Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 201951

Area Forecast Discussion
National Weather Service Blacksburg VA
351 PM EDT Wed Jul 20 2016

High pressure was over the mid Atlantic region today and will
remain over the area through Thursday night. Two weak cold fronts
will approach the area later this week into early next week. The
first front crosses the Ohio valley and northeast United States
on Friday night and Saturday, and the next on Monday night and


As of 345 PM EDT Wednesday...

Good mixing has lowered dew points into the 50s over the mountains
this afternoon. Water vapor loop showed a pocket of mid level dry
air over the Carolinas today. Environment is dry and stable
enough to keep precipitation out of the forecast until Thursday
afternoon. Hi-res NMM guidance had a reasonable placement along
the southern Blue Ridge after noon for the most likely area where
isolated thunderstorms will develop. Temperatures will be near
normal tonight and Thursday.


As of 330 PM EDT Wednesday...

Will be increasing maximum temperature on Friday based on rising
500mb heights and forecast 850mb temperatures around +22C. Heat
index values will be at or just above 105 in the far eastern
county warning area on Saturday afternoon.

A cold front will move gradually south through Ohio and Pennsylvania
on Friday night and may continue to drift into Virginia on Saturday.
While the front may not be much of a change of air mass it will be
an area of better low level convergence and deeper moisture and when
combined with the upper support will result in an increases
probability of showers and thunderstorms. Even without the boundary
passing south of the forecast area, it will be close enough that
convergence along the boundary or along outflow boundaries will aide
in storm initiation. Precipitable water values are back up over 1.0
inch on Friday afternoon then closer to 1.75 inches on Saturday.


As of 230 PM EDT Wednesday...

Upper ridge will extend from coast to coast Sunday through
Wednesday. In the northern stream the next synoptic scale wave
crosses through the northeast United States on Tuesday. Models were
similar bringing moisture back into the region on Monday and Tuesday
ahead of the front. Therefore this will be the time frame with the
highest probability of showers and thunderstorms.


As of 215 PM EDT Wednesday...

With some upper level short wave energy moving through the region
in northwest flow aloft combining with diurnal instability,
believe Cu field will be rather extensive but remain essentially
as sct/v/bkn with VFR heights. There may be an isolated
shower/storm along and east of the Blue Ridge but coverage will
not warrant any mention in TAFs. NAM has been an outlier solution
in generating convection across the piedmont into early tonight
but currently do not see a lot of support for this as the best
instability will likely be further to the south and east. Will
continue to monitor to see if later runs of meso models start to
support something along these lines, and may adjust KDAN and KLYH
if needed.

Surface high will be sliding off to our east and return flow of
moisture will be working in from the east. With good radiational
cooling expected this will aid in fog formation and there is the
possibility of some lower clouds working in across the piedmont.
Will advertise SCT lower clouds overnight at KLYH and KDAN but
these clouds may need to be increased/lowered if clouds are more
robust than anticipated. Fog will generally be MVFR with a tempo
to IFR at KLWB and KBCB, and no OBVIS currently expected for KROA.
After any fog/stratus burns off, Thursday looks to feature VFR
conditions with the possibility for diurnal convection mainly from
the Blue Ridge eastward.

Winds will be light through the period.

Extended aviation discussion...

Strong high pressure aloft will move east across the region
into next weekend. Cannot totally rule out an isolated storm
each afternoon/evening through the period but appears overall
VFR outside of the typical late night valley fog in spots. Hot
and humid conditions east of the Blue Ridge this weekend which
may impact density altitude, and also slightly better thunderstorm
chances across the Appalachians.




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