FXUS62 KRAH 231900
Area Forecast Discussion
National Weather Service Raleigh NC
300 PM EDT Wed Aug 23 2017
A cold front will continue to cross the area this afternoon and
linger across the east this evening. High pressure for the end of
the week will bring cooler and drier weather to the area.
.NEAR TERM /THROUGH TONIGHT/...
As of 300 PM Wednesday...
Showers and thunderstorms associated with a cold front are
continuing to fill in along a line from just south and east of the
Triad northeastward to north and west of the Triangle area. This
increase in activity is expected to continue this afternoon as
storms move into a more favorable airmass for development and are
accompanied by an increase in dynamical forcing. ML CAPE values of
1500-2000 J/kg will be common and effective shear values will reach
upwards of 30 knots across the north which will most likely lead to
a broken line of multicellular development with damaging winds the
most likely threat for severe weather. The best DCAPE values however
are expected to remain out ahead of the advancing convection and
will continue push eastward through the evening which could mitigate
somewhat the potential for downbursts. Although there is the
potential for some rotation aloft in storms, LCL values are very
high and low-level helicity values are near non-existent.
A secondary threat from these storms would be localized flooding,
especially in the south and east where high resolution models
indicate a slowing down of the system over the southeastern counties
into the evening and early overnight areas which could extend the
amount of time that areas could potentially see heavy rainfall. As
far as timing is concerned, the Triad will see the most activity
from now through mid-afternoon, with the Triangle seeing the best
coverage from 19-23Z and the Fayetteville area closer to 00z
potentially through 6z if enough slowing occurs.
After frontal passage expect locations to see a switch to
northwesterly and then northerly winds with dewpoints eventually
dropping about 10 degrees or so into the 60s in the Triad with
locations to the southeast maintaining upper 60s to low 70s
dewpoints into Thursday. Lows overnight in the mid 60s NW to lower
70s in the southeast.
.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 300 PM Wednesday...
For Thursday expect the frontal zone to hang up either in far
southeastern areas of the state or just offshore. With the exception
of a lingering afternoon shower in the far southeastern portion of
the forecast area, much of the CWA should remain dry and
significantly cooler than the past week or so. Expect high
temperatures only in the low to mid 80s with north winds at 5-10
kts. Skies will continue to clear as the day progresses with the
Triad seeing the most sun. Lows in the low to mid 60s across the
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 210 PM Wednesday...
An extended period of mostly dry and cooler-than-normal weather
appears likely. Cool Canadian high pressure will build in strongly
from the north through the period, as its center drifts from N
Ontario early Fri to New England early Mon, then weakens just off
the Northeast and Mid Atlantic coast Tue/Wed. The only significant
rain chance through the period appears to be in the far SE, closer
to the old frontal zone where PW will be higher. The far NW
including the Triad will see a smaller chance of light precip,
driven largely by moist upglide and shallow instability, mainly Fri
night into Sat, with overrunning clouds dominating there through
Sun. Will start to edge pops up closer to climatology for early next
week, given the uncertainty with a potential tropical-type low off
the SE coast, along with the weakening of the surface high and
resultant increase in onshore-directed low level flow drawing in
Atlantic moisture. Expect high temps in the low-mid 80s Fri, before
trending down to the mid 70s to near 80 by Tue as the stable wedge
noses down through central NC. Some rebounding back to highs in the
low-mid 80s is expected by Wed as low level thicknesses begin to
inch back up toward normal. -GIH
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 225 PM Wednesday...
Showers and thunderstorms are expected to move through the area this
afternoon and evening in association with a cold front. Current
radar shows convection in the vicinity of KINT and KGSO but pushing
eastward with a few showers near eastern airports as well. Coverage
will continue to increase this afternoon for eastern sites whereas
the Triad terminals should see decreasing trends as the front moves
past. Winds will be light and variable outside of gusts within
thunderstorms which could reach 20-30 kts. Overnight expect
potential visibility restrictions as well as some possible IFR
ceilings at eastern locations, especially where rain lingers into
the overnight hours. Winds will switch to northerly after frontal
passage and conditions are expected to return to VFR after 15z
Thursday. Cant rule out a shower in the east tomorrow afternoon but
confidence is low at this time.
Long Term: High pressure over the area should yield an extended
period of VFR conditions.
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