Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
551 am EST sun Nov 29 2015
high pressure over the southeast today will give way to a backdoor cold
front that drops toward the area late tonight and early Monday.
Much stronger high pressure will move into New England on Monday and
build south into the area through Tuesday. A cold front will then
push through from the west late Wednesday into Thursday. More high
pressure will return to the area by the start of next weekend.
Near term /through tonight/...
early this morning...a little transient ground fog will be found
across the area...but given the warm grounds it shouldn/T be too
extensive or last too long. Otherwise...scattered-broken middle
level clouds will be the rule with mainly calm winds and temperatures
starting out 5-10f above late November norms.
For today...the middle/upper ridging of the past few days has
transitioned into a more zonal flow overhead as a occasional short
waves pass by to the north. At the surface we find a bubble of high
pressure over the southeast...while a notable baroclinic boundary that
has been stalled to the north begins to sag south from Virginia
into northern NC by sunset. There is plenty of moisture in advance
of this feature in the 700-500 mb layer...but not much down below.
So we/ll remain warm and dry with varying amounts of clouds around
10-20k feet to prevail. Overall though there looks to be a mix of
sunshine and clouds...and an ample supply of insolation. That
along with warm advection and a downslope flow throughout much of
the vertical will lead to another unseasonably warm day. Temperatures
will again peak in the middle or upper 70s...except for upper 60s and
lower 70s near the coast.
Tonight...a part of the frontal system in NC will transition into
a backdoor type cold front that is forced toward or just over the
SC border with NC by daybreak...as a strong Continental high
builds out of Canada and starts to wedge into the middle-Atlantic
region. But the better forcing stays outside the County warning forecast area to the
north/northwest and although there is some lowering and further
moistening of the middle levels...downstairs we still remain
generally void of moisture. Thus we have maintained a rainfree
forecast...with probably the closet showers to occur in the SC
midlands and maybe the Pee-Dee late. Blanketing effects of
extensive middle and high level clouds will hold overnight mins to
nothing lower than middle or upper 50s in most communities. The
exceptions will be a few lower 50s far south where cloud cover is
Short term /Monday through Wednesday/...
Monday and Monday night...shortwave ridging aloft will push to the
east across the eastern Continental U.S. Ahead of a massive upper low centered
over the northern plains/upper Midwest. This will result in rather
uneventful zonal flow across the forecast area during this time. At
the surface...a 1034 mb high over New England will ridge down the
eastern Seaboard while a convergence and moisture zone sets up well
to the north. In fact...model agreement with this feature and the
associated precipitation is good and lends confidence to a dry
forecast for the entire forecast area on Monday. Overnight...the
overall pattern remains the same...though a few of the models depict
some shower activity developing within an embedded surface trough
along the coast. The majority of the area should remain dry...though
areas across eastern Charleston/Berkeley counties and the coastal
waters could see a few showers. Considerable middle/high level
cloudiness is expected to cover the area...thanks in part to a
strengthening upper level jet across the central/Southern Plains.
Highs will continue the above normal string of days...with
temperatures reaching the low 70s in most areas. Overnight lows will
be in the middle/upper 50s.
Tuesday through Wednesday...the pattern aloft will begin to change
as the large upper low moves into the Great Lakes region and the
prevailing flow across the region turns more southwesterly with
time. Tuesday will be dry as the forecast area will be positioned
ahead of a developing cold front to the west. By Wednesday...the
cold front will push eastward and begin to cross the area. Models
continue to be at odds regarding how much precipitation will develop
along the front...with the European model (ecmwf) still the wettest solution. There
are also some timing differences...so given the inconsistencies
nothing more than chance probability of precipitation are in place. The warm/above normal
trend will continue as highs reach the low 70s each day.
Long term /Wednesday night through Saturday/...
the long term period features cooler temperatures behind a departing
cold front that pushes offshore Wednesday night. High pressure will
begin building into the region from the west...though the models
continue to show a wave developing off the southeast coast in
response to a lifting shortwave that approaches the area through
Thursday. The proximity to the coast and the degree of moisture that
is pushed back to the west and inland will determine how much...if
any...precipitation is able to develop across land areas. Given that
the models continue to struggle with consistency on this
features...probability of precipitation have been limited to the 20-30 percent range. By
Friday and Saturday...high pressure will prevail and conditions look
quite benign. Temperatures are expected to see an extended period
below normal...with highs in the low 60s and lows in the low/middle 40s.
Aviation /12z Sunday through Thursday/...
some ground fog through 13-14z this morning...otherwise VFR
conditions will prevail.
Extended aviation outlook...mainly VFR conditions will prevail.
Flight restrictions will be possible Wednesday and Wednesday night
with showers and a passing cold front.
today...a bubble of high pressure over SC and Georgia will equate to a
slack pressure gradient across our local waters...as light to
gentle northerly breezes give way to weak sea breeze circulations
this afternoon. A bigger issue will be in regards to seas...with
lingering modest swells due to several days of NE winds. Those
swells will be as high as 5 or 6 feet across the outer Georgia waters
beyond 30 or 40 nm out...and for that reason a continuation of the
Small Craft Advisory. Closer to shore seas won't be as large...but
still at 3 or 4 feet in height.
Tonight...the bubble high holds near the coast in the
evening...but gives way to a backdoor cold front that makes it
maybe as far south as near Myrtle Beach by 12z Monday. Land breeze
influences will allow for winds to back to the NE...although
speeds won't be any higher than 5 or 10 knots. Wave energy will
again be in the form of swells...although they do drop about a
foot from today.And the Small Craft Advisory on amz374 will have ended prior to
Monday through Friday...high pressure will be the primary feature
into the middle week period with an unimpressive pressure gradient
resulting in around 10 knots of northeast flow into Tuesday. The flow
will then turn more southerly ahead of an approaching cold front
that will push through the waters sometime Wednesday night. Winds
will increase as high as 15-20 knots as a cooler airmass filters in
on Thursday. Seas will also tick upward...and small craft
advisories could return to the waters...especially the outer
Marine...Small Craft Advisory until 5 PM EST this afternoon for amz374.