Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
628 am EST Monday Nov 30 2015
a cold front will drop south across the area today bringing a
chance of light rain...mainly across the NC portions of the
forecast area. The front will lift back north as a warm front on
Tuesday with a return to warmer and drier weather. A stronger cold
front will cross the area late Wednesday...accompanied by a brief
chance of showers. Strong high pressure will follow and bring cool
temperatures and benign weather for the end of the week and into the
Near term /through tonight/...
as of 615 am Monday...the movement of the cold front across
portions or the entire forecast area will be the problem child this period.
Models do indicate the back door front to slide further south
across the forecast area before stalling in the vicinity of the ilm and chs
County Warning Area border to just south of there. Nevertheless...the cool air
will lag and primarily only reach just halfway through the ilm County Warning Area
when all is said and done. What makes it difficult is the surface high
wedging southward...thinking its pushing the cold front further
south which in this case its not. During tonight...the surface pg and
the re-enforcing cool air relaxes across the forecast area as the parent surface
high moves offshore from the NE states.
Precipitation chances will primarily be driven by dynamics associated with
isentropic lift ie. Overrunning. And the precipitation will occur behind
the front within the weak wedging. In addition...weak middle-level
short wave troughs/vorts will also aid precipitation development. Overall...the
steadiest light rain will occur along the northern periphery of
the ilm County Warning Area...and areas further north of the ilm County Warning Area. Look for
probability of precipitation to steadily drop across the ilm County Warning Area...with patchy light rain
or no precipitation at all once you reach the southernmost portions of the
forecast area. Total quantitative precipitation forecast fields through Tuesday daybreak will roughly range from a
trace to less than one tenth of an inch...hiest amounts across
the northern County Warning Area. Used a consensus amongst the available model MOS
guidance with maxes/mins...with low 70s/upper 50s across the
southern portions...ranging to the upper 50s/around 50 for the
Short term /Tuesday through Wednesday night/...
as of 3 am Monday...high pressure wedge will completely break
down Tuesday with southerly flow and warm advection developing Tuesday
night into Wednesday. Aloft the weak middle level ridging over the western
Atlantic and closed 500 mb low moving into the Great Lakes will result
in southwest flow over the region. Abundant dry air over Gulf of
Mexico will spread into the area Tuesday and Tuesday night. This air
combined with middle level subsidence should keep precipitation chances Tuesday
and Tuesday night quite low for most areas. Southerly flow at first
aloft and then developing at the surface will push temperatures above
climatology Tuesday and well above climatology Tuesday night.
Southerly flow increases Wednesday as cold front...associated with upper
low/surface low combo crossing the Great Lakes moves across the
area later Wednesday. Narrow band of deep moisture along the front may
produce some scattered convection but forecast soundings do not
show an environment that is favorable for or even supportive of
widespread showers. There will be convergence along the front but
middle level forcing remains limited. Will maintain inherited chance
pop for second half of the period. Temperatures Wednesday and Wednesday night
will run above to well above climatology with highs in the 70s and lows
in the middle to upper 40s.
Long term /Thursday through Sunday/...
as of 3 am Monday...cold front moves off the coast early Thursday before
stalling over the western Atlantic. Cutoff over the Great Lakes
opens up into a trough Thursday and moves off to the northeast. A
southern stream shortwave hanging back over Texas will keep middle level
flow over the southeast out of the southwest. This is what
ultimately allows the front to stall in the area. The proximity of
the boundary to the coast will determine how much...if any...precipitation
falls over the area late Thursday and Friday. Previously mentioned southern
stream shortwave helps induce cyclogenesis off the southeast coast
Friday with this feature then lifting northeast Friday night into Sat as
the shortwave continues moving east. Still plenty of uncertainty
concerning the end of the week and given the low confidence do not
feel making significant changes to the inherited forecast would add
any value at this point. For now will carry silent pop for portions
of the area Thursday night through Friday night then drying conditions for
Temperatures for much of the period will be near to slightly below
climatology. Regardless of rainfall early in the period the boundary and
low level moisture will result in increased cloud cover. Clouds
combined with northeast flow as high pressure builds in will keep
highs in the 50s with lows around 40. Skies will clear for the
weekend with air mass modification trending temperatures toward
Aviation /11z Monday through Friday/...
as of 12z...front is now moving through the County Warning Area with east northeast
winds behind it. Looks like IFR ceilings will slowly push south as
The Wedge begins to set up. Isentropic lift will start the precipitation
process...however the hrrr model keeps the precipitation over the northern
portion of the County Warning Area...likely only drizzle as well. Look for IFR
conditions to set in...some areas through the end of the forecast
Extended outlook...unsettled weather through late
Tuesday with possible MVFR/IFR conditions from ceilings and
reduced visibility from precipitation and areas of fog. Otherwise
near term /through tonight/...
as of 615 am Monday...the main concern will be the cool front
dropping and stalling across or south of the local waters...
although the surface pressure fields will support NE wind directions
thruout the near term period. The high ridging/wedging south...
will have its tightest surface pg behind the cold front where
resulting speeds will run 10-15 knots. Do not expect gusts to
exceed 20 knots since the best cold air advection surge will remain north of the
Significant seas will range from 2 to 4 feet...with the 4 footers
occurring from Cape Fear northward. The easterly ground swell of
the past few days affecting the local waters is finally
dissipating now...but still remains at a healthy 3 feet at 11
second periods. This easterly swell will have to push across the
shallow bathymetry associated with Frying Pan Shoals before
finally affecting the ilm coastal waters south of Cape Fear. The
processes of refraction/reflection will reduce the height of this
ground swell prior to affecting the waters south of Cape Fear.
Wind driven waves will aid the significant seas initially but as
winds diminish late...the ground swell will become more dominant.
Short term /Tuesday through Wednesday night/...
as of 3 am Monday...easterly flow at the start of the period will
become southerly late Tuesday as the high to the northeast retreats
and The Wedge breaks down. Gradient on Tuesday is light and winds will
be under 10 knots. Stronger southwest flow develops late Tuesday night
into Wednesday as cold front slowly approaches from the west. Speeds
peak around 15 knots Wednesday evening before front crosses the waters and
offshore flow develops. Gradient and cold advection in the wake of
the front will increase speeds to 15 to 20 knots by the end of the
period. Seas 2 to 3 feet Tuesday into Wednesday build to 2 to 4 feet late Wednesday in
response to gradually increasing southwest flow. Development of
strong offshore flow will maintain 2 to 4 feet seas Wednesday night.
Long term /Thursday through Friday/...
as of 3 am Monday...front stalled east of the waters and high
pressure building in from the west will maintain a pinched
gradient over the near shore waters. Potential development of
surface wave along the stalled boundary would lead to further
increased northeast flow later in the period. More northerly flow
on Thursday will be in the 15 to 20 knots range with speeds increasing to
20 to 25 knots later in the day Friday and on Friday night. Initially
northerly flow will push highest seas beyond 20 nm but as winds
veer to northeast flow will become parallel to the coast resulting
in building seas. Thursday into Friday seas will run 2 to 4 feet but by the
end of the period 6 feet will be possible in some some areas.