Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Charleston SC
723 am EDT Monday Apr 21 2014

Synopsis...
high pressure will build over the region through tonight. A weakening
cold front will move across the area early Tuesday night. High pressure
will then prevail into the weekend.

&&

Near term /through tonight/...
an upper trough and series of short waves over the plains states
was steadily shifting a short wave ridge eastward toward Georgia
and the Carolinas this morning. This pattern will continue to boot
the low pressure off the Carolina coast further offshore into the
western Atlantic.

The arrival of the upper ridge and deep layered dry air will spell
sunshine and milder temperatures for the forecast area. Along the eastern
half of the forecast area...we should be able to shake most of the
lingering stratocu by middle morning at the latest per NAM and local
WRF forecast soundings.

Low level thickness forecasts and 00z guidance suggest our forecast temperature
profiles including highs middle/upper 70s are on track. Coastal areas
will notice a definite decrease in wind speeds this afternoon as
the gradient GOES flat with a weak sea breeze likely along beaches
and barrier islands later this afternoon.

Tonight...mostly clear skies with a few high clouds. Radiational
cooling potential looks good inland with rural areas possibly dipping
into the upper 40s with lower to middle 50s low temperatures anticipated along
coastal areas.

&&

Short term /Tuesday through Thursday/...
Tuesday...a middle and upper level shortwave trough will move across
the area Tuesday afternoon...followed by the passage of a weak cold
front from the northwest by early Tuesday night. Forcing associated
with these features should result in a slight chance to chance of
showers throughout the area Tuesday afternoon into early Tuesday
night...with greatest chances expected Tuesday evening into early
Tuesday night as the cold front shifts over the area. Precipitation will
likely end with frontal passage early Tuesday night. Sbcapes between 500-1000
j/kg and lifted index values between -2 to -4 c could support a few
thunderstorms ahead or along the front...but the severe weather
threat will remain quite low given weak downsloping wind fields over
the region. The downsloping wind component along with compressional
heating ahead of the front should result in afternoon temperatures in the
lower 80s away from the coast. Overnight temperatures will cool off quickly
Post frontal passage...reaching the middle 50s inland to low 60s along the coast.

Wednesday and Thursday...high pressure will build from the
north/northwest behind a cold front shifting well into the western
Atlantic on Wednesday...before gradually sliding off the middle
Atlantic coast on Thursday. The pattern will result in quiet/dry
conditions into midweek...with slightly cooler temperatures on Wednesday
modifying on Thursday as a northerly flow becomes southerly in
response to the position of the high pressure center shifting
offshore. In general...overall high temperatures will range in the
middle/upper 70s on Wednesday...with a few 80s in southeast Georgia
away from the coast. By Thursday...the southerly flow will favor
afternoon high temperatures in the low 80s for most locations away from the
coast.

&&

Long term /Thursday night through Sunday/...
the area will remain along the western edge of high pressure
centered over the western Atlantic into the weekend. Southerly flow
over the area should favor periods of showers and/or thunderstorms
each afternoon as surface temperatures peak into the low to middle 80s away from
the coast...especially with enhanced troughing from the north
Saturday. There are some indications of another cold front
approaching the southeast early next week...but confidence remains
low in the timing and position of the front into early next week. At
this time...have maintained overall high temperatures in the lower 80s
Sunday and Monday...with a slight chance or showers and/or
thunderstorms Monday as moisture deepens over the southeast.

&&

Aviation /11z Monday through Friday/...
VFR conditions through 12z Tuesday with occasional wind gusts 15-18 knots
from the north possible during the middle to late morning hours...otherwise
light surface winds this afternoon with near calm conditions tonight.

Extended aviation outlook...VFR conditions expected Tuesday. There
is a small chance of some IFR/MVFR conditions with thunderstorms
Tuesday evening into early Tuesday night. VFR ceilings/visibilities will then
prevail Wednesday through late week.

&&

Marine...
we were able to lower the Small Craft Advisory in the Charleston
Harbor and near shore coastal waters south of Charleston County
earlier. We maintained the advisory for Charleston County near
shore waters until later this morning given the proximity to a
tighter offshore gradient allowing sea heights to diminish slower
along the central South Carolina coast.

Otherwise...winds and seas will diminish through tonight as
high pressure builds from the west. By later tonight...a light
offshore flow should dampen near shore seas to less than 3 feet
with seas over the Georgia waters closer to the Gulf Coast
falling below advisory criteria by this evening with 3 to 5 feet
seas overnight.

Tuesday through Saturday...winds/seas will likely remain below Small
Craft Advisory thresholds through early this weekend. In general...a
southwest flow will strengthen Tuesday and Tuesday evening ahead of
an approaching cold front...with speeds peaking around 15 knots. Seas
will peak between 2-4 feet...highest in offshore Georgia waters. The
front will then move offshore Tuesday night...leading to improving
conditions as high pressure builds from the north/northwest and
dominates the waters through late week.

&&

Chs watches/warnings/advisories...
Georgia...none.
SC...none.
Marine...Small Craft Advisory until midnight EDT tonight for amz374.
Small Craft Advisory until 11 am EDT this morning for amz350.

&&

$$

Synopsis...
near term...
short term...dpb
long term...dpb
aviation...
marine...dpb