Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
644 am EDT Tuesday Oct 21 2014
a cold front will approach from the northwest today and push
offshore late tonight. High pressure will dominate through late
Near term /until 6 PM this evening/...
added a mention of patchy dense fog and issued a Special Weather
Statement for areas that saw rain overnight. Do not anticipate the
need for a dense fog advisory with sunrise approaching...but
trends are being monitored.
Any lingering shower/thunderstorm activity developing ahead of a
pronounced surface trough moving across the central parts of North
Carolina... South Carolina and Georgia will be well offshore by
sunrise as the trough shifts off the coast. Expect conditions to
rapidly dry out in the wake of the trough as the tail end of its
supporting short wave pivots off to the north. Dry conditions will
persist through the rest of the day under mainly sunny skies.
Solid westerly flow necessitates going slightly above guidance to
for highs today given guidance tends to run a bit too cool in
westerly flow regimes. Highs will generally top out in the lower
80s...even all the way to the coast where the sea breeze will be
pinned near or just offshore.
Short term /6 PM this evening through Friday/...
tonight...cold front will rapidly approach from the northwest this
evening as a frontal wave over the middle-Atlantic pushes offshore.
The front is forecast to clear the coast by late evening with
modest Post-frontal cold air advection setting in after midnight.
Although some middle-level cloudiness will likely accompany the front...
expect mostly clear skies and dry conditions to dominate for much
of the night with lows bottoming out in the upper 40s inland to
the middle-upper 50s at the coast.
Wednesday...the upper level flow will be quite amplified with a deep
closed upper low off the Delaware-Maryland-Virginia coast and a narrow deep layer ridge
from the Great Lakes to the southern MS River Valley. Our region
will be on the southern periphery of the upper low with upper level
northwest flow. At the surface...a polar ridge will build from the
northwest behind a cold front that will be south of the area by
afternoon. Still expect this front to push through dry due to
limited deep layer moisture. Despite mostly sunny skies...maximum temperatures
only in the lower 70s. By Wednesday night...the surface ridge
continues to build in from the northwest...but the center will still
be well northwest of the region over the Ohio River valley. Thus...not
perfect radiational cooling conditions...but guidance still showing
this period to be the coolest for the week...with lows in the lower
40s inland to middle 40s to around 50 coast.
Thursday...the deep upper low moves only slightly northeast to just
southeast of New England by late day. The upstream ridge starts to
flatten/weaken with a pretty weak low level pressure gradient over
the region. Temperatures will moderate slightly into the middle 70s most areas
/near to slightly below normal/. Given the light pressure
gradient...may see a late day sea breeze near the coast. Thursday
night...a broad upper level short wave trough moves in from the
northwest...replacing the weak ridge. This will veer low level winds
to westerly...and along with some mixing due to the short
wave...expect lows to be a bit warmer than the previous night...in
the middle to upper 40s...except lower 50s coast.
Friday..the upper level short wave trough moves across the southeast
u... with relatively dry conditions through the middle and upper
levels...no precipitation expected. Low level winds will be light westerly
with an afternoon sea breeze. The westerly flow will help moderate
maximum temperatures into the middle to upper 70s...near to slightly above normal.
Long term /Friday night through Monday/...
global models have come into fair agreement through Monday...but
then start to diverge by Tuesday. Friday night and Saturday...a weak
upper level short wave trough moves offshore but is quickly followed
by a sharper short wave moving down in the northwest upper flow.
This short wave moves southeast near the region Saturday...but
models differ slightly on its track. If this feature remains as
sharp as models currently show...and moves closer to the area..would
not be surprised if later forecasts need to add at least slight
chance probability of precipitation for first part of Saturday. By Sunday and Monday...a
broad/deep layer ridge builds across the south and southeast states.
This upper ridge is slower to move east in the European model (ecmwf) than GFS on
Generally dry conditions with no probability of precipitation mentioned through Sunday. Some
marginal deep layer moisture begins to return later Monday and
Tuesday with low level east-southeast flow. This has prompted
mention of slight chance probability of precipitation Monday night and Tuesday. Temperatures
slightly above normal /especially maximum temperatures/ through the period.
Aviation /12z Tuesday through Saturday/...
Extended aviation outlook...no concerns.
today...winds will turn westerly as a surface trough pushes
offshore around sunrise and remain so through the day. Winds will
generally be 10 knots or less withs seas 1-3 feet.
Tonight...westerly winds will turn north late as a cold front
pushes through the local marine area. A Post frontal surge looks
decent with winds increasing to 15-20 knots by sunrise Thursday. Seas
will build slightly to 2-4 feet...but will be mitigated somewhat by
the strong offshore fetch.
Wednesday through Sunday...another polar cold front moves through
the waters from north to south on Wednesday. Models continue to
show sustained winds of 15 to 20 knots with gusts near 25 knots just
behind the front. Conditions still too marginal to go with a Small
Craft Advisory for Wednesday morning. If winds do reach Small Craft Advisory
levels...looks like it would be for a short duration...most likely
ending by early afternoon. Otherwise...no highlights expected
later Wednesday through Sunday. High pressure over the region
through Saturday...which becomes reinforced Saturday afternoon
behind an upper level disturbance.