North Myrtle, South Carolina 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

574
FXUS62 KILM 220529
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
1229 AM EST Sun Dec 22 2024

.SYNOPSIS...
Cold, dry air will remain through the weekend as Arctic high
pressure moves across the eastern U.S.  The high will move
offshore Monday as a coastal trough develops off the Southeast
Coast. This could lead to clouds and rain chances beginning as
early as Monday night or Tuesday.

&&

.NEAR TERM /THROUGH TODAY/...
High pressure will result in clearing skies tonight and mainly sunny
skies Sunday.  Overnight, wind looks to remain up enough to prevent
a significantly cold night due to radiational cooling.  Lows tonight
are forecast to fall to the mid to upper 20s.  If winds drop off
more than expected overnight, temperatures could be significantly
cooler in rural areas than currently forecast.  Highs Sunday will be
cold, reaching the low to mid 40s.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM MONDAY/...
Sunday night appears to the be the coldest night of this arctic
outbreak. 1039 mb high pressure centered across New England
will ridge southward across Virginia and the Carolinas. Model
temperatures have been relatively stable for the past few days
for Sunday night and the ECMWF remains on the low edge of the
guidance envelope averaging 2-3 degrees colder than other
models. While a radiational inversion will develop Sunday night,
there will be 10-15 kt of wind just above the surface that may
help keep surface temps from dropping to their clear sky
potential. Forecast lows are generally in the lower 20s inland
with mid to upper 20s near the coast. Low temps over pocosins
and peatlands should still dip into the teens.

A coastal trough appears likely to begin to take shape from
south of Cape Fear to the Florida East Coast Monday. The GFS is
among the fastest models to spread overrunning moisture back
across our cold airmass and implies mid level clouds could
arrive from Florence and Marion to Myrtle Beach by mid Monday
afternoon. I`ll go with a slower consensus solution that delays
the arrival of clouds with Monday`s highs still able to reach
near 50 degrees.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Model consensus is lacking for Monday night through Christmas
Day regarding how quickly and how significant the coastal
trough becomes off the Southeast coast. Operational runs of the
NAM, GFS, and Canadian continue to suggest a quick development
of this trough into a formidable entity just offshore, complete
with moist isentropic over our cold low level airmass creating
clouds and rain late Monday night into Tuesday. The ECMWF and
many ensemble members within the National Blend of Models (NBM)
suggest a much weaker and slower-to-develop system that brings
muted effects beginning as late as Christmas Day.

I can`t find an obvious initialization error that leads me to
choose one solution over another. The predicted strength of the
coastal trough shown on the 12z GFS and Canadian cannot easily
be ignored given the huge region of satellite cloud streets and
implied airmass modification/destabilization ongoing across the
western Atlantic currently. I`ve increased forecast PoPs for
late Monday night into Tuesday into the 20-40 percent range, but
am nervously eyeing those 60-80 percent PoPs shown on the latest
GFS MOS bulletins.

Also of possible concern for Monday night: if rain arrives
inland Monday night it`s possible it will encounter surface
temperatures still near freezing. This could lead to a period
of freezing rain at the onset in the Lumberton/Bennettsville/
Darlington vicinity. With such low confidence I did not include
this in the forecast, but it`s a factor to watch over the
coming days.

The remainder of next week`s forecast has low confidence due to
unresolved timing issues with the upper level pattern. A
shortwave aloft is shown on the GFS and Canadian to arrive
Wednesday night, while the ECMWF washes the feature out within a
developing ridge along the Southeast coast. This unfortunately
leads to a forecast with low range (20-30 percent) PoPs through
a good deal of the extended period. The one area where there is
at least some confidence is lower pressures will exist offshore
with higher pressures across New England which should maintain a
northeasterly wind with significant maritime influence across
the Carolinas. The source region for this airmass won`t be
interior Canada so temperatures shouldn`t run particularly cold
late in the week.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Very dry atmospheric column will allow VFR conditions to
continue through the period.

Extended Outlook...VFR conditions are expected through much of the
extended period, though there could be restrictions due to clouds
and showers Monday night into Tuesday.

&&

.MARINE...
Through Sunday...N to NE winds to 10 to 15 KT tonight will increase
to 15 to 20 KT for Sunday with higher gusts.  No flags attm.  Seas
will run 2 to 4 FT.

Sunday night through Thursday...1039 mb high pressure over New
England will build southward along the East Coast through
Monday. Chilly 15 knot northeast breezes will continue through
at least the first half of Monday.

By late Monday, most models begin to develop a coastal trough
from south of Cape Fear down to the Florida East Coast. There
are lingering questions concerning how quickly this feature
becomes a significant weather maker. The GFS and Canadian models
show this process occurring quickly Monday night into Tuesday
with increasing winds and rain developing across the beaches and
offshore. The ECMWF is considerably slower and delays any
significant impacts until Christmas Day. Given the large number
of models now showing earlier impacts, I`ve increased our wind
speed and rain chance forecasts for late Monday night into
Tuesday. Should the GFS and Canadian progs verify, there also would
be the potential for 20-25 kt north winds Tuesday as the
coastal trough reaches its peak intensity.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
NC...None.
SC...None.
MARINE...None.

&&

$$

SYNOPSIS...TRA
NEAR TERM...31
SHORT TERM...TRA
LONG TERM...TRA
AVIATION...SHK
MARINE...31