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Area forecast discussion 
National Weather Service Blacksburg Virginia
902 am EDT Friday Jul 31 2015

high pressure will extend eastward from the lower Missouri Valley
into the middle Atlantic today providing lower humidity. This high
will stay over most of region this weekend. A couple of upper
disturbances may bring a few spotty showers to the mountains late
Saturday or Sunday...but the majority of our area will stay dry.


Near term /through tonight/...
as of 900 am EDT Friday...
made some minor adjustments in isc grids to lift morning fog. Also
modified temperatures and dew points for latest surface
observations and trends. Thursdays frontal boundary has push
southeast of forecast area. In its wake...high pressure will
build east across this afternoon into tonight. Enjoy the great
weather !

As of 720 am EDT Friday...

Patchy fog over the southeast WV valleys will fade by 9 am.

High pressure centered over Kansas this morning will extend eastward
into our area today while the cold front tracks to the Outer Banks.
Expect to feel a less humid air mass today with dewpoints dropping
into the 50s over the mountains to lower to middle 60s southeast.
Should be mainly sunny though a few cirrus should ride the upper
trough axis into the middle Atlantic from time to time. A northwest low level
wind flow will help to bring temperatures up in the Lee of the still looking at seasonal norms for highs...ranging
from around 80 over the near 90 southeast.

Tonight...the flow starts to back to the west as a weak upper
shortwave pivots under the broad trough across the middle Atlantic. At
this time...will see a few clouds but no rain we stay
in the drier air mass. Some MOS numbers have the deeper valleys
and/or higher valleys approaching 50 degrees late tonight...Burkes
Garden for instance. Expect this will occur if we decouple and that
should happen with high pressure overhead. Therefore...will go with
lows in the deeper valleys in the lower to middle upper 50s to
lower 60s elsewhere.


Short term /Saturday through Monday night/...
as of 230 am EDT Friday...

Large upper level troughing...centered over Hudson expected
to hold in place through the period...keeping the middle Atlantic
situated in west northwesterly upper level windflow. Couple that
with dry high pressure across the Tennessee Valley...and we can
expect mainly dry conditions under mostly clear skies through the
Saturday to Monday timeframe. The exception will be Monday evening
as forecast models are hinting at another cold front sinking
southward from the Great Lakes...triggering an increase in shower
and thunderstorm activity. That support for rainfall
will remain north of the area...and will maintain low rain chances
for now on Monday night.

High pressure will bring with it lower humidity...making for more
comfortable afternoons. Abundant sunshine and light downslope
windflow will keep afternoon high temperatures similar each day...
ranging from a few upper 70s to the middle 80s across the mountains...
while the Piedmont will climb into the upper 80s/low 90s.

The effects of the drier air will be more noticeable at night.
Strong radiational cooling Saturday night will push overnight lows
into the middle/upper 50s most spots across the mountains...and the low
60s across the Piedmont. With cold air drainage...would not be
surprised to see a few reports of middle/upper 40s come from a few of
the deeper mountain valleys. Overnight temperatures will warm 2 to 4
degrees each Sunday and Monday nights as the airmass modifies.


Long term /Tuesday through Thursday/...
as of 1230 PM EDT Thursday...

Mean 500 mb trough to remain across the middle Atlantic region through much of
next week with steady northwest flow aloft between upper level low pressure
well to the north and strong ridging over the SW states. This should
allow for an overall persistence type forecast through the extended
with tolerant humidity levels along with lows mostly in the 60s and
highs 80s to lower 90s. Coverage of showers and storms also likely
limited pending progression of the next possible cool surge late in the
period. However will also have to watch lingering moisture with the
residual front near the coast which could be lifted back north by
approach of weak impulses aloft especially early next week. This along
with heating may be enough to spark isolated convection along a
passing shortwave trough axis crossing from the northwest Tuesday...but
low probability of precipitation at best.

Upper trough just north of the lakes will deepen again by midweek as
more shortwave energy rotates through and slides an associated cold
front south toward/into the region. However models disagree on the
amplitude of the digging trough with the GFS most aggressive while
other solutions slower/weaker while maintaining more convection along
the boundary. For now will go with a weaker/slower scenario but lean
toward the GFS in driving the cool advection in by the end of the
period since it has been best of late.


Aviation /13z Friday through Tuesday/...
as of 719 am EDT Friday...

VFR to prevail over taf sites this period. Exception will be lwb
where dense fog will burn off by 13z.

Extended aviation forecast...

Mainly VFR this weekend with high pressure in place. A few upper
disturbances may bring a few VFR ceilings to the mountains later
Saturday into Sunday. The threat of showers will be low though a
backdoor front may allow for some again later Monday or Tuesday.
With sustained winds staying light to calm at night and mainly
clear skies...the fog threat will exist in the typical predawn
hours at lwb/bcb by early next week.


Rnk watches/warnings/advisories...


near term...kk/wp
long term...jh

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