Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
401 PM EST Sat Nov 28 2015
high pressure inland will gradually weaken through Sunday as a cold
front becomes positioned to the north. Much stronger high pressure
will move into New England on Monday and build south into the area
through Tuesday. A cold front will then push through from the west
late Wednesday into Thursday.
Near term /until 6 am Sunday morning/...
tonight...high pressure at the surface and aloft will weaken
slightly as a baroclinic boundary over the middle-Atlantic moves a
little closer to US. Some high clouds embedded within the northwest flow
are expected to move over US tonight. They should provide enough
of an influence to prevent fog from forming...especially inland.
But even with these clouds they will not be very thick...which
will allow for some radiational cooling. That combined with the
light/calm winds and the dry low levels should allow temperatures
to fall into the upper 40s across the interior and the low to middle
50s along the coast.
Short term /6 am Sunday morning through Tuesday/...
Sunday...weak high pressure will be in place over the
southeastern United States...supporting a mainly dry forecast
given the lack of strong forcing mechanisms and low level moisture.
However...a series of 500 mb shortwaves will round the northern edge
of a middle level ridge centered to our south...resulting in showers
that develop over the midlands. A few of these showers could drift
over locations well inland Sunday night...but the dryer low levels
will likely limit activity. The more likely scenario will be
increasing middle and upper level clouds through the overnight period.
Temperatures will remain above normal for this time of year...with
afternoon highs in the low/middle 70s over most areas. Sunday night
temperatures will also be mild under increasing cloud cover from the
west. In general...low temperatures should only dip into the low/middle 50s
away from the coast.
Monday...high pressure will shift over the northeastern United
States and build south along the eastern Seaboard...setting up a
slight chance of showers over northern areas where low level
moisture increases and 500 mb shortwave energy briefly touches. Temperatures
will be slightly cooler under The Wedge type feature and
associated cloud cover. Afternoon highs should range in the upper
60s to around 70 in northern areas and peak in the middle 70s in
southeast Georgia. Monday night lows should range in the low to
Tuesday...we could see a few showers in northern areas
early...but The Wedge of high pressure appears to be short-lived
as it breaks down well in advance of cold front associated with
deep low pressure tracking over the the midwestern states. Surface
flow should gradually become south by the afternoon...leading to
warmer temperatures. In general...high temperatures should range in the lower
70s in northern areas to middle 70s in southern areas.
Long term /Tuesday night through Saturday/...
overall confidence in the details of the long term period is not
very high...thanks to poor consistency among the models. While there
is good agreement that a cold front will push through the area
sometime Wednesday/Wednesday night...the European model (ecmwf) has widespread
precipitation along it while the GFS is completely dry.
Thereafter...strong high pressure is prognosticated to build into the area
with some potential for a southern stream system to draw close
enough to the southeast coast to bring deeper moisture and a period
of precipitation. The models have not shown great run to run
consistency so the overall confidence in the late week time period
is low. Once the front moves through on Wednesday...temperatures
looks to be significantly cooler. In fact...highs could be as much
as 10 degrees below climatology for the late week period.
Aviation /21z Saturday through Thursday/...
VFR will prevail.
Extended aviation outlook...mainly VFR conditions will prevail.
Flight restrictions will be possible middle week with showers and a
passing cold front.
tonight...the pressure gradient will weaken slightly as high
pressure over the western Carolinas moves southward...over Georgia.
NE winds will back to the north and ease to around 5-10 knots while seas
subside to 3-4 feet. The exception is the outer Georgia
waters...where seas will remain in the 5 to 7 feet range...causing
the Small Craft Advisory to remain in effect for that marine
Sunday through Thursday...marginal Small Craft Advisory
conditions will continue in offshore Georgia waters into early
Sunday...mainly due to persistent northeast winds and fetch over
the western Atlantic. High pressure will weaken throughout the
day...supporting a weaker gradient that eventually results in
lighter winds and subsiding seas. Stronger high pressure will then
become centered to the northeast and build southward along the
eastern Seaboard on Monday...driving a northeast flow over coastal
waters through Monday night. The increase looks to be
modest...with winds increasing to around 15 knots. The flow will then
weaken and eventually turn more southerly Tuesday and Wednesday
well ahead of a cold front approaching from the west. Another
surge of winds should occur Post frontal passage on Thursday...but the
offshore wind component should limit seas from building to
Marine...Small Craft Advisory until 5 PM EST Sunday for amz374.