke and New River Valleys. Rainfall intensity will also vary
greatly from moderate to possibly heavy rain south of highway
460 to light rain and drizzle north. Low clouds and fog will
also be present Tuesday night and Wednesday morning. Saturated
soils and warm moist air from a passing warm front will bring
areas of fog to the area again Wednesday night.
Diurnal temperatures ranges will remain small while this wedge
hangs over the region. Overnight lows will be in the upper 40s
to lower 50s Tuesday night and Wednesday night. High
temperatures Wednesday may warm into the upper 50s to lower 60s.
Areas that see the wedge erode Wednesday (Mountain Empire and
Bluefield) could see temperatures warm into the upper 60s to
lower 70s Wednesday afternoon.
.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 240 PM EDT Monday...
A warm front will move north of the region on Thursday. With
the wedge gone, temperatures will warm into the mid to upper 70s
across the mountains and lower 80s east of the Blue Ridge. A
cold front slides across the region Thursday night into Friday
morning. Mostly showers will accompany the front, but a few
rumbles of thunder are possible. Temperatures Friday afternoon
will be slight warmer than normal, mid to upper 60s west to mid
to upper 70s east. High pressure builds in Friday afternoon and
will keep the area dry until Sunday. A closed low tracking east
from the Midwest is expected to bring strong to severe storms to
the area Sunday. Models differ on the track of the upper low
but agree on timing for Sunday. This weekend`s temperatures will
depend on the timing and track of the low. For now, we will
keep temperatures near guidance which is near normal.
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
As of 714 PM EDT Monday...
Ceilings/visibilities mainly VFR, outside of a temporary MVFR
shower at Blacksburg and Danville through 01z. VFR is generally
maintained through 04z, with lowering MVFR ceilings at Danville
and perhaps as far west as Blacksburg, Bluefield and Roanoke
after 04z. This is from a building ridge of high pressure to our
north with associated easterly flow allowing for potential for
MVFR ceilings. That said, confidence is medium to low on
ceilings overnight; feel lowest ceilings by morning would be
mainly along the southern Blue Ridge away from any TAF sites.
Winds generally light and variable (though will trend north to
northeast) through 04z, with light east winds overnight.
Should see continued BKN/OVC VFR/MVFR into Tuesday. Ongoing
clouds and rain will likely lead to continued obscured mountains
in the North Carolina high country. Rain shield makes some
northeastward advance into Blacksburg and Bluefield near the end
of the valid TAF period, with potential MVFR ceilings/visibilities
at these two TAFs. Should see easterly winds increase to speeds
around 4-8 kts Tuesday.
Extended Aviation Discussion...
Surface high pressure will wedge southwest into the area later
Tue-Wed resulting in a more stable air mass and allowing the
front to be pushed a little further south, thus no threat for
convection during the Tue-Wed period with the possible exception
of KBLF late Wed. Some showers could get as far north as KDAN
late Tues perhaps resulting in MVFR conditions but at this time
they appear more likely to remain to the south.
By Thursday, the front will return north as a warm front as a
new front approaches from the northwest once again. Showers and
thunderstorms will be on the increase Thu-Fri as this front also
drifts into the area and stalls. This front will return to the
north as a warm front Saturday as a much stronger weather system
moves into the southeast U.S. Between the wedge Tue-Wed and the
frontal systems in/near the area through the week, multiple and
extended periods of sub-VFR aviation conditions are expected
through the week, but most likely by later in the weekend.