Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 240706
Area Forecast Discussion
National Weather Service Raleigh NC
305 AM EDT SAT SEP 24 2016
Weak high pressure will hold over the area today. A backdoor cold
front will approach from the north early tonight, and then move
southward through the area late tonight through Sunday morning.
A cooler air mass will push in from the north Sunday morning through
Monday. The front will move back northward as a warm front late
Monday, with brief high pressure following, before a cold
front crosses the region west to east late Tuesday.
.NEAR TERM /today through tonight/...
-- Changed Discussion --As of 305 AM Saturday...
Today: Once the areas of shallow fog wear off an hour or two after
daybreak, a fairly quiet and warm day is expected with plenty of
sunshine. The latest surface analysis shows the remains of the weak
trough just off the coast, with weak high pressure covering the rest
of the region, although weak Piedmont trough development is
anticipated this afternoon. Pronounced ridging is noted throughout
the mid and upper levels centered just to our west, with a weak mid
level flow from the NW or NNW over our area, and observed PW
according to blended TPW imagery is low (1.0-1.4"). With deeply dry
and stable air in residence and upstream, expect mostly sunny skies
today. Thicknesses are expected to be 10-20 m above normal, favoring
highs in the 86-90 range, highest west.
Tonight: Warm conditions will hold through the evening, then the
backdoor front currently stretching across central IN/central OH/
southern PA will push southward into NE NC overnight, propelled by
cool dense high pressure to the north and flow around a strong
vortex over SE Canada. Plenty of low stratus is currently found near
and north of this front, and see no reason why this won`t hold as
the front drops into NC. Models agree on light precip near the front
with considerable low level moisture pooling taking place, and will
hold onto low chance pops over the NE and far N CWA tonight, with
low QPF overall given the shallow nature of the incoming moisture.
Lows in the mid-upper 60s. -GIH
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.SHORT TERM / /...
-- Changed Discussion --As of 320 PM Friday...
To be updated shortly.
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.LONG TERM /SUNDAY THROUGH FRIDAY/...
As of 245 PM Friday...
The timing of the back-door cold front through the area on Sunday is
still in question. The GFS and NAM are much quicker to blow the
front south through the area late Saturday night/ear Sunday, while
the ECMWF suggest the frontal boundary will tend to "hang up" or
slow down across the forecast area on Sunday, which is very
plausible given weak sfc pressure rises from the transitory parent
high center retreating off the Northeast-Southern New England Coast.
These models discrepancies are leading to lower than average
forecaster confidence, making for a challenging temperature forecast
on Sunday and likely setup a sharp temperature gradient across the
area. For now will continue a "middle of the road approach" with
highs ranging from mid 70s northeast to mid 80s southwest.
Additionally, given the potential for the front invof the area, will
continue isolated to slight chance chance pops.
Mid/upper level ridge will build east over the area on Monday in
advance of a closed low and upper trough progressing eastward into
the Upper Great Lakes/Southern Canada. With the transitory parent
high quickly moving off the Southern New England Coast, south-
southeasterly return flow will quickly return to the area late
Monday with rain chances generally restricted to
upslope/differential heating over the higher terrain, while ridging
aloft should keep the remainder of NC dry. SELY moisture advection
and resultant weak isentropic upglide in advance of a cold front
approaching from the west could produce showers across the area as
early as Monday night/Tuesday morning with another round of showers
and storms expected to accompany the frontal passage Tuesday
afternoon/evening. Highs Monday and Tuesday slightly above normal
with mild overnight lows in the 60s.
In the wake of the cold front, high pressure will bring dry
seasonable weather for the later half of the work week. Highs 75-80.
Lows the 50s.
.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
As of 150 AM Saturday...
IFR/LIFR conditions will hold over the NE CWA including RWI through
daybreak, while at RDU/FAY, a trend to IFR conditions by 09z are
less certain but still likely. VFR conditions are likely to hold
over the western CWA including INT/GSO. Any sub-VFR conditions will
trend to VFR by 14z this morning, mixed out by dry air aloft. Dry
weather and very few clouds are expected areawide from mid morning
through the evening. As a backdoor front moves in from the NNE, cigs
will trend to IFR at RWI/RDU after 04z, with light/variable surface
winds becoming light from the ENE or NE.
Looking beyond 06z early Sun morning, sub-VFR cigs (likely IFR or
LIFR) will spread over all of central NC late tonight as the
backdoor front progresses toward the SSW through the area. Patchy
light rain or drizzle is possible. These low cigs will trend slowly
to MVFR during Sun, with a slight chance of light rain lingering,
especially over the west and south at INT/GSO/FAY. The chance for
light rain will increase in the west (INT/GSO) Sun night with IFR
conditions, while MVFR conditions are expected elsewhere. A trend
back to VFR conditions are expected Mon as the front starts to head
back northward as a warm front. MVFR to IFR fog is expected late Mon
night into early Tue morning. VFR conditions will dominate Tue into
Wed, although passage of a cold front late Tue or Tue night will
bring shifting winds from light/variably to N and NE. -GIH