Area forecast discussion
National Weather Service Charleston SC
214 am EDT Wednesday may 22 2013
Synopsis...
Atlantic high pressure will prevail through Thursday. A
cold front will move through the area on Friday with dry high
pressure building in next weekend into early next week.
&&
Near term /until 6 am this morning/...
the forecast area lies underneath a well-defined middle level
impulse across Florida with strung out vorticity stretching north
and NE overhead to off the coast of NC and southeast Virginia. This feature
will move little through the night. Meanwhile...the Bermuda high
will lie atop the region as a subtle trough develops over the
nearby Atlantic late.
Much of the night will be rain free...although with the short wave
aloft and some convergence downstairs...given that precipitable waters are near
2 Standard deviations above normal for late may...we look for an
increase in convection again over the Atlantic overnight. We/re
already seeing signs of that out near the Gulf Stream. Within the
southerly synoptic flow we anticipate some of this activity will
move into Charleston and far southeast Berkeley County by sunrise.
Given the copious amount of rains from earlier today...fog will
become problematic again overnight as the middle/high level
convective debris cloud cover diminishes. We have expanded the
patchy fog a little further southeast with the late evening update...and
included areas of fog along parts of the northwest tier where some of the
better rainfall occurred. Locally dense fog is certainly a concern
and we will re-evaluate again with future updates.
Conditions will be sticky and balmy tonight...with minimum temperatures
no lower than the middle-upper 60s inland and around 70 near the shore.
&&
Short term /6 am this morning through Friday/...
a fairly similar pattern will persist Wednesday and Thursday with
broad upper troughing inland and high pressure over the Atlantic.
This pattern will maintain deep moisture over the area with decent
rain chances through the period...mostly confined inland during the
day and over the Atlantic at night. The risk for severe weather
appears low given the lack of organization potential...although
heavy rainfall could result in localized flooding. High/low
temperatures will ultimately depend on cloud cover/rainfall but
generally should be close to slightly above normal.
A cold front should push through Friday morning...although the
northwest downslope flow will help to offset the cold advection.
This should lead to temperatures close to normal in the middle 80s. The
bigger change will be the drier air which will make it feel a lot
more comfortable.
&&
Long term /Friday night through Tuesday/...
there is good model agreement that dry Canadian high pressure will
expand southeast into the forecast area over the weekend then shift
offshore. Dewpoints look to drop into the lower 50s Saturday and
Sunday...which combined with highs in the lower 80s will result in
pleasant Spring weather. Overnight lows will probably drop into the
upper 50s in spots. Low-level moisture increases early next week as
the surface high shifts offshore...but we did not see any strong
synoptic scale features to warrant adding precipitation.
&&
Aviation /06z Wednesday through Sunday/...
better chances for visibility/ceiling restrictions at both terminals due
to substantial rainfall on Tuesday. Ksav will likely continue at
least MVFR ceilings with possible brief drops to IFR before
daybreak. We still show kchs dropping to MVFR ceiling/visibility prior to
daybreak as well. The best chance of dense fog or the like will be
inland from either terminal.
For the rest of today the main issue is another round of convection
developing along the seabreeze. We included prob30 rain showers at both
terminals for the afternoon hours given pretty good indications
that a line of showers/storms will roll through the airports.
Extended aviation...sporadic reductions in ceilings/visibilities mainly in
afternoon/evening showers or storms through Thursday.
&&
Marine...
tonight...the typical sub-tropical ridge of high pressure will
continue to stretch across the coastal waters...generating southeast and
south winds of less than 10 or 15 knots. Seas will hold in a fairly
steady state at 2-4 feet...mainly in a southeast swell. While the risk is not
particularly high...there is nonetheless a chance of isolated
stronger storms moving in after 06z.
Wednesday through Sunday...Atlantic high pressure will dominate
with southerly flow until a cold front pushes through Friday. The
much cooler and drier air mass behind the front will move in and
lead to increasing winds and building seas...possibly reaching
advisory levels...at least across the waters beyond 20 nm.
&&
Tides/coastal flooding...
high astronomical tides and favorable north/northeast winds could
lead to minor saltwater inundation near the coast during the high
tide Friday and Saturday evening. By the time of the high tide
Sunday evening as well as Monday evening...winds will not be as
conducive but minor saltwater flooding will still be possible.
&&
Chs watches/warnings/advisories...
Georgia...none.
SC...none.
Marine...none.
&&
$$
Synopsis...
near term...jrl
short term...rjb
long term...jrl
aviation...
marine...
tides/coastal flooding...
