Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 221158
Area Forecast Discussion
National Weather Service Raleigh NC
758 AM EDT Sat Apr 22 2017
A cold front will settle south through VA this morning and into
central NC this afternoon through tonight. The front will stall over
southeastern NC by Sunday, in advance of a slow-moving area of low
pressure that will track along the coast of the Carolinas through
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 435 AM Saturday...
Downstream of a mid-upper low that will deepen as it tracks across
the middle MS Valley to west-central TN/KY by 12Z Sun, a series of
low amplitude disturbances in WSW flow aloft will track ene across
the srn Middle Atlantic states and Carolinas, with an associated
corridor of steady 20-30m/12 hr mid level height falls, through
At the surface, a synoptic cold front stretched from a 1010 mb
surface low over the Chesapeake Bay vicinity swwd through wrn/swrn
VA and TN, to a 1008 mb surface wave over swrn AR, then swwd through
west-central TX. This front will settle slowly swd today, to the nrn
NC Piedmont and nrn Coastal Plain late this afternoon and early this
evening (between 5 pm and 9 pm), and likely be accompanied by a weak
lee surface wave forecast to develop over swrn VA this afternoon.
Meanwhile, to the south of this front, an outflow boundary (from
earlier and ongoing convection) remains draped from SW to NE across
central NC from near CLT to JNX to EDE; and this feature will likely
linger in that general area, or retreat slightly nwd, today.
A continued threat of showers, and patchy low clouds and/or fog in
the rain-cooled air, will result along and north of the outflow
boundary through daybreak. Warm and breezy conditions will otherwise
develop by midday-early afternoon. Strong diurnal heating, with
temperatures comparable to those of Fri (well into the 80s, to
around 90 degrees over the Sandhills), and surface dewpoints in the
middle 50s to lower 60s and maximized along the aforementioned cold
front, will yield weak to moderate instability by mid afternoon. The
greatest concentration of resultant showers and storms will occur
along the approaching front, focused initially over southside VA,
before drifting swd across the NC state line late this afternoon.
However, isolated to more widely scattered activity may also fire
along both the aforementioned outflow boundary, as well as any
soil/surface moisture gradients resulting from earlier convection.
25-40 kts of WSWly mid level flow, strongest north, will favor multi-
cell storm modes, and probably a few supercells in the vicinity of
the front and preceding the aforementioned weak lee surface wave,
where locally backed low level flow and shear will become maximized
and yield perhaps 100-150 m2/s2 effective srh. While mean storm
motion will be around 210-220/30kts, right-moving storm motion
vectors will be closer to 260 degrees and consequently be aligned
more parallel to the approaching cold front. So while strong to
marginally severe wind gusts would be favored with multi-cellular
storms, any supercells --near the VA border-- will also be capable
of producing hail, and perhaps a tornado owing to updraft
propagation contribution from both shear/dynamical influences and
surface boundary ones, which would favor storm motion roughly along
the relatively helicity-rich front.
Post-frontal low overcast, patchy light rain/showers, and and gusty
post-frontal NEly winds, will develop behind the synoptic surface
front as it settles south through central NC tonight. Cooler, with
lows in the upper 40s to around 50 degrees nw to around 60 degrees
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.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 400 AM Saturday...
This long duration rain event on tap through the short term forecast
has the potential to produce widespread 2-3 inches of rain. This
will ultimately be beneficial in alleviating the abnormally dry to
moderate drought conditions which have been gradually developing
through the late winter/spring across central NC. The heavier rain
focus shifts from the west initially Sunday to the east on Monday,
which will help mitigate the potential for widespread flooding, but
some flooding is possible on creeks and streams, and even our larger
rivers may have some minor flooding from Sunday night into early
As mentioned earlier, the initial focus for heavier rain will be in
the western Piedmont on Sunday as low level isentropic lift will be
focused on the frontal/CAD zone. Rain will ramp up over the
remainder of the forecast area later in the day and peak Sunday
night over the Piedmont as low level flow backs southeasterly as the
surface low pressure system moves slowly east across South Carolina.
The heavier rain then shifts east as the digging cutoff low phases
with the surface system Monday morning and begins to lift slowly up
the coast through Tuesday. Categorical PoPs through the period with
QPF amounts ranging from slightly >3 inches across the north to 2.5
inches in the southeast. CAD-flavored high temperatures in the Triad
will struggle into the mid and upper 50s Sunday and Monday with the
southeast reaching low 70s. Scattered non-elevated thunderstorms
will be possible around the periphery of the wedge, with lesser
potential for elevated convection heading into the deeper cool air
north and northwest.
.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 400 AM EDT Saturday...
Precip chances diminish rapidly Tuesday, with only slight chances in
the northeast by late afternoon. Shortwave ridging is expected in
the wake of the upper wave on Wednesday with dry conditions and a
warming trend through Saturday as an upper level ridge builds over
the southeast CONUS. Highs Tuesday will reach 70 to 75, with a
return to mid and upper 80s for Friday and Saturday.
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --As of 755 AM Saturday...
VFR conditions and a warm and breezy SW wind are expected today, at
least until showers and storms move into the NC Piedmont from the
west, and also fire in-situ along both old outflow boundaries from
earlier convection and a cold front that will settle south from VA
late this afternoon and evening. MVFR ceilings, patchy light
rain/showers, and gusty post-frontal NEly winds will develop behind,
and with the passage of, the front this evening.
Outlook: A prolonged period of rain/showers and sub-VFR ceilings and
visibilities --in springtime cold air damming-- can be expected
later tonight through Tue night, as an area of low pressure tracks
east along the aforementioned front, then slowly up the coast of the
Carolinas. Conditions will be slow to improve as the coastal low
drifts only slowly away from our region, with a return to VFR on
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