Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
323 PM EDT Monday Jul 6 2015
an upper low over region will weaken and shift northeast tonight.
A cold front approach from the northwest Tuesday into Tuesday
night. The front is expected to stall just north of the region by
Wednesday...then lift back north as a warm front late in the
week...as high pressure aloft builds across the southeast states.
Near term /through Tuesday/...
as 323 PM EDT Monday EDT...
An upper low and associated weak surface low over the region will
lift northeast tonight. Scattered showers and a few thunderstorms
will continue to move northeast across our area this afternoon into
tonight. Some of the storms could contain locally heavy rains.
Overall areal coverage looks too limited to support Flash Flood
Watch. Als0 can not completely rule out a strong storm in the
east...but the best instability...MLCAPE values of 500-1000 and
forcing are northeast of our area. This is highlighted in the day 1
convective outlook from Storm Prediction Center with a marginal risk of severe
thunderstorms with gusty winds the main threat. Convection will
diminish this evening with loss of solar heating and upper low
lifting away. With some clearing...added the mention of fog to
grids overnight. Low temperatures tonight will range from around
60 degrees in the mountains to the upper 60s in the Piedmont.
A cold front will approach our region from the Ohio Valley on
Tuesday. Cloud cover will increase ahead of the boundary. Allowed
for isolated probability of precipitation of convection in the west Tuesday afternoon.
However...most areas will be dry for Tuesday. Southwest flow will
boost high temperatures into the upper 70s in the northwest
mountains to the lower 90s in the Piedmont.
Short term /Tuesday night through Thursday night/...
as of 320 PM EDT Monday...
Strong cold front by July standards will approach the forecast area
from the northwest Tuesday night. In spite of the progressive
flow...the front is expected to stall just north of the region per
building heights associated with high pressure aloft across the
southeast Continental U.S.. result will be for our forecast area to remain on
the warm/moist side of the front...and subject to daily threat for
Models are in agreement that convergence along the front will
provide track for organized deep convection with marginal risk for
severe weather per faster westerlies aloft near the frontal zone.
Increasing instability outside of the higher wind envelope will also
support pulse strong-severe storms during the peak heating
Wednesday...and possibly Thursday pending extent of warming aloft
associated with the building upper level ridge. Forecast for the
forecast area will reflect higher probability of precipitation across the northern County Warning Area
closer to the front...and to a much lesser degree across the
south...across our NC counties.
Temperatures for middle week will favor above normal readings per
increasing heights/thicknesses and a westerly wind component which
should aid in adiabatic warming east of the Blue Ridge. With 850 mb
temperatures approaching +20 degree c...surface reading should easily climb
well into the 80s and possibly the l-M 90s pending sunshine.
Minimum temperatures will also average above normal...per the high
moisture content of the atmosphere.
Long term /Friday through Monday/...
as of 200 PM EDT Monday...
Models are in agreement the subtropical ridge that builds over the
southeast states for middle/late week will retrograde toward
Texas/Oklahoma for the weekend then expand northwest into The
Rockies for the first part of next week...July 13-17. Short wave
energy which will initially traverse the northern tier states this
week with an active frontal zone to our north...will begin to track
farther south over the weekend as the upper ridge wanes over the
eastern Continental U.S.. as troughing aloft increases...expect frontal
boundary to drift south over the region providing a better
opportunity for showers/storms in addition to more cloud cover and
lower daytime high temperatures.
Have not been able to identify any given day where we could
completely remove threat for showers/storms...thus entire extended
period of the forecast will reflect daily chance of showers.
Temperatures...although nothing extreme...will favor the warm side
of guidance this weekend...then retreat to something near or just
below normal for the start of the following week.
Aviation /19z Monday through Saturday/...
as of 136 PM EDT Monday...
MVFR scattered to broken clouds with pockets of IFR/LIFR in convection this
afternoon into tonight. Overall best coverage of showers and
thunderstorms this afternoon into tonight will be in the northeast
portion of forecast area.
The upper shortwave/low pivots northeast into pennnsylvania later
tonight. Showers/storms will diminish or dissipate this evening with
VFR expected early before potential fog rolls in overnight.
Locations which received rainfall this afternoon will have a good
chance of fog overnight. Taf sites will the potential for fog are
lwb...bcb and lyh after midnight local time.
A cold front will approach from the Ohio Valley by Tuesday night
into Wednesday. Between these two systems will be a longer period
of VFR weather on Tuesday. This front is expected to stall just north
of the region per building heights associated with high pressure
aloft across the southeast Continental U.S.. south of the boundary...we will
remain on the warm/moist side of the front...and subject to daily
threat for MVFR showers/storms.
Medium to high confidence in ceilings...visibilities and winds
during the period.
Extended aviation discussion...
Once the front stalls across or just north of the area on
Wednesday...periods of showers and thunderstorms will continue
with sub-VFR conditions through the end of the week.
Expect widespread late night/early morning low clouds/fog with
IFR-LIFR cigs/vsbys. Overall...conditions should improve to MVFR-
VFR outside rain showers/thunderstorms and rain activity during the afternoons.