Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1048 PM EST Thursday Mar 6 2014
strengthening low pressure will track up the Carolina coast
tonight. The deepening low will lift northeast through Friday...
allowing high pressure to return and prevail Saturday through
Tuesday. A southern stream system will likely impact the area
during the middle of next week.
Near term /until 6 am Friday morning/...
a powerful closed upper low continues to move east along the
central Gulf Coast region this evening while a surface low
strengthens off the Georgia/SC coast. Water vapor imagery continues to
show a large dry slot spreading across southeast Georgia into southern
SC. This has caused the rain to taper off across southeast Georgia due
to significant middle and upper level drying. Overnight the best
upper dynamics will continue to shift away from the area. The 130
knots jet streak has shifted off the southeast coast...pushing the
left exit divergence region off the coast as well.
The best slug of Omega will continue to shift north overnight into
the SC midlands and points north with the rain mostly ending
during the early morning hours. However as the upper low shifts to
the east and the surface low off the SC coast wraps up...wrap
around moisture and isentropic ascent will spread rain back into
the area late tonight. The best chances for precipitation late tonight
will be the northern and western areas though anywhere could see
some rain from time to time.
Only minor tweaks were made to the going forecast. Temperatures
will cool slightly far inland while warming a couple degrees far
Lake winds...strong northeast winds up to 25 knots are expected
on Lake Moultrie through the first half of tonight. Thus...a lake
Wind Advisory remains in effect and boaters are urged to stay off
Short term /6 am Friday morning through Sunday/...
Friday...a robust closed upper low will be directly over the
southeast states by daybreak...with the associated surface low
having tracked or re-developed off the Georgia/Carolina coastlines.
Both the latest GFS and European model (ecmwf) model solutions suggest plentiful deep
moisture will be wrapping around the back side of the coastal low
during the morning hours...and with a significant cold pool aloft
and decent middle level lapse rates...will support solid rain chances
through at least the early afternoon. The best rain coverage will
occur across northern and western zones closest to the center of the
coastal low. There is still a small chance that showers could
produce soft hail or graupel considering 500 mb temperatures aloft
will be falling to -20 c Friday morning. Periods of rain during the
morning hours...when combined with thick cloud cover...will keep
high temperatures well below seasonal normals. Expect temperatures
to only peak in the upper 40s inland to the lower 50s near the coast.
Friday night...the dynamic coastal low system will become nearly
vertically stacked by the evening hours...while lifting farther
east/northeast away from the area. A few isolated showers could
linger across the Charleston tri County area around sunset. Rain
chances will decrease below 15 percent across the entire forecast
area overnight...as dry high pressure finally pushes into the
southeast states. Clearing skies and light winds will support
ideal radiational cooling conditions...allowing temperatures to
fall into the middle to upper 30s away from the coast. Patchy frost
is still possible during the pre dawn hours...and will continue to
include in the forecast for the northwest tier zones. Will also
maintain mention of a small potential for a frost advisory if
coverage looks to become more extensive.
Saturday through Sunday...the center of surface high pressure
will descend into the southeast states early Saturday and
gradually drift south/southeast overnight. A frontal system will
attempt to shift toward the region from the northwest Sunday
within weak shortwave energy aloft...yet lacking a tap into deep
moisture and eventually becoming parallel to flow aloft...should
result in little sensible weather impacts. Dry and warm
west/northwest flow in the middle to upper levels will assist in a
notable warming trend. Under mostly clear to partly cloudy
skies...high temperatures will rise to around 70 degrees away from
the coast on Saturday...and into the low to middle 70s inland Sunday
afternoon. Coastal areas will be notably cooler both days.
Long term /Sunday night through Thursday/...
the surface ridge will become oriented to the south early next
week...and when combined with a deep offshore flow through the
vertical...temperatures will continue to be above normal. A piece
of energy from an earlier closed low in northern Mexico and the
Southern Plains will head toward the area by middle week...yet dampens
upon approach. Thus there is some uncertainty how much wet weather
will accompany the feature. Will bring in a slight chance of
showers south for Tuesday...than slight chance/chance probability of precipitation
Wednesday. A phasing of the northern and southern streams will
take place late in the forecast period or beyond...and eventually
a more organized southeast storm system could occur.
Aviation /04z Friday through Tuesday/...
IFR ceilings likely to continue through the night at both
terminals. The brunt of the rain is finished at ksav at least
until early Friday morning...then some showers may move back in as
the upper low approaches. Periods of rain will persist at kchs
through early morning before tapering off briefly. Ceilings on
Friday are tricky. It looks as though IFR will continue through
early afternoon at kchs as low-level wrap-around moisture lingers.
However we bumped ceilings up to MVFR at 14z at ksav due to some
slight drying with the departure of the low pressure system.
Extended aviation outlook...VFR conditions are expected Friday
night through Monday.
the tightest gradient for the rest of the night will be across the
SC waters...mainly north of Edisto Beach as the surface low
strengthens and lifts north. We allowed the gale warnings for the
Georgia waters to expire earlier this evening and replaced them with
small craft advisories. The gale for the SC nearshore waters south
of edisto will likely be dropped at midnight while the remaining
Gale Warning for the Charleston waters runs through much of the
Friday...a rapidly deepening low system will be along the Carolina
coastline by daybreak...steadily lifting farther east/northeast
away from the area as the day progresses. Solid Small Craft
Advisory conditions will be ongoing across all waters Friday
morning and could continue into the nighttime period under a
strong 30 to 40 knots jet and enhanced pressure gradient.
Saturday through Tuesday...marine conditions will be on an
improving trend Saturday...as the strengthening low is found far
off into the northwest Atlantic and Continental high pressure
builds from the west. Marine conditions will remain relatively
quiet Sunday under the influence of high pressure...before a
stronger pressure pattern develops in wake of a weak cold front
for Monday and Tuesday. While winds and seas will be higher behind
the front...expect conditions to remain below any Small Craft
we pulled the trigger on a coastal Flood Advisory for the SC coast
earlier this evening due to rather impressive anomalies of about 2
feet above predicted. The anomaly is coming down a tad as we
approach a midnight high tide but it will probably hit 7.0 feet MLLW
at the peak of the tide. It does not look like levels will reach
9.2 feet MLLW at feet Pulaski.
High surf...seas up to 13 feet are expected within the Charleston
County nearshore waters as northeast winds gust to 40 knots and such
conditions should produce breaker heights in the surf zone of 5 to
7 feet. Some beach erosion and dangerous rip currents are also
expected. Thus...a high surf advisory remains in effect..
SC...lake Wind Advisory until 5 am EST Friday for scz045.
High surf advisory until 10 am EST Friday for scz050.
Coastal Flood Advisory until 2 am EST Friday for scz048>050-
Marine...Gale Warning until midnight EST tonight for amz352.
Gale Warning until 5 am EST Friday for amz350.
Small Craft Advisory until noon EST Friday for amz354.
Small Craft Advisory until noon EST Saturday for amz374.
Small Craft Advisory until 10 am EST Friday for amz330.