Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 242049

Area Forecast Discussion
National Weather Service Raleigh NC
450 PM EDT Sat Mar 24 2018

An area of low pressure and upper level disturbance will move
northwest to southeast over North Carolina through tonight. Chilly
high pressure will build into the Carolinas from the north Sunday
through Tuesday. This high will move to our southeast and off the
coast Wednesday, bringing a warming trend.


As of 415 PM Saturday...

Update: Based on new guidance, have expanded the winter weather
advisory area to include northern portions of Alamance, Orange, and
Durham counties for the potential for a half to a much as an inch of
snow, mainly on grassy and elevated surfaces.

The dampening mid level shortwave trough moving into IL will
continue a SE motion, passing through the Carolinas late tonight
into Sun morning. The associated surface low over SE MO will track
SE along the strengthening low level frontal zone, moving toward SW
NC tonight, followed by secondary cyclogenesis just off the SC coast
late. Mostly light precip associated with a weak leading
perturbation has spread across NC, and the initially high dewpoint
depressions have begun to decrease as cloud bases lower. We`ve
already seen a band of higher precip rates passing over the Triad
produce a period of snow, despite wet bulb temps sitting just above
freezing. That such cooling of the column is already occurring is
concerning, in that it suggests that perhaps a larger area of the
northern Piedmont may see a risk of snow bursts this evening into
the overnight hours. It`s expected that as the stronger forcing for
ascent arrives this evening (including low level frontogenetic
forcing, incoming mid level DPVA, and increasing upper divergence
associated with the northwesterly jetlet moving from the W Ohio
Valley through the Carolinas), precip rates will pick up, with any
spotty areas filling in by mid evening. Where the rates are highest,
dynamic cooling is likely to prompt a rain/snow mix to switch over
to mostly snow, not unexpected given projections of a deep near
freezing isothermal layer. Surface temps should in general stay just
above freezing, however a period of surface cooling is apt to occur
within the heaviest precip over the northern Piedmont, causing an
accumulation of snow, primarily on grassy and elevated surfaces. But
if snow comes down heavy enough, some accumulation on roads,
especially bridges/overpasses, is not out of the question. Expect
precip totals of around a half to one inch across central NC, with
far northern Piedmont snowfall of one half to one inch, highest over
northern portions of the advisory area. Once the mid level wave
passes through late tonight, taking the heaviest precip to our east,
temps should rebound a degree or two, such that icy roads won`t be a
big concern Sunday morning. Lows will be 31-38, again with the
cooler readings occurring during the heavier precip in the predawn
hours. -GIH


As of 425 PM Saturday...

The by-now-shearing shortwave trough will be exiting to our SE Sun
morning, with the primary surface low dissolving to a weak inverted
trough over the S Appalachians and the secondary surface low moving
further offshore. Copious low level moisture will remain,
particularly over the W and S CWA, although the chilly wedging
surface high may allow for some low level drying over the NE CWA.
Nevertheless, expect a cloudy to mostly cloudy and cool day over
much of the area, and we may see lingering drizzle over the
Piedmont, especially west sections. Highs 43-50. Nocturnal cooling
with the wedge holding firm Sun night will prompt the low clouds to
hold firm, especially over the S and W. Lows 30-37. -GIH


As of 200 PM Saturday...

Longer range forecast remains on track with much warmer weather
returning by mid week.

Cold air advection will continue Monday as high pressure ridges down
the Atlantic coast. The cool ridge holds through Tuesday, though
gradually weakening and lifting north into New England. The surface
high lifting out combined with a mid level ridge axis over the area
edging east and offshore Tuesday night will result in deep
SW return flow with strong warm air advection setting up
early Wednesday and continuing into Thursday. Temperatures on
Wednesday will rise into the 60s and then soar into the 70s on

While all of this is going on locally, a long wave trof will be
deepening over the Plains, with strong frontogenesis stretching out
of the Gulf northeastward into the Ohio Valley during the mid week.
The mid level ridge just east of the area will block and slow down
the eastward progression of this surface front, allowing deeper
layer moisture advection into the area, with precipitable waters
edging above 1.5 inches prior to the front`s passage early Friday.
A lot of favorable ingredients will be also be present which would
support stronger shower and thunderstorm activity, which would most
likely manifest as a line of strong convection immediately ahead of
the front. Timing will be key, as just a little delay of frontal
passage from Thursday night into Friday would add increased
instability to the mix. Highs Friday will be in the mid 60s north to
mid 70s south.  Ridging builds in Friday night into Saturday with
cooler and dry weather.  Highs Saturday will range from 55 north to
65 south.


As of 145 PM Saturday...

Aviation conditions, particularly cigs, will deteriorate over the
next several hours and remain MVFR to IFR this evening into early
Sun morning. A surface-850 mb low and mid level shortwave trough
will approach central NC from the NW this afternoon and cross the
region tonight. Precipitation is already spreading in from the NW
ahead of this system, although it`s only reaching the ground at the
Triad terminals so far. Cloud bases will steadily lower areawide
this afternoon through early evening. INT/GSO are already MVFR and
should drop to IFR with precip becoming more steady (mostly rain,
but will mix at times with snow, and may briefly become all snow on
occasion this evening). RDU/RWI/FAY will dip to IFR after 04z,
remaining so through the night with steady rain, potentially mixing
with snow at RDU/RWI. Improvement to MVFR is expected Sun morning
around 11z-15z as the disturbance pushes to our ESE and the precip
ends NW to SE. Surface winds will be light/variable, becoming mainly
from the NE tonight, and we may see some gusts after 15z Sun.

Looking beyond 18z Sun, within the cool surface ridge wedging down
into central NC, cigs will stay mostly MVFR at INT/GSO, with a trend
to VFR elsewhere Sun afternoon. MVFR conditions should dominate at
INT/GSO through Sun night, with VFR conditions elsewhere. By midday
Mon, VFR conditions are expected areawide, although sub-VFR
conditions may linger at INT/GSO. As the surface high builds
overhead and then drifts SE midweek, VFR conditions should dominate,
although there are signs that the Piedmont terminals may see periods
of sub-VFR clouds Tue into Wed as moisture increases aloft. Cigs
should be VFR Thu with a chance of showers areawide, within
southwest flow ahead of the next approaching storm system. -GIH


Winter Weather Advisory from 8 PM this evening to 5 AM EDT Sunday
for NCZ007-008-021>025.



NEAR TERM...Hartfield
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LONG TERM...mlm/Franklin
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