Area Forecast Discussion
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FXUS62 KRAH 270838
Area Forecast Discussion
National Weather Service Raleigh NC
338 AM EST Mon Feb 27 2017
High pressure will move offshore today, followed by a warm front
lifting through the area tonight. Meanwhile, warm southwesterly
flow will continue ahead of a cold front approaching from the
west through midweek.
.NEAR TERM /THROUGH TONIGHT/...
As of 340 AM Monday...
A 1028mb surface high is centered off the Delmarva this morning
and will continue to shift east today, resulting in a light
southerly flow that will increase 1000-850mb thickness by about
25m over Sunday. Thin high clouds will spread in from the
southwest ahead of a shearing shortwave currently over MO/AR,
but thicker mid clouds should hold off until this evening and
the impacts on highs look negligible. The 25m increase in thicknesses
supports guidance consensus of lower 60s northwest to 70
The aforementioned sheared shortwave will cross the region
tonight, leading to increased cloud cover, initially mid/high
level and then later in the form of stratus associated a warm
front and strengthening warm advection. Most models continue to
be essentially dry overnight, as upstream precip should
dissipated with eastward extent this evening. However, the NAM
still indicates some light showers breaking out with the warm
front after midnight, due at least in part to some questionable
elevated instability, and the 00Z ECMWF supports at least a
slight chance POP after midnight. Mid and high clouds look like
they`ll move east by midnight and may yield a period of brief
clearing before stratus develops across the west. This should
allow temps to fall into the mid 40s west to lower 50s east.
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 340 AM Monday...
West-southwest flow will ensue on Tuesday as a surface warm
front lifts north of the area. Morning stratus will likely hold
longest across the west but full heating is expected for a large
portion of the area as period of high clouds spread east in
relatively unamplified flow. 1000-850mb thicknesses support
highs in the lower 70s west to near 80 east. Dewpoints creeping
into the upper 50s and modest 6.5-7 C/KM mid level lapse rates
will lead to weak instability, but forcing is largely lacking
outside of warm advection. Currently think showers and a few
storms will be widely scattered across the Piedmont and coastal
plain. Tuesday will be rather mild in the warm sector of a
stronger low pressure system moving through the Midwest, with
lows in the upper 50s and lower 60s.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 255 PM Sunday...
Tue/Tue night: The most likely scenario is that the warm front will
be pushing NNW into the area early Tue, with the morning hours
featuring low stratus in the west, where the stable pool should
linger, and partly cloudy in the east, with isolated light precip in
the west supported by moist isentropic upglide. Models show the
entire area mixing and destabilizing during the afternoon, although
climatology would suggest that the NW CWA could stay somewhat stable
all day. Models depict marginal to moderate instability developing
mainly along and east of Highway 1 in the mid-late afternoon, with
good low level moisture streaming in, improving deep layer shear,
and decent mid level lapse rates of 7.0-7.25 C/km. Dynamics are slim
however, with a fairly flat mid level flow, and only weak upper
divergence. Will have a slight chance of showers in the afternoon in
the west, with a better chance of showers and thunderstorms in the
east, lasting into the evening before the loss of heating prompts a
trend down to small shower chances and the development of
stratocumulus overnight. These clouds should mix out with heating
Wed as we`ll be firmly in the warm sector, with a stout gusty breeze
from the SW ahead of the cold front, which should push SE through
the area Wed evening or Wed night (the GFS is several hours faster
than the ECMWF and NAM). GFS instability is a bit higher Wed
afternoon as compared to Tue, reasonable given the even greater
influx of low level moisture, and if the slight cap noted around 800
mb on GFS forecast soundings comes to fruition, in conjunction with
the GFS`s projected 7.5-8.0 C/km mid level lapse rates and
strengthening deep layer bulk shear to 55-65 kts, we could get rapid
development and intensification of convection during the afternoon,
especially over the eastern CWA, with some late-day severe storms
possible. This convection should remain supported by a pocket of
strong upper divergence as it shifts over eastern NC through late
evening, followed by frontal passage, although high clouds should
persist over the area through Wed night as the positively tilted mid
level trough will still be well off to our NW. With warm
thicknesses, expect highs of 70-77 Tue except for mid-upper 60s NW.
Morning thicknesses Wed around 1380 m, nearly 60 m above normal,
will support highs from the mid 70s NW to lower 80s SE.
Thu through Sun: A generally tranquil period with dry weather
likely. The cold front will be pushing southeast ward off the coast
Thu morning. Broad mid level troughing will persist over
central/eastern Canada and the northeast CONUS into Sat, with the
core of the polar low transferring from Hudson Bay to Newfoundland.
An initial ridge of high pressure nosing in from the WSW Thu will
bring thicknesses that are close to seasonal normals. Then, energy
that swings through the trough base across the Mid
Atlantic/Northeast on Friday will bring a reinforcing dry cold front
southeastward through the area, followed by chilly high pressure
that will build overhead by Sat morning. This should knock temps
down to below normal for Fri night/Sat, with a good chance of
orographically enhanced high clouds over the Piedmont early Sat
within fast perturbed mid level flow. Temps should moderate for Sun
as the highs drops to our SE with return flow and weak lee troughing
for the latter half of the weekend. -GIH
.AVIATION /08Z MONDAY THROUGH FRIDAY/...
As of 1245 AM Monday...
High confidence in VFR today under influence of high pressure. A
light south-southwest wind will develop today as the high moves
east. Mid and high level clouds will increase this evening as a
weakening upper level disturbance moves overhead and a warm
front lifts north into the Carolinas. More substantial stratus,
MVFR to IFR, will likely come after 06Z, but there is a small
chance some MVFR ceilings, along with a few weakening showers,
could develop at GSO and INT by 06Z Tuesday.
Outlook: Stratus developing early Tuesday will burn off prior to
midday, with scattered showers and storms possible during the
afternoon and evening. A more substantial threat of sub-VFR is
expected late Wednesday and early Thursday a cold front crosses
the region. VFR will then return for the end of the week.