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Area forecast discussion 
National Weather Service Blacksburg Virginia
702 am EDT Mon Jul 25 2016

strong high pressure aloft will continue to result in hot and
humid weather early this week. A weak cold front approaching from
the north should bring increasing chances of showers and
thunderstorms over the mountains today, and across the region on
Tuesday. This boundary looks to linger over the area through the
rest of the week with added showers and storms possible each day.


Near term /through tonight/...
as of 300 am EDT Monday...

Upper ridge will continue to hold for the most part for one more day
before slowly weakening/flattening overnight as shortwave troughing
passes to the north. This continued subsidence along with progged 850
mb temps of around +24c espcly east will make for another very hot
afternoon. Still appears that dewpoints may again fall with mixing
later on but given more of a southwest trajectory and slowly rising
pwats, may see values out east stay a bit higher than the last few
days. This supports, espcly for impact, keeping the heat advisory
headlines going where in place with indices even around 100 back west
to the Blue Ridge. Expect actual high temps again in the 95-100 range
just east of the Blue Ridge, per latest slightly higher forecast
thickness, with 87-92 west where a bit more cloudiness and convection
could occur. Again appears that bcb and blf have the best shot at
high temp records today.

Expanse of afternoon shra/tsra still a bit iffy given faint late day
cooling aloft far west/NW and slightly better moisture under strong
instability/Theta-E. However forcing to remain well to the north closer
to the upstream front with orographics aided convection more likely
espcly I-77 corridor and perhaps southern Blue Ridge to start. Expect
some of this to slowly spread North/East with possible better
coverage and stronger storms affecting the far north late where
closer to the front/wave per latest WRF/cam solutions. Otherwise still
mainly chance pops with little coverage southeast where will
remain under the ridging aloft for now.

Boundary sinks southward to just north of the area late tonight with
the axis of higher pwats and weak lift strung out from the western
slopes to across the north overnight. This may allow a corridor
for added convection to track along espcly during the evening
given likely leftover cape from such a hot afternoon. This seen in
a few models in showing weak low level convergence under
diffluence aloft far west and along the swath of higher Theta-E
exiting the east. Will also have more shearing energy aloft across
the north along the bottom of the passing mid level trough, so
likely need to keep some pops in north-west overnight. Otherwise
partly to mostly cloudy and very muggy/warm with lows mostly in
the 70s, except for a few 60s in the cooler valleys, including
where earlier showers occurred.


Short term /Tuesday through Thursday night/...
as of 330 am EDT Monday...

The frontal boundary will wash out across the area tonight, then linger
across the region through the middle of the week. Meanwhile quasi zonal
flow aloft will keep pieces of short wave energy streaming in our
direction, followed by a more significant short wave that will Bend the
flow to more of an eastern trof by the end of the week. There are also
indications that we will be in the right rear quad of a series of jet
streaks moving by to our north, providing US with some enhanced
synoptic lift. This all makes for unsettled weather with a good chance
for thunderstorms through midweek. Individual upstream short waves will
play a large role in triggering and maintaining convection but there is
too much uncertainty to get very specific deep into the forecast, so
will bias the pops with a typical diurnal peak in the late afternoon
and will linger activity a bit linger into the night time periods.

While there will be ample instability to support vigorous convection,
the absence of significant shear will continue to limit our chances for
large scale organized severe weather, making pulse storms/clusters our
main threat. Pwats will also be climbing into the 1.5 to 2 inch range
so locally heavy rain will be an increasing concern, though the warm
and relatively dry antecedent conditions will be a limiting factor.

Temperatures will continue to a few degrees above normal through the
period. Highs will be in the low to mid 90s east of the Blue Ridge with
mid/upper 80s to the west.


Long term /Friday through Sunday/...
as of 315 PM EDT Sunday...

Amount of troffing in the eastern United States for the end of
the week is questionable. GFS was the more amplified while the
European model (ecmwf) was slightly flatter. Friday looks to be the next day with
any potential for decent upper support. Will have the higher
probability of precipitation on Friday and Saturday afternoon and


Aviation /12z Monday through Friday/...
as of 640 am EDT Monday...

Other than for patchy fog/stratus in the valleys, mainly VFR to
start this morning under increasing high cloud canopy that will
likely be over the region this morning. Thus may need to include
brief IFR/MVFR at klwb/kbcb pending release observations.

Otherwise ridging aloft will remain in place today with a bit
better low level convergence developing over the mountains in the
afternoon ahead of a weak cold front to the northwest. This should
lead to a scattered to broken VFR cu field by afternoon with cigs
most likely across the far west where moisture is a bit better.
Also given strong instability would expect somewhat better tsra
coverage mainly west of the Blue Ridge during the afternoon, with
perhaps some of this shifting slowly east by late in the day.
Still overall coverage appears scattered to widely scattered but
more clustering potential mountains given slow movement. Thus
confidence remains high enough to keep thunderstorms in the vicinity at most western sites
including kblf/kbcb and possibly klwb by mid to late afternoon at
this point.

Despite loss of heating the approach of an upstream cold front and
leftover instability/outflow may keep at least isolated convection
going into late this evening. Looks like best coverage would be
across the north and west but too iffy to include additional
shra/tsra mention into late tonight for now. Otherwise should
return to VFR outside of any leftover tsra this evening prior to
patchy fog formation again late.

Extended aviation discussion...

Ridge will finally weaken through mid week as an initial cold
front sinks toward the area from the northwest. This should bring
about an increase in daily convective coverage Tuesday into
Friday with periodic MVFR/IFR possible especially Tuesday
afternoon and again Wednesday pending exactly how far south the
front makes it. Late night and early morning fog will likely
occur at the usual valley locations, and those chances increase
across the entire region if any rain occurs during the afternoon
or evening at any site.


record high temperatures for Monday (7/25)

Roanoke.....100 in 1934
Lynchburg...102 in 1934
Danville....102 in 2010
Blacksburg...92 in 1987
Bluefield....90 in 1987


Rnk watches/warnings/advisories...
Virginia...heat advisory from noon today to 8 PM EDT this evening for


near term...jh
short term...mbs
long term...ams/mbs

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