Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 280905
Area Forecast Discussion
National Weather Service Raleigh NC
404 AM EST Tue Feb 28 2017
A warm front lifting through the area this morning will result
in a mild southerly wind through Wednesday. A strong a cold
front will cross the area Wednesday night.
.NEAR TERM /THROUGH TONIGHT/...
As of 330 AM Tuesday...
The 00z/28TH showed pretty decent warm advection in the low
levels, with a pronounced warm front just inland from the
Carolinas coast early this morning. A sheared disturbance aloft
is exiting the coastal plain, taking most of the high clouds
with it. A few showers have broken out south and east of FAY in
the past couple hours in response to the warm advection, though
hires guidance tends to keep the best isentropic lift focused
east of I-95, and any stratus looks to be fairly thin if it
develops in the next few hours.
The warm front will lift through the area this morning and yield
a southerly wind with 1000-850mb thicknesses reaching around
1385m, suggesting highs well into the 70s to around 80. Mid-
level lapse rates steep to 6.5-7 C/km this afternoon, but
strong warm near 850mb also creates a modest cap, per forecast
soundings, which will be hard to break given low-amplitude
southwest flow aloft and no good trigger for convection.
However, guidance is in pretty good agreement on the remnants of
convection on the Tenn Valley clipping the northwest Piedmont
after ~22Z, though generally remaining west of the better
destablization and limiting any thunder this evening. Chance
POPs will accordingly be highs in the northwest this evening.
Expect stratus overnight in a steady 5-10kt southerly flow,
resulting in very mile lows in the 60s.
.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --As of 400 AM Tuesday...
Wed-Wed night: A complex mid-upper level trough compromised of
multiple embedded shortwave perturbations will move E from the
Plains states early Wed to the Northeast by Thu morning. At the same
time and at the surface, related waves of low pressure will migrate
from the mid MS Valley to New England, while the trailing cold front
will move from the Appalachians late Wed-Wed evening to the Atlantic
coast by Thu morning.
It will be warm and windy, but dry for most of the day Wed, owing to
a stout capping inversion that will be only gradually lifted and
eroded Wed afternoon, in response to height falls accompanying the
aforementioned trough aloft. 925 mb wind progs and BUFR forecast
soundings indicate strong SWly flow will develop in the warm sector,
with sustained winds of 20-25 mph and gusts to around 40 mph.
Morning stratus, trapped beneath the aforementioned inversion, will
disperse by midday or early afternoon, so temperatures should
consequently rise rapidly into the upper 70s to lower 80s. Pre-
frontal showers and storms will be possible over the far wrn
Piedmont, where the aforementioned removal of the preceding cap will
be most likely by around sunset. The better chance of showers and
storms will occur Wed evening and early Wed night, as frontal
forcing accompanying the surface front sweeps Ewd. Strong SWly deep
layer flow, oriented mainly parallel to the frontal zone, will favor
linear convection --amidst an environment characterized by around
250-750 J/kg of CAPE-- that would pose primarily a damaging wind
threat from both momentum transport and mesovortices embedded within
a probable broken band or two of convection. An isolated tornado
will also be possible, given the degree of low and deep layer shear,
though a a relative lack of more robust instability suggests
damaging winds will prove a greater threat. Blustery post- frontal
NWly winds will follow in strong CAA late Wed night- early Thu, with
lows in the low- mid 40s west to middle 50s east.
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.LONG TERM /THURSDAY THROUGH MONDAY/...
-- Changed Discussion --As of 345 AM Tuesday...
A broad trough aloft will migrate across the eastern U.S. during the
end of the week, and reach maximum amplitude as a shortwave trough
in NW flow aloft amplifies into the Middle Atlantic states during
the day Fri.
Considerable high cloudiness, within the axis of a 150 kt WSWly
upper level jet, will stream across NC on Thu, before the S of our
region Thu night. Downslope NWly flow will help offset waning CAA.
MOS high temperatures typically perform well in such downslope
regimes, with upper 50s to lower-middle 60s anticipated. A
reinforcing nrn stream surface cold front will accompany the
aforementioned shortwave trough in NW flow aloft; and this front
will approach from the NW Thu night, then sweep across central NC
during the day Fri. Downslope flow will again develop behind the
reinforcing front on Fri, so MOS temperatures in the middle 50s to
lower 60s are favored. Cold and dry advection within a deeply mixed
(800-750 mb) boundary layer will support afternoon wind gusts around
Fri night through Mon: The trough will have moved offshore by this
weekend, with increasingly zonal flow aloft and/or broad/flat
ridging across the srn and sern U.S. Temperatures will consequently
moderate into the 70s by Mon, after a probable hard freeze with
excellent radiational cooling of a fresh 1030-1035 mb cP surface
high Sat morning, when temperatures are expected to fall into the
lower-middle 20s over the Piedmont, to upper 20s to around 30
degrees over the Sandhills, srn Coastal Plain, and urban areas.
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.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
As of 100 AM Tuesday...
VFR conditions prevail at 06Z/28th as high clouds continue to
move east across the area. An area of showers south of CHS
should remain confined to coastal SC, but the advancement of a
warm front and southeasterly low level flow may bring some MVFR
stratus north into southern and western NC. Models seem to
indicate late development of MVFR ceilings with fairly thin
moisture, with higher confidence at FAY, INT and GSO after 09.
there are some MVFR ceilings already developing south of VUJ,
which lends some confidence to the forecast through early
What stratus that does develop should be quick to disperse and
give way to VFR (or near MVFR) ceilings this afternoon and some
southwesterly wind gusts to near 20kt). Some showers will be
possible near INT and GSO late this afternoon and evening as an
impulse and associated convection move through the Tenn Valley
and across the mountains, which could result in a brief period
of sub-VFR conditions.
Outlook: Sub-VFR ceilings, most likely IFR, are expected late
tonight, along with low-level wind shear, as a 40-50kt low level
jet traverses the area. Wind gusts around 30kt will develop on
Wednesday ahead of a strong cold front and eventual line of
strong to severe storms that will cross the area Wednesday
evening/night. VFR will return on Thursday.