Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 061203
Area Forecast Discussion
National Weather Service Charleston SC
703 AM EST Tue Dec 6 2016
A warm front will lift north through the area this morning, then
a cold front will sweep through this afternoon. High pressure
will then build in through Thursday. A strong cold front will
move through Thursday night followed by cold high pressure
through the weekend. Another front may approach early next week.
.NEAR TERM /THROUGH TONIGHT/...
Predawn hours: Rounds of light to moderate rain continue to
redevelop within the large area of deep forcing and moisture,
tracking to the northeast and across the forecast area.
Occasional lulls in rainfall are intermittent as these heavier
rounds moves through. So far, only a few lightning strikes have
occurred over land and this will likely remain the case until
the warm front situated to the south can make some northward
progress and the low level theta E can surge. No significant
changes through sunrise.
Today: Most of the action in the forecast will be this morning
and early afternoon as a surface low tracks into the Tennessee
Valley and secondary cyclogenesis takes place along the North
Carolina coast. The aforementioned warm front will gradually
push northward and begin to scour out the cold air damming
airmass, though this transition will likely be slower than
depicted by the models as is usually the case. Through about mid
morning, the bulk of the precipitation will be similar to what
it has been overnight, just rounds of developing moderate
rainfall. Then late in the morning and through the early
afternoon, a well defined and deamplifying mid level shortwave
will take on a neutral to slightly negative tilt as it pushes
into the southern Appalachians. This will push a channeled
vorticity max into the area, coincident with the main cold front
associated with the system. The main forecast question will
revolve around how quickly temperature recover and the degree to
which surface instability develops. The timing of the front is
not completely ideal being late morning and early afternoon.
However, the near storm environment will be strongly sheared
with local low level vorticity enhancement in the vicinity of
the advancing warm front. If we are able to destabilize
sufficiently, we could see a linear cluster of thunderstorms
capable of producing damaging winds and an isolated tornado. The
models generally all show some degree of convection during this
time, though its hard to ascertain its strength. The convection
we will be dealing with is currently moving across the Florida
panhandle and will soon enter Georgia. We will just have to
monitor its evolution through the morning. Once the convection
pushes through the atmosphere will dry out considerably and rain
chances will decrease. Forecast highs are in the mid to upper
Tonight: Dry forecast overnight in the wake of the departing
coastal low and cold front. The main issue could be the
lingering low level moisture and cooler airmass that could
result in fog/stratus development. Model guidance is quite mixed
and we did not introduce any fog to the forecast as of yet, but
it will need monitoring. Lows are forecast to fall into the
upper 40s in portions of the Tri-County, ranging to the mid 50s
in most other areas.
.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Dry high pressure will briefly build across the area on
Wednesday before a southern stream shortwave pushes a cold front
through Thursday night. Cold Canadian high pressure will then
build into the area late Thursday night into Friday. Mainly dry
weather will prevail during the period. Highs Wednesday and
Thursday will be moderated by downslope flow, with temps in the
mid/upper 60s. Friday looks much cooler with highs in the 40s.
.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
Cold high pressure will persist Friday night through Saturday
night before shifting offshore, allowing for warming temps. A
cold front is expected to approach Monday or Tuesday but given
the uncertainty with timing and moisture we kept the forecast
dry at this point.
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Solid IFR conditions have persisted at KCHS this morning, and
are expected to stick around through midday. At KSAV, conditions
have been much more variable. This may also continue there as
the rain upstream is more in patches so the prevailing flight
category could be determined by the rain that is falling at the
time. This morning, a warm front will lift northward across the
area and a cold front will move through from the west. The 2
main forecast issues are how long will the IFR ceilings hang
around and will there be thunder with the cold front. IFR
conditions will linger longest at KCHS, though both sites will
likely stay IFR into the afternoon. Regarding thunder, it is
still unclear how much destabilization will result with the lack
of insolation. Have kept the mention of thunder out with this
set of TAF`s, but it still remains a possibility as the cold
front comes through. VFR will return late this afternoon before
attention turns to the overnight period. Model guidance is
persistently showing fog/stratus developing from the north late
tonight. Have started to introduce lowering ceilings and
visibilities after 06z, but have kept the forecast MVFR at
Extended Aviation Outlook: Visibility and/or ceiling restrictions
possible late Wednesday night and Thursday morning due to low
stratus and fog. Otherwise VFR.
Today: Ongoing northeast flow will remain enhanced along the
coast within the tight pressure gradient. Eventually this
morning, a warm front will lift northward through the waters and
winds will gradually turn more southerly and southwesterly.
Current winds are supportive of Small Craft Advisories for the
South Carolina waters, and winds will remain enhanced even
within the transition to southerly flow. Seas will increase,
becoming 4-6 feet for the South Carolina waters and the outer
Georgia waters. Thunderstorms could also impact the waters, and
there is a risk for an isolated water spout.
Tonight: The coastal low and cold front will pull away from the
area and winds will veer to be more northwesterly. Winds will
diminish with the loss of the tight gradient and seas will also
come down through the night. The Small Craft Advisories are
expected to come down in the evening for the southern South
Carolina waters, and at midnight for the northern South Carolina
waters and outer Georgia waters.
Tranquil conditions expected Wednesday into Thursday before a
cold front sweeps through the waters. Small Craft Advisory
conditions expected over the offshore GA waters and likely the
Charleston nearshore waters Thursday night into Friday morning.
MARINE...Small Craft Advisory until 7 PM EST this evening for AMZ352.
Small Craft Advisory until midnight EST tonight for AMZ350-374.