Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
333 am EDT Sat Aug 23 2014
a cold front will slip southward through the area on Saturday.
This front will bring a good chance for showers and thunderstorms
Saturday...before cooler and drier air filters into the region
for Sunday. High pressure expanding south from New England will
maintain cooler and drier weather for the first half of next week
with a return to more seasonable weather later in the week.
Near term /through tonight/...
as of 3:30 am Saturday...an unseasonably strong cold front will drop
south across the forecast area today...likely briefly becoming hung
up over the southern portion of the County Warning Area this afternoon...before
pushing more definitively south of the area overnight. We can still
count on another hot day though...with heat index values ranging
from the middle 90s up north to 103 down south...as cold air advection
as indicated by thickness packing will lag front by a good bit. Do
not expect cooler and somewhat dryer air to arrive until after
midnight. However...today will be a few degrees cooler than
yesterday as cloud cover and precipitation will keep maximum
temperatures down a notch.
A reasonably moist column combined with frontal passage...the sea breeze front
and other residual boundaries will allow for scattered
convection...especially during the heat of the afternoon and early
evening. At the upper levels...disturbances embedded within a deep
northwesterly flow regime will kick off stronger rounds of convection. Timing
of these events is uncertain. A weak impulse is entering the County Warning Area
from the northwest at this time...but in the early morning hours we have an
unfavorable environment for convection...and the activity is fading.
Water vapor loops show the next disturbance may move in late this
Model soundings show ample low level moisture through the overnight
hours as dryer air will also lag frontal passage. Keeping in slight chance
probability of precipitation as a result...but with only minimal quantitative precipitation forecast.
Short term /Sunday through Monday night/...
as of 300 am Saturday...Ridge becomes highly amplified up the
Mississippi Valley into the northeast early next week and builds
eastward with time. At the same time surface high pressure builds
down from the north. Increasing subsidence and dry air will act to
inhibit convection. Overall moisture through the column will be
diminishing with pcp water values dropping from close to 2 inches
early Sunday down to 1.25 by Sun night and less than an inch by
Monday morning. May feel more like early Fall-like weather for the
start of the week with cooler and drier northerly flow offset
slightly by late Summer sunshine...with temperatures reaching below
normal into the low to middle 80s. Any clouds early Sunday will
dissipate as dewpoint temperatures drop from near 70 down to near 60 by
Monday morning. These lower dewpoint temperatures will allow temperatures to
drop into the middle 60s most places overnight.
Long term /Tuesday through Friday/...
as of 300 am Saturday...continued cool and dry weather through
middle week as high pressure ridges down from the northeast into the
Carolinas and upper ridge continues to build eastward. The cooler
northeast flow will be offset by plenty of sunshine to produce
temperatures near normal...in the middle 80s. 850 temperatures and low level
thicknesses will be on the rise as ridge builds over the southeast
and 500 mb heights increase Wednesday. Moisture may be on the rise by late
Wednesday into Thursday depending on the exact track of tropical system
forecast to move up through the off shore Atlantic waters to our
east late Wednesday/Thursday time frame. The European model (ecmwf) continues to the be the
fastest and furthest east with the system while the GFS remains
the slowest and farthest west. At this point looks like main
effects of this tropical system will be along the coast with
increased on shore winds and swells through middle week. High
pressure should hold over land with ridge holding strong aloft.
For now it looks like this should help to suppress shower activity
through much of the week but may see some clouds and showers move
on shore...mainly over coastal areas as tropical system passes to
our east through middle week. GFS also shows cold front moving into
the Carolinas from the northwest by the weekend. Temperatures near or below
normal to start will begin to moderate as moisture increases
through the column Thursday into Friday with deeper on shore flow.
Aviation /06z Saturday through Wednesday/...
as of 06z...kilm is the cool spot across the County Warning Area tonight thanks to
the earlier torrential rainfall. Have included tempo MVFR visibilities for
kilm in the early morning hours...but increasing middle/high clouds
overnight should again lower the fog threat. Despite dewpoints in
the upper 70s at kcre/kmyr...surface winds will likely inhibit br
formation at these terms. Convection over central NC associated with
another upper disturbance is moving toward our area...but the hrrr
tends to weaken the activity as it nears the County Warning Area. Therefore will not
mention vcsh during the overnight hours.
A cold front will drop southward across NC this morning...
approaching klbt/kilm around 12z. Models suggest the front may get
hung up across our County Warning Area during the day before clearing the Carolinas
later in the period. We could see some showers across our northern
zones this morning...but confidence is fairly low. Better chances
for convection will be this afternoon with the front lingering over the
area...enhanced by sea breeze and boundary collisions. Have included
vcsh for all terms after 18z. Light/variable winds in the early morning
will become north and then northeast behind the front...remaining
below 10 knots. Kcre/kmyr will likely see east-southeast winds in the afternoon behind
the sea breeze before the front passes through.
Extended outlook...MVFR/IFR ceilings/visibilities possible on Sun morning.
Otherwise expect VFR to prevail sun through Wednesday as high pressure
ridges over the East Coast in the wake of a cold front.
near term /through tonight/...
as of 3:30 PM Saturday...a cold front will drop south across the
waters this morning...stall briefly this afternoon over our SC
waters...then push south of the forecast area overnight. Winds will
swing from the west early this morning to the NE and then east later
this morning and afternoon...becoming firmly NE overnight. No real
cold surge initially means winds will be light for much of the
period...picking up to around 15 kts by daybreak on Sunday. Seas
will gradually increase as a result...from present 1 to 2 feet range
to 2 to 3 feet overnight.
Short term /Sunday through Monday night/...
as of 300 am Saturday...northerly surge as cool and dry high
pressure builds down from the northeast. Winds will rise sharply
through Sunday up to 15 to 20 kts across the waters. The increase
in winds will in turn produce an increase in seas up close to Small Craft Advisory
thresholds by sun evening. Seas will remain up close to 4 to 6 feet
over a good portion of our local coastal waters through Monday
night and beyond in persistent strong northeasterly winds.
Long term /Tuesday through Wednesday/...
as of 300 am Saturday...high pressure building down from the
northeast through the Carolinas will provide a continuous
northeast flow up to 15 to 20 kts through middle week. This will keep
seas up to 4 to 6 feet possibly increasing further Wednesday into Thursday
due to increasing swells from a tropical system most probably
moving north through the off shore waters. At this time much
uncertainty still exists concerning the development and fate of
this potential tropical system.