Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
648 am EST Monday Jan 26 2015
a cold front will pass through the region this morning as low pressure
develops off the middle-Atlantic coast. A reinforcing cold front will
move through late Tuesday into Tuesday night. High pressure will
prevail during middle week...before another cold front pushes through
the area on Friday. High pressure will then prevail through the
weekend. Another cold front could shift through the area early next
Near term /through tonight/...
a potent short wave will cross the area early as it rounds the base
of a longwave trough becoming negatively tilted over the eastern
United States. At the surface...cyclongenesis off the North Carolina
coast this morning will rapidly intensify as it lifts northeast
toward the New England coast tonight. Skies cleared overnight in
the wake of a pre-frontal band of clouds as a result of strong
upper difluence but areas of stratocu are expected to redevelop over
the csra and midlands later this morning and across eastern South
Carolina by early this afternoon. Moisture in the 3-6k feet layer
combined with the cold pool aloft could result in the development
of isolated showers across the area mainly north of a line from
Hampton to Edisto Beach this afternoon. We maintained some slight
chance probability of precipitation for the Charleston tri-County area. There is a very
small possibility that some brief small graupel could occur as
well given the steep lapse rates.
Breezy to windy weather will develop late this morning and continue
into this evening when cold air advection then builds in. The most
impressive areal corridor for gusty winds in a deeply mixed layer
this afternoon looks to run along I-16 into the Savannah area
where we painted some of the higher wind gusts in our grids.
Depending on how warm it gets and the amount of cloud cover...there
looks like a potential for gusts in the 30-33 knots range at times.
We can easily envision a Special Weather Statement for strong
gusty winds on elevated bridges and surfaces this afternoon in
some areas. We played down cloud coverage in our southern zones a
bit today given the amount of slightly downward momentum seen in
model fields along and south of I-16 plus drying patterns seen on the
latest NAM and Gem sky cover forecasts. Afternoon temperatures in the upper
50s with highs reaching around 60 degrees from Savannah to
Strong cold air advection will occur tonight but radiational effects
will be limited by a good bit of mixing in the boundary layer. Residual
evening clouds across southeast South Carolina will clear overnight with
mainly clear skies by dawn on Tuesday. A fairly uniform low temperature regime
was maintained with middle 30s most areas.
Lake winds...we held off on issuing a lake Wind Advisory as yet given
Santee Cooper water temperatures in the upper 40s. Gusty west winds should
develop along western and Southern Lake shores this afternoon but
extent of gusts topping 25 knots would seem to be limited to a small
portion along west-side boat landings. Cold air advection after
sunset looks like a better candidate for more robust advisory
conditons and a lake Wind Advisory may be hoisted later today.
Short term /Tuesday through Thursday/...
Tuesday and Wednesday...low pressure off the middle Atlantic coast will
deepen substantially while lifting north/northeast and away from the
region...allowing a reinforcing cold front to shift over the area by
Tuesday night. A downsloping westerly wind along with a lack of deep
moisture supports dry frontal passage. High pressure will then build from the
north and northwest through Wednesday with cool and dry conditions
persisting into midweek. In general...expect overall high temperatures in
the low/middle 50s on Tuesday ahead of the front...then low 50s on
Wednesday. Temperatures will range in the low/middle 30s away from the
coast Tuesday night and Wednesday night.
Thursday...surface high pressure will become centered over the
southeastern United States early...then slide offshore ahead of a
low pressure system passing over the Midwest. The pattern will favor
slightly warmer temperatures 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 over most areas...with a few
locations peaking near 60 in southeast Georgia.
Long term /Thursday night through Sunday/...
an area of low pressure will advance over the northeastern United
States with a trailing cold front that pushes through the area
Thursday night into early Friday. Deep moisture will be 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 as the front
pushes offshore. Fairly dry and slightly below normal temperatures are then
anticipated on Saturday as surface high pressure builds from the north
and again on Sunday as a weak but dry cold front shifts over the
area along with the presence of a strong h25 jet aloft. A weak
coastal trough could develop off the southeast coast before the cold
front shifts through the area...but confidence remains too low to
include any precipitation mention in the forecast at this time. High
pressure will return from the west on Monday ahead of a low pressure
system swinging through the upper Midwest...bringing slightly warmer
temperatures as southwesterly flow returns over the southeast.
Aviation /12z Monday through Friday/...
VFR weather will prevail. A very small risk for isolated rain showers at
kchs Monday afternoon as strong energy aloft swings through.
Surface winds will be the main issue at hand after late morning
with prevailing wind gusts over 20 knots likely through the remainder
of taf cycle and even chances for 30 knots gusts during peak mixing
this afternoon. Gusty west flow should persist into the evening hours
as a strong pressure gradient remains in place. Gust potential should
gradually subside after 06z Tuesday.
Extended aviation outlook...VFR conditions are expected at both chs
and sav terminals through late week...but a cold front could bring a
few showers to the terminals Thursday night into early Friday.
we upgraded a gale watch to a Gale Warning for 20-60 nm waters later
today into tonight on this package. Small Craft Advisory conditions
already ongoing beyond 20 nm are expected to expand over the near
shore legs today in the wake of a cold front. The strongest flow
with this event looks to be setting up through and just south of
the Savannah River entrance region given the snappy trajectory of
the passing upper level energy and various momentum forecasts. A good
setup for strong jetting profiles to develop in places like fort
Pulaski and Grays Reef. Small Craft Advisory conditions will
persist into tonight for all near shore waters and the Charleston
Harbor as improved mixing profiles take shape. The wavewatch
appeared woefully underdone in this event off our southern coast
and adjustments were made to bring seas to 8-9 feet nearing the Gulf
Stream tonight...they could certainly be locally higher over
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 will likely remain above
Small Craft Advisory thresholds through late Tuesday morning for all
waters outside the chs Harbor...while possibly lingering in outer
Georgia waters into Tuesday afternoon.
Wednesday through Sunday...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...slightly enhancing
and changing a southerly wind to northerly as high pressure builds
in behind it. A weak coastal trough could develop offshore on
Saturday...with a few showers eventually shifting over nearshore
waters...but another cold front should put an end to activity as it
shifts offshore on Sunday. Winds/seas are expected to remain below
Small Craft Advisory levels this weekend into early next week.
Marine...Small Craft Advisory from 11 am this morning to 11 am EST
Tuesday for amz330.
Small Craft Advisory until 11 am EST Tuesday for amz350-352-
Small Craft Advisory until 2 PM EST this afternoon for amz374.
Gale Warning from 2 PM this afternoon to 7 am EST Tuesday for