Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
154 am EDT Tuesday Mar 11 2014
the region will remain between a trough of low pressure to the north
and high pressure to the south through Tuesday...as unseasonably
warm weather continues. An area of weakening upper level energy will
then track from the Gulf of Mexico Tuesday night to off the southeast
coast on Wednesday...bringing chances for rain. A strong cold
front will move through the area Wednesday night...followed by
much cooler high pressure through Friday. Another cold front and
developing low pressure system could affect the region early later
this weekend and into early next week.
Near term /until 6 am this morning/...
early this morning...no changes needed to the going forecast.
Clear skies should prevail through sunrise...though there may be a
slight increase in thin high clouds.
Tonight...flat ridging will prevail aloft while at the surface a
Lee side trough will linger northwest of the area with high
pressure positioned to the south. Skies will remain clear through
the night and a deep westerly flow will result in dry conditions
across the area. The westerly flow at the surface may not fully
decouple in all areas...and despite good radiational cooling
conditions otherwise...the downslope flow should result in
slightly above normal temperatures tonight. Lows will generally
range from the upper 40s inland to the lower and middle 50s closer to
Short term /6 am this morning through Thursday/...
other than some slight timing differences with the weakening upper
level trough and associated precipitation later Tuesday and
Wednesday...the models generally in good agreement for this period.
Temperatures expected to continue above normal through
Wednesday...then well below normal by Thursday behind the next cold
Tuesday and Tuesday night...a low amplitude middle and upper level
ridge will hold on most of the day Tuesday with low level
west-southwest flow. An advancing...but weakening...upper trough
will be approaching from the southwest by late day. Given warm middle
level temperatures...along with downslope low level flow...expect
high temperatures to near 80 to the lower 80s most areas /10-15 degrees
above normal/. By Tuesday night...the upper trough over the Gulf
continues to advance east-northeast...stationed over the region by
12z Wednesday. Increasing deep layer moisture and lift associated
with the upper trough will produce scattered showers. Middle level
lapse rates may be sufficient enough to produce some isolated...
mainly elevated rumbles of thunder...but have kept thunder of grids
for now. Probability of precipitation will increase to high end chance/low end likely from
west to east through the night. Expect quantitative precipitation forecast values to be mainly less
than 0.25 inches. Low temperatures remaining mild in the middle to upper 50s.
Wednesday and Wednesday night...the weakening upper trough...along
with associated lift and moisture...should be departing during the
morning. Thus...feel best chance for precipitation will be the first half
of the day. The NAM indicates a narrow band of moisture and light
precipitation with the cold front late day/early evening. Thus...have kept
chance probability of precipitation all day. Low level flow will be breezy from the
southwest...and is some sun peaks out...think temperatures will have no
probability getting into the lower to middle 70s most areas. By Wednesday
night...the strong cold front pushes through in the evening with
decreasing clouds/moisture under brisk northwest winds for the first
part of the night. Expect temperatures to dip into the upper 30s inland and
lower 40s rest of the region by sunrise.
Thursday...a deep layer ridge of high pressure builds in from the
west with decreasing northwest wind through the day. Despite sunny
skies...high temperatures not expected to get out of the 50s...and may be
even a little cooler than current guidance and forecast depict.
Lake winds...conditions still look favorable over Lake Moultrie for
a lake Wind Advisory later Wednesday through the first half of
Thursday behind a strong cold front.
Long term /Thursday night through Monday/...
Thursday night still looks to be very cold as Continental high
pressure settles into the area and provides ideal radiational
cooling for the entire region away from the barrier islands.
As a result a freeze is likely along the northwest tier...and a frost
advisory is possible over much of the rest of the area inland from
Flat ridging aloft and surface high pressure in the Atlantic will
allow for air mass modification Friday and Saturday...maybe with a
coastal trough to form out near the Gulf Stream. But any showers
look to remain over the Atlantic.
The forecast gets murky for early next week in response to a cold
front that approaches from the northwest and southern stream energy that
traverses the area. Too much uncertainty to show anything more than
slight chance to chance probability of precipitation...with temperatures not far from normal.
Aviation /06z Tuesday through Saturday/...
VFR conditions will prevail at kchs and ksav through 06z Wednesday.
Similar to Monday...southwest winds could gust into the 18-20 knots
range in the afternoon. High clouds will increase from the west
late and skies should become overcast very late in the period.
There is a low chance that showers could begin to approach ksav
close to 06z Wednesday...but felt like the likelihood was low
enough to not include another from group to introduce vcsh or -shra.
Extended aviation outlook...deteriorating conditions early Wednesday
morning with flight restrictions possible. VFR again Wednesday
night through Friday. Winds will be gusty both in advance and
behind the cold frontal passage Wednesday into Thursday morning.
tonight...southwest winds will gradually veer to westerly late and
be in the 5-10 knots range as the synoptic flow reestablishes itself.
Seas will be no higher than 2 to 3 feet...highest in northern SC waters
and outer Georgia waters.
Atlantic high pressure Tuesday will shift eastward as a developing
strong low pressure system tracks across the Ohio River valley later
Tuesday and the Middle Atlantic States Wednesday. Winds will gradually
increase...possibly reaching low end Small Craft Advisory levels by later Wednesday
just ahead of a strong cold front. The strongest winds will likely
be over the outer waters. By Wednesday night...a strong cold front
will move through with increasing winds from the northwest to high
end Small Craft Advisory...possibly low end gale...especially over the outer waters.
Even if sustained winds stay in the Small Craft Advisory level...gale force gusts
will be possible. Winds and seas will gradually decrease later
Thursday and Thursday night below highlight levels as high pressure
builds over the region.
Friday through Saturday...no high lights are expected at this
point as high pressure over the region Friday shifts into the
Atlantic by Saturday. An inverted trough may form out near the
Gulf Stream during Saturday...perhaps delaying the veering of
winds to southerly.