Scientific Forecaster Discussion
fxus62 krah 212348
Area forecast discussion
National Weather Service Raleigh NC
645 PM EST Thu Nov 21 2019
surface high pressure will shift southeast and offshore tonight. A
cold front will move into the region from the northwest late Friday
and stall over the area on Saturday. A low pressure system will
track northeast along the front on Saturday and Saturday night,
before pushing the cold front through the area. Weak high pressure
will extend into the region for Sunday and Monday.
Near term /through tonight/...
as of 230 PM Thursday...
The N-S elongated surface high centered over the Carolinas and Virginia at
15z will continue shifting southeast and off the Carolina coast this
aft/eve. The upper level ridge will continue ridging northward into
the region through tonight. A cold front to the west will push
eastward toward the mid-Atlantic, with southwesterly flow increasing
ahead of it. The front will slow and become more W-E oriented as the
parent low swings through eastern Canada and the cold Canadian high
surges southward into the Midwest tonight. The weather through
tonight is expected to remain dry, with increasing cloud cover and
winds overnight. Lows will generally be in the low to mid 40s.
Short term /Friday and Friday night/...
as of 245 PM Thursday...
As the front slips toward central NC the best forcing with the
parent low will race away from the region, resulting in slowing of
the frontal progression and lessening of precipitation chances. With
good warm southwesterly flow into the area on Friday, highs could
top out in the low to mid 60s. However, winds and wind gusts will
likely increase as well. The best chances for rain during the
morn/aft Friday will be across the north along the Virginia border as the
front slides south toward NC. The best chances will shift more to
the west overnight, though that will be determined by the location
of the front. There are still some questions as to whether/how far
the front will slide into the area late Friday/Friday night. This
will impact both whether some of the cold air behind it will surge
in and where the best rainfall chances will be. There is a chance
that a good portion of the area could remain dry through Friday
night. As alluded to above, temperatures will depend on the
progression of the front, but for now generally expect lows in the
low to mid 40s north and low 50s south.
Long term /Saturday through Wednesday/...
as of 300 PM Thursday...
Southern stream shortwave crossing the south-central US early
Saturday is forecast to reach neutral or slightly negative tilt by
the time it crosses NC Saturday evening, bringing a punch of strong
DCVA and 100+ meter height falls and cold frontal passage Saturday
night. Ahead of the cold front, an in-situ cad airmass should
linger Saturday and be temporarily reinforced by the onset of rain
early Saturday, eventually eroding as warm advection increases
overwhelms the shallow airmass. Latest guidance suggests The Wedge
front will retreat to the northwest Piedmont Saturday afternoon, possibly
with a weak triple point low, before the cold front sweeps across
central NC. Temps should hold in the upper 40s across the north
Saturday afternoon, possibly reaching the lower 60s in the south.
Expect rain to transition to more showery activity Saturday evening,
and whole forecast soundings suggest almost zero instability, the
pattern would suggest the potential at least a brief period of thin
elevated instability that, along with with strong upper forcing,
could support an isolated storm. Uncertainty and coverage wouldn't
support including thunder in the forecast, but it could be an
outside chance. Otherwise, models are just a tad slower with the
timing of the front and main precip band, so have slowed the highest
pops a bit. Quantitative precipitation forecast amounts still look like one half inch to an inch,
highest in the west with additional of the earlier rain.
Behind this system, modified high pressure will build in across the
southern US for sun-Tue, supporting highs slightly above normal. The
midweek system is plagued by wide model spread, but with a primary
storm track west of the mountains and general westerly mid-level
flow, model pops seem too high, with the potential for this system
to present a drier trend in the models with time.
Aviation /00z Thursday through Tuesday/...
as of 645 PM Thursday...
24 hour taf period: generally VFR conditions will continue through
Friday. An increase in mid/high clouds around 8-10 kft is likely
tonight and will persist through Friday as the cold front moves
east. The winds are expected to be primarily southwesterly and
increase during the day Friday to 10-15kts with gusts upto 20kts.
Looking ahead: a cold front will move into and through the area
between late Friday and early Sunday, accompanied by rain, gusty
winds and sub-VFR aviation conditions. A return to VFR conditions is
expected on Sunday, persisting through Tuesday.