Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
400 am EST sun Jan 25 2015
high pressure will move across the area today. Low pressure will
pass north of the region Sunday night into Monday. This will allow
a cold front to swing through the area late Sunday night and early
Monday...with another reinforcing cold front on Tuesday. High
pressure will then prevail through Thursday...before another cold
front pushes through the area Friday. High pressure will then
prevail through next weekend.
Near term /through today/...
surface ridging will extend across the region today as a sharp
upper trough begins to dig across the Central Plains. This will
result in a continuation of some much needed dry weather for the
lowcountry and coastal Empire. A few whips of thin cirrus elements
could traverse the area from time-to-time...but sunny skies will
prevail for much of the day. Full sun thickness schemes support
highs in the lower 60s for most locations away from the
beaches...which is at or just slightly above normal for late
January. A weak sea breeze circulation is likely to develop by
middle-late afternoon...which will keep beach locations considerably
cooler where influences from the chilly Atlantic shelf waters will
be the most prominent.
Short term /tonight through Wednesday/...
tonight...the sharp upper trough and its attendant clipper system
will approach rapidly from the northwest tonight. The 25/00z
NAM/GFS/ECMWF with support from the 25/03z sref are similar in
showing a band of mainly light showers developing over northern
Florida into the western wall of the Gulf Stream off the lower
South Carolina coast late tonight where the combination of deeper
moisture...DPVA induced by the upper trough and 160 knots left exit
region of the 250 hpa jet will align. A few showers could brush
portions of the Georgia coast late...but the bulk of this
activity is expected to remain just offshore and to the south. Dry
conditions will prevail otherwise. Lows will range from around 40
well inland to the middle-upper 40s at the coast.
Monday...an impressive shortwave will round the base of longwave
trough shifting over the eastern Continental U.S.. the shortwave will help push
a surface low through the Middle Atlantic States near daybreak...with a
trailing cold front that extends southward. Deep moisture will be
lacking over the southeast as cold frontal passage occurs early Monday...but a
strong cold pool associated with the shortwave aloft will produce
steep lapse rates and the possibility of a few showers...mainly over
northern areas. Given the strength of the cold air off the
surface...there remains a possibility of some graupel with any
showers...but given the small chance precipitation and westerly winds
quickly drying out conditions Monday afternoon/evening have opted to
mention just showers at this point. A downsloping wind component
will likely offset some cold air advection...but temperatures should only
peak in the upper 50s over most locations. Despite cooler afternoon
temperatures...gusty winds between 20-25 miles per hour are possible throughout the
day. Dry conditions will prevail Monday night while temperatures cool into
the middle to upper 30s.
Tuesday and Wednesday...low pressure off the middle Atlantic coast will
deepen substantially while lifting northeast and away from the
region...allowing a reinforcing cold front to shift over the area.
Moisture will once again be lacking over the region...thus dry frontal passage
is anticipated. High pressure will then build from the north and
northwest through Wednesday with cooler and even dryer conditions
into midweek. In general...expect overall high temperatures in the low/middle
50s on Tuesday ahead of the front....then low 50s on Wednesday.
Overnight lows will range in the low/middle 30s away from the coast
Long term /Wednesday night through Saturday/...
surface high pressure will build from the north/northwest Wednesday
night...become centered over the southeastern United States early on
Thursday...then continue to shift offshore ahead of another low
pressure system passing over the Midwest. The pattern will favor a
slight warming trend through early Thursday night as weak middle level
ridging occurs and a light southerly flow develops well ahead of the
low pressure system passing to the north. In general...afternoon
high temperatures should peak in the upper 50s to around 60 on Thursday. A
cold front extending southward from the low pressure system passing
over the northeast will then shift over the southeastern United
States Thursday night into early Friday. Moisture is rather lacking
during the time of frontal passage...so have maintained a dry forecast at this
point...but a few showers are not out of the question. Dry and
slightly below normal temperatures are then anticipated as high pressure
builds from the north behind the departing cold front on
Friday...but a weak coastal trough could develop off the southeast
coast during the weekend...thus increasing precipitation chances along the
Aviation /06z Sunday through Thursday/...
Extended aviation outlook...VFR conditions are expected at both chs
and sav terminals through Thursday. However...we could see gusty
winds at both terminals on Monday behind a passing cold front.
today...offshore winds will turn southerly this afternoon as the
surface ridge shifts offshore. A weak sea breeze circulation is
expected to develop along the beaches late...but should have
little impact on speeds given the weak nature of the circulation.
Seas will average 2 feet or less.
Tonight...southwest winds will increase ahead of a clipper system
and the associated upper trough. Winds look to peak 15-20 knots...but
may be closer to 20 knots over the Georgia offshore leg. Seas will
build to 2-4 feet nearshore and 4-5 feet offshore. Conditions will be
close to Small Craft Advisory criteria for the Georgia offshore
leg...but conditions look to remain just shy of criteria at this
time. Flags will not be issued with this forecast cycle...but may
eventually be needed.
Monday and Tuesday...an area of low pressure will track over the Middle
Atlantic States then push offshore with a cold front that extends
southward over the region. A tightened pressure gradient associated
with the passing low pressure system and cold front will likely
maintain elevated winds and enhanced seas through much of Monday and
Monday night...possibly resulting in Small Craft Advisory conditions
over coastal waters outside chs Harbor...and likely continuing
Small Craft Advisory conditions in offshore Georgia waters. By
Tuesday...low pressure will deepen while lifting northeast along the
New England coast...allowing a reinforcing cold front to shift over
coastal waters by Tuesday night. Winds/seas should be just below
advisory criteria for most waters during frontal passage...except in outer
Georgia waters where marginal Small Craft Advisory conditions should
Wednesday through Saturday...high pressure will build over the
waters behind a departing cold front...with much quieter conditions
over the coastal waters through Thursday. A cold front will then
shift over the area Thursday night into early Friday...changing a
southerly wind to north/northwest as high pressure builds in behind
it. A weak coastal trough could develop offshore next weekend...with
a few showers eventually shifting over nearshore waters.
However...winds/seas are expected to remain well below Small Craft
Advisory levels during this time frame.
Marine...Small Craft Advisory from 8 am Monday to 11 PM EST Tuesday for