Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
1010 am EDT Tuesday Jul 22 2014
a stationary front along the coast will slowly move inland today and
dissipate tonight. Bermuda high pressure will build into the area
Wednesday and Thursday. A cold front will approach from the
northwest late Thursday...stalling near the coast for the weekend.
Another cold front will approach from the northwest Monday or
Near term /through tonight/...
as of 1000 am Tuesday...the synoptic pattern features an upper low
over coastal Alabama and an upper ridge off the southeast coast. In
between these two features a stream of deep tropical moisture being
lifted from the Caribbean across Florida and over the Carolinas. At
the surface an old stationary front still lies from near Cape Fear
to east of Georgetown SC.
Widespread low stratus and fog last night is taking its time burning
off inland. The stationary front offshore will probably redevelop in
the next 1-2 hours along the eastern edge of the low clouds...with
this boundary becoming the preferential development region for new
showers and thunderstorms. Precipitable water values are
exceptional: 2.1 to 2.3 inches on model soundings. This coupled
with slow storm movement should lead to more heavy rainfall and
flooding this afternoon. A Flood Watch was issued earlier today and
still appears warranted...especially for regions east of Interstate
Flash flood guidance values from the National Weather Service southeast river forecast
center are 1.5 to 2.5 inches in 1 hour...and 2.2 to 3.2 inches in 3
hours. These values will not be hard to reach given the anticipated
setup this afternoon. Freezing levels have risen from yesterday and
will approach 16000 feet this evening. This will create a very deep
region for efficient warm-cloud coalescence rainfall processes.
Rainfall amount forecasts on the broad scale are 0.5 to 1.0 inch
east of Interstate 95 with isolated areas probably picking up
another 4-5 inches. West of I-95 storm coverage may be a little more
sparse with rainfall rates will be just as heavy.
Highs today should range from 83 on the beaches to the middle 80s
inland. Some upper 80s may still occur across the Pee Dee region
assuming low stratus Burns off on schedule.
Short term /Wednesday through Thursday night/...
as of 330 am Tuesday...should see a lull in widespread
convection Wednesday as upper ridge builds in briefly and a deep SW flow
will veer becoming more westerly allowing for some middle level
drying. The deepest moisture will remain to our east over the
waters where pcp water values will be maxed out around 2.3 inches
Wednesday afternoon. Expect more localized convection on Wednesday especially along
the sea breeze in the afternoon and the westerly component to the winds
should help to keep sea breeze pinned closer to the coast and help
storms move off to the east over the waters.
By Thursday flow will increase out of the southwest as gradient
tightens as cold front moves in from the northwest. Models look
faster with the digging middle to upper trough pushing the cold
front into the coastal Carolinas by Thursday night. The day should
start out drier with pcp water values down closer to 1.5 inches.
NAM and European model (ecmwf) are a little more aggressive with southward
progression of front shifting it south of area by Friday morning
while the GFS hangs it up right along the coast as the 500 mb trough
lifts north. Either way...should see stronger and more numerous
showers/thunderstorms on Thursday ahead of front inland initially and then
shifting closer to the coast. Will need to keep a close eye on how
fast this system moves.
Temperatures will rise through the period reaching normal or slightly
above normal as heights rise through middle week as ridge builds in
on Wednesday. Temperatures may lower Thursday as trough digs down lowering 500 mb
heights and producing more in the way of clouds and pcp ahead of
cold front. Overnight lows should remain above normal...in the middle
70s...in a cloudier and more humid air mass.
Long term /Friday through Monday/...
as of 330 am Tuesday...cold front may be hung up right along the
coast Friday morning but NAM wants to push it south and east of area
leaving high pressure in control. Not confident that the boundary
will get too far south as 500 mb trough lifts north leaving a very
broad middle to upper trough anchored over the Great Lakes
maintaining more of a SW flow aloft and not giving much of push to
the cold front. Therefore will keep front just to our northwest
on Friday. Deep SW flow will keep a warmer and more humid air mass
over the area leaving potential for localized convection through
Middle to upper trough will dig down from the Great Lakes come Monday
pushing another cold front into the Carolinas. This will produce
more widespread convection in increased upper level support later
on Monday. Once again upper level trough will remain to our west
leaving a flow running more parallel to front and not giving it
too strong of a push through the area. Therefore may not see too
much of an air mass change behind front.
Overall expect greatest potential for more widespread convection
early Friday and again Monday afternoon into early Tuesday...but expect more
typical diurnal type shower activity most days. Some drier air should
make it into inland areas on Friday and on Tuesday behind fronts...but
will most likely remain just to the west of forecast area. Temperatures will
basically be above climatology with overnight lows in the 70s and day
time highs into the 90s most days with lower temperatures expected. As
trough digs down Thursday into Friday and again Monday into Tuesday may see
below normal temperatures in lowered 500 mb heights.
Aviation /12z Tuesday through Saturday/...
as of 12z...widespread MVFR/IFR this morning due to low ceilings and
areas of fog...improving to VFR though reduced periods of MVFR/IFR
are possible with increasing chances for shra/tsra. Into the
overnight hours rain showers/thunderstorms and rain tapers off with MVFR/IFR due to low ceilings
and areas of fog.
Low ceilings and areas of fog are creating widespread IFR this
morning...with the exception of kilm where conditions have improved
to VFR. VFR will prevail later this morning...though periods of
MVFR/IFR are likely as chances increase for widespread
shra/tsra...with heavy downpours possible at times. This will create
periods of reduced visibilities with accompanying low ceilings. As for
winds...light northeast flow this morning will become
east/east-southeast throughout the day...at or below 10 kts. Into this
evening...shra/tsra will taper off though could not rule out a
lingering rain showers after 00z. Overnight...winds will become light and
low ceilings and fog may create MVFR/IFR through the early morning hours
Extended outlook...chance of showers/thunderstorms will persist through the
extended period. Expect predominantly VFR conditions with tempo
periods of MVFR/IFR ceilings/visibilities in storms.
near term /through tonight/...
as of 1000 am Tuesday...the old stationary front is still here..and
at 10 am extends roughly from Cape Fear southwestward across the
coastal waters east of Georgetown. The overall weather pattern is
retrograding today...meaning it is shifting westward rather than
the typical eastward progression we see. The front should shift
inland by middle to late afternoon...with winds veering from the
northeast around to the south by late in the day. Speeds will also
increase with the tighter pressure gradient on the east side of the
front between it and Bermuda high pressure well offshore. This will
increase wind speeds to near 15 knots by evening...with gusts
exceeding 20 knots at times late this evening.
Widespread thunderstorm activity offshore this morning will shift
largely onshore by this afternoon. While this will decrease the
number of storms occurring over the coastal waters there should
still be a few storms offshore even this afternoon. Coverage of
storms may actually increase overnight.
Seas currently around 3 feet will build toward 4 feet away from
shore tonight in response to the increasing south winds. Wave
spectra will be evenly split between 7 second southeast swell and
shorter period wind waves.
Short term /Wednesday through Thursday night/...
as of 330 am Tuesday...Atlantic high pressure will build westward
through middle week with a S-SW return flow up to 15 kts. A cold
front will approach from the northwest late Thursday with winds
possibly making it up to 20 kts in tightened gradient flow. Seas
2 to 4 feet on Wednesday into Thursday will increase up to 3 to 5 feet by late
Thursday ahead of cold front but wna model remains consistent keeping
seas below Small Craft Advisory thresholds...although a precautionary statement may
Long term /Friday through Saturday/...
as of 330 am Tuesday...cold front reaches into the Carolinas early
Friday but will most likely stall and dissipate over inland Carolinas
over the weekend. Expect to maintain a SW flow around Bermuda high
weakening as gradient relaxes through Friday into Saturday as
front dissipates over the Carolinas. Seas up to 3 to 5 feet early
Friday will fall back down to 2 to 4 feet through late Friday into
SC...Flood Watch until 6 PM EDT this evening for scz017-023-024-032-
NC...Flood Watch until 6 PM EDT this evening for ncz087-096-099-