Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
742 PM EDT Sat Aug 29 2015
a weak upper level disturbance will lift north along the Appalachians
Sunday into Monday...bringing a greater chance for showers and a few
thunderstorms to the region. Upper level high pressure will then
strengthen and keep US in a rather stagnant pattern...with a chance for
afternoon and evening showers and thunderstorms through the middle of
Near term /through Sunday/...
as of 730 PM EDT Saturday...
Showers are few and far between and not really seeing any on radar
in our County Warning Area...though some light returns are just south of the NC
mtns/foothills. Seems the threat will be a bit limited so cut back
probability of precipitation this evening..and tried to capture some of the hi-res arw as
it kept things dry over most of the County Warning Area.
Will be dealing with middle and high clouds through the night with
possible lower clouds in the west and middle part of the County Warning Area. This
will be obscuring for most folks the supermoon that is expected
Previous valid discussion...
Generally expecting low to middle 60s across the Piedmont to upper
50s/lower 60s west of the Blue Ridge. There may also be some fog
development in the valleys west of the Blue Ridge for areas that
manage to see any substantial breaks in the clouds.
Then after several days of little change in the synoptic pattern...a
closed low that has been spinning over the northern Gulf of Mexico will
be opening up and throwing short wave energy in our direction tomorrow.
Water vapor imagery also shows excellent moisture transport from the
Gulf which will boost our precipitable water values into the 1.0 to 1.5
inch range. This will be enough to generate a more widespread chance
for showers/slight chance for thunder on Sunday with a local downpour
possible. There remains little in the way of instability or shear so do
not see any threat of severe weather. Highs tomorrow will range from
the middle/upper 80s east to upper 70s/lower 80s west.
Short term /Sunday night through Tuesday/...
as of 355 PM EDT Saturday
A piece of the upper trough and vorticity maximum tracks slowly north
across the southern and central Appalachians Sunday night. At the
same time a weak short wave tracking the the base of an upper trough
over New England will cross through the Ohio Valley. By Monday
evening the models have the upper trough axis east of the forecast
area. The combinations of the lift from these features will result
in showers and thunderstorms Sunday night and Monday. Moisture below
850 mb is not as high as would be optimal and surface/low level
winds will not contribute to lift or moisture advection. Will have a
small increase in probability of precipitation on Sunday night and
500 mb temperatures will cool late Sunday night and Monday morning
but lifted index values and heating will be meager on Monday. Convective available potential energy
around 500 j/kg but are at a relative minimum over the forecast area
with higher values surrounding US. Kept probability of thunder at
Precipitable water values and dew points will be slowly increasing
Sunday night and Monday. This plus the cloud cover will limit drop
in minimum temperatures on Sunday night. Clouds and any
precipitation will hold down rise in maximum temperatures on Monday.
Little change needed to forecast for Monday night and Tuesday.
Probability of precipitation decreases and temperatures will be near
normal. A majority on the deep moisture will stay just south and
southeast of the forecast area.
Long term /Tuesday night through Saturday/...
as of 255 PM EDT Saturday...
Long wave synoptic pattern through the period keeps upper trofing
over the Pacific northwest and an large ridge over the central
United States. At the surface a broad area of high pressure will
remain over the eastern United States. Models not showing any well
defined or organized smaller scale features that will trigger
showers and thunderstorms through day 7. Bulk of showers and
thunderstorms will be typical afternoon and evening orographically driven
coverage. Steering flow will remain relatively weak so any
stronger cells will have the potential to produce heavy rain.
No exceptionally warm or cool temperatures through day 7.
Aviation /00z Sunday through Thursday/...
as of 730 PM EDT Saturday...
A VFR forecast with mainly middle/high clouds. Some period of
clearing late tonight may allow for fog formation especially at
lwb...so no changes to the previous taf forecast of dense fog
here. Confidence is low though due to the cloud cover.
Any fog dissipated after daybreak Sunday and it looks like shower
coverage will be better Sunday afternoon...but still seeing only
scattered threat...so left out of tafs. As a good dose of short
wave energy rises out of the Gulf Coast and into the
region...better development expect more Sunday night into Monday
Extended aviation discussion...
generally expect the best chances for MVFR/IFR to be late
night/early morning due to fog and stratus development from the
Blue Ridge west especially at klwb/kbcb. Will then remain in a
weakly forced synoptic environment through midweek with chances
for diurnal convection mainly from the Blue Ridge west...and some
MVFR/IFR fog/stratus development at night especially at kbcb and
as of 400 PM EDT Saturday...
The dew point reading at kjfz...Richlands Virginia AWOS...is incorrect.
At this time we do not know when this sensor will be repaired.
short term...air mass
long term...air mass