Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Wilmington NC
838 PM EST Wednesday Dec 24 2014

Synopsis...
periods of rain and isolated convection will continue this evening
ahead of a cold front that will across the Carolinas and off the
coast late tonight. Sunshine is expected to make a return
Christmas day as dry high pressure southwest of the area
overspreads the Carolinas Thursday into the early weekend. A cold
front will drop into the southeast on Sunday with a few waves of
low pressure developing Monday through Wednesday next
week...resulting in unsettled weather across the Carolinas.

&&

Near term /until 6 am Thursday morning/...
as of 745 PM Wednesday...the severe weather threat has waned across the
ilm County Warning Area. The worst convection is now over the offshore waters
between Cape Fear and Charleston...and pulling further offshore
at this time. This update will concentrate on lowering probability of precipitation from west to
east thruout the evening and overnight. The cold front remains
slated to push from west-southwest to east-northeast across the ilm County Warning Area and off the
coast during the late evening and pre-dawn Thursday hours. Latest hrrr
indicates a thin band of Post frontal -shra to occur across the
forecast area...and will leave in a small pop chance up to around or just
after daybreak Thursday. Have tweaked overnight mins to account for
late afternoon and early evening both temperature and dewpoint trends.
Lows for tonight will likely occur at or just after daybreak Thursday.

Previous discussion...............................................
as of 334 PM Wednesday...a messy day continues across the eastern
Carolinas on this Christmas evening.

Christmas time weather is not usually thought of as temperatures around 70
with heavy rain and severe thunderstorms. However...that is just
what we are experiencing today. A deep upper trough moving slowly
overhead the MS valley is driving strengthening low pressure which will
move up into the Great Lakes...dragging a cold front across the area
late tonight. Ahead of this front...widespread showers with embedded
thunderstorms will continue...with some residual light rain persisting even
a bit behind the frontal passage.

No less than 3 convergent boundaries have crossed the ilm County Warning Area
today...the last of which is currently moving into the Cape Fear
region. These boundaries have been primarily characterized by
torrential rainfall and flooding...but some isolated wind gusts and
even a brief tornado have also occurred. The WRF has outperformed
all other high-res guidance thus far today...and is leaned on
heavily for the remainder of the near term. This suggests that the
heaviest rainfall will slowly wind down this evening as what instability
exists...as limited as it is...erodes due to continued rainfall and
loss of diurnal heating. Forecast profiles do continue to keep
decent saturation into late tonight...and thus expect more
stratiform rainfall...with embedded convective elements...to
continue until frontal passage...which should occur an hour or so either side
of midnight EST. The severe threat is basically 0 for the remainder
of the period...except the next few hours where the stronger
convective elements could still bring down a wind gust from the
50kt/2kft low level jet. Behind frontal passage...some very light rain may continue into
morning...but in a rapidly drying state.

Temperatures until frontal passage will remain nearly stationary thanks to
warm air advection...but will begin to crash behind the cold front after midnight.
Only a few hours of cooling before daybreak will limit mins to around
50 well inland...and near 60 right along the coast.

&&

Short term /6 am Thursday morning through Friday night/...
as of 334 PM Wednesday...main weather headline is that sunshine is
slated to make a debut Christmas day as sharp drying follows a
cold front sweeping out to sea by daybreak Thursday. High pressure
of Gulf Coast origin will result in weak cool air advection and
maximums will rebound slight above normal Thursday and Friday for
late December. Friday daybreak likely the coldest temperatures this
period with 30s widespread across the area...climbing 25-28
degrees f by afternoon into the low and middle 60s under sunshine
and a few strands of cirrus.

&&

Long term /Saturday through Wednesday/...
as of 330 am Wednesday...beginning of the weekend pleasant but
height falls and an approaching cold front into Sunday will bring
clouds and an increasing chance of rain into Sunday night.
Indications are the front may stall over or near the forecast area
Monday through mid-week...allowing for unsettled weather as a
series of waves travel along the stalled boundary. By days 6/7
Tuesday and Wednesday...a cold front looks to bring cooling and
undercuts the SW flow aloft. This may lead to murky conditions
and multiple chances of rain/showers.

&&

Aviation /01z Thursday through Monday/...
as of 00z...a mixture of VFR/MVFR/possible IFR expected through
tonight due to varying low ceilings...areas of fog...and scattered
showers in association with an approaching cold front. Conditions
gradually improve late overnight into Christmas day as cold front
pushes offshore.

Latest radar imagery depicts light to moderate showers pushing
eastward across the forecast area in association with an approaching
cold front. As a result...areas of low ceilings and fog as well as
rain are creating MVFR at a majority of the terminals.
While could not entirely rule out brief dip in restrictions to
IFR in some locations...confidence is low. South-southwest winds
at or below 10 kts...with occasional gusts up to 20 kts...will shift to
the west behind the front overnight. Behind the front...expect
improving conditions to begin with widespread VFR by Christmas
morning. Expect VFR and gradually clearing skies throughout the
day...with westerly winds at or below 10 kts through the end of the valid
period.

Extended outlook...VFR Thursday through Saturday. Rain returning
Sunday and possibly Monday.

&&

Marine...
near term /through tonight/...
as of 745 PM Wednesday...based on latest buoy observation...winds and
seas across the ilm waters have basically peaked during the middle-
afternoon hours. And are now holding steady. Expect another
temporary increase in winds and resultant seas later tonight into
early daylight Thursday during and just after the cold frontal
passage. Wind directions to veer from the current south-southwest
direction...to westerly late tonight into daylight Thursday. A
tightened surface pg will yield speeds between 15 to 25 knots...with a
few gusts to 30 knots leading up to and just after the cold front passage.
Significant seas will hold relatively steady in the 5 to 8 feet
range overnight...highest across the local waters between Cape
Fear to Little River Inlet. Average periods will run 5.0 to 6.0
seconds.

Previous discussion...............................................
as of 330 PM Wednesday...tropical airmass continues to advect
across the waters on strong S/SW flow. Although dewpoint
temperatures have risen to around 70 over the coastal
waters...strong winds of 20 kts or more and air-to-ocean temperature
differential have been outside the criteria typically used for
marine fog...and thus have dropped the marine dense fog advisory.
The Small Craft Advisory remains unchanged however...as winds and
seas are well above thresholds. In fact...Wilmington Harbor buoy
/41108/ recently hit 9 feet...with Frying Pan Shoals /41013/ up to
11 feet. Local Swan guidance initialized too low so bumped forecast
wave heights about 1 feet across all waters...and expect seas to
remain well above 6 feet until frontal passage after midnight. At
that time...winds will shift quickly to the west/northwest with speeds
continuing around 20 kts. However...the offshore wind component
will push the highest seas away from shore...and seas will fall to
4-6 feet by Thursday morning.

Short term /Thursday through Friday night/...
as of 330 PM Wednesday...moderate winds Thursday will ease and
turn northwest later in the day. Residual wave energy will take morning
to settle and recover...and the advisory may need to run through
most if not all of morning. Thursday any storms will be confined
to the Gulf Stream and points farther to sea. Light winds Friday
and pleasant as surface high pressure moves nearly overhead or just
north of the area. Winds Friday 10 knots or less from NE-ESE.

Long term /Saturday through Monday/...
as of 330 PM Wednesday...Saturday features a surface high
migrating offshore and weak return winds from the S. A cold front
will drop from the north very late in the period Monday night and
bring increasing NE winds...although at this time an advisory may
not be needed. Rain may reduce visibilities below 2-3 nm Sunday night
through Monday in periods of light rain or drizzle.

&&

Ilm watches/warnings/advisories...
SC...none.
NC...none.
Marine...Small Craft Advisory until 1 PM EST Thursday for amz250-252-
254-256.

&&

$$
Synopsis...mjc
near term...dch/jdw
short term...mjc
long term...mjc
aviation...sgl

National Weather Service Glossary of Abbreviations