Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
334 am EST Friday Dec 26 2014
high pressure will persist today...before shifting off the coast
Saturday. A weak warm front will lift north Saturday night into
Sunday...then a cold front will move through the area Monday. High
pressure will build into the region for much of next week.
Near term /through today/...
through sunrise...temperatures continue to fall early this morning
within a decoupled boundary layer and mainly clear skies. A few
locations inland will likely drop to near freezing just before
sunrise. Wet grounds and small dewpoint depressions will continue
to support some patchy ground fog. The fog should remain patchy
and fairly shallow...but could become dense at times...especially
in and near low lying areas such as swamps...rivers...marshes and
ditches. With temperatures expected to drop to near freezing well
inland...this opens the possibility that a little freezing fog
could develop. While this is not expected to be significant...a
few slick spots could occur...especially on small bridges
traversing swamps and small rivers. Will monitor trends carefully
in case a freezing fog advisory is needed.
Today...high pressure will remain anchored over the region today
as upper level ridging builds aloft. Models show a weak coastal
trough feature forming late this afternoon as the center of the
surface high shifts to the North Carolina Crystal Coast and
southern Outer Banks. This will result in a veering of the low-
level wind field to the northeast through the day with directions
becoming more directly onshore near the immediate coast later this
afternoon as a weak resultant sea breeze develops. Highs will
generally top out in the middle 60s with temperatures likely falling
at the coast during the middle-late afternoon as the resultant sea
breeze moves inland. Dry weather will prevail with mostly sunny to
partly cloudy skies.
Short term /tonight through Monday/...
tonight...the coastal trough will become a bit more defined
offshore overnight...although the 26/00z NAM looks too aggressive
with its development. The weaker amplitude depicted in the 26/00z
GFS/European model (ecmwf) is preferred given the positioning of the surface high
over the North Carolina Outer Banks. Although some subtle
isentropic assent along the 295k surface will likely support some
stratocumulus over the coastal counties...expect mainly dry
conditions to prevail with relative high condensation pressure
deficits in place...although a few very light sprinkles could
certainly occur over the coastal waters closer to the western wall
of the Gulf Stream. Model relative humidity time sections show cirrus steadily
increasing overnight as the upper level ridge axis shifts slightly
to the east in response to deepening trough over the central and
southern rockies. Mostly clear skies will gradually give way to
partly cloudy conditions overnight...possibly becoming mostly
cloudy prior to sunrise Saturday. Increasing cloud cover and 850
hpa warm air advection will result in a considerably warmer night
with lows ranging from the lower 40s well inland to the middle-upper
40s at the coast with Lower-Middle 50s at the beaches.
Saturday...expansive upper ridging will linger over the Bahamas
and stretch into the southeast states. High pressure at the
surface will be more Mobile...slipping off the East Coast ahead of
a developing frontal system over the Tennessee and lower
Mississippi valleys. Northerly flow will steadily veer as a result
of the shifting surface high...becoming southeast by the
nighttime period. Numerical models indicate moisture increasing
along and ahead of the developing frontal zone...yet suggest that
the bulk of the precipitation will be found outside the forecast
area to the west/northwest. Will continue to indicate a dry
day...while trending toward lower rain chances overnight. Have
capped probability of precipitation below 30 percent Saturday night...with the best
potential along the far western border of the forecast area toward
daybreak Sunday. Temperatures will peak in the middle to upper 60s
despite increasing cloud cover during the afternoon...while low
temperatures remain quite mild in the low to middle 50s.
Sunday...a weak warm frontal feature will have lifted through the
area by daybreak...placing the southeast states within warm
southerly flow on the periphery of Atlantic surface high pressure.
Expect high temperatures to rise well above seasonal
normals...reaching the low to middle 70s under mostly cloudy skies.
Model solutions are indicating varying degrees of organization to
a wave of low pressure along the cold front approaching from the
west. Regardless...most solutions are rather conservative with rain
potential on Sunday ahead of the system...with best chances
overnight when the front is just along the western edge of the
Monday...numerical model solutions remain in some disagreement
regarding the strength of low pressure along the cold front that
will be crossing the area during the early to middle afternoon time
frame. The stronger feature depicted by the European model (ecmwf) will result in
better rain coverage early morning through the afternoon...while
the weaker GFS solution suggests less overall coverage. Will
indicate a general 30 percent rain chance for the forecast area
until there is better model agreement. Expect Monday to be another
unusually warm day...with high temperatures in the low 70s away
from the locally cooler coastline.
Long term /Monday night through Thursday/...
there remains continuing discrepancies between model solutions
regarding the progression of a cold front and the
placement/strength of associated low pressure off the East Coast
from Monday night through middle week. Prefer to keep mention of
isolated rain in the forecast Monday night through
Tuesday...accounting for some weak precipitation generated by
both GFS and European model (ecmwf) solutions on the back side of the front and
along the periphery of building high pressure. Expect dry weather
to prevail middle to possibly late week...as the expansive surface
high builds across the southeast United States. Latest model
trends have slowed the development of a storm system over the
western Gulf of Mexico...thus rain chances currently in the
forecast for Thursday night into Friday could be decreased if
these trends continue. Expect a cooling trend back toward seasonal
normals Tuesday through late week.
Aviation /07z Friday through Tuesday/...
ground fog could occasionally/briefly reduce visibility at kchs
and ksav overnight/early Friday. 06z tafs limit the mention to a
couple of hours of MVFR visibility in bcfg around daybreak. VFR
conditions will otherwise prevail through Friday.
Extended aviation outlook...low chances of MVFR ceilings/visibilities Saturday
into Tuesday as moisture increases over the area.
today and tonight...winds will veer to the northeast today and
persist through tonight as a weak coastal through develops
offshore. Winds look to remain 10 knots or less through the period
with seas 2 feet or less.
Saturday through Tuesday...high pressure will steadily slip off
the East Coast Saturday...with a weak cold front moving into the
marine zones Monday night into Tuesday. Winds will veer south
ahead of the front by Sunday...becoming northeast on the back side
of the feature early next week. Wind speeds could increase on
Tuesday as the gradient tightens...however winds and seas are
expected to remain below Small Craft Advisory criteria through the