Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 240828

Area Forecast Discussion
National Weather Service Blacksburg VA
428 AM EDT TUE MAY 24 2016

Our stretch of cool weather will be coming to an end as high pressure
builds over the southeast United States and ushers much warmer air into
the region. Temperatures will be well above normal for most of the week
with highs by Thursday ranging from the upper 80s across the piedmont
to the lower and middle 80s west of the Blue Ridge. However along with
the warm temperatures will come increasing humidity and the chance for
afternoon showers and thunderstorms.


As of 430 AM EDT Tuesday...

After some dense valley fog burns off early this morning...the upper
low which has been with us for several days will still have enough
influence over our weather today to keep a just a slight chance of
showers across the region...especially far north and east...thanks to
the combination of diurnal instability and steep lapse rates in the
cold pool of air aloft. The prospects for thunder look to be very
limited indeed so will not include in the grids. As the day wears on
and the low continues pulling off to the northeast much warmer air will
begin to surge in from the southwest. This will give our temperatures a
much needed boost to slightly above normal...which should feel like a
tropical heat wave after our recent stretch of cool weather. Expect
highs today to reach the lower 80s east of the Blue Ridge with
generally middle and upper 70s to the west. Tonight looks to be quiet
with mostly clear skies and lows ranging from the middle and upper 50s
east to upper 40s and lower 50s west. There may also be valley fog
forming once again late tonight into early Wednesday morning.


As of 400 am EDT Tuesday...

Upper heights and 850mb temps continue to rise through the period
as the northeast U.S. upper low continues to lift northeast into
the north Atlantic and troughing deepens and shifts inland across
the southwest U.S. Upper heights across our region will be
nearing 588dm with 850mb temps averaging near +16C through the
period. This will result in much warmer temps than we have seen
over the past 14 days...with temps actually above normal through
the entire period...generally lows in the 50s to lower 60s and
highs in the 70s mountains and 80s elsewhere...nearing 90 across
the Piedmont.

Little if any synoptic-scale forcing is evident on Wednesday with
weak upper ridging in place...but all models depict an area of
moisture pooling across the Appalachians..typical of differential
heating across the mountains...which could yield isolated to
widely scattered afternoon showers/thunderstorms. Instability is
minimal at this with no dynamics...activity would be
diurnally driven and non-severe.

On Thursday...the pattern becomes slightly more interesting and
more active convectively speaking. While the region is still under
broad upper ridging...the southwest U.S. tough continues to shift
inland...but more importantly a notable short wave is ejected to
the northeast of the parent upper low into the TN/OH valley by
afternoon. The NAM hits the feature the hardest...but it is
evident via all of the longer range models. This increase in
forcing along with increased thermodynamics...should yield
scattered showers and thunderstorms...again largely diurnally

By Friday...the aforementioned disturbance has moved to our
northwest...but again a notable area of moisture pooling is
evident across the mountains...but the best area of such has
shifted slightly northwest from Thursday`s location. Of more
importance at this point is a potential tropical system apparent in
most models developing off the southeast U.S. coast. While all
models indicate this system in varying degrees...there are vast
differences in the track of such system...with the GFS most
aggressive in taking in inland into SC/NC...where it circulates
about into the weekend and early next week. This feature may serve
initially to induce increased subsidence across the south and east
portion of our CWA Friday...but beyond that...cannot hinge on any
one solution at this point.


As of 415 am EDT Tuesday...

As noted in the section conditions across the
region through the weekend and into early next week will depend
largely on the track...intensity...and evolution of a potential
tropical system moving from the Bahamas northwest into the
southeast states per GFS...or hugging the SC/NC coast line per
most other models. Clearly...the GFS solution would have a
significant impact on our region in terms of cloud cover and
precipitation...while other model solutions keeping the low track
closer to the coast...would result in more subsidence across our
region and minimal impacts. For sure temperatures will remain on
the warm side with no significant change in air mass underneath a
continuing large-scale ridge...with humidity levels high through
the period. Meanwhile...the western system remains mostly intact
across the western states while overall weakening and lifting more
north than east. Thus...outside a potential tropical system...the
pattern is becoming more-and-more summerlike than we have seen so
far this year. Look for a continuation of highs in the 70s
mountains and 80s elsewhere...with lows mostly in the 50s and 60s.


As of 145 aM EDT Tuesday...

We start the period a closed upper low continuing to spin off the
mid Atlantic coast. This will throw some mid/high clouds mainly
into the eastern sites with SKC expected elsewhere. However wet
antecedent conditions in the cool airmass and decent radiational
cooling will allow for some fog to develop. Expect the clouds will
limit fog to MVFR east but IFR/LIFR conditions are expected west.

Any fog/stratus will burn off early and we should see some widely
scattered showers develop with the cold pool aloft continuing to
generate steep lapse rates. The best chance for showers will
likely be near KLYH but will use VCSH at all sites to to cover
the low probability shower activity. Expect VFR conditions by
early this evening with the loss of daytime heating to drive

winds will generally be light through the period.

Extended discussion...

We will be going to a more summer like pattern mid to late week
with high pressure offshore providing south to southwest flow.
Thus, mainly VFR weather expected.

However, the potential exists for late night/early morning fog at
times around KLWB/KBCB and in some of the deeper mountain valleys.
Also some convection could pop up each afternoon in the mountains
Thursday into Saturday, making for localized afternoon/evening
MVFR restrictions.




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