Scientific Forecaster Discussion
fxus61 krnk 261125
Area forecast discussion
National Weather Service Blacksburg Virginia
725 am EDT Wed Jun 26 2019
high pressure will cover our area through the reminder of the
workweek bringing mostly dry weather. The next chance for
showers and thunderstorms will be associated with a cold front
that arrives later in the weekend.
Near term /through tonight/...
as of 230 am EDT Wednesday...
Other than some River Valley fog early this morning, tranquil
weather conditions are forecast through the near term period
with building heights aloft and high pressure at the surface.
This has lead to some usually dry conditions, with the 0.68 precipitable water
value from the 00z/26 rnk sounding near the 10% minimum moving
Very few changes were made to the forecast for today, other than
to increase cloud cover across the area, especially across the
southern portion of our region from a veil of cirrus to our
south and west. These clouds may keep highs from reaching their
full potential in the south today, but with 1000-850mb thickness
surging upward, highs should be a few degrees warmer today
compared to Tuesday, especially in the mountains.
Confidence is low on how this canopy of high cloudiness will
impact lows tonight, with most models pushing the high clouds
into our NC. As a result, kept lows tonight on the warm side of
guidance in and near this region, such as Dan, but went below
guidance for many of the mountain sites closer to the sfc ridge
axis. Areas of valley fog will again be possible late tonight.
Short term /Thursday through Saturday night/...
as of 230 am EDT Wednesday...
A broad upper level ridge will span the United States east of the
Rocky Mountains for Thursday and Friday. While the ridge aloft and
surface high pressure should keep the atmosphere mostly capped, the
mesoscale models indicate that a couple showers and thunderstorms
may fire along the southern Blue Ridge on Thursday. The chances of
convection increase slightly by Friday as the heat and humidity
gradually increase, and the areal coverage could expand to all
locations along and west of the Blue Ridge. Meanwhile, it may remain
dry east of the foothills during these two days.
By Saturday, an upper level trough and an associated backdoor cold
front will dip southward over the northeast. As it approaches, this
extra dynamical support combined with the heat and humidity could
allow the cap to more notably weaken. While some model differences
still exist on how much that could increase the extent and intensity
of any developing convection, confidence is modest enough to paint
slight chance to chance pops across the region. Following the same
pattern that is depicted in prior days, the best chance for
thunderstorms should be along and west of the Blue Ridge.
Overall, high temperatures will run around five degrees above normal
for this time of year. Lower 80s to lower 90s should persist
throughout this period. Low temperatures should hover near normal
during Thursday night and Friday night with upper 50s to upper 60s
expected. However, these lows will gradually increase toward above
normal territory as dewpoints increase into the weekend. Most
locations will likely not drop below 60 degrees by Saturday
Long term /Sunday through Tuesday/...
as of 345 PM EDT Tuesday...
Expect upper level ridging across the central United States
toward the end of the week, resulting in northwest windflow
aloft across the mid-Atlantic. Given strong heating on Sunday,
will have to keep an eye on any disturbances approaching from
the Great Lakes region, which could trigger a line of strong
thunderstorms. Confidence on timing, track and even development
of these storms is low that far into the future. Chances for
thunderstorm activity do increase Sunday night however as a cold
front is expected to approach from the north, with the front
possibly entering and stalling across our area on Monday.
Aviation /12z Wednesday through Sunday/...
as of 735 am EDT Wednesday...
At 730 am EDT, LIFR cigs and vsbys were reported at klwb, with
VFR conditions at all other taf sites. These conditions will
rapidly improve with VFR conditions forecast for the entire
region between 13z (9 am edt) and 14z (10 am edt)
The combination of a weak surface ridge and zonal flow aloft will
allow for VFR continues to persist today and into this evening,
with scattered cumulus clouds in the mountains and a canopy of
high cirrus clouds overspreading the area later today. Winds
under 15 knots are expected.
Similar to early this morning, River Valley fog will again
develop late tonight/early Thursday morning, primarily along the
new and Greenbrier rivers and impacting klwb with IFR vsbys due
Extended aviation discussion...
High pressure is expected to take up residency over the region
into Friday. For the most part, VFR conditions are expected
outside of late night/early morning fog. Also, as we approach
the weekend showers and storms will be on the increase, and
these too may bring some temporary reductions to visibility and
Late Friday into Saturday, the chances of sub-VFR conditions
increase espcly across the mountains with heating of low level
moisture aided by orographics. The arrival of a backdoor cold
front late in the weekend should allow for an increase in
coverage of showers and storms by Sunday afternoon.