Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 221036

Area Forecast Discussion
National Weather Service Wilmington NC
638 AM EDT Thu Mar 22 2018

Low pressure far off the New Jersey coast will lift farther away to
the northeast through the morning as Canadian high pressure builds
in from the west. Well-below normal temperatures will continue for
the next several days. Low pressure will move across the Carolinas
Saturday night and early Sunday bringing rain, followed by another
round of below normal temperatures by early next week.


As of 220 AM THURSDAY...Weak cyclonic flow continues across the area
with the old area of low pressure now far off the Jersey coast. The
low will lift away to the northeast through the morning. Residual
stratocumulus will result in sct-bkn cloudy skies in some areas,
however downslope flow will help to erode the lingering low-level
moisture with mostly sunny skies on tap during the day through
tonight. Clear skies and less wind tonight may allow temperatures to
radiate to near freezing in some areas. Will hold off on any freeze
warning at this time given the areal extent of freezing temperatures
across any one county is confined to a handful of locations. The day
shift can re-assess with newer model data. Otherwise, high
temperatures today will be well below normal given the air-mass
in spite of good insolation.


As of 220 AM THURSDAY...A winter-like feel will continue into the
weekend as this anomalously cool March continues. Friday will likely
be a pretty nice day locally despite highs a degree or two either
side of 60, as a dry column and dry W/NW flow allow for abundant
sunshine through the evening. Things begin to change late on Friday
however. Surface high pressure which initially drapes across much of
the eastern CONUS will begin to retreat to the north as a warm front
lifts north from the Gulf Coast states. This front is extended from
a surface low which will be consolidating across the middle of the
country in response to a shortwave digging down from western Canada.
This shortwave will race SE around the longwave trough over New
England through Saturday night, pushing the surface low offshore by
Sunday morning.

As this evolves, moisture will steadily increase in response to
moist advection within the lower portion of the column, forcing
thanks to PVA in the vicinity of the shortwave, and Pacific moisture
streaming overhead within the cirrus level. Cloud cover will
increase Friday night into Saturday, with showers likely developing
by Saturday aftn. The surface low will race along the warm front,
which will then shift south as a cold front as the low moves
offshore. Guidance suggests most of the rainfall will occur behind
the cold front, with isentropic lift atop a developing wedge driving
much of the precip. This would lead to simply a cold rain, but with
deep column saturation QPF could be significant, 0.25 to 0.50 inches
is possible. Highs Saturday will struggle only into the low 50s
across NC zones, but may climb as high as the mid 60s far SW zones
depending on the exact timing of the warm front and WAA racing the
advancing cloud cover and showers. Mins both nights should be too
warm for any frost concerns, although some mid/upr 30s are possible
Friday night across NC zones, depending on how quickly cloud cover
develops. Saturday night lows are likely to remain much warmer,
falling only into the mid 40s.


As of 300 PM WEDNESDAY...Model differences with the next shortwave
are generally minor, however the ECMWF is stronger and a little
slower with the shortwave than the GFS. Although both models show
rain developing into Sunday, this probably explains the better
developed low-level thermal/moisture advection fields shown on the
ECMWF. PoPs have been increased to 50-60 percent for this period,
and it`s looking more and more likely we`ll see a widespread 0.20 to
0.30 inch rainfall event. The ECMWF shows a stable airmass through
the event.

The surface low should jump the Carolinas early Sunday morning,
redeveloping just off the coast where low-level baroclinicity is
significantly greater than inland. Cold northerly winds should punch
southward behind the developing low. Sunday`s high temperature
forecast is actually quite difficult since it`s tough to know
exactly where the front will be located at 7 AM, and temperatures
could actually fall throughout the day in the strong low-level cold
advection. A model blend gives mid to upper 50s across SE North
Carolina and upper 50s to around 60 in South Carolina, however that
could easily be 10 degrees lower if faster cold frontal movement
(like shown on the GFS) occurs. Light rain should taper off during
the afternoon with skies partially clearing Sunday night as moisture
thins from north to south.

Dry and unseasonably chilly weather is expected Monday and
Tuesday as Canadian high pressure builds down the East Coast.
Our 850 mb temps should hover in the +1C to +3C range both days,
between the 10th and 20th percentile for late March. Of
agricultural concern is a possible frost or even freeze event
coming up Monday night as surface winds drop off with the
incoming high. On Wednesday the surface high should finally move
off the East Coast. A westerly component to the low-level flow
will finally bring warm advection and temperatures should pop
back to seasonal norms.


As of 12Z...High confidence in VFR conditions prevailing today
and tonight as high pressure builds in from the west. No real
aviation concerns except the winds which will become gusty by mid
morning. Northwest flow will continue through the afternoon hours,
diminishing by sunset. Light winds overnight with little or no fog
expected as dewpoints will remain in the 20s.

Extended outlook...VFR Friday into Saturday. MVFR/IFR/Rain
developing Saturday night and Sunday. Conditions improving again
for Monday.


As of 220 AM THURSDAY...Latest marine observations indicate
northwesterly winds of 20-25 knots with gusts to around 30 knots.
These winds should begin to gradually subside as high pressure
builds in from the west during the day. Cut back the time of the
Small Craft Advisory by a few hours as a result. Cold air
advection will persist and a bump up in winds to around 20 knots
is possible again tonight. The fetch direction will create a
range in seas with 5 to 7 footers expected away from the coast
through the morning, down to around 3 ft across the inshore
waters. 5 ft seas tonight will be likely while inshore seas of
2-3 ft are expected.

As of 220 AM THURSDAY...Gusty NW winds greet the period but will
wane to 10-15 kts and veer to the N as high pressure ridges down
from the Great Lakes through the day. A more convoluted pressure
pattern develops Saturday as a warm front lifts into the area and
stalls in response to low pressure moving along it. This low will
then skirt overhead to become offshore by the end of the period,
dragging a cold front with it. The wavering of this boundary
combined with the low pressure means that winds will feature a
variety of directions Saturday, with a period of gusty SW winds
south of the front likely across SC waters in the aftn before NE
winds develop late. Speeds should be 10kts or less outside of the
narrow winds of SW winds, so seas are expected to be 1-3 ft most of
Saturday before amplifying late. After a brief period of 3-4 ft seas
early on the stronger NW winds, wave heights fall by Saturday to the
aforementioned 1-3 ft.

As of 300 PM WEDNESDAY...Low pressure redevelopment just off our
coast early Sunday will drag a front southward again in the
morning. Mariners should expect a sudden increase in north-
northeasterly winds as the front dives through, with Small Craft
Advisory conditions developing and likely persisting through
Monday as strong Canadian high pressure builds southward. Our
forecast shows 20-25 kt winds Sunday afternoon through Monday,
but it`s possible there will be some 30+ knot gusts thrown in
there during the period of most rapid thermal advection Sunday
afternoon or evening.


MARINE...Small Craft Advisory until 11 AM EDT this morning for



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