Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 120830
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
330 AM EST Tue Dec 12 2017

.SYNOPSIS...
Today will be breezy and the warmest day of the week. The passage
of a strong cold front later today will usher in Arctic air
tonight and through Wednesday night. Temperatures will quickly
moderate Thursday and Friday. A cold front may bring some light
rain Friday and a brief cool down Saturday before seasonable
temperatures return Sunday followed by the risk for showers on
Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Tuesday...KLTX VAD wind profile showing that just
above the well defined surface-based inversion low level jetting
is increasing, already up to 30kt at 1kft. This is in response
to the strong upper trough and surface cold front approaching
from the NW. Low level wind fields will remain this strong or
even strengthen another 5kt through daybreak, the ramifications
of which mainly confined to aviation. Given a little daytime
heating however gusty winds should quickly materialize at the
surface soon after sunrise. The resulting rapid erosion of the
inversion should lead to an impressive temperature spike (15
degrees from 14-15Z?) followed by more typical if not slightly
rushed rises in the moderately strong prefrontal WAA regime. By
midday into early afternoon the front will rapidly cross the
region, reversing the diurnal temperature curve as afternoon
values drop rather quickly and the still gusty winds turn to the
NW. Almost ironically tonight`s temperature curve may be fairly
typical due to conflicting/offsetting factors. It will be
breezy enough for mixing and thus normally a slower, flatter
temp curve. This will be offset by the fairly robust CAA behind
the front.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 300 AM Tuesday...The Arctic surge will drop dewpoints into
the single numbers and teens on Wed as 850 mb temps drop as low
as -11C. It will be sunny and cold with highs in the lower to
mid 40s. NW to W winds of 10 to 20 mph will make it feel as if
it were below freezing for much of the day. Minimum relative
humidity will be as low as 25 to 30 percent Wed afternoon.

As one deep trough lifts out Wed, another will begin to dig
more modestly across the Great lakes and Midwest and then across
the east coast late Wed night and Thu. It now looks like the
brunt of the cloud cover will brush us by to the N. However, an
impressive wind field will overspread the area with 50-60 kt of
wind lowering to around 2 kft. These very strong winds will tend
to keep the air near the ground moving and with the brunt of the
cold and dry advection having passed, it should not be as cold
Wed night. We should see dewpoints recover Wed night with low
temps no lower than the upper 20s and lower 30s. The strong
winds in the lower levels of the column will lift out Thu and
under the influence of SW flow, highs should reach the mid 50s
with plenty of sunshine. Light surface winds will return Thu
night and we will begin to see clouds increasing from W to E
ahead of yet another deep trough and surface cold front. These
clouds will cap minimums in the mid and upper 30s with lower 40s
at the coast.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 300 PM Monday...The East Coast longwave trough will reload
late this week as another strong shortwave moves through the
Carolinas on Friday. This upper system should induce low pressure to
develop at the surface over North Carolina during the day Friday.
Moisture is going to be tough to find given deep layer winds have so
much offshore component, virtually eliminating Gulf of Atlantic
inflow. In fact the only moisture I can find arrives in the 850-700
mb layer from the northwest -- most likely Pacific moisture that
came onshore in British Columbia several days earlier. Dynamics are
going to be so strong that I still think there will be some light
measurable rainfall around, and I`m including a 30 percent chance of
showers in the forecast for Friday.

Dry weather will develop for Saturday and Sunday as a weak upper
level ridge pokes north from the Caribbean and surface high pressure
moves eastward along the Gulf Coast. Model depictions of another
shortwave trough arriving on the East Coast Monday vary quite a bit
from model to model, reducing confidence about what impacts we may
see. PoPs of 30 percent have been introduced into the forecast for
Monday along with some increased cloud cover.

Temperatures will be on a roller coaster ride through the weekend,
likely coolest on Saturday as the upper trough moves overhead and
offshore.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 06Z...Though VFR expected through the period still not
the smoothest of sailing for aviation concerns. Winds are very
light/less than 5-7kt across the area as high pressure sinks
into the Gulf. An approaching front and disturbance aloft will
really tighten the gradient as the night wears on, increasing
wind speed through the column. As the stalwart surface-based
inversion holds strong this will mean a wind shear layer
develops atop the inversion. By mid morning the inversion
quickly mixes out for a windy afternoon in the prefrontal flow
regime. FROPA will then bring a sharp change in direction by
early afternoon. Wind may stay gusty through the evening albeit
with a gradual decreasing trend.

Extended Outlook...VFR.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Tuesday...Westerly winds to back to SW and increase
ahead of a fairly sharp cold front approaching from the NW.
Expect advisory criteria to be met by daybreak and continue
through the period. The actual wind shift and FROPA will come
late this afternoon and steepen wave faces while slightly
decreasing nearshore dominant wave height as wave shadowing
effects start to develop.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 300 AM Tuesday...Small Craft Advisory conditions are
expected to linger across at least portions of the waters Wed
morning with the dry and cold surge slowly waning during Wed.
However, a developing deep and strong WSW flow should keep winds
elevated through much of the period. Winds will likely be near
Small Craft Advisory criteria, 20 to 25 kt, Wed night into Thu
with a 50 kt jet at 2 kft. Seas Wed morning will be highest
offshore, up to 4 to 6 ft. Seas will subside during Wed before
building to 3 to 5 ft Wed night into Thu with perhaps a few 6 ft
seas across the outermost northern waters. Diminishing winds
late Thu and Thu night will result in subsiding seas.

LONG TERM /FRIDAY THROUGH SATURDAY/...
As of 300 PM Monday...An active and windy weather pattern will
continue Friday as a Canadian cold front slides across the area.
Low pressure is expected to develop along the front, helping
produce a surge of offshore winds Friday night. The latest GFS
model is actually showing gale-force winds Friday afternoon and
night, but other model guidance is not that strong, instead
keeping winds strong, but below 30 knots. Our forecast will go
with this weaker wind forecast for now, implying a period of
Small Craft Advisory conditions (W winds 20-25 kt) Friday into
Friday night. Winds and seas should improve on Saturday as
Canadian high pressure builds in from the west.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...Small Craft Advisory from 6 AM this morning to noon EST
     Wednesday for AMZ250-252-254-256.

&&

$$

NEAR TERM...MBB
SHORT TERM...RJD
LONG TERM...TRA
AVIATION...MBB



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