FXUS62 KILM 181958

Area Forecast Discussion
National Weather Service Wilmington NC
258 PM EST Sun Feb 18 2018

A front stalled south of the area overnight will return north
as a warm front Monday. Bermuda High pressure will bring
temperatures well above normal beginning Monday with possible
record warmth for the middle of the week. A cold front will
approach from the north on Friday, but may end up stalled before
reaching the area. The Bermuda High will expand over the region
for the weekend. A cold front will approach from the northwest
Sunday night.


As of 3 PM Sunday...A front stalled just south of Savannah, GA
will begin to lift northward late tonight as high pressure over
the Delmarva Peninsula moves offshore. Mid-level cloudiness is
already thickening south of Florence and Myrtle Beach, and a few
showers have even showed up on radar recently. This little
pulse of lift should dissipate over the next couple of hours,
but isentropic upglide over the frontal surface should redevelop
by late evening with more scattered showers expected overnight
into Monday. PoPs around 30 percent are forecast with QPF only
around a few hundredths of an inch expected.

The warm front should slowly move northward tomorrow, but models are
not unified with their depiction of how quickly the front moves
farther north through North Carolina. The GFS and ECMWF push it
through Lumberton and Florence during the afternoon while the NAM
and the ARW/NMM variants of the WRF aren`t quite as fast. Given a
deep bank of low clouds expected ahead of the front and relatively
weak southerly winds to drive the front northward, I`ve lowered high
temperature forecasts northwest of I-95 for Monday mainly into the
60s, with 70s across most of the remainder of the area inland from
the beaches. If the NAM is completely correct, that gradient in
temperatures Monday afternoon could be even more extreme with temps
hung in the mid 50s near and west of I-95!

One more possible forecast issue to keep in mind is sea fog. Sea
surface temperatures are coldest in the shallow water near the Grand
Strand, and this is where high dewpoints behind the warm front will
have the best potential to create sea fog during the day Monday.
Some of this fog could slip onshore at times mainly affecting areas
within a mile of the beaches.


As of 3 PM Sunday...Bermuda surface high pressure and 595dam
ridge at 500mb both off the coast through the period. This will
catapult temperatures well above climatology with nighttime lows
higher than seasonable norms as well as offer near record
afternoon warmth. Something that will also be out of the norm
will be the level of humidity in the air as dewpoints surge into
the low to maybe mid 60s. While sea fog (see marine section) is
not a certainty quite the different situation over land however
where saturation and fog look quite attainable. This idea very
supported by SREF probs both nights.


As of 3 PM Sunday...Main theme for the extended will be strong
surface and mid-level ridging sitting off the coast. Strong mid-
level subsidence and deep southerly flow will contribute to an
extended period of temperatures well above climo. While there is
high confidence in a warm and mostly dry period, there area a
few times within the forecast with much lower confidence. The
first concerns a backdoor cold front Thu night into Fri.
Previous solutions had this feature moving into the area late
Thu night and lingering for much of Fri before returning north
as a warm front. However, recent guidance has shifted away from
this scenario, the both the GFS and ECMWF being quicker to move
the 1040 high across the Great Lakes and into the Northeast.
Given the propensity for ridging to hold on longer than the
guidance expects, am leaning in favor of a warmer, drier
solution Thu night and Fri. Other area of uncertainty concerns
potential cold front late in the period. GFS/ECMWF currently
bring this feature into the area later Sun but not confident it
will arrive that early, which would contribute to warmer temps
Sun night.

Temperatures, as previously mentioned, will be significantly above
normal for much if not all of the period. Medium range guidance
continues to depict heights at level not seen before during the last
week of Feb. At the same time 850 temps will flirt with 15C. Away
from the coast highs will run in the upper 70s to lower 80s through
the period with the possible exception of Fri. Unfortunately, closer
to the coast the combination of water temps in the mid 50s and
onshore flow will keep highs much cooler. The large temperature
gradient will also create rather windy conditions on the cool side
of what should be a strong sea breeze. Lows will range from upper
50s to mid 60s through the period. Average daily temperatures could
run 20-25 degrees above normal each day. Another way of putting it
would be that the departure from normal next week will be equal to
what the area experience during the first week of January 2018, just
in the opposite direction.


As of 18Z...Currently VFR. Northeast winds will veer to easterly
later this afternoon as high pressure moves off the Mid-Atlantic
coast. Winds will continue light east to northeast tonight. A
warm front begins to return north overnight. Increasing low and
mid level moisture and weak isentropic lift will bring MVFR
cigs and patchy light rain into the terminals this evening.
Overnight there is high confidence IFR cigs cigs will develop
although confidence in timing is low attm. Precipitation should
increase in coverage but it should remain light with weak
forcing. LIFR cigs possible 11-15Z mainly coastal terminals as
the frontal inversion lowers. Cigs increase to IFR mid to late
morning with some MVFR possible.

Extended Outlook...VFR with periods of MVFR through Fri. Good
chance of extended periods of IFR/LIFR in sea fog coastal
terminals Tues-Fri.


As of 3 PM Sunday...A cold front pushed south across the area
early this morning and has stalled out just south of Savannah.
1031 mb high pressure over the Delmarva Peninsula will move off
the Mid- Atlantic coast overnight, with return flow behind the
high gradually starting to lift the front back to the north on
Monday. Northeasterly winds behind the front will continue to
increase in speed through this evening, and we`re issuing a
Small Craft Advisory for the NC waters through midnight for
winds up to 25 kt and 6 foot seas inside 20 miles of shore. An
`exercise caution` headline will continue for the SC waters
where conditions should not become quite as severe. Winds and
waves should diminish overnight.

On Monday the front, now a warm front, will lift northward across
the area during the morning hours. Winds shifting to the south will
bring much more moisture across the area, and this will create the
potential for sea fog mainly over the South Carolina coastal waters.
SREF probabilities for visibility less than 1 mile are over 70
percent just off Murrells Inlet Monday afternoon, and it`s possible
we`ll need a marine Dense Fog Advisory.

As of 3 PM Sunday...Quite the summer-like pattern in store for
the short term. High pressure well off the coast to bring a
light southerly wind (whereas a closer to shore Bermuda high
usually brings SW winds). Wave spectral bulletins show that
light seas will generally be in the wind-wave period, with a
weak swell component not really materializing locally until
later in the week. A point of uncertainty will be the
development of sea fog given these dewpoints. We`ve already had
a few setups this season and some have panned out while other
have not. The short term seems more like the latter where
dewpoints are not quite elevated sufficiently and the airmass
grows so warm that saturation becomes difficult.The SREF
probabilities disagree to an extent, especially over SC waters
where SSTs are a tad cooler.

As of 3 PM Sunday...Bermuda High will extend across the waters
through the period, maintaining south to southwest flow with
speeds 10 kt or less. Weak backdoor cold front will try to drop
in from the north early Fri, but it is starting to look like the
front will stall before reaching the area. Flow may become a
little more easterly during Fri, depending where the front ends
up, but speeds would drop closer to 5 kt. Seas will run 2 to 3
ft through the period with occasional 4 ft possible near Frying
Pan Shoals later Thu and Thu night.


MARINE...Small Craft Advisory until midnight EST tonight for AMZ250-252.




NWS ILM Office Area Forecast Discussion