Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 251012

Area Forecast Discussion
National Weather Service Wilmington NC
612 AM EDT Mon Oct 25 2021

Showers are likely along the coast this morning as low pressure
develops just offshore. A cold front will sweep across the
Carolinas tonight, potentially accompanied by a few showers.
High pressure Tuesday and Wednesday will bring dry weather, but
strong low pressure is forecast to develop to our west Thursday,
bringing increasing winds and rain through early Friday.


An upper level disturbance moving along the Southeast coast
this morning is helping develop low pressure just off the GA/SC
coast. The coupled upper jet structure (left exit region of a
jet streak across FL and right entrance region of a jet streak
across VA) is perfect to help quickly deepen this low. The GFS
shows 12 millibars of deepening over the next 12 hours! Precip
is being generated through two means: mid level ascent from
isentropic lift throughout the 305-315K layers, and upright
convection enhanced by 70+ degree dewpoints and steep mid level
lapse rates over the region.

Model blends and radar imagery suggest the best rain potential
will exist along the coast where I`m drawing in 60-80 percent
chances this morning. Thunder has been added across Georgetown,
Myrtle Beach, and the coastal waters. Inland, where rain
generated from mid level isentropic lift will have to fall
through a deep sub-cloud dry layer, forecast PoPs are
considerably lower as it should be tougher to get measurable
rainfall. Up to a quarter inch of rain is possible along the
coast -- every bit of it welcome given the very dry last few
weeks we`ve had.

As the upper disturbance and its associated lift moves east of
the region this afternoon, clouds should break and sunshine will
develop across the Pee Dee region. Temps here should reach the
lower 80s, but may remain stuck in the mid-upper 70s closer to
the coast.

A cold front extending south from low pressure over the eastern
Great Lakes will sweep across the area tonight. While a few
days ago there was concern that severe thunderstorms might
accompany this feature, the deepening low offshore should veer
low level winds and slightly reduce helicity, and more
importantly will reduce low level convergence along the front
itself. Only 20-30 percent rain chances are forecast as the
front moves offshore after midnight. Post- frontal cold
advection should keep atmospheric profiles well mixed late
tonight and forecast lows are on the upper edge of the guidance
envelope with upper 50s to lower 60s expected.

Sunshine and breezy northwest winds will occur Tuesday as high
pressure builds southward across the Great Lakes toward the
Carolinas. Highs should reach the low to mid 70s.


Cool and dry conditions in store for the mid-week period as
high pressure briefly ridges down from the north Wednesday
before shifting offshore Wed night. Tightened pressure gradient
around exiting low to the north will prevent winds from
decoupling Tuesday night, but strong CAA will drop temps down to
mid to upper 40s. Cool high temps Wed around 70 degrees with
scattered high clouds. Onshore low level flow Wed night will
keep low temps near normal around 50 degrees.


Next system is still expected to impact the area late Thursday
into Friday. Deep upper level cutoff low/trough over the central
US early Thursday will slowly move eastward, with strongest PVA
forecasted to move across our area Thursday afternoon and
night. As frontal system lifts north across the area late
Thursday, expect moderate rainfall with QPF around 1-1.5"
currently forecasted by WPC. While wind profiles will be
particularly strong, most of the instability for the event is
forecasted to remain offshore. Will still have to keep an eye
out for any changes to potential severe weather near the coast.

The cutoff low lingers over the eastern US Friday into Saturday
before lifting northeastward late Saturday, with flow aloft
becoming zonal for Sunday. Dry air moves in aloft on Friday, but
with lingering low level moisture and cutoff low nearby have
kept low pops in the forecast for the day. Rain chances drop off
Saturday and disappear completely by Sunday. Temperatures will
be on a slight cooling trend from Thursday into the weekend.



Low pressure deepening offshore will bring light showers to the
coastal terminals this morning. MVFR conditions are expected
after daybreak. As the low tracks off to the northeast, expect
precip to end by late morning with MVFR ceilings into the
afternoon hours. Becoming VFR by late afternoon.

Extended Outlook...Low clouds, showers, and low level wind
shear conditions will develop Thursday as strong low pressure
approaches from the west.


Through Tuesday...Low pressure will develop this morning off
the South Carolina coast and move northeastward and away from
the area this afternoon. The biggest impact from this low should
be a period of rain with embedded thunderstorms this morning.
With the low remaining offshore we`ll likely experience a period
of moderate east to northeast winds through early afternoon
before the low away. Winds should then turn southwesterly in
advance of a cold front that should reach the beaches after
midnight tonight. Behind the front winds will shift westerly and
increase to at least 20 knots, perhaps even 25 knots. A Small
Craft Advisory may be needed for late tonight into Tuesday
morning. High pressure building southward across the Great Lakes
will bring dry weather but will also maintain breezy offshore
winds through Tuesday afternoon.

Tuesday Night through Friday...Northwest winds will be a bit
gusty Tuesday night due to tightened pressure gradient around
exiting low, sustained 15-20 kts and frequent gusts to 25 kts.
Seas 3 to 4 ft Tuesday night. Winds slowly relax by Wednesday
afternoon to 10 kts or less out of the north as high pressure
briefly builds in from the north. Seas will diminish to around 2
ft by Wednesday evening as wind chop weakens. As a strong upper
low approaches the area late week, a frontal system will move
across from the southwest Thursday afternoon into Thurs night
bringing increased rain chances, windy conditions, and building
seas. By Thursday evening forecasted S winds 15-20 kts with
gusts to 25 kts, veering to southwesterly overnight. Southwest
winds increase in strength Friday to 20-25 kts and gusts to 30.
As a result seas are forecasted around 5-8 ft Thursday night
through Friday night and a Small Craft Advisory looks likely.


MARINE...Small Craft Advisory from 2 AM Tuesday to 3 AM EDT Wednesday
     for AMZ250-252.


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