Area forecast discussion
National Weather Service Charleston SC
435 am EDT Wednesday may 22 2013
Synopsis...
Atlantic high pressure will prevail through Thursday. A cold front
will move across the area Thursday night with high pressure then
building over the region through early next week.
&&
Near term /until 6 PM this evening/...
weak shortwave troughing at upper levels to persist today while
Atlantic high pressure extends west into the southeast states at
the surface. The in-situ airmass remains quite moist with precipitable water
values hovering at or above 1.60 inches. Through daybreak a few
showers are possible over the coastal waters and immediate SC
coast mainly northeast of Charleston in some weak moisture
convergence. After sunrise...the deep-layered southeast flow will
allow the seabreeze to develop fairly early. With temperatures pushing
into the middle to upper 80s...moderate instability will develop
yet again. Showers and thunderstorms will increase in coverage from late
morning into the afternoon with the activity likely shifting
gradually inland. Convective parameters are not terribly
impressive but an isolated severe storm or two cannot be ruled
out.
&&
Short term /6 PM this evening through Saturday/...
diurnal convection will taper off early this evening over land but
isolated showers or storms will remain possible over the coastal
waters overnight. Some fog is possible late tonight...especially
in areas where rain occurs today.
Thursday...Atlantic high pressure will prevail while weak troughing
persists inland. A shortwave embedded within broad upper level
troughing will cross the region and push the deep layered moisture
offshore as the day progresses. There is the potential for isolated
convection across the area in the morning ahead of the short
wave...with the coverage increasing to scattered in the afternoon
across much of southeast South Carolina where precipitable water
values and low level convergence will be maximized. A
westerly/downslope flow aloft will push temperatures to highs in the
upper 80s to around 90 away from the immediate coast.
Thursday night...an upper level trough will dig toward the
Appalachians...pushing a cold front across the area. Other than some
isolated convection early in the evening mainly across the
Charleston tri-County area...the front should pass through relative
rain-free due to a lack of deep layered moisture. Lows will be in
the lower to middle 60s.
Friday...the upper level trough will move over the middle-Atlantic as
surface high pressure begins to build in from the Great Lakes region
in wake of the departing cold front. Much drier air will filter into
the area with a strong northwest/downslope wind component. There
will be considerable sunshine along with breezy conditions in the
afternoon. The downslope flow will negate much of the cold air
advection...allowing temperatures to reach highs in the middle and
upper 80s across the area away from the immediate coast.
Friday night...radiational cooling will be limited by a coupled
northerly flow through much of the night...but the dry airmass and
clear skies should still allow temperatures to fall into the the middle
and upper 50s...with some lower 50s possible well inland.
Saturday...an extremely dry airmass will be in place to start the
weekend...with precipitable water values as low as .25 to .50 inches
which is more than 2 Standard deviations below normal for this time
of year. Given this dry airmass...there will be considerable
sunshine but a north-northeast flow will limit highs to the upper
70s to lower 80s across southeast South Carolina and the lower to
middle 80s across southeast Georgia.
&&
Long term /Saturday night through Tuesday/...
medium range guidance is in good overall agreement through the long
term period. The middle and upper level pattern will feature a nearly
zonal flow over the region late in the weekend into early next
week...with a ridge then building toward the middle of next week. At
the surface...high pressure will pass north of the area late in the
weekend...then settle over the western Atlantic through the middle
of next week.
Rain-free conditions are expected to persist into early next
week...then increasing moisture could allow for some mainly diurnal
isolated convection along and ahead of the sea breeze Tuesday and
Wednesday. Temperatures will be slightly below normal Sunday...then
return to near or slightly above normal next week.
&&
Aviation /08z 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...Atlantic high pressure will prevail through
Thursday. A cold front will move across the area Thursday night
with high pressure then building over the region through early
next week.
&&
Marine...
marine conditions look pretty quiet through tonight as the area
remains on the western periphery of Atlantic high pressure. The
seabreeze should develop late this morning but wind speeds at the
coast are not expected to be terribly impressive.
Thursday through Monday...Atlantic high pressure will dominate
with southerly flow until a cold front pushes offshore early
Friday. A northerly surge is expected to develop in wake of the
front Friday night into early Saturday and could result in Small
Craft Advisory conditions. Conditions will then improve later in
the weekend into early next week with winds/seas expected to
remain below Small Craft Advisory thresholds.
&&
Tides/coastal flooding...
Atlantic high pressure will prevail through Thursday. A cold front
will move across the area Thursday night with high pressure then
building over the region through early next week.
&&
Chs watches/warnings/advisories...
Georgia...none.
SC...none.
Marine...none.
&&
$$
Synopsis...
near term...jrl
short term...jaq
long term...jaq
aviation...jaq/jrl
marine...jaq/jrl
tides/coastal flooding...jaq
