Area Forecast Discussion
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FXUS62 KILM 200739
Area Forecast Discussion
National Weather Service Wilmington NC
339 AM EDT Mon Mar 20 2017
High pressure across the Carolinas this morning will settle
across Florida tonight. A cold front approaching from the north
will move across the area Wednesday morning. Canadian high
pressure building southward will provide chilly conditions
Thursday with the potential of frost or another freeze. The high
will move offshore Thursday night with moderating temperatures
expected for the weekend.
.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Monday...Nearly ideal radiational cooling ongoing early
this morning, and temps are falling faster than any available
guidance can depict. Many sites are 34 or less as of 3am, with a few
of the typically colder spots, Back Island RAWS, Conway AWOS, Supply
RAWS, at or below freezing. Despite the colder temps, do not expect
a widespread freeze event, and issuing a freeze warning at this time
would do little to help agricultural interests anyway. Have shown
mins tonight falling to 32 or less in several spots, with widespread
sub-35 expected, and the ongoing frost advisory continues. This
means you can expect some frost on those eggs this morning if you
try to balance them - the vernal equinox occurs at 6:28 AM!
The synoptic pattern responsible for this cold night is a large area
of high pressure ridging down from the Great Lakes, combined with
dry NW flow through much of the column upstream of a closed mid-
level low off New England. This flow will allow the surface high to
gradually shift SE today and re-center across the Gulf Coast and
into the western Atlantic. With dry W/NW flow persisting aloft,
abundant sunshine and a slowly rising thicknesses will allow temps
to recover close to seasonable norms this aftn. Highs will range
from the low 60s in the vicinity of Cape Fear, to the upper 60s
along the South Santee and in the Pee Dee. This is on the warm side
of the guidance and in some places even a bit above the warmest
numbers, as strong March sunshine combined with downslope flow
should warm the area nicely from the cold morning lows.
A cold front will begin to approach from the north tonight as the
high shifts further to the SE, and between these two features SW
winds will begin to increase. This will drive warm advection
tonight, which will work in tandem with increasing cloudiness
advecting southward to insulate the surface and create a much warmer
night. Lows by Tuesday morning will fall only to around 50 at the
immediate coast, mid to upr 40s elsewhere.
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 300 AM Monday...Surface high pressure over Florida and the
Bahamas will weaken Tuesday as the upper level ridging across
the Gulf gets beaten down by a developing longwave trough over
the eastern U.S. A surface cold front across the Mid-Atlantic
states will slip southward into North Carolina Tuesday night and
into our area just before daybreak on Wednesday. The spread in
model timing with this front is still a bit larger than we`d
normally see at 60 hours out. The 00z GFS is faster than the 00z
ECMWF or NAM despite similar timing of the 500 mb shortwaves
embedded within the developing longwave trough. I favor the
slower ECMWF/NAM timing.
There is not a great inflow of moisture into this system on
Tuesday. The flow aloft is generally westerly and 850/700 mb
moisture appears to arrive on a circuitous route from the Texas
and then eastward across Arkansas and Tennessee. For this reason
I am not keen on bringing PoPs into the forecast until Tuesday
evening and night when significant lift develops in association
with a train of shortwave disturbances. Lapse rates appear steep
enough aloft to continue to mention thunder in the forecast as
The cold front will push through from north to south Wednesday
morning. Shallow cold advection initially extending only up to
around 4000 feet AGL will probably create persistent clouds and
potentially some patchy light rain or sprinkles during the day.
Drier air should arrive by Wednesday evening with clearing skies
and continued cold advection. Unfortunately for farmers or just
those of us ready to get our spring gardens planted, another
freeze or frost event is possible late Wednesday night,
especially across SE North Carolina.
.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 300 AM Monday...Canadian high pressure over the eastern
Great Lakes Thursday morning will move off the Mid-Atlantic
coast Thursday night and farther offshore Friday. After a chilly
day Thursday with highs only in the 50s we could see one last
night of frost or freeze conditions Thursday night with light
winds in the vicinity of the high. By Friday return flow around
the high should begin to modify the airmass with highs returning
to the 70s by Saturday.
The next synoptic frontal system should begin to move across the
Southeast states this weekend, perhaps spreading showers and
t-storms into the Carolinas Saturday, but with better chances
by Sunday. SPC, in their extended range convective outlook,
mentions weak instability across the warm sector including the
Carolinas but with too much uncertainty to consider a severe
weather risk for now.
.AVIATION /06Z MONDAY THROUGH FRIDAY/...
As of 06Z...High confidence in VFR through the valid period.
Expansive high pressure ridging down from the Great Lakes will push
southeastward through today, orienting offshore tonight. This
creates a weak gradient with winds less than 10 kts, slowly backing
from north early, to southwest late. W/NW flow through much of the
column combined with this dry high pressure will keep SKC the rule
as well, although some mid-level cloudiness begins to advect into
the NC terminals late with no cig or restrictions forecast. Despite
the clear sky and light winds, the surface appears too dry for any
fog and have removed inherited TEMPO groups for vsby
Extended outlook...VFR expected through the period except for
possible MVFR/IFR conditions from low ceilings and pcpn ahead of
the next cold front Tuesday night into Wednesday.
NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Monday...Expansive high pressure will build across the
waters today before re-centering to the S/SE tonight. This will
persist a weak gradient through the day, so this mornings north
winds of 10-15 kts will ease quickly to become light and variable
through the aftn before rising again to 10-15kts from the SW
tonight. An easterly swell will remain in the wave spectrum today at
around 11 sec, and will likely be the dominant wave group this aftn
during the period of lightest winds. However, this will become
increasingly masked by an amplifying SW 5 sec wave tonight. Seas of
2-4 ft this morning and again tonight will bookend otherwise more
placid wave heights of 1-3 ft much of the aftn.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 300 AM Monday...High pressure over Florida and the Bahamas
will dissipate Tuesday as a cold front moves south across the
Mid-Atlantic states and into North Carolina Tuesday night.
Admittedly models still have a 6-to-8 hour spread in timing of
when the front will actually arrive, ranging from midnight (00z
GFS) to around sunrise Wednesday morning (00z ECMWF and NAM). I
am still favoring the later timing and my forecast shows
southwest winds Tuesday continuing through Tuesday night. Once
the front does go through Wednesday morning, strong
northeasterly winds will develop with a Small Craft Advisory
almost certainly needed for Wednesday night, if not beginning
during the day on Wednesday.
LONG TERM /THURSDAY THROUGH FRIDAY/...
As of 300 AM Monday...Canadian high pressure over the Great
Lakes on Thursday will sink southeastward to the Virginia coast
Thursday night, then will move offshore Friday. Clockwise winds
blowing around the high will probably maintain Small Craft
Advisory conditions for most of Thursday, if not Thursday night.
By Friday a weaker pressure gradient on the west side of the
high should allow veering winds to diminish to less than 15
knots. A significant east to northeast backswell is expected to
continue through Friday due to the large area of strong winds
covering the western and central Atlantic around the periphery
of this high.
SC...Frost Advisory until 8 AM EDT this morning for SCZ017-023-024.
NC...Frost Advisory until 8 AM EDT this morning for NCZ087-096-099-