Scientific Forecaster Discussion
fxus62 kilm 200542
Area forecast discussion
National Weather Service Wilmington NC
1242 am EST Mon Nov 20 2017
high pressure will control area weather through Monday. A coastal
trough and approaching cold front may bring some showers late
Tuesday and Tuesday night. Low pressure is expected to develop in
the eastern Gulf of Mexico mid week and may bring unsettled weather
to the eastern Carolinas Thursday and Friday as it moves northeast.
High pressure early next weekend will be followed by the passage of
a cold front next Sunday.
Near term /through tonight/...
as of 8 PM Sunday...have added Columbus County to the frost
advisory although this is expected to be a marginal event due to
very dry air over the forecast area. Patchy frost is a good bet
here and there overnight, but widespread frost may be tough to
get given dry low levels. Previous discussion from this
Surface high pressure will build in under a northwest flow
aloft. The airmass is once again just cold enough to cause some
frost/freeze concerns as a good part of our area remains at
least officially in the growing season. It appears via guidance
and some residual low level mixing that any freeze conditions
will be a stretch. There is enough of a threat/concern for frost
especially late when the winds diminish. Will go ahead and
issue a frost advisory for areas where mins are 35 degrees and
under. This will preclude most of the coastal areas. Overnight
lows will general be in the middle 30s. Highs Monday will be
middle to upper 50s under mostly sunny skies.
Short term /Tuesday through Tuesday night/...
as of 300 PM Sunday...high pressure previously overhead takes on a
very west-east elongation Monday night bringing a light onshore flow
to coastal areas, especially SC. The ocean influence paired with the
radiational cooling inhibition could add a few degrees to the
seasonably cool nighttime lows. Neither should hold true over northwest
zones and there may be a large than normal northwest to southeast gradient in low
temps, those areas ending up almost as cool as the previous night.
On Tuesday warm advection will both shoot highs back to climatology
if not a few degrees warmer but also yield increasing cloud cover
and some slowly increasing rain chances. These rain chances appear
to increase and shift from inland to the coast Tuesday night as the
warm air advection interacts with stronger vorticity centers in the SW mid level
flow. The warm air advection and cloud cover will keep Tuesday night lows elevated
a good 10 degrees above climatology.
Long term /Wednesday through Sunday/...
as of 300 PM Saturday...lingering rain is possible early Wednesday as
an upper trough moves out and a cold front moves out to sea. Another
short wave trough could spawn low pressure development along the old
front off the southeast U.S. Coast. This will bring another chance
of rain to the area Wednesday night into Friday, though the exact
details of this scenario are still in doubt. Dry weather is expected
for the remainder of the long term but light showers are possible
with another frontal passage and vigorous upper trough on Sunday.
Temperatures will be near seasonal normals of mid 60s Wed before
falling back into the mid to upper 50s for Thu and Fri. Slightly
warmer temperatures are expected Sat and sun with highs in lower
60s. Mins temperatures Wednesday night will fall to the upper 30s to
lower 40s with higher numbers southeast and along the immediate coast.
Temperatures in the mid 30s to around 40 are expected Thu night and
Friday night before rebounding to the mid to upper 40s Saturday
Aviation /06z Monday through Friday/...
as of 06z...high confidence in VFR through the valid period. High
pressure will shift eastward today, moving atop the terminals this
aftn and then offshore tonight. This occurs in conjunction with west/northwest
flow aloft creating nearly cloudless sky conditions and northerly
winds of 10 kts or through the aftn. As the high shifts offshore
winds will begin to shift to the east in response to a developing
coastal trough, but at still light speeds. No low level clouds are
expected within this valid period, but mid-level flow becoming SW
will drive increasing cirrus level moisture and a broken cirrus cig is
forecast Monday night, but VFR will persist.
Extended outlook...MVFR conditions may develop in low clouds
and light rain Tuesday through Wednesday morning, then MVFR to
IFR conditions are possible Thursday night into Friday in low
clouds, rain, and fog.
near term /through tonight/...
as of 8 PM Sunday...have dropped exercise caution headlines for
our southern 3 marine zones as conditions continue to improve.
For amz250 we are just barely within criteria with 15 to 20 kt
winds and 3 to 5 ft seas, but expect this too will improve by
around midnight. Previous discussion from this afternoon
Winds and seas on the way down this afternoon as although cold
air advection continues, the stronger low level wind fields were
ahead of the front that has long since passed. North to
northwest winds of 15-20 knots will prevail most of the late
afternoon hours and night. On Monday surface high pressure
settles over the area and winds decrease dramatically, down to
the single digits by late afternoon. Seas are down to just over
six feet at 41013 and I will wait til the last minute but most
likely cancel the Small Craft Advisory just a touch early and
issue an exercise caution statement. Overall seas will settle
into a 2-4 foot range overnight and even less later tomorrow.
Short term /Monday through Tuesday night/...
as of 300 PM Sunday...things just about as quiet as they get for the
marine environment for most of the period. West-east elongated high
pressure to keep just a light onshore flow of just a few knots. A
weak coastal trough will develop on the periphery of the high later
Tuesday into Tuesday night veering flow to southeast and adding a few knots
of wind speed, bumping the forecast up a category or more. Seas will
be following suit, showing a gradual growing trend.
Long term /Wednesday through Friday/...
as of 300 PM Saturday...north to NE winds in vicinity of 15 knots are expected
through much of the period though a peak of 15 to 20 knots is possible
Thu night into Friday. On the open waters, seas of 3 to 5 feet are
expected through the period. Depending on low pressure development
off the southeast U.S. Coast, conditions in this period could be hazardous
and it is possible that winds and seas could exceed thresholds for
small craft advisories, 25 knots winds and/or seas of 6 ft, during this
SC...frost advisory from 4 am to 9 am EST this morning for scz017-
NC...frost advisory from 4 am to 9 am EST this morning for ncz099.