Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
714 am EDT Monday Mar 10 2014
the region will remain between a trough of low pressure to the north
and high pressure to the south through Tuesday...as unseasonably
warm weather continues. Weakening middle level energy will track from
the Gulf of Mexico Tuesday night to off the southeast coast on Wednesday.
A strong cold front will move through the area Wednesday
night...followed by much cooler high pressure into next weekend.
Another cold front and developing low pressure could affect the
region early next week.
Near term /through tonight/...
today...another quiet and tranquil day is on tap. The pattern aloft
will continue to feature zonal flow with channeled vorticity energy
passing through. The surface will feature a low pressure system
passing north of the Great Lakes and high pressure well south of the
forecast area with a Lee trough noted across Georgia and the
Carolinas. Model time heights and cross sections feature a very dry
atmosphere with precipitable waters falling to around 0.5 inches.
Therefore...expect to see sunny skies throughout the day. Low level
thickness forecasts for high temperatures have been noted to be too cool
the past couple of days. With west to southwest flow noted and
little change from the setup from Sunday...highs should be quite
similar if not a degree or two higher. As such...the forecast is
primarily persistence with a slight nudge upward. This results in
many areas reaching 80...and temperatures will generally run 10-12
degrees above climatology.
Tonight...little change to the overall setup as the Lee trough
persists inland. Clear skies will prevail...though a few high clouds
may make a run for the far western zones very late.
Regardless...expect things to be clear and quiet with lows falling
into the upper 40s inland ranging to the low to middle 50s at the coast.
Short term /Tuesday through Thursday/...
Tuesday...a deep offshore flow between a Lee side trough inland and
an expansive sub-tropical ridge to the south will provide US with
yet another very warm day. Short wave ridging aloft and the lack of
moisture means there is yet again no risk for any showers. Plentiful
insolation and an expansion of the low level thickness of some 10-15
meters will support maximum temperatures in the upper 70s and lower 80s. But
the resultant sea breeze will limit shoreline communities to about
10-15 degrees cooler.
Tuesday night through Wednesday night...the synoptic situation will
become more progressive and also more active. A southern stream
impulse will trek steadily east along the northern Gulf Coast
Tuesday night...while the out of phase northern stream trough digs
through the northern and Central Plains to the middle and upper MS
valley. Falling heights aloft and increasing positive vorticity
advection will combine with an increase in mainly middle/high level
moisture to result in slight chance to chance probability of precipitation arriving from
west/SW to east/NE late Tuesday night. The southern stream short
wave will dampen with time and shifts into the Atlantic off the southeast
coast Wednesday morning. Further upstream the northern stream trough
amplifies further as it heads toward the Appalachians by late in the
day. Out in advance but associated with the digging trough aloft is
a deepening low pressure system that shifts east/NE through the
virginias to New Jersey and Delaware. Trailing from a 985 mb low
will be a significant cold front that looks to approach from the northwest
late Wednesday and travels rapidly through Wednesday night in
conjunction with the upper trough swinging to the east and southeast coast.
There remains some uncertainty as to exactly how the weather pattern
unfolds for Wednesday. Is there a break in the precipitation
produced by the initial southern perturbation and the precipitation
resulting from the deep layer forcing ahead of the upper
trough/associated cold front...or do showers could persist through
the day. Thus the timing...distribution and magnitude of probability of precipitation remain
uncertain. For now we have played middle of the Road with 40-50
probability of precipitation...before activity ends with the frontal passage Wednesday
night. We feel a little higher confidence that temperatures will again be
far above normal Wednesday...although not quite as warm as recently.
Temperatures will crater behind the front Wednesday night...possibly as
much as a 30-35 degrees colder by daybreak Thursday.
While we can/T entirely rule out some T-storms Wednesday
afternoon/evening if we are able to get some surface based
instability...odds at this stage suggests that T-storms are a low
possibility. And any severe weather...while not zero...is even less
likely with only marginal shear and the forecast area lies within
the unfavorable right exit region of the upper jet.
Thursday...although cold advection in the morning does slacken in
the afternoon...the change in weather will be a shock to the system
after several days of temperatures way above normal. Despite plenty of
sunshine...we Haven/T strayed far from the pure low level thickness
forecast. This supports highs only in the lower and middle
50s...with a risk that some far northern locations could struggle to
get out of the 40s.
Lake winds...conditions on Lake Moultrie appear moderate to highly
favorable for a lake Wind Advisory Wednesday through Thursday.
Long term /Thursday night through Sunday/...
you/re not reading the forecast incorrectly for Thursday night...as
cold Continental high pressure settles into the area and provides
ideal radiational cooling for just about everywhere away from the
barrier islands. As a result a freeze is likely along the northwest
tier...and a frost advisory is possible over much of the rest of the
area inland from US-17.
Flat ridging aloft and surface high pressure in the Atlantic will
allow for air mass modification Friday and Saturday...maybe with a
coastal trough to form out near the Gulf Stream. But any showers
look to remain over the Atlantic.
The forecast gets murky for early next week in response to a cold
front that approaches from the northwest and southern stream energy that
traverses the area. Too much uncertainty to show anything more than
slight chance to chance probability of precipitation...with temperatures not far from normal.
Aviation /12z Monday through Friday/...
VFR conditions will prevail at kchs and ksav through 12z Tuesday.
As mixing heights peak this afternoon we/ll experience some gusts
in the middle and upper teens for several hours...before dropping off
Extended aviation outlook...VFR into Tuesday night. Flight
restrictions possible associated with a cold front middle week. VFR
again Wednesday night through Friday. Winds will be gusty both in
advance and behind the cold frontal passage Wednesday into
today and tonight...quiet and rather benign conditions will persist
for the local waters. The pattern will feature a Lee trough
positioned inland which will drive a west to southwest flow across
the waters. Wind speeds are expected to be 15 knots or less with seas 3
feet or less. Locally along and near the beaches...winds may back
around to more southerly for a few hours this afternoon due to a
subtle sea breeze. Otherwise...west to southwest flow will be the
predominant wind direction.
Tuesday...the sub-tropical Atlantic ridge situated to the south of
the local waters with a weakening Lee side trough found inland over
the Carolinas. Westerly winds will back around to the SW in the
afternoon in response to sea breeze circulations. Winds and seas
will hold under 15 knots and 2-3 feet respectively.
Wednesday through Thursday...conditions take a turn for the worse as
a strong cold front approaches from the northwest late Wednesday and moves
through Wednesday night. Warm advection will limit mixing in advance
of the front...but small craft advisories are possible.
However...behind the front there are huge isallobaric pressure
rises...perhaps as much as 1 mb/hour if not more. When combined with
intensifying cold advection...we/re looking at the potential for
gales across all Atlantic waters. In Charleston Harbor it will
definitely be strong Small Craft Advisory conditions...but a few
hours of gales can/T be ruled out. Conditions begin to improve by
late Thursday as pressure rises slow and cold advection shuts off.
Friday through Saturday...marine conditions are much better under
the influence of high pressure. An inverted trough may form out near
the Gulf Stream during Saturday...perhaps delaying the veering of
winds. Either way we/re well below any Small Craft Advisory criteria
during this time.