Area Forecast Discussion
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FXUS62 KRAH 181132
Area Forecast Discussion
National Weather Service Raleigh NC
632 AM EST Wed Jan 18 2017
A cold front will track southeast through central North Carolina
today. In the wake of the front, high pressure will build into the
region from the northwest tonight and Thursday.
.NEAR TERM /THROUGH TONIGHT/...
As of 320 AM Wednesday...
Cold front approaching the area is currently settled along the WV/VA
border. Out ahead of the front, radar showing some light rain along
the VA/NC border north of the Triad and that will gradually work its
way into the northern tier today. Short term models do not show a
lot of precipitation with the front as it moves through the area.
There will be a few wind gusts however up to 20 kts or so.
Temperatures will be tricky as the timing of the front could mean
near steady state or slightly falling temperatures through the
afternoon hours. Regardless highs will be in the lower 60s across
the north and near 70 degrees in the south. Lows in the upper 30s to
.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 320 AM Wednesday...
High pressure will be in control for much of the day on Thursday as
an upper level ridge moves over central North Carolina. A bit cooler
with temperatures in the upper 50s to lower 60s. Winds will be light
and variable under the surface high and the airmass will be dry.
A southern stream low will start to encroach on the area by early
Friday morning with increasing clouds throughout the night on
Thursday night but all precipitation is expected to hold off until
Friday. Lows Thursday night in the low to mid 40s.
.LONG TERM /Friday through Tuesday/...
As of 420 AM Wednesday...
Model agreement with the general pattern continues to be better than
usual through the weekend, although some important differences in
the low level pattern are evident, and notable timing differences
crop up by Mon/Tue. Models are overall trending wetter in this time
frame. Temps will remain quite mild, with all cold air staying
bottled up over northern Canada and the Arctic region.
Fri/Fri night: The mid level trough extending from the Midwest
through the Ohio Valley to SC early Fri will continue to pivot to
the NE through NC and into the Mid-Atlantic and Northeast Fri, and
will be followed by prominent shortwave ridging over the Southeast
Fri night. Focused mid level DPVA and upper divergence associated
with passage of the trough, along with high PW, will support a band
of rain shifting through central NC Fri morning, with a west-to-east
tapering down Fri afternoon, and dry but mostly cloudy conditions
Fri night as low level moisture pools over the area with a light
surface flow. Will go with likely pops Fri morning, trending
downward Fri afternoon. The ECMWF/NAM bring today`s surface front
back northward into NC, albeit in a very diffuse form, while the GFS
is more defined in keeping the frontal zone near the NC/SC border,
favoring thick low clouds and cooler temps, especially over northern
NC. With well-above-normal thicknesses tempered a bit by the morning
rain and lingering clouds late Fri into Fri night, expect above
normal temps with highs from the mid 50s N to lower 60s S. Lows 45-
Sat/Sat night: What once appeared to be a fairly dry day now looks
be trending wetter. Thanks to a powerful mid and upper jet from CA
across the Desert Southwest and adjacent Mexico to TX, a strong low
will be closing off over OK/TX before shifting to AR/LA through Sat
night. Subtle perturbations ejecting from this low/trough will swing
NE into the Carolinas Sat afternoon/night, while bands of enhanced
upper divergence spread in from the SW, a product of ideally
juxtaposed upper jetlets over the Ohio Valley and over the NE Gulf.
Low level flow will be ramping up with an 850 mb jet nosing into the
Carolinas, fostering moist isentropic upglide along/above the
diffuse surface frontal zone. And models agree on PW staying well
above normal as they generate precip over the area, mainly across
the southern and western CWA Sat and areawide Sat night as heights
aloft continue to fall with the approaching trough. Will bring in
low chance pops mainly S on Sat, trending up to good chance Sat
night. The rain and clouds will lead to a tighter diurnal temp
range. Highs in the low-mid 60s Sat followed by lows in the mid 40s
to lower 50s.
Sun into Mon: The mid level low is expected to cross the lower Miss
Valley, Gulf States, and Carolinas before moving into the interior
Mid-Atlantic region through late Mon. This system will be
accompanied at the surface by a complex but likely occluded frontal
system, with vigorous deep forcing for ascent promoted by a 40-50 kt
low level jet punching into the area, intense upper divergence
within a zone of ascent between two ideally juxtaposed upper jets,
and large mid level height falls. Confidence is high in a period of
potentially heavy rain and embedded storms with strong kinematics
and marginal instability and lapse rates, but the timing is less
certain, as the GFS becomes much slower (farther SW) than the ECMWF
with the upper low and trough as it swings ENE through our area with
a negative tilt. Will lean toward the faster ECMWF, which has good
agreement with its ensemble mean. Will have likely pops Sun/Sun
night, with the best chance of heavy rain and storms Sun evening,
followed by a SW-to-NE tapering down of pops on Mon as some drier
mid level air works in from the SW. A strong storm or two remains
possible given the energetic wind field, despite the weak
instability noted by the models. Lingering instability showers and
isolated storms will persist Mon with indications of high lapse
rates and abundant moisture. Temps should remain above normal
despite the clouds/precip.
Tue: We should be on the west side of the departing low/trough
shifting to our east and north, with yet another mid level ridge
building in. Expect dry weather and a trend to fair skies. With no
cold air available, temps will remain above normal. -GIH
.AVIATION /12Z THURSDAY THROUGH SUNDAY/...
-- Changed Discussion --As of 630 AM Wednesday...
24 Hour TAF period: VFR conditions across the area this morning as
winds remain between and 5-10 kts with a few gusts of 15-20 kts. As
a front approaches the area later this morning, there is some
uncertainty whether or not low ceilings will develop. At this point,
these ceilings don`t appear to be coming any time soon. Some very
light precipitation may accompany the front but that will be of
minimal impact. At this time, precipitation on radar is not
reaching the ground save for a few sprinkles. Some gusty winds up to
20 kts this afternoon are expected.
Long term: VFR is expected to hold until Friday when the next system
is expected to move through from the southwest. A stronger system is
expected to impact the area early next week.
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