Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
931 am EDT Tuesday Jun 2 2015
a cold front will approach from the west today...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 /until 6 PM this evening/...
a very active day is anticipated for the region. Favorable
instability and moisture profiles juxtaposed with upper level
difluence will support numerous showers/thunderstorms this afternoon;
possibly beginning as early as late morning for the Charleston
tri-County area. High resolution models show a similar signal in a
large sea breeze and outflow collision occurring over interior
areas roughly from Springfield and Statesboro northeast to
Walterboro. Capped probability of precipitation to 70 percent for most areas for now until
mesoscale trends become a bit more apparent. Categorical probability of precipitation may
eventually be needed. The risk for isolated severe thunderstorms is there
with marginally severe hail and damaging wind gusts being the
primary severe threats. Locally heavy rainfall is also a
possibility with a ribbon of high precipitable waters in place and fairly slow
storm motions expected.
For the late morning update..
* adjusted hourly probability of precipitation slightly based on the latest rap/h3r runs.
* Introduced rain may be heavy at times qualifier to account for
locally excessive rainfall rates.
* Minor adjustments to hourly temperature and dewpoints through
Short term /6 PM this evening through Friday/...
tonight...convection will diminish as the main shortwave shifts
offshore but continued deep moisture and upper jet divergence
could lead to lingering rains much of the night...especially
across coastal SC. Lows mainly in the upper 60s inland to lower
70s at the coast.
Wednesday and Wednesday night...a closed upper level low will slowly
shift from the eastern Tennessee Valley to the southern
Appalachians. As this occurs...a cold front will gradually approach
from the west...shifting into the area Wednesday night. A deep south-
southwest flow in place ahead of the approaching cold front will
allow for strong moisture advection with precipitable water values
remaining up around 1.75 inches. Not only is there deep
moisture...but strong upper level divergence provided by the right
entrance region of a jet maximum revolving around the upper low will
provide the forcing for ascent needed for showers and thunderstorm
development. It appears that numerous showers and thunderstorms can
be expected with the best coverage in the afternoon. Coverage should
diminish to isolated or scattered Wednesday night. There is a
potential for localized flooding given the high precipitable water
values and weak storm motion of less than 10 miles per hour...especially if any
training occurs. The region is also in a marginal risk for severe
weather during the afternoon and evening with cape values upwards of
1000-1500 j/kg expected. The greatest threat is an isolated damaging
wind gust associated with a wet microburst...however an organized
severe weather threat is not anticipated given poor lapse rates and
weak shear. Cloud cover and precipitation will limit heating...with
highs in the lower to middle 80s expected. Lows Wednesday night will be
in the middle to upper 60s.
Thursday and Thursday night...the closed upper level low will remain
over the southern Appalachians on Thursday...before beginning to
shift east over the Carolinas Thursday night. At the surface...a
front will remain stalled over the area. Short wave energy along the
southeast periphery of the upper low combined with low level
convergence associated with the stalled front will provide ample
forcing for numerous showers and thunderstorms to develop once again
during the day. The best focus will then shift toward the coast
Thursday night as coverage diminishes. The area is yet again in a
marginal risk for severe thunderstorms. Similar to
Wednesday...surface based instability will be sufficient but a lack
of organization is expected given poor lapse rates and limited
shear. So...isolated damaging winds will be the primary threat if
any storms become strong/severe during the afternoon and evening.
Still cannot rule out the potential for localized flooding if any
training occurs. Little change in temperatures is expected from
Friday...the upper level low will finally shift off the Carolina
coast...allowing the stalled front to lift northward out of the
area. Scattered showers and thunderstorms are expected in the
afternoon as short wave energy drops down within the northwest flow
aloft. Highs will remain in the middle and 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 /14z Tuesday through Saturday/...
kchs...numerous showers and thunderstorms will develop late this
morning and this afternoon as convection moves in from the west
and interacts with the developing sea breeze. Have added a tempo
group from 15-19z to indicate flight restrictions within
thunderstorms. Have maintained vicinity thunderstorms through 21z
to account for any lingering thunderstorms in the vicinity as the
sea breeze pushes inland. The rest of the evening and early
overnight hours should be rain-free...but that coastal convergence
could lead to additional showers with the potential for some lower
ceilings late tonight.
Ksav...numerous showers and thunderstorms will develop early this
afternoon along the sea breeze and could continue through much of
the afternoon. Have added a tempo group from 18-22z to indicate
flight restrictions within thunderstorms...but bracket vicinity
thunderstorms from 17-00z. Some convection could try to come back
toward the terminal later in the evening...but overall think the
remainder of the forecast period should be rain-free thus
maintaining VFR conditions.
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.
today and tonight...winds mostly southerly between high pressure
to the east and an approaching weak cold front. Speeds mainly
10-15 knots with seas 2-3 feet. Conditions look somewhat supportive of
waterspouts this morning so will keep an eye on any convective
Wednesday through Sunday...a front will stall out across the area
through Thursday...before lifting out of the area on Friday. Another
cold front will drop toward the area on Saturday. Wind directions
will be somewhat variable...but overall a weak pressure gradient
will keep speeds less than 15 knots. Seas will generally be 2 to 3 feet.