Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 240937
Area Forecast Discussion
National Weather Service Raleigh NC
437 AM EST Tue Jan 24 2017
Mild high pressure will build into the area in the wake of the deep
low pressure system lift northeast up the northern Mid Atlantic
coast. A cold front will push east across Central NC on Thursday.
.NEAR TERM /THROUGH TONIGHT/...
As of 305 AM Tuesday...
In the wake of deep low pressure system lifting up the Mid-Atlantic
Coast, shortwave ridging extending from the GOM northward into the
Middle MS Valley will shift east over the area. Resultant strong
subsidence will lead to rapid clearing this morning with breezy
conditions developing in response to the tight gradient between the
low to our northeast and the ridging building from the west. Expect
sustain winds of 12 to 15 kts, gusting to 25 to 28 kts through the
afternoon. Winds will decouple this evening as surface ridge builds
briefly over the area overnight. Low-level thicknesses support highs
ranging from upper 50s north to lower 60s south. Good radiational
conditions tonight will support lows in the mid 30s north/northwest
to lower 40s elsewhere.
.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 305 AM Tuesday...
Ridging over the area to start the day on Wednesday will shift east
and offshore during the later half of the afternoon, in advance of a
lead positively tilted shortwave trough ejecting eastward through
the Central Plain and MS Valley, with attendant cold front progged
to reach the central and southern Appalachians around midnight
Wednesday night. Temperatures ahead of the front on Wednesday will
warm well into the 60s across all of Central NC, and will flirt with
70 across the southern half. Additionally, with the approach of the
front, we will also see some breezy swly winds materialize by the
late afternoon, but certainly by the evening, gusting into the upper
A 50 to 60kt LLJ racing out ahead of the system and underneath the
entrance region of a 125-135kt jet streak moving into the Mid-
Atlantic region will lead to rapid 1000-700mb moistening Wednesday
evening/night, and bringing a quick moving band of low topped
showers into the area after midnight. Due to fast-progressive nature
of the system, qpf amounts will be light, generally a tenth of an or
less. Lows Wednesday night ranging from mid to upper 40s NW to
lower/mid 50 east.
.LONG TERM /THURSDAY THROUGH MONDAY/...
-- Changed Discussion --As of 400 AM Tuesday...
Thursday: Light rain associated with low-mid level frontogenesis
along and behind a cold front progressing across central NC is
expected to end from west-east Thursday morning as the front tracks
east of central NC/offshore and the parent shortwave/sfc cyclone
lift NE through New England toward the Canadian Maritimes. A rapid
clearing trend is expected in the wake of the front in assoc/w
strong low-level cold advection. Forecast soundings show low-level
lapse rates rapidly steepening (becoming dry adiabatic from the SFC-
H85) as CAA coincides with peak heating Thu afternoon, a favorable
setup for strong W/WNW winds. 00Z GFS/NAM/ECMWF guidance differ with
regard to the precise evolution of the parent cyclone in New England
during the day Thu. The GFS solution indicates a stronger cyclone
and tighter mslp/height gradient over the Mid-Atlantic/Carolinas
than the NAM, while the ECMWF is somewhere in-between. Although the
difference in the synoptic pattern is relatively subtle, the
difference is sufficient enough that westerly flow within the mixed
layer is ~10 knots stronger on the GFS in comparison to the NAM. At
A blend between the GFS/NAM suggests that W/WNW winds will become
sustained at 15-25 mph with frequent gusts to 30-35 mph during the
strongest pressure rises (6-8mb/6-hr between 18-00Z) Thursday
afternoon. Additionally, although less likely at this time, 40+ mph
convective gusts could accompany shower activity in vicinity of the
front along/east of I-95 late Thu morning or early Thu afternoon.
Expect highs in the mid/upper 50s to near 60F (warmest near SC
border). Lows Thu night in the lower to mid 30s.
Fri-Sun: Long range guidance continues to indicate dry conditions,
below normal temperatures and a brisk W/WNW breeze during the
afternoon hours Fri-Sun.
Sunday Night-Monday: The latest 00Z guidance suggests that Canadian
shortwave energy digging southward through the Upper Great Lakes and
western Ohio Valley on Sunday may dig further south/west than in
previous runs. As a result, light precipitation (and ptype issues)
may accompany the deeper /more amplified/ upper level wave progged
to track across the region Sunday night/Monday. -Vincent
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.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 1255 AM Tuesday...
24-Hour TAF period: Deep low pressure will move northeast, away from
Central NC through the day on Tuesday. Very light rain on the
back side of the departing low will overspread the Triad the next
couple of hours, but precip is so light, NSW is expected. In the
wake of the low pressure system, drier air will filter into the area
from west. MVFR ceilings have already scattered out at KINT and
KGSO. And we will see this trend continue from west to east
between 06 to 12z.
Breezy NWLY winds will develop everywhere by mid to late
morning with sustained winds of 14 to 17kts, gusting to
25 to 30kt through the afternoon. Winds should decouple
by the evening as surface ridge axis extends into the
area from the south.
Looking ahead: VFR conditions are expected through Wednesday. A cold
front will cross the region late Wednesday night/early Thursday,
bringing with a chance of showers and sub-VFR ceilings to the area.
VFR conditions should return late Thursday afternoon/evening.