Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 260729

Area Forecast Discussion
National Weather Service Blacksburg VA
329 AM EDT Wed Oct 26 2016

Cool high pressure will remain wedged along the eastern slopes of
the Appalachians today before weakening and sliding east tonight. Low
pressure crossing the Great Lakes will push a cold front through
the region later Thursday and offshore Thursday night. High
pressure follows the front for the end of the week.

As of 245 AM EDT Wednesday...

Weak wedge of high pressure along the eastern slopes of the
mountains will linger today before slowly weakening and pushing east
tonight in advance of the next upstream cold front. This should
continue to keep overall quiet weather in place today although the
degree of cloud cover espcly north/west remains iffy despite dry air
in place. Latest guidance tending to gradually lift the shear axis
responsible for the ongoing streak of mid deck across the north out
of the area this afternoon as deepening warm advection aloft works
in from the southwest. However as this canopy erodes, expect to see
more in the way of sheared mid/high clouds advect in from the west
as weak shortwave ridging across the region slowly breaks down. This
looks to translate to more periodic cloudiness north and west with
more sun southern/eastern sections overall.

With the low level wedge deeper across the east under the lingering
cooler 850 mb cool pool, but weaker far west per increasing warm
advection, appears warmer highs west/southwest sections where
likely to reach well into the 60s. Otherwise should be cooler
than the last few days given light east/southeast flow, with
potential for northeast sections to stay in the 50s, while slowly
recovering into the low 60s elsewhere pending clouds.

Weak surface warm front will be lifting northeast through the area
overnight allowing deeper southwest flow aloft to take shape as the
eastern wedge slowly departs late. Models show much of the region
still removed from deep moisture which will remain west of the
ridges and closer to the cold front that will lag back in the
Ohio Valley around daybreak. Also little in the way of lift with
perhaps some warm advection driven low clouds developing over the
south/east, with more in the way of a mid deck canopy over the
west after midnight per latest forecast soundings. However much of
the sub cloud layer over the mountains appears quite dry, so
removing most going pops overnight and trending more in the way of
increasing clouds at this point.

Low temps tricky with potential to see readings quickly drop over
the west this evening before rising with clouds/mixing increasing.
Expect the overall coldest lows out east where still under the
residual surface ridge and likely to see less overall cloud cover
until late. Therefore trending toward a more non diurnal temp
curve mountains where the ridges could bounce back into the 50s
overnight. Otherwise overall lows in the 40s except a few 30s
valleys early, and outlying areas in the east during the early
morning hours.

As of 330 AM EDT Wednesday...

A fairly vigorous short wave will move through the Great Lakes and into
the middle Atlantic region on Thursday. This will push a surface low
from the Lakes well into New England with the trailing cold front
moving through the Appalachians. A bit of a spread has developed in
solutions with this system, but there is still consensus in keeping the
best dynamics well off to our west and north. The overall trend is for
lower POPs on Thursday with the best chances for precipitation west of
the Blue Ridge mainly up towards western Greenbrier county. Mid level
lapse rates have cooled a bit more since previous runs so a slight
chance for thunder seems reasonable especially west. All in all this
looks like a rather dry FROPA that will continue our overall dry
pattern. The low level wind field will be energized and good mixing
with the front will make for some blustery conditions Thursday into
early Friday before winds relax Friday afternoon. A quasi zonal upper
pattern will then keep high pressure in place at the surface with quite
warm conditions expected into the first part of the weekend.

Temperatures east of the Blue Ridge will start the period near normal,
then steadily warm to well above normal with highs generally in the
middle 70s by Saturday. Locations west of the Ridge will see a brief
cool down behind the front on Friday, but then warm to above normal on
Saturday with highs in the low/mid 70s.

As of 250 PM EDT Tuesday...

Low pressure over the Great Lakes will travel northeast across
New England Sunday and push off into the Atlantic Sunday night. A
nearly dry cold front associated with low center will move south
across our area. The richest moisture along with most of the
convections remains north of our area. The ECMWF remains stronger
further south with shortwave compared to GFS. This difference
effect the timing of frontal passage. High pressure will settle
south for the end of the weekend into early next week.

Temperatures may cool behind the front Sunday especially in the
northwest, but for most areas will remain above normal into early
next week.


As of 1255 AM EDT Wednesday...

Band of mid/high clouds will continue to affect the northern third
of the region, primarily from KLWB to KLYH overnight where will
see periods of bkn altocu into Wednesday morning. Some periodic
mid deck may also spill off into KBLF/KBCB/KROA corridor, otherwise
VFR expected overnight. High and mid clouds may continue to spill
into the region during Wednesday with some Cu around although
still appears VFR as winds turn more east/southeast Wednesday
afternoon. High pressure across eastern sections weakens Wednesday
night ahead of an approaching cold front that will remain west of
the mountains into early Thursday. Expect some added mid/high
cloud canopy into Wednesday night while deeper moisture remains to
the west allowing for continued good flying conditions overnight.

Extended aviation discussion...

Thursday...Low pressure is forecast to move across the upper
midwest and into the Great lakes with a surface front crossing the
Ohio Valley. Threat for showers and sub-VFR will be possible along
this front which would impact the central Appalachians by Thursday
afternoon. However given best support passing to the north and
limited moisture, expecting best potential for lower cigs/vsbys to
occur across the western mountains and across northern portions of
the area at this point.

High pressure builds in from the northwest Friday, with potential
MVFR ceilings at KBLF/KLWB Thursday night before the high
arrives. Another cold front will approach from the north on
Saturday and pass through the region Sunday with possible showers
and MVFR ceilings mainly in the mountains. However, models were
still showing differences in the timing of the weekend system with
potential for showers to stay mainly north of the region.




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