Scientific Forecaster Discussion
fxus62 kilm 230907
Area forecast discussion
National Weather Service Wilmington NC
407 am EST Thu Nov 23 2017
high pressure will build over the Carolinas through today as low
pressure begins to move slowly up from the Gulf of Mexico spreading
clouds and some rain over the southeast. The low may track close
enough to the Carolina coast to produce some intermittent rain
mainly along the immediate coast late today into Friday before
departing on Saturday. A dry cold front will move through Saturday
night followed by Canadian high pressure through the middle of
Near term /through tonight/...
as of 300 am Thursday...high clouds were streaming northward in
SW flow on the front end of mid to upper trough. This trough
will dig southward today into the Gulf before pushing eastward
by tonight. Shortwave energy rotating around the main trough
will produce waves of low pressure which will track northward up
from the eastern Gulf to just off the southeast coast through
tonight. The best lift associated with this low pressure will
remain mainly off the coast, but a low end chc of pcp will exist
into SC and mainly along the coast into NC later today into
tonight. For now will keep any measurable pcp out of the
A tight gradient will exist between cooler and drier high
pressure to the west and low pressure to the east. Pcp water
values will remain under a half inch from I-95 and west and up
to 1.6 inches off the coast. Dewpoint temps were down below 30
inland and up closer to 40 along the immediate coast this
morning and will remain low through the period. Temps will only
reach into the 50s today in cool northerly flow.
The mid to upper trough will nudge the greatest moisture east
through tonight. This will clear out most of the clouds over
western portion of forecast area while clouds will remain along
the coast through tonight. This will produce another large
spread in overnight lows tonight with mid 30s inland to mid 40s
along the coast.
Short term /Friday through Saturday night/...
as of 300 am Thursday...finally, models are all trending
together in keeping the main area of pcpn just off the ilm County Warning Area
coasts early Fri before, finally progressing this pcpn well
offshore during daytime Friday. The drying trend amongst the
models are likely mainly due to a northern stream mid-level S/W
trof that dives southeast to the Gulf Coast states during Thu, then
progressing eastward Thu night thru Friday. This upper S/W trof
remains positively tilted and much less amplified than what
prior models forecast several days ago up until yesterday. With
a flattened mid-level S/W trof, the easterly component in the
wind fields aloft will push the sfc low and ultimately the
baroclinic zone it's feeding off of, to well offshore from the
Carolina coasts by late Friday. As mentioned in prior fcsts, a
decent moisture and pop gradient will exist late Thu thru Friday
before finally shifting well offshore by late Friday. With that
said, have kept pops in the low chance for light rain across
the coastal counties early Fri. The tight moisture gradient will
also result in sky conditions going from cloudy to clear as the
back edge of this cloud field pushes east. Weak sfc high will
prevail late Fri thru daytime Saturday. Moisture profiles across
various ilm County Warning Area locations indicate a dry mid and upper levels
to exist Fri night thru Sat resulting in mainly clear Fri night
and mostly sunny for Sat. For late Sat thru Sat night, a
vigorous sfc cold front will drop southeast and across the forecast area
Sat evening and off the Carolina coasts and offshore after
midnight sun. A potent and southeast moving mid-level S/W trof
will help amplify the longwave upper trof across the eastern
U.S. As well as accelerating the sfc cold front across the forecast area.
Moisture will remain starved for this cold front, with enough
for cloudiness but not deep enough for any pcpn. This a result
of the downslope wind field within the atm column that will tend
to scour out moisture. With that said, did not include pops and
have kept a partly to variably cloudy sky conditions Sat night.
The temp fcst during this 2 day period will be unremarkable,
meaning expect Max/min temps near their respective climo norms.
Long term /Sunday through Wednesday/...
as of 300 PM Wednesday...primary weather caption for this time
frame remains 'seasonably cool, and dry' as a series of upper
troughs progressively traverse the coast, the strongest brings
cold air advection Sunday. The coolest portion of this time
period looks to be daybreak Monday, when high pressure becomes
centered over the inland Carolinas under clear skies at first
light. The breeziest part of the forecast will be Sunday as
high pressure builds in from the west. Late in the extended
period for days 6/7, a return and moisture flow slated, as a
moderately strong upper trough digs into the central MS valley,
hence, a warm air advection trend appears on tap for next
Tue/Wed, with a slight chance of rain as a warm front arrives
from the south in the return flow.
Aviation /06z Thursday through Monday/...
as of 06z...high pressure will build in from the west as clouds and
rain spread up along the southeast coast from low pressure moving up
from the Gulf. The tightened gradient between these two systems
along with clouds streaming northward will prevent prevent fog in
the forecast tonight. Winds will remain 5 to 10 kts overnight into
thurs as they veer from the north to NE.
Overall expect mainly VFR conditions, but the model soundings
were hinting at some MVFR ceilings around 2k ft to affect the
coastal tafs. Otherwise expect some strato cu around 4k ft at
times today and good deck of mid to high clouds between 15k to
20k ft. Warmer and moister air streaming up from the south over
the relatively cooler denser air in place will produce some rain
to the south and east but some of this pcp may brush the
coastal tafs but not high enough confidence to include in 06z tafs.
Extended outlook...low confidence for MVFR to IFR conditions
near the coast late Thursday through Saturday morning in low
clouds and rain.
near term /through tonight/...
as of 300 am Thursday...northerly surge through this morning
will produce marginal Small Craft Advisory conditions. North-NE winds up to 20 kts
with higher gusts will produce seas up over 6 ft with wna model
showing highest within the first few hours after daybreak today.
The high will shift east with winds veering to northeast
through today. Northeast winds around 20 kt continue into this
morning before surge eases and the gradient relaxes. Winds will
diminish to 15 kt by midday, but should see winds increase
slightly tonight as low pressure moves up from the south and
gradient tightens again. Seas will remain 4 to 6 ft through this
morning before starting to decrease as wind speeds drop off.
Seas should remain 3 to 5 ft through tonight but may be on the
high end overnight into early Fri.
Short term /Friday through Saturday night/...
as of 300 am Thursday...Small Craft Advisory will likely be ongoing at the start of
this period due to a tightened sfc pg as the sfc low just offshore
pulls away from the Carolina coasts. Weak sfc high and it's
elongated center, will push across the eastern Carolinas and off the
coast Fri night thru midday Saturday. NE 15 to 20 g25 kt winds early
Fri will back to the north thru northwest Fri aftn thru early Sat
with wind speeds subsiding to 10 to 15 kt as the sfc pg relaxes. The
sfc pg will re-tighten-some Sat aftn and evening due to the approach
and passage of the next cold front. This cold front passage not as dramatic as
previous ones but nevertheless westerly winds to increase to around
15 kt ahead of the front becoming northerly 10 to 20 kt with few
gusts up to 25 kt. Significant seas will have peaked at the start of
this period followed by a general subsiding trend Fri aftn thru
midday Sat before bouncing back into a slight uptrend Sat aftn and
night. With wind directions generally offshore, there will be a
limited fetch for which seas to build upon during Sat aftn and
night. At best, a short term scec remains possible for late Sat aftn
Long term /Sunday through Monday/...
as of 300 PM Wednesday...high pressure will build into the area
waters behind cold front through the day Sunday. The breeziest
day and highest seas will be Sunday as north winds up to 20 knots
prevail, with a few higher gusts. Wave guidance showing 4-5 feet
offshore sun, thus a precautionary headline may be needed. As
the high pressure center nears, north winds will veer to NE and
weaken on Monday.
Marine...Small Craft Advisory until 3 PM EST this afternoon for amz250-