Area Forecast Discussion
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FXUS62 KRAH 211954
Area Forecast Discussion
National Weather Service Raleigh NC
255 PM EST Tue Feb 21 2017
High pressure extending along the East Coast will move offshore
tonight. A slow-moving upper level trough will cross the Southeast
and Mid Atlantic states through Wednesday night.
.NEAR TERM /THROUGH TONIGHT/...
As of 255 PM Tuesday...
Rain chances late tonight look pretty small outside of the far W and
NW CWA. The split mid level trough, consisting of a broad low-
amplitude wave crossing the eastern Great Lakes/Quebec/Northeast
states and a prominent deep low moving from NE LA into the NE Gulf,
will bring increasing moisture and forcing for ascent to our area.
But forecast soundings show a notable dry layer in the mid levels,
likely leading to smaller hydrometeors, and DPVA with the
approaching trough will be trending lower given the weakening mid
level winds. Model-generated precip, including from the
SREF/GFS/ECMWF, is generally confined to western NC, where the
better moist upglide and upper divergence will reside, while the
slowly departing low- and mid-level ridges should protect much of
the central and eastern CWA from measurable precip. Will restrict
pops through tonight to just the far W and NW CWA. With gradually
increasing and thickening clouds from the west, expect a trend to
mostly cloudy skies areawide. Lows from the mid 40s NE to the lower
50s SW. -GIH
.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 245 AM Tuesday...
The closed low aloft will slide further southeast through the
eastern Gulf of Mexico and over FL through Wednesday night, taking
the best moisture with it. There is still a chance for some light
rain to occur over Central NC on Wednesday as the weakened northern
stream trough passes overhead, but exactly where the rain will fall
is somewhat uncertain. Regardless, skies will be cloudy throughout
the day and rainfall totals are not expected to be very high. The
highs on Wednesday (like the temperatures the previous 24 hours)
will depend on the return flow into the region from the high
offshore. For now, expect a 10-15 degree temperature gradient from
NW to SE (60 degrees NW to low-mid 70s SE). There will be enhanced
east-southeasterly flow into the southeast U.S. to southern Mid-
Atlantic coast Wednesday night as a result of being sandwiched
between the Gulf low and the high over Bermuda. Though the best
warm, moist advection will be south of the NC coast, expect a
continuation of the above normal temps and overnight lows warmer
than the previous night (low to mid 50s NW to SE).
.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 325 AM Tuesday...
The upper air pattern across central NC will continue to support
very warm conditions though the atmosphere will be slightly
unsettled. A strong cold front will cross our region this weekend
followed by a slightly cooler and tranquil weather regime.
A s/w ridge will build into our region Thu=Fri in response to the
departure of an upper level low off of south FL. These rising upper
heights will maintain very warm conditions across our region. Closer
to the surface, low level southerly flow will gradual increase the
moisture content of the column, yielding variably cloudy skies. With
weak speed convergence occurs, a few stray showers will likely
develop. This scenario appears more plausible over the western
Piedmont both Thursday and Friday though most locations will remain
rain free. With surface based CAPE approaching 1000 j/kg Thursday
afternoon, a thunderstorm may be possible. Temperatures will remain
a solid 15-20 degrees above normal though still a couple of degrees
shy of record warmth.
A mid-upper level s/w crossing the Great Lakes Fri-Sat will drive a
sfc cold front southeastward into the Carolinas Saturday. This front
will encounter a adequately sheared and slightly unstable air mass
to support broken bands of showers and thunderstorms Saturday
afternoon, primarily along and east of highway 1. Cannot rule out
the possibility of a few strong/severe storms as mixed layer CAPE
approaches 1000 j/kg though low level helicity is lacking.
Blustery nw winds behind the front Saturday night/Sunday will usher
a cooler/drier air mass into central NC. While air mass is cooler,
afternoon temperatures will still average 4-6 degrees above normal
for late February. Dry weather anticipated Saturday night into
Monday as deep wly flow will limit precipitation chances.
.AVIATION /17Z TUESDAY THROUGH SATURDAY/...
As of 1210 PM Tuesday...
Expect VFR conditions through this evening with mainly mid and
high clouds increasing from the southwest.
Tonight, low pressure will move into the Gulf Coast states,
sending low level moisture northward to the Triad/Triangle and
eventually the coastal plains. Will start to see sub-VFR cigs
and vsbys working to most terminals after 06z with best threat
of any rain over INT/GSO, with drizzle toward RDU and RWI after
08z. With high pressure keeping flow off the Atlantic will see
some fog as well, so vsbys could drop to IFR, though confidence
is not high enough to add in the terminals except INT closer to
As we head into Wednesday will be tough to dislodge the lower
cigs but models favor most sites going to VFR after 15z, though
in-situ damming over the Triad should keep INT/GSO IFR til the
end of this taf period.
Looking ahead: Expect cigs in the MVFR/low end VFR range to persist
through Wednesday afternoon, mainly west of RDU. With continued
southeast flow through Friday, the early-morning sub-VFR cigs
and visbys will likely be a reoccurring theme. Low clouds may
scatter out enough during the daytime hours for a return to VFR.
Winds will slowly veer through the period ahead of the
approaching cold front. Showers and sub-vfr conditions will also
be possible ahead of the front, which is expected to move
through Central NC on late Saturday.