Area Forecast Discussion
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FXUS62 KRAH 200721
Area Forecast Discussion
National Weather Service Raleigh NC
220 AM EST Fri Jan 20 2017
An upper level trough will pivot northeast across western North
Carolina into this morning. This will be followed by a brief quiet
period Friday afternoon and night. A strong storm system is expected
to affect the region over the weekend into Monday.
.NEAR TERM /OVERNIGHT/...
As of 935 PM Thursday...
Evening upper air analysis depicts a narrow ridge of high pressure
over the state. Immediately on the back side of the high, clouds
were thickening/lowering with patches of light rain developing over
the southern mountains. The ridge is expected to drift offshore
later tonight, leading to increasing cloud cover over our region,
with a good chance for light rain by daybreak across the western
Piedmont. At this time, the bulk of the rain should remain west of
the Triangle, and west of Fayetteville through 7 AM. Rain chances in
the Triangle and Fayetteville quickly reach their peak by mid-late
Mid evening temperatures varied from near 40 across the far
northeast to the upper 40s/around 50 over the far south and west.
As clouds thicken overnight, expect temperatures to hold steady or
rise a degree or two prior to the arrival of the precip. Min temps
will vary from the upper 30s/around 40 northeast to the mid 40s west.
.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 255 PM Thursday...
Rain is expected over the region Friday morning... tapering off
from the west during the afternoon. QPF will be highest in the NW,
lowest SE, ranging from around 0.25 NW to less than 0.10 SE.
Temperatures will remain rather cool or held down by the rain
and clouds. Light flow even behind the departing system will
generally yield cloudy skies with some breaks during Friday
Expect highs in the 50s north, lower to mid 60s south.
Friday night... Patchy fog and variably cloudy skies expected as
we will be between systems. The main issue is the potential
for dense fog if we get some partial clearing. Lows in the upper 40s
to mid 50s.
.LONG TERM /Sunday through Thursday/...
-- Changed Discussion --As of 220 AM Friday...
Earlier thinking remains valid. Warm and stormy weather will rule
Sun through Mon, followed by dry and mild weather Tue through Wed. A
pattern shift toward lower (higher) heights over the eastern
(western) CONUS will commence Wed night, with cooler temps arriving
Sun through Mon night: Widespread showers and perhaps a storm or two
should be ongoing across central NC early Sun, within vigorous
forcing for ascent generated by DPVA with a wave tracking NNE
through the area, having emanated from the deep low over the lower
Miss Valley, along with a 50 kt low level jet punching into the area
from the south, and intense upper divergence. PW of 200-300% of
normal in conjunction with this strong lift will support a period of
heavy rain Sun morning into early afternoon, as an occluded surface
low tracks NE over the NC Piedmont. A slug of relatively drier mid
level air will move in from the south Sun afternoon, leading to a
short relative lull in coverage and intensity, and will have
categorical morning pops dipping to good chance/likely for a period
in the afternoon within brief shortwave ridging between the exiting
wave and the upper low crossing the Gulf States. This lull will be
short-lived as the upper low shifts east over AL/GA then NE over the
Carolinas, bringing another round of strong deep lift. The ECMWF/GFS
have come into better agreement on timing, although the ECMWF is
still a bit faster than the GFS. The slightly slower GFS speed is
preferred based on the strength of this system. Will ramp pops back
up to categorical Sun evening into the early overnight hours,
followed by another downturn in coverage and intensity late as a mid-
upper dry punch arrives along with cooling low levels. Scattered to
numerous showers will persist through Mon as the upper low crosses
the region with ~7 C/km mid level lapse rates and lower but still
above-normal PW. Precip chances will wind down Mon night as the low
shifts to our north. A few strong storms remain possible, mainly
from midday Sun into Sun evening, with a 70+ kt mid level jet streak
accompanying powerful upper divergence and steep 700-500 mb lapse
rates over 7 C/km according to the GFS. CIPS analog guidance
continues to suggest more of a severe threat for FL compared to our
area, historically speaking, although GFS forecast soundings for
central NC still show long wavy hodographs and marginal to moderate
instability, suggestive of at least a modest risk of a few strong
wind-producing storms, and perhaps a tornado as well along and north
of the occluding frontal system. Highs in the mid 60s to around 70
Sun, lows from the upper 40s to mid 50s Sun night, and mid 50s to
lower 60s for highs Mon. Lows in the low-mid 40s Mon night.
Tue through Thu: Mid level heights rise over the Southeast as a mid
level ridge axis shifts over the region, while surface high pressure
crosses the northern Gulf and FL. Expect fair skies Tue/Wed with
slightly cooler but still above normal temps. The aforementioned
pattern change will begin late Wed night or Thu morning (ECMWF
brings a cold front through earlier than the GFS) as a strong EPac
trough this weekend shifts eastward and begins to tap into cooler
polar air that has been bottled up well to our north. Expect highs
back down into the 50s Thu. A few showers are possible with the cold
front, although will keep pops on the low side given the significant
model timing differences. -GIH
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.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
As of 110 AM Friday...
24 Hour TAF period: VFR conditions across the area this morning
should remain so for the next few hours before ceilings start to
come down at the Triad sites in advance of a system that is expected
to track through the area later today. Expect MVFR after 9Z with IFR
following shortly after, closer to 12Z. Eastern sites will come down
a few hours later from west to east. Short term models show
precipitation moving into the Triad around 12z and losing intensity
as it crosses the northern tier. This will leave some question as to
whether or not KFAY will see any rain or not. Other sites to the
east still should see some light rain late morning through early
afternoon before the system quickly moves out to the northeast.
Conditions should begin to improve thereafter.
Long term: Expect fog early Saturday morning and then attention
turns to a stronger system expected to bring the possibility of
thunderstorms to the area on Saturday. Conditions should return to
VFR on Sunday.