Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Charleston SC
626 am EDT Thursday Apr 24 2014

Synopsis...
high pressure will shift off the coast today through Friday.
A weak cold front could drift in from the north this weekend
before high pressure builds over the area through early next week.
A stronger cold front will cross the region next Tuesday or
Wednesday.

&&

Near term /until 6 PM this evening/...
24/06z guidance including the 09z rap have trended warmer with highs
this afternoon across interior southeast Georgia. Will expand the
area of middle-80s to match this. No other major changes will be
made.

An upper level ridge axis will pass overhead this afternoon as
surface high pressure shifts off the coast. The synoptic flow will
become southeast this afternoon and eventually to the south
tonight as the high shifts farther offshore and a cold front
approaches from the west. Low-level moisture return will generally
remain focused across northern Florida and far southern Georgia
through much of the day...although mixing ratios will begin to
increase across the far southern zones late. A robust sea breeze
circulation will develop early this afternoon along the beaches
and move steadily inland...aided by the increased southeasterly
flow. There may be just enough low-level moisture flux convergence
to support an isolated shower or to across interior southeast
Georgia...mainly south of I-16...but probabilities look too low to
mention slight chance probability of precipitation at this time. Highs will range from the upper
70s/near 80 across the Charleston tri-County area to the Lower-Middle
80s across elsewhere...warmest far interior southeast Georgia.
Beach locations will remain considerably cooler with the shelf
waters still rather cool.

&&

Short term /6 PM this evening through Sunday/...
tonight...return flow will be in full swing as a cold front
approaches from the west and high pressure slips farther offshore.
Models show some weak isentropic assent developing from south-
north as the night progresses...but none of the various members
are overly aggressive in the development of nocturnal shower
activity as most of the lift will go towards cloud formation given
the high condensation pressure deficits. Will keep the forecast
dry with the exception of the Charleston County coast where some
marine based convection could brush areas from roughly Folly Beach
to McClellanville very early Thursday. It will be a warm night
with nocturnal jetting likely keeping the boundary layer from
fully decoupling. Lows will range from the upper 50s far interior
southeast South Carolina to the Lower-Middle 60s elsewhere. This is
slightly above the 00z guidance consensus.

Friday...we should see a fair amount of clouds to start off the day
as modest isentropic ascent occurs ahead of an eastward advancing 500 mb
shortwave just to our north. We could see a few showers during
morning hours as a result...mainly along the coast in southeast
South Carolina. A slight chance of showers and/or thunderstorms will
then be possible by Friday afternoon as instability increases during
peak heating with sbcapes approaching 700-1200 j/kg and lifted index
values between -1 to -3c. Thunderstorm chances appear highest over
inland areas in southeast South Carolina where forcing from the 500 mb
shortwave and a arriving cold front are greatest. Although a capping
inversion will suppress most deep convection...we can not rule out a
stronger thunderstorm or two by Friday evening. Activity will likely
diminish with cold frontal passage and diurnal heat loss early Friday night.
1000-850 mb thickness values along with some compressional heating
support overall high temperatures in the low/middle 80s away from the coast.
Overnight lows will range in upper 50s inland to lower 60s along the
coast behind the front.

Saturday...high pressure will hold over the area under a building
ridge aloft. A downsloping wind component will likely support another
day of warm temperatures with afternoon highs in the middle 80s over most
locations away from the immediate coast. A weak and dry cold front
should stall or dissipate north of the forecast area Saturday
night...with little to no influence over the southeast. Thus a
rain-free day is expected. Strong radiational cooling will allow
overnight temperatures to reach the upper 50s inland to lower 60s along the
coast.

Sunday...conditions look fairly dry to start off the week as
Atlantic high pressure lingers over the area well ahead of a strong
low pressure system tracking east over the central United States.
Light southerly flow along with middle level ridging should result in
even warmer temperatures than the previous day. Latest 1000-850 mb
thicknesses favor overall high temperatures in the middle/upper 80s away from
the coast...warmest in southeast Georgia.

&&

Long term /Sunday night through Wednesday/...
light southerly flow along with middle level ridging over the southeast
will likely keep warmer temperatures over the southeast into early next
week ahead of the approaching low pressure system. In general...high
temperatures will be in the low/middle 80s Monday and Tuesday before cooling a
few degrees on Wednesday as cloud cover increases with the low
pressure system shifting over the eastern Continental U.S.. a slight chance of
showers and thunderstorms will remain in the forecast on Monday as
southerly flow deepens moisture over the area while an 500 mb shortwave
passes overhead. Precipitation chances should then increase Tuesday and
Wednesday ahead of an eastward moving cold front associated with the
low pressure system. There are indications that we could see an
enhanced period of showers and/or thunderstorms late Tuesday into
Wednesday as stronger instability and wind fields set up over the
southeast ahead of the front. A few thunderstorms could be
strong...especially on Wednesday during peak heating. Showers and/or
thunderstorms could persist into much of Thursday as the cold front
shifts offshore early while the large middle/upper level trough remains
positioned over the eastern Continental U.S.. overall temperatures should cool off
Post frontal passage...with highs only in the middle/upper 70s on Thursday.

&&

Aviation /12z Thursday through Monday/...
VFR...although the risk for sub-VFR ceilings will increase at ksav
towards the end of the 12z taf period.

Extended aviation outlook...low chances of MVFR ceilings/visibilities late
Monday and Tuesday with showers and/or thunderstorms.

&&

Marine...
today...east to northeast winds will gradually veer more southerly
this afternoon as high pressure shifts off the coast and a robust
sea breeze circulation takes hold. Winds will generally be 10-15
knots with seas 1-3 feet.

Tonight...southerly winds will dominate as high pressure shifts
even farther offshore winds. Winds will be 10-15 knots with seas 2-3
feet.

Friday through Tuesday...a weak cold front will quickly advance over
the waters Friday night...leading to a marginal surge of winds
between 15-20 kts late. High pressure will then build over the
waters Saturday and persist into early next week ahead of a low
pressure system advancing to the eastern Continental U.S.. winds/seas are
expected to remain below Small Craft Advisory levels through early
Tuesday...but should approach Small Craft Advisory levels by Tuesday
night as the pressure gradient enhances ahead of a cold front
advancing to the southeastern United States by midweek. In
general...south/southeast winds will remain at or below 15 kts
through early Tuesday while seas are no higher than 3-4 feet. By
Tuesday night...winds/seas should increase/build to 20-25 kts and
4-6 feet...highest beyond 10 nm from the coast.

&&

Chs watches/warnings/advisories...
Georgia...none.
SC...none.
Marine...none.

&&

$$

St/dpb