Scientific Forecaster Discussion
fxus62 kchs 132030
Area forecast discussion
National Weather Service Charleston SC
330 PM EST Wed Dec 13 2017
high pressure will persist across the region through Thursday.
A mainly dry cold front will then push through later Friday and
Friday night before high pressure returns Saturday and Sunday.
Another cold front will move through Monday into Tuesday before
high pressure returns during the middle of next week.
Near term /until 6 am Thursday morning/...
as of 325 pm: a secondary surge of cold air advection is expected to push
across the southern Appalachians early this evening. The primary
cold air advection is expected to remain across the mid Atlantic states.
However, 850 mb winds are forecast to veer from the northwest and
increase to 50 kts across the higher terrain of the western
Carolinas. The downsloping flow should result in a well defined
sfc wave/Lee trough over the adjacent foothills. The forecast
area will remain between the Lee trough to the west and sfc high
pressure centered over Florida. As a result, the pressure gradient
should range between 3-4 mbs. Forecast soundings indicate a
brisk llvl SW jet near 40kts just 2 kft agl. These winds should
bring rounds of 850 mb warm air advection across the cwa, resulting in little to
no momentum Transfer over land. I will forecast steady SW winds
around 10kts, keeping the bl mixed. The mixed layer near the
coast may remain through tonight, resulting in gusts around 20
kts. Low temperatures are forecast to range from the mid 30s
inland to around 40 near the coast.
Short term /6 am Thursday morning through Saturday/...
pretty high confidence this period with no significant weather
expected. Surface high pressure will prevail, although a generally
dry cold front will move through later Friday and Friday night.
Temperatures will be above normal Thursday in the mid 60s aided by
the downslope westerly flow ahead of the approaching cold front,
then return closer to normal Saturday, then below normal Saturday
when most places should stay in the mid to upper 50s. Low
temperatures will be near freezing Saturday morning well inland.
Long term /Saturday night through Wednesday/...
high pressure centered over the area Saturday night will lead to
strong radiational cooling and temps that dip into the mid/upper 30s
inland to low/mid 40s near the coast. Conditions will then become
noticeably warmer on Sunday as a light southerly wind develops on
the west side of high pressure shifting offshore. Temps should
approach the mid 60s Sunday afternoon before clouds develop as
moisture and isentropic ascent increase late. The next chance of
showers should begin Sunday night and increase in coverage on Monday
as a plume of moisture characterized by pwats near 1.75-2.0 inches
advects over the southeast along/ahead of a cold front approaching
from the west. Temps could peak into the upper 60s to near 70
degrees on Monday before fropa occurs. Models insist that mid-lvl
energy will traverse over the southeast before the main mid-lvl
trough axis passes over the area on Tuesday. For this reason, at
least slight chances of showers will be possible Monday night into
Tuesday before dry high pressure returns mid week.
Aviation /21z Wednesday through Monday/...
VFR. Mixing will increase through the morning daylight hours on
Thursday. West-southwest winds are expected to develop gusts into the upper
teens by late morning.
Extended aviation outlook: no significant concerns through Sunday
but restrictions are likely Monday as moisture increases the risk
for low clouds and rain ahead of an approaching cold front.
tonight: a secondary surge of cold air advection is expected to push across the
southern Appalachians early this evening. The primary cold air advection is
expected to remain across the mid Atlantic states. However, 850 mb
winds are forecast to veer from the northwest and increase to 50 kts
across the higher terrain of the western Carolinas. The downsloping
flow should result in a well defined sfc wave/Lee trough over the
adjacent foothills. The marine area will remain between the Lee
trough to the west and sfc high pressure centered over Florida. As a
result, the pressure gradient should range between 3-4 mbs. Forecast
sounding over the edisto buoy 41004 indicates that the mixed layer
will remain above 3 kft, resulting in average momentum Transfer of
low 30 kts gusts. This supports gusts in the mid 20 kts across outer
Georgia waters and the majority of the near shore zones. Tonight, wave
heights will increase to 5-6 ft across amz350 and 374 and 3-4 ft
across the near shore waters south of the edisto river. A Small
Craft Advisory will be in effect starting at 10 PM.
Thursday through monday: small craft advisories will continue into
Thursday morning for the coastal waters outside Charleston Harbor.
Winds/seas will then improve until reaching close to advisory levels
again late Friday/Friday night as a generally dry cold front moves
through, mainly over the Charleston County nearshore waters and
offshore Georgia waters. No concerns then until possibly Monday when
another cold front approaches.
Marine...Small Craft Advisory from 10 PM this evening to 10 am EST
Thursday for amz350-352-354.
Small Craft Advisory from 10 PM this evening to 1 PM EST
Thursday for amz374.