Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
956 PM EDT Tuesday Apr 21 2015
high pressure will prevail tonight through Wednesday. A weak cold
front will drop through the area Thursday evening...then stall to
the south Thursday night. A storm system will affect the region
Friday night through Saturday night. High pressure will build in
from the northwest Sunday into Monday. A cold front may affect the
area next Tuesday.
Near term /until 6 am Wednesday morning/...
very few changes required with the late evening update. Mainly
some adjustments to sky cover and hourly temperature grids.
Since the boundary layer has decoupled and surface winds have
become light or calm this will allow for good to excellent
radiational cooling. One possible caveat for temperatures getting too
cool would be an increase in middle/high level clouds associated with
a 130 knots upper jet that pushes into the area overnight. While
some of these clouds seen on satellite over Alabama and
Mississippi are mainly translucent there are some thicker clouds
in southern Georgia. Overall we are showing little impact from the
cloud cover...as skies trend to partly cloudy. Lows will range
from upper 40s far northwest tier to the lower and middle 50s most
elsewhere...with some upper 50s on the barrier islands.
Short term /6 am Wednesday morning through Friday/...
Wednesday...a quiet weather day is anticipated with high pressure
dominated the southeastern United States under a zonal flow aloft. A
lack of strong forcing and moisture in the low/middle levels will keep
conditions dry over the area...but a strong h25 jet will likely
contribute to cirrus clouds moving over the area late in the day and
overnight period. Overall high temperatures will peak in the lower 80s over
most areas away from the coast. Overnight lows will range in the
upper 50s inland to lower 60s closer to the coast.
Thursday...the best chances of precipitation will occur with a backdoor
cold front that begins to shift into parts of the area from the
north/northwest at the same time a 500 mb shortwave quickly progresses
over the area from the west during afternoon/evening hours. The GFS
solution continues to be an outlier in regards precipitation coverage and
accumulation...while most model output insists on light precipitation and
low coverage over most areas. Have maintained a slight chance of
thunderstorms over all areas...before quickly decreasing probability of precipitation during
the overnight period as diurnal heating is lost. Overall high temperatures
should range in the middle/upper 70s in northern areas where frontal passage will
occur first...and lower 80s in southeast Georgia where peak heating
potential occurs ahead of the front. Expect the front to stall south
of the region Thursday night. Behind the front...cooler temperatures are
anticipated...with lows generally ranging in the middle 50s inland to
lower 60s in southeast Georgia.
Friday...dry conditions are expected Post frontal passage early this weekend
as surface high pressure dominates the pattern and a light northerly
flow occurs over the southeast. Despite some middle-level ridging over
the area...cold air advection from the north will likely offset
afternoon high temperatures. In general...overall high temperatures will range in
the low 70s in northern SC areas to middle 70s in southeast Georgia.
Long term /Friday night through Tuesday/...
a potent shortwave will move through the area Friday night and
Saturday...off the coast Saturday night. A warm front will develop
over the area and slowly lift north during the day Saturday. Backing
low-level flow ahead of the shortwave will support overrunning
precipitation Friday night and Saturday morning...then some
convective rains possible Saturday afternoon and evening as the
front lifts north. There is increasing model consistency with this
scenario so we bumped probability of precipitation up to 50% on Saturday.
Dry high pressure builds in from the north Sunday into Monday with
temperatures slightly below normal. There are some hints that another
system will affect the area next Tuesday but due to large model
differences we maintained a dry forecast and persistence temperatures.
Aviation /02z Wednesday through Sunday/...
VFR conditions will prevail at kchs/ksav through 00z Thursday.
Winds will become gusty Thursday afternoon in advance of a cold
front near the southern Appalachians and sea breeze
circulations...peaking at 15-20 knots.
Extended aviation outlook...low stratus or fog possible Thursday
night into Friday morning as a front drops through. Ceiling and/or
visibility restrictions possible on Saturday with showers and
Continental high pressure will build over the waters tonight
allowing for quiet marine conditions to persist. Slight pressure
rises will keep west/southwest winds around 10-15 knots early
especially in the SC waters...before it subsides to around 5 knots
towards daybreak as land breeze circulations veer winds some
30-50 degrees. Seas will be 1-2 feet...highest in the outer
Wednesday through Sunday...high pressure will dominate the coastal
waters on Wednesday with wind/seas remaining well below Small Craft
Advisory levels. A brief surge is then anticipated behind a cold
front that approaches from the north/northwest Thursday night into
early Friday...with gusts as high as 20 kts over South Carolina
waters and offshore Georgia waters. Increasing westerly flow is then
anticipated next weekend as a storm system passes through...during
which advisories are possible.