Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
1036 PM EDT Sat Jul 4 2015
low pressure moving off the middle Atlantic coast will push a cold
front southward tonight into Sunday. This will result in rounds of
showers and thunderstorms. The unsettled weather will continue to
affect the region for the next several days...keeping a chance of
showers and thunderstorms in the forecast through the first part of
next week...as temperatures begin a gradual warming trend.
Near term /through Sunday/...
as of 1030 PM EDT Saturday...
Several models showing precipitation associated with closed upper
low over western Tennessee will move into southwest Virginia and
northwest North Carolina early Sunday morning. Have increased the
probability of precipitation in that area from 2am through 8am
A wavy frontal boundary remain across the region on Sunday.
Shortwaves continue to travel east along the upper trough. Showers
and thunderstorms will become numerous by Sunday afternoon.
Short term /Sunday night through Tuesday night/...
as of 330 PM EDT Saturday...
Models are in agreement with respect to the development of a weak
closed upper low across the southeast states and its subsequent
northward drift into the first part of next week.Tail end of long
standing eastern U.S. Trough will become cutoff across northern
Georgia/al/eastern Tennessee from the parent upper trough...which will shear
out across New England as a short wave ridge drifts into the Ohio
Valley. The upper low will then drift slowly northeast into
Monday...finally lifting north of the region by Tuesday as the next
upstream trough digs into the Great Lakes region.
As the low moves north from Georgia it takes on a negative
tilt...which will further enhance overall weak dynamics/lift and
certainly prolong the wet weather pattern. Abundant deep moisture
will remain in place with precipitable waters in the 1.75 to 2.0 inch range
across much of the County Warning Area. Extensive to near solid cloud cover will
limit heating...so instabilities remain meager and overall
dynamics are weak.
Models are in good agreement with a large swath of deep
moisture...associated with the upper low and overrunning existing
surface frontal boundary...tracking from Georgia/SC northward into the
rnk County Warning Area by Sun afternoon...drifting into the northern parts of the
County Warning Area Monday...then finally lifting northeast of the County Warning Area by Tuesday. This
will support high probability of rainfall from Sunday through
Monday across much of the County Warning Area...with a limited diurnal swing
of temperature given the upper low will essentially be drifting
right across The Heart of the County Warning Area.
The path of the upper low should focus the heaviest rainfall
across the western part of the County Warning Area...Blue Ridge and west.
With 3hr ffg values averaging in the 1.5 to 2.5 inch range across
much of the County Warning Area and the recent prolonged wet spell...we will need
to monitor rainfall amounts carefully...however...the lack of any
organized or strong convection...given the meager lapse rates and
lack of instability/dynamics...should hold hourly rainfall amounts
in check. Will continue to highlight threat of poor drainage flooding
in the severe weather potential statement...but potential for flash flooding does not appear to
be a concern at this time.
As the upper low drifts north of the area Tuesday...we should see
enough subsidence and drying to finally squelch the shower threat
providing a break before new frontal system approaches Tuesday
night or Wednesday.
Maximum temperatures should remain below normal through
Monday...trending closer to normal values Tuesday with greater
insolation. Minimum temperatures will remain above normal with
Long term /Wednesday through Saturday/...
as of 445 PM EDT Saturday...
Unsettled weather destined to continue. After a very brief
respite from widespread precipitation Tuesday...a new frontal
system will drift into the region from the west by Wednesday and
then become elongated west-east across the region and stall for
the latter half of the week. With subtropical ridging to our
south and faster westerlies to our north...this will favor active
baroclinic zone with daily threat for showers/storms. Pattern
supports some organization of storm activity and potential for
strong/severe storms per presence of with associated upper level
short wave energy that will be passing through the faster
westerlies to our north.
The upper flow attempts to transition back to northwest flow
toward the weekend as upper riding amplifies across the west-
central Continental U.S.. this could reduce the potential for prolonged
convection/rainfall...but will nonetheless support an active and
unsettled weather pattern.
With above average cloud cover and moisture levels continuing...expect
near to slightly below normal maximum temperatures and well above
normal minimum temperatures through the week.
Aviation /03z Sunday through Thursday/...
as of 740 PM EDT Saturday...
Cluster of thunderstorms on the northeast side of the kdan
Airport will be more than 10 nm away from the Airport by the 00z
start time of the taf. No other showers or thunderstorms close
to...or expected at the other (klwb/kblf/kbcb/kroa/klyh) for the
rest of the evening.
Surface low pressure was over northeast Virginia with a cold front
extending from the low into northern Tennessee. This boundary will
move slowly east tonight. Expecting IFR stratus north and west of
the low overnight...with the highest confidence of ceilings below
500 feet at klwb and kblf. Locations that had rain Saturday
afternoon and evening will also have patchy fog with occasional
MVFR to LIFR visibilities.
A closed low over western Tennessee will move northeast on Sunday
and spread showers and thunderstorms into the middle Atlantic region
after 12z/8am. Lower confidence on the arrival time of the rain
and when the best chance for thunder will be...but high confidence
of precipitation...especially over the mountains during the day
Extended aviation discussion...
Poor aviation conditions to continue into next week...but windows
of opportunity for VFR conditions increase Tuesday. Upper low/trough
will move into Ohio by Monday. Meanwhile...a cold front will
approach from the Ohio Valley by Wednesday. This leaves a very
unsettled/wet pattern across the region through the period.
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. At this
point...Tuesday appears to offer the best opportunity for more
widespread VFR conditions.