Scientific Forecaster Discussion
fxus61 krnk 251409
Area forecast discussion
National Weather Service Blacksburg Virginia
1009 am EDT Tue Jul 25 2017
a weak stationary front across northern North Carolina will
remain in place this afternoon before sliding to the south
overnight into Wednesday. High pressure building north of the
region should keep overall dry weather in place through midweek.
Another cold front approaches from the northwest Thursday into
Friday exiting to our southeast by Saturday morning.
Near term /through tonight/...
as of 955 am EDT Tuesday...
Surface front has dipped into far southern sections this morning
with much drier air aloft working in from the northwest as seen
in the latest water vapor loop. This along with continued weak
dry advection under light low level northerly flow should keep
things mainly dry through the afternoon under mostly sunny skies
once any lingering western low clouds fade. Only exception
perhaps will be near the front over northwest NC where guidance
shows a sharp instability gradient and enough residual low level
moisture under a weak passing wave to possibly spark a shower
to two with heating. However many short term solutions remain
basically dry with most convection just south of the cwa, so
only keeping in isolated pops where ongoing for now. Otherwise
expect subsidence in conjunction with very dry air aloft per the
morning rnk raob to make for a little more comfortable
afternoon with heat and humidity down a bit behind the front.
This along with morning thickness supports highs mostly 80s
mountains, to upper 80s to lower 90s from the Blue Ridge east.
Previous discussion as of 320 am EDT Tuesday...
Have a little fog/low clouds banked up across southern WV into the
mountain Empire where an inverted sfc trough lingers.
Expect these clouds/fog to erode after 8-10am.
High pressure will bring drier airmass/dewpoints to much of the
region today, with models showing deeper moisture shunted south of
our forecast area. Still enough of a gradient plus some return flow
and inverted trough along the southern Appalachians to maybe
generate isolated storms across the NC high country possibly moving
into the NC foothills this afternoon.
Otherwise enough subsidence for overall mostly sunny skies with
highs low/mid 80s mountains to upper 80s to around 90 east of
the Blue Ridge.
Any convection weakens and shifts out of our ares this evening with
skies staying generally clear. High pressure will be over New
England late Tuesday night so some return flow may still generate
lower stratus/fog along the southern Appalachians, but overall
confidence is low and another day of drying should limit this. Lows
running close to normal with upper 50s to lower 60s mountains, to
mid to upper 60s east of the Blue Ridge, but including Roanoke-
Short term /Wednesday through Thursday night/...
as of 330 am EDT Tuesday...
High pressure over New York Wednesday morning will slide east in the
Atlantic Ocean Wednesday night into Thursday. Some weak orographic
lift may combine with solar heating to create isolated to scattered
diurnal showers and thunderstorms mainly along the southern Blue
Ridge. High temperatures Wednesday will range from the the mid 70s
in the mountains to the mid 80s in the Piedmont. Any convection
will taper off quickly Wednesday evening with loss of solar heating.
Under partly cloudy skies, low temperatures Wednesday night will
vary from around 60 degrees in the west to near 70 degrees in the
east. Low pressure with a trailing cold front will move east across
the Ohio Valley Thursday into Thursday night. The timing looks a
little faster than yesterday. Thus, increased pops on Thursday and
bring likely into the western mountains Thursday night. High
temperatures on Thursday will climb to around 80 degrees in the
mountains to about 90 degrees in the Piedmont. Storm Prediction Center has placed most
of the forecast area in a slight risk for severe weather Thursday
afternoon into Thursday evening. The main threat is for fast moving
bands with damaging winds. Also, any thunderstorm could produce
locally heavy rains. With clouds and rain, low temperatures
Thursday night will generally be in the mid 60s in the mountains to
the lower 70s in the Piedmont.
Long term /Friday through Monday/...
as of 1245 PM EDT Monday...
Upper pattern amplifies starting on Friday with the upper ridge over
the western United States slightly retrograding and a trof digging
in the east. An upper low may eventually close off somewhere over
the Tennessee Valley or mid Atlantic region by Sunday or Monday.
This closed low solution was not supported by a majority of the
extended guidance. Probability of showers and thunderstorms will
increase on Friday and Saturday with some vorticity advection and
lowering heights. Air mass ahead of the trough stays in the +16 to
+20 range for temperatures at 850mb and will be a little cooler on
Sunday and Monday.
Aviation /13z Tuesday through Saturday/...
as of 702 am EDT Tuesday...
Only area with sub-VFR conditions is blf and cigs are starting
to rise to MVFR. Should be VFR by 14z, with all sites staying
VFR through the period thanks to high pressure working southward
from the Great Lakes into New York. Any storms this afternoon
will be isolated and stay confined to the mountains south of
hlx-vji. Winds are going to be light, from the northwest most of
Fog threat late tonight expected to be light, so kept it out of
the tafs for now, with best chance of fog in the typical spots
like lwb. If enough of an east wind arrives, fog forming over
the Greenbrier River could push into lwb after 09z.
Aviation extended discussion...
Should stay VFR under high pressure into Wednesday though some
sct-bkn VFR cigs possible in the mountains (blf-lwb-bcb).
Should start to see front approaching with better threat of
showers/thunderstorms Thursday into Friday. Outside of storms
expect VFR conditions, with possible late night fog by Friday
Saturday looks drier with northwest flow, but could see
lingering low end VFR/high end MVFR ceilings in southeast WV.
as of 345 am EDT Tuesday...
The temperature sensor on the observing equipment at Lynchburg
has failed, therefore no temperature data will be available
until technicians can replace the defective part later this