Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
343 PM EDT Tuesday Jun 2 2015
a cold front will approach from the west tonight...stalling over the
area Wednesday into Thursday before slowly shifting off the coast
late week. Another cold front will affect the area over the
weekend...with a trough of low pressure then becoming established
inland early next week.
Near term /through tonight/...
convective temperatures have finally been reached after a slow
start and convection is beginning to pop across the area. The
atmosphere has been sufficiently overturned along the Highway 17
corridor from Charleston to McClellanville so do not anticipate
much more activity in that area until possibly later tonight. The
atmosphere continues to destabilize farther inland aided by broad
upper difluence ahead of the upper low meandering over eastern
Tennessee which will support further convective development
through the remainder of the afternoon hours. Rap soundings show
dcapes rising to 800-1000 j/kg...so there will be a continued risk
for a isolated severe thunderstorms--mainly west of the I-95 corridor.
0-6km bulk shear remains weak...although a bit higher than
previous days. Could see few loosely organized convective clusters
develop as a result...especially along mesoscale boundary
collisions. Wind fields will support convective training and a
risk for localized flooding.
Convection will likely linger for much of the evening hours with
high resolution guidance suggesting outflow from activity to the
west and southwest potential colliding with the inland moving sea
breeze after sunset. High-end likely probability of precipitation of 70 percent will
be maintained for most areas through the remainder of the
afternoon hours with the higher gridded probability of precipitation shifting inland
through the evening hours. Depending on how much activity
organizes farther inland...a weakening cluster of showers and
thunderstorms could approach the coast after midnight. Will keep 30-40
percent probability of precipitation in place to account for this possibility.
Lows will range from the middle-upper 60s inland with upper 60s to
lower 70s at the coast...except middle 70s at the beaches.
Short term /Wednesday through Friday/...
Wednesday...at daybreak a closed upper low will be located over the
Tennessee River valley near the Appalachians. Through the day the
low and associated vorticity maximum will slowly swing east into the western
Carolinas. Meanwhile...a surface cold front will remain nearly
stationary over the region. Strong upper divergence...convergence
along the stalled boundary...and precipitable waters of 1.60-1.75 inches will
support the development of showers and thunderstorms. Despite
unimpressive middle level lapse rates...0-6 km bulk shear does increase
in the afternoon to around 20-25 kts and with cape on the order of
1000-1500 j/kg...a few stronger to severe storms will certainly be
possible. Steep low level lapse rates and dcape values around 600
j/kg would suggest damaging wind gusts as primary threat. Storm Prediction Center does
have the area in a marginal risk of severe weather. Periods of heavy
rain will be possible as well given high moisture content. High
temperatures will be a bit cooler than normal...ranging from low 80s
across northern zones to middle/upper 80s south. Activity may linger
into the overnight period as decent forcing remains in place. Low
temperatures expected to mainly be in the middle/upper 60s.
Thursday...closed low over the Carolinas will weaken as it continues
to shift east towards the coast. The stalled front will still be in
the vicinity so there will again be forcing mechanisms present to
kick off convection. Instability is marginal and middle level lapse
rates are quite poor...but decent shear could support a few stronger
storms and Storm Prediction Center has the area in another marginal risk. High
temperatures will be close to normal mainly in the middle to upper 80s.
Best upper support will shift out of the area later in the day...so
coverage is expected to decrease overnight. Lows will be in the
upper 60s inland/low 70s at the coast.
Friday...the upper low will finally move northeast off the
coast...helping to push the front away from the area.
Shower/thunderstorm coverage is expected to be less than previous
days...and mainly confined to development along the sea breeze. Have
decreased probability of precipitation a bit to low chances with this package as latest
model solutions have backed off on convective activity. Weak
shear...poor lapse rates and marginal instability will keep severe
threat limited. High temperatures will be in the middle/upper 80s.
Long term /Friday night through Monday/...
broad upper level troughing will prevail over the region through the
weekend...as a cold front drops into the area Saturday night then
retreats to the north on Sunday. The upper level trough will linger
to some degree into early next week...with a surface trough of low
pressure becoming established inland. This pattern will favor
unsettled conditions...with a chance of showers and thunderstorms in
the forecast just about every day. Temperatures should be near
normal through the weekend...possibly even rising just above normal
early next week.
Aviation /19z Tuesday through Sunday/...
kchs...the seabreeze has moved inland of kchs as of 18z...though
thunderstorms forming along the boundary continue to advect over the
terminal area. Expect this to continue well into the afternoon.
Thunderstorms should transition to mainly showers as the atmosphere
becomes more stable and the convection weakens by late afternoon.
The early overnight hours should be rain-free...but showers may
begin to move back into the area during the late overnight hours and
through tomorrow morning thanks to deep moisture advection ahead of
a cold front. VFR conditions should persist this evening through
Ksav...thunderstorm coverage across southeast Georgia has been less
than anticipated so far today...but thunderstorms are beginning to
form along the sea breeze front nearly overhead of ksav at 18z. The
window for thunderstorms and associated visibility reduction for
ksav looks to be 19z to 22z. VFR ceilings and dry conditions will
fill in for the late evening hours. Showers will move into the area
through the overnight hours and continue into the early morning
hours. VFR conditions are expected throughout this period.
Extended aviation outlook...numerous showers and thunderstorms will
affect the area through Thursday...becoming more scattered Friday
and Saturday. This convection could produce occasional ceiling and
visibility restrictions...especially in the afternoon and evening
when storms are most probable.
tonight...no concerns. South winds 10-15 knots with seas 2-3 feet.
Wednesday through Sunday...a front will remain stalled over/near the
area Wednesday into Thursday before pushing off the coast on Friday.
With the front in the vicinity...wind directions will be tricky at
times however weak pressure gradient will keep speeds generally less
than 15 knots. Another cold front is expected to impact the waters over
the weekend. No headlines expected at this time. Seas through the
period will be 2-3 feet on average.