Area Forecast Discussion
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FXUS62 KRAH 011101
Area Forecast Discussion
National Weather Service Raleigh NC
558 AM EST Wed Mar 1 2017
Warm southwest flow will continue across the region today ahead
of a strong cold front approaching from the west. The cold front
will cross the area tonight, followed by cool high pressure for
the latter half of the week.
.NEAR TERM /THROUGH TONIGHT/...
As of 320 AM Wednesday...
Big stories today will be near record heat and potential for
severe storms this evening...
Deep southwesterly flow downstream of a trough over the Plains
will likely result in record highs as 1000-850mb climb to 1395m,
which suggests upper 70s to mid 80s. High clouds are thinning
out this morning and should remain fairly thin for most of the
day before deeper moisture moves with the cold front and
convection this evening. Wind gusts of 30-40kt are also
expected, the strongest of which may be over the northern
coastal plain through midday as mixing taps into a departing low
level jet, which VWP indicates is around 50kt. 925mb and 850mb
winds relax during the day before strengthening again as the
pressure gradient tightens ahead of the front, so gusts should
remain below Wind Advisory criteria.
The warming and steepening mid-level lapse rates -near 7.5 C/km-
will yield some modest MLCAPE this afternoon, but a fairly
prominent capping inversion and CINH should inhibit prefrontal
convection until the upstream squall line over IN/IL/MO/AR and
strong height falls arrive this evening. Despite poor diurnal
timing -between 8pm and midnight per most hires guidance- and
the squall line having to cross the mountains, forecast
soundings show up to 1000 j/kg MLCAPE and a 2-3hr window with a
weakened cap where the CAPE/shear parameter space would support
sustained convection. Wind damage is the main concern given
linear forcing and 50kt ambient winds, particularly into the
coastal plain, though hail is also likely with an elevated
mixed layer. The tornadic threat is much smaller owing to long
straight hodographs, but subtly veering and the strength of the
flow may lead to some curvature and the possibility of embedded
mesos along the line. the SPC day 1 Outlook was essentially
unchanged and includes all of central NC in a Slight Risk.
Expect rapid clearing behind the line after midnight, with temps
falling into the 40s and lower 50s.
.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
As of 400 AM Wednesday...
After lingering mid level ceilings and perhaps a few sprinkles over
the far sern counties early Thu, cirrostratus within the axis of a
150 kt WSWly gradually edge Swd and out of central NC throughout the
day. Downslope NWly flow will help offset waning CAA. Highs in the
upper 50s to lower-middle 60s, with gusts up to 25 mph until midday-
early afternoon, before CAA diminishes by afternoon.
Surface high pressure will ridge overhead from the SW in advance of
a clipper frontal system approaching from the NW, so temperatures
will have the potential cool into the upper 20s to lower-middle 30s.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 355 AM Wednesday...
A progressive pattern aloft will result in a transition from a
departing trough in the eastern U.S. Fri-Sat, to ridging
through early next week. The trough will reach maximum amplitude
as a shortwave trough in NW flow aloft amplifies across the
Middle Atlantic states during the day Fri. This trough will be
followed by a less amplified/shear vorticity maximum that will
migrate through the NW flow, with a brief period mid level WAA
cloudiness, on Sat.
At the surface, a clipper surface wave accompanying the
aforementioned shortwave trough in NW flow aloft will track
across the nrn Middle Atlantic states, while the trailing nrn
stream surface cold front will sweep across central NC during
the day Fri. Given both 1) a tendency for the models to advect
cold air across the Appalachians too quickly, and 2) the
prevalence of a downslope/compressional warming flow component
throughout the day, temperatures are expected to recover into
the middle 50s to lower 60s. Cold and dry advection within a
deeply mixed (800-750 mb) boundary layer will support afternoon
wind gusts up to 25-30 mph, which will make it feel cooler.
Incoming cP surface high pressure behind the front on Fri will
result in a hard freeze Fri night-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. Temperatures
will gradually moderate thereafter, as the surface ridge moves E
and modifies, with 50s on Sat replaced by 60s-70s by early next
After a dry weekend as the ridge moves overhead and offshore,
the approach of the next frontal system will result in a chance
of showers late Mon-Tue.
.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
As of 1235 AM Wednesday...
Strong winds expected today, with storms late this evening...
Despite a weakening band of light showers crossing the area,
conditions are VFR at most all terminals early this morning.
Stratus has formed over much of eastern SC and southeastern NC,
and southerly flow will cause the IFR ceilings to spread north
across central and eastern NC over the next few hours, impacting
mainly RDU/FAY/RWI, with greatest confidence at FAY and RWI
between 08Z and 14Z. Forecast soundings also suggest low level
wind shear is possible through 12Z, moreso at GSO and INT where
the surface inversion is strongest, as a 40-50kt low level jet
translates across the area. However, surface winds will also be
increasing overnight and near surface mixing may mitigate the
intensity and/or duration of the LLWS.
VFR is expect to day with strong southwesterly winds that will
likely gust to around 35kt at time. A line of strong/severe
storms will move into the areas from the west this evening, with
may locally enhance wind gusts and cause a period of sub-VFR,
primarily between 2/00Z and 2/06Z.
Outlook: Skies will clear out for Thursday with VFR conditions
and NW winds. VFR conditions will hold Thu through Sun as high
pressure builds over the area.
As of 550 AM Wednesday...
Critical, or nearly so, fire weather conditions still probable Thu
and especially Fri.
Much drier air will overspread central NC following a cold frontal
passage, and accompanying line of showers and storms, tonight. The
drier air, combined with afternoon temperatures in the upper 50s to
middle 60s on Thu, will result in minimum relative humidity values
between 20 and 25 percent Thu afternoon. However, NWly winds, which
will gust between 20-25 mph through 1 PM, will subside during the
afternoon (when critical RH values are met). Nonetheless, there may
be a several hour period centered around noon Thu when marginally
critical relative humidity values between 25-35 percent overlap with
the aforementioned stronger winds; and increased fire danger may
These conditions will also set the stage for Fri, when daytime
heating and a secondary cold frontal passage during the afternoon
will result in critical RH values for several hours during the
afternoon. In addition, breezy Wly to NWly surface winds are
forecast to be sustained between 15-20 mph, with 25-30 mph gusts.
These conditions for increased fire danger to red flag will likely
be coordinated with the NCFS later today and/or on Thu.
Record highs for March 1st:
RDU: 82 (set in 1997)
GSO: 77 (set in 2012)
FAY: 87 (set in 1918)