Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Blacksburg Virginia
417 am EDT Sat Aug 30 2014
a stalled front trailed from South Carolina to Illinois this
morning. This front will move north and dissipate over the middle
Atlantic region by Sunday. A low pressure system will move across
the Great Lakes tonight and Sunday with a cold front trailing from
the upper Mississippi Valley to the Central Plains by Sunday
Near term /through tonight/...
as of 410 am EDT Saturday...
Radar showed a narrow band of showers from Ashe County NC to Halifax
County Virginia. Hrrr moves this precipitation north then has it
dissipating by 12z/8am. In contrast the 4km NAM has the
precipitation moving all the way into central Virginia by noon. Will
lean toward the NAM solution.
Front was stationary from Illinois to South Carolina. Models take
surface high pressure off the New England coast today...allowing the
boundary to move north...but expect it will take much of the day to
move out of the County Warning Area. Winds coming around to the
south and any clearing in the afternoon will influence how much
temperatures will rise today. Cloud cover will also limit
instability today...so even with the front moving through the
coverage of showers and thunderstorms will remain isolated to
scattered. 00z Canadian starts breaking out cloud cover around
14z/10am but does not have all the low clouds eroding until nearly
19z/3pm. Will stay close to this timing.
Upper ridge axis is just off the southeast coast by tonight. Broad
southwest flow from the lower Mississippi Valley to the eastern Great
Lakes tonight. The short wave coming out of the northern Gulf and
the best q-v forcing along the approaching cold front will still be
west of the forecast area by Sunday morning. Middle and high clouds
will cover the western County Warning Area overnight...then
increasing probability of precipitation in the far west. With the
increasing clouds and since the forecast area will be well within
the warm sector tonight...not much drop in temperatures is expected.
Used the warmer guidance for overnight lows.
Short term /Sunday through Monday night/...
as of 310 am EDT Saturday...
A stubborn upper level ridge will hug the southeastern coast longer
than previously expected. From a model stand point...this upper
ridge is also farther inland...which will lower the chance of
showers and thunderstorms as the short wave track is pushed
westward. The latest 00z models tracks a tropical short wave on the
outer rings of the ridge across eastern Tennessee and central
Kentucky Sunday morning...then over the Ohio Valley in the
afternoon. As this short wave moves over the Ohio Valley in the
afternoon...middle level capping weakens allowing storms to generate
along out flow boundaries and in modest instabilities. With the
strongest low level jet remaining over the Tennessee and Ohio
valleys...disorganized pulse-like storms are expected over the
mountains in the afternoon and may drift east of the Blue Ridge in
the evening...if the ridge does jog to the southeast. There will
also be a Lee trough over the Piedmont that may help fire storms
east of the Blue Ridge during the late afternoon and evening hours.
Can not rule out the chance for a few storms to become severe where
the cap is the weakest...mountain Empire to the Bluefield Richlands
area. Since the models have moved organized convection to the
west...lowered probability of precipitation especially in the east. Since the chances of
showers is lower and scattered in nature...increase temperatures
across the mountains into the middle 80s and u80s-l90s east of the Blue
On Monday...models once again drift upper level ridge to the
south...placing the outer rings across the forecast area. A weak
short wave is expected to track along the southern Appalachians
bring a chance for showers and thunderstorms to the area Monday.
Once this short waves tracks north of the area...possibly by early
afternoon...surface high pressure will build across the region
Monday night. With the area remaining in a muggy air mass...patchy
dense fog is likely for mountain valleys. If showers are primarily
during the morning...Monday afternoon temperatures will warm into
the middle 80s in the west to u80s-l90s east of the Blue Ridge.
Long term /Tuesday through Friday/...
as of 330 PM Friday...
Flat upper ridge is expected to dominate our middle-week weather
pattern across the central appalachian and middle-Atlantic region. This
should maintain Summer-like temperatures through the entire period
with highs near 90f in the Piedmont and middle-80s in the mountains
along with night-time lows in the 60s to low 70s. Could end up being
one of the warmest weeks of the Summer even as the so-called
meteorological Summer ends on August 31. Precipitation will also
generally be of Summer-like character with diurnally driven
convection providing the best chances for rainfall. Wednesday
afternoon looks like the most promising day for storms as weak
frontal boundary pushes across the County Warning Area. Thursday and Friday likely
to be drier although widely scattered showers still possible.
Aviation /08z Saturday through Wednesday/...
as of 140 am EDT Friday...
Broad area of stratus had spread west across the region. The
western edge was close to klwb and kblf. These airports may go
back and forth between scattered VFR clouds and MVFR ceilings
through 14z/10am. For kbcb/kroa/kdan and klyh higher confidence
that ceilings will lower to MVFR or IFR.
Improvement in conditions will be slow this morning as a front
lifts north through the area. Only medium confidence as to when
ceilings will lift back to VFR. The threat of showers and
thunderstorms through the taf period remains low enough to keep
out of the forecast for now.
Any isolated or scattered showers and storms will be mainly
along and north of a khsp-kfvx line this evening...just south of
the again stalled frontal boundary.
Late tonight through Sunday evening an area of low pressure will
head eastward through the Great Lakes region toward New England.
Its associated cold front will sweep through the region bringing a
generous coverage of showers and some storms. Sub-VFR conditions
are expected to accompany the system and precipitation.
Another cold front is expected to produce similar conditions Tuesday
into Wednesday. However...model guidance for this one offers
precipitation in a more scattered distribution. As such...the
magnitude of sub-VFR conditions may be less.
as of 730 am EDT Friday ...
The visibility sensor at kdan...Danville Regional Airport...will
be out of service until further notice. A part has been back-ordered.
near term...air mass