Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KRNK 251748
Area Forecast Discussion
National Weather Service Blacksburg VA
148 PM EDT Mon Jul 25 2016
-- Changed Discussion --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 this afternoon, 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.
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.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 100 PM EDT Monday...
Increased pops for this afternoon matching closer to HiResw-arw
and the NAM. Regional WSR-88d showed scattered convection forming
across the mountains in the unstable air with li around minus 4.
more changes later this afternoon...
As of 956 AM EDT Monday...
Made some minor adjustments in temperatures for this morning into
this afternoon utilizing sfc obs,and their trends, then leaned
temperatures towards lamp guidance. As supported by Highres
models, allowed for some isolated cooling convection, mainly in
the mountains. May still have to adjust pops up for this afternoon
depending on the evolution of convection early this afternoon.
There is a slight risk to our north across northern West Virginia
and northern Virginia associated with shortwave rotating east.
Another hot and humid afternoon expected...with high temperatures
ranging from the mid 80s in the mountains to around the century
mark in the Piedmont. Heat advisory look good with heat indices
as high as 105 in the far east. More changes later...
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.
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.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
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 /18Z MONDAY THROUGH SATURDAY/...
-- Changed Discussion --As of 148 PM EDT Monday...
SCT to BKN MVFR clouds this afternoon with isolated to widely
scattered IFR conditions near thunderstorms. Ridging aloft will
remain in place this afternoon into tonight, with a bit better
low level convergence developing over the mountains ahead of a
weak cold front to the northwest. Given strong instability would
expect somewhat better tsra coverage mainly west of the Blue Ridge
this 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
Will keep VCTS at most western sites including KBLF/KBCB and
KLWB this afternoon into tonight. Added the mention vcsh for KROA
with nearby convection.
Despite loss of heating the approach of an upstream cold front and
leftover instability/outflow may keep at least isolated convection
going this evening into tonight. The best chance for any storms
will occur across the north and west. Otherwise should return to
VFR outside of any leftover tsra this evening prior to patchy fog
formation again late.
Ridge is slowly breaking down Tuesday with scattered MVFR/IFR showers
and thunderstorms possible mainly during the afternoon and
Medium to high confidence in ceilings, visibilities and winds
during the taf period.
Extended aviation discussion...
The ridge will 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 late afternoon
and evening into Friday with periodic MVFR/IFR possible depending
on 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.
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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
VA...Heat Advisory until 8 PM EDT this evening for VAZ046-047-058-