Scientific Forecaster Discussion
fxus62 kilm 131133
Area forecast discussion
National Weather Service Wilmington NC
633 am EST Wed Dec 13 2017
Arctic air will pour into the eastern Carolinas this morning. The
cold won't last long as temperatures will return to normal Thursday
and Friday. Another cold front will bring chilly temperatures Saturday,
before seasonable weather returns on Sunday. Low pressure approaching
from the Gulf Coast may bring rain to the area early next week.
Near term /through tonight/...
as of 300 am Wednesday...deep cold and dry air mass settling
into the Carolinas this morning. Northwest winds picked up this
evening with gusts up to 30 kts at ilm, but have begun to settle
down a bit with most places 5 to 10 mph with some higher gusts
mainly along the coast. Temps have fallen into the mid 30s and
should continue to drop just below freezing most places right
around daybreak in continued cold air advection. GFS showing 850 temps
bottoming out right around daybreak today at -8c. The stiff northwest
winds this morning will make it feel 5 to 10 degrees colder. The
wind chill temps will not reach above freezing until early this
afternoon and even then, the temps will only reach into the 40s
as winds lighten up, under full sunshine. Overall a cold and
very dry day ahead.
Gusty northwest winds will lighten up and back to the SW by late
today. This will allow for a slight return in moisture, but only
slight as dewpoint temps rise from the single digits and teens
this afternoon to mid to the upper 20s overnight. The actual
temps will drop close to freezing tonight in most places. The
next shortwave will ride across the Carolinas tonight. This will
produce some passing mid level clouds after midnight and will
kick the winds up once again as winds above the surface, in the
low levels of the atmosphere, reach up to 45 to 50 kts.
Short term /Thursday through Friday night/...
as of 300 am Wednesday...a strong shortwave will be exiting
the area Thu morning. A strong wind field is expected to develop
in association with this feature, with a jet maxima of 50-60 kt
down to around 2 kft. This low-level jet will be lifting out
Thu morning, keeping a deep and dry westerly flow in place.
Sunshine should be plentiful and we should see a good temp
recovery with highs in the mid and upper 50s, so a good 10 or
more degrees warmer than on Wed.
A cold front will reach the area late Thu night and Fri morning
and should stall for a time near or just offshore. Weak waves
of low pressure are expected to consolidate near the Outer Banks
with low pressure strengthening as it moves to the NE Fri
night. This will allow for increasing clouds and it should
become mostly cloudy overnight Thu into Fri and then clearing
Fri night. A strong and deep westerly flow dominates the column
during this portion of the forecast and significant shortwave
energy is not able to directly influence the eastern Carolinas
until Fri night. Although the column does undergo some modest
moistening as we move through Thu night and into Fri, dry air in
the mid and lower levels of the column will be tough to erode
in this type of flow. It looks like the showers that do develop
will be mainly offshore. We will continue to monitor, but our
latest forecast will be dry.
Lows Thu night will be in the mid 30s to around 40, coolest well
inland. Although the current set of grids do not explicitly
indicate a non-diurnal temp curve due to timing differences by
the models, it certainly is plausible to believe that lows may
occur early in the night and then stabilize if not rise with the
arrival of thick cloud cover. Highs on Fri will be similar to
Thu. The influx of colder and drier air Fri night should help
to knock minimums to freezing, a little lower inland and perhaps
a degree or two above at the coast.
Long term /Saturday through Tuesday/...
as of 300 PM Tuesday...model consensus is still not great in the
long term. It's a common problem in the winter: shortwave
energy splits as it exits The Rockies with part coming eastward
and part dropping southwestward into baja Mexico. Each model is
slightly different with the specifics how this energy cuts off
over Mexico late this week, and then how it rejoins the
westerlies early next week.
Saturday should see chilly temperatures with mainly clear skies
in the Canadian airmass in place. Surface high pressure will
move off the coast Saturday night, with a moderating return flow
setting up Sunday.
The difference in model handling of the baja Mexico shortwave
energy really becomes apparent Sunday through Tuesday. The European model (ecmwf)
is easily the fastest model to kick the low back into the
westerlies, and shows rain breaking out during the day Sunday in
association with a developing surface wave of low pressure
along the Gulf Coast. Other models are at least 12 hours slower.
There are some GFS ensemble members that show an early start to
precip Sunday, but I don't show rain developing until Sunday
evening to maintain consistency with surrounding National Weather Service offices and
the bulk of our deterministic model guidance. Even the slower
12z GFS and Canadian runs still show rain becoming a good bet
Sunday night into Monday, and pops have been increased to 40-50
percent for this period. Temperatures should remain well above
freezing during this event with no p-type concerns.
Aviation /12z Wednesday through Sunday/...
as of 12z...VFR through 14/12z. West-northwest winds this morning, with a few
gusts coastal terminals, will back to the SW this afternoon. As
a surface based inversion sets up this evening, winds just
above the inversion will increase ahead of the next system. Low level wind shear
will be likely at kflo/klbt this evening. The surface based
inversion should decrease at the coastal terminals so low level wind shear
should be less likely. Will monitor. Generally sct mid/upper
clouds this evening/overnight.
near term /through tonight/...
as of 300 am Wednesday...a strong rush of cold and dry air over
the waters will produce gusty northwest winds this morning, 15 to 25
kt with higher gusts. This off shore flow is keeping seas the
highest in the outer waters but overall, seas were up to 5 to 7
ft. These Small Craft Advisory conditions will improve briefly
through this aftn as winds lighten and back to the SW, but
another disturbance will move across the waters after midnight
tonight producing another rise in both winds and seas.
Therefore, the Small Craft Advisory will remain in effect
although there will be a lull this afternoon as winds back to
the SW and diminish to 10 to 15 kt allowing seas to drop to 2 to
3 ft. The increase tonight should come near midnight with winds
up to 15 to 25 kt and seas up to 5 to 7 ft.
Short term /Thursday through Friday night/...
as of 300 am Wednesday...a strong shortwave will be exiting the
area Thu morning. A strong wind field is expected to develop in
association with this feature, with a jet maxima of 50-60 kt
down to around 2 kft. This low-level jet will be lifting out Thu
morning. Another cold front will reach the waters Fri morning
with one or more waves of low pressure migrating along the
front. Low pressure is expected to consolidate near the Outer
Banks of North Carolina during Fri and then strengthen as it
moves NE Fri night.
The strongest winds this period will occur Thu morning, up to 20
to 25 kt. A Small Craft Advisory has already been issued through
noon Thu. The direction will be west. Seas will still be in the 4
to 7 ft range Thu morning. West winds will decrease to 10 to 15 kt
during Thu afternoon as seas subside to 3 to 4 ft. Northwest winds Thu
night will decrease to 10 kt or less and may become variable in
direction due to the proximity of a front and weak low pressure
late. Seas will subside to 2 to 3 ft. Winds will increase during
Fri and may be near Small Craft Advisory levels Fri afternoon
and eve. The direction will be veering from west to northwest during this
time. Seas will build, reaching 4 to 5 ft with at least some 6
ft seas possible across the outermost northern waters.
Long term /Saturday through Sunday/...
as of 300 PM Tuesday...breezy west winds will continue through
Saturday morning before diminishing as high pressure moves in
from the west. The next low pressure system is now expected to
move eastward and toward the Carolinas a little faster than we
thought yesterday, perhaps reaching the area Sunday night with
rain and strengthening southerly winds.
Marine...Small Craft Advisory until noon EST Thursday for amz250-252-