Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1101 am EST sun Mar 1 2015
high pressure will continue to wedge southward over the region today
while a coastal trough lingers off the southeast coast. A cold front
will shift over the area late Monday then stall just south of the
area Monday night as high pressure builds from the north. The front
will lift back north as a warm front Tuesday afternoon ahead of a
cold front that shifts through the area late Wednesday into Thursday.
High pressure will then build over the area through the weekend.
Near term /through tonight/...
today...a well pronounced coastal trough lingers just off the
southeast U.S. Coast...while a surface wedge remains firmly
entrenched across inland areas with the weakening parent high
positioned near the middle-Atlantic coast.
Abundant low and middle level moisture combined with isentropic
ascent continues to support good coverage or rain across mainly
central and northern portions of the forecast area late this
morning. The hrrr and other high resolution mesoscale models
appear to be handling location/coverage of the precipitation
fairly well...and generally show the rain shield lifting northward
through the afternoon. As a result...the pop forecast shows
lowering rain chances across southeast Georgia through the
day...but probabilities peaking at 60-80 percent in southeast
South Carolina early this afternoon before rain chances lower as
well late in the day.
The temperature forecast remains very tricky. While the coastal
trough is not expected to shift inland due to the cool/stable
shelf waters...most of the models continue to show some warmer air
in the boundary advecting just inland along the coast. With the
most recent update...have lowered temperatures along the coast
just a bit to account for the latest model trends...but tightened
the gradient further by lowering temperatures well inland near the
core of The Wedge. High are now forecast to range from the middle 40s
well inland to the middle 50s near the coast.
Tonight...widespread low clouds will blanket the region going
into tonight with stratus potentially building down enough to be a
concern for dense fog in some areas tonight as significant drying
advects NE into the 925-850 mb layer. We have fairly low
confidence at this juncture but enough to justify upgrading patchy
fog to areas of fog as a trend. There will probably be patchy
drizzle around the region tonight given forecast sounding profiles
and the synoptic overview. Low temperatures mainly 40 to 45 degrees but
readings many be steady or rising late.
Short term /Monday through Tuesday/...
Monday...a brief warmup will occur in advance of a cold front that
approaches from the north late in the day. Temperatures should peak in the
middle 60s north to around 70 south of Interstate 16 in southeast
Georgia. Slight chances of showers are possible ahead of the
front...followed by chances of showers as the front stalls just
south of the area Monday night. Precipitation coverage should remain
highest in northern areas through the overnight period. Low temperatures
will be warmer than the previous night...in the upper 40s north to
low/middle 50s in southeast Georgia.
Tuesday...high pressure will wedge southward into the area
early...before a stationary front lifts north as a warm front during
the afternoon. Chances of showers will be possible north of the
front...before most precipitation shifts to our north Tuesday night. High
temperatures will be largely dependent on the position of the warm front
over the course of the day. Cloud cover and a few showers will also
pose some limiting factors as to how warm conditions will get during
typical peak heating hours. At this time...have maintained temperatures in
the low/middle 60s for most areas...with perhaps some low 70s for
locations south of Interstate 16 in southeast Georgia.
Wednesday...strong warm air advection will occur as southerly flow
strengthens over the southeast United States well ahead of a cold
front approaching from the west late Wednesday night. Breaks in
cloud cover as well as some compressional heating support the
warmest temperatures of the week...with high temperatures in the middle/upper 70s
over most areas before the onset of showers late Wednesday
Long term /Tuesday night through Saturday/...
a cold front will approach western zones Wednesday night with mainly
showers. However...strong forcing will be associated with the
front...supporting the need for a few thunderstorms over inland
areas early Wednesday night. The cold front will then continue to
push through the area early Thursday...with greatest coverage of
showers Thursday morning and afternoon. Most showers will then shift
offshore Thursday night into early Friday as cooler high pressure
builds behind the front. Thursday and Friday night low temperatures should
be the coolest of the week...in the middle/upper 30s. Afternoon highs
will only be in the low/middle 50s into the weekend. High pressure
should prevail through the weekend...but there are indications that
some showers could develop mainly along the coast as a surface low
develops offshore and deepens while lifting to the north/northeast.
Aviation /16z Sunday through Thursday/...
at kchs...ceilings should become IFR later this morning as light
rains develop and spread both inland and north along the coastal
corridor. At sav...ceilings likely already locked into IFR or lower
through 12z Monday.
Both sites can expect periods of light rains and drizzle today
with precipitation probably lasting longer into the afternoon at kchs.
Despite the high confidence in ceilings below 1 kft...confidence is
not good with how far down ceilings will build and at what time later
today and tonight. The synoptic pattern favors fog and drizzle
in the wake of light rains and we played continued deterioration
this afternoon and tonight with lower IFR cigs/vsbys. There is a
chance for build down fog this evening or overnight and widespread
LIFR through the coastal corridor.
Extended aviation outlook...VFR conditions are expected Monday. A
backdoor cold front could produce a round of flight restrictions
Monday night and then again on Tuesday as it returns as as warm
front. VFR conditions should return on Wednesday...before another
round of flight restrictions occurs Wednesday night into Thursday
as a cold front shifts through the area.
high pressure will wedge inland on today while a coastal trough
lifts north along the southeast coast. A strong pressure gradient
between these two features is forecast to decrease with a much
lighter gradient by later today and tonight. It will difficult to
turn directions away from a northerly component given the stable
chilly shelf waters but they could become more northwest to north later
tonight. Seas should fall below 5 feet tonight except over outer
Georgia waters where elevated seas will maintain advisory levels
until at least late in the night. Stratus clouds could lower to
1-2 hundred feet over cool stable waters along the land/sea
interface overnight. We included areas of fog as visibilities likely will
be lowered at least somewhat by lower ceilings.
Monday and Tuesday...winds/seas should remain below advisory levels
as a cold front approaches from the north on Monday...then stalls
just south of the coastal waters Monday night. However we could see
winds between 15-20 knots over northern SC waters late. The front will
then lift back north as a warm front Tuesday afternoon with dewpoints
that approach the upper 50s to around 60 late in the day. Sea fog
could be an issue...mainly over southern waters Tuesday night.
Wednesday through Saturday...greatest chances of sea fog will be
possible on Wednesday and Thursday as deep moisture advects over
cooler waters ahead a cold front. Winds and seas will also gradually
increase/build ahead of the front...likely supporting the need for
solid small craft advisories Thursday evening into Friday as the
cold front shifts over the waters and is followed by colder high
pressure. Conditions should slowly improve late weekend as the
pressure gradient becomes more relaxed over coastal waters.
Marine...Small Craft Advisory until 4 PM EST this afternoon for amz350-
Small Craft Advisory until 5 am EST Monday for amz374.