Area Forecast Discussion
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FXUS62 KRAH 171944
Area Forecast Discussion
National Weather Service Raleigh NC
244 PM EST Tue Jan 17 2017
A cold front will approach from the northwest this evening, then
track southeast through central North Carolina Wednesday morning. In
the wake of the front, high pressure will build into the region from
the northwest Wednesday night and Thursday.
.NEAR TERM /THROUGH TONIGHT/...
As of 100 PM Tuesday...
Surface observations indicate visibilities have risen above 3 miles
in most locations as of 16Z, indicating that top-down erosion of the
CAD wedge has commenced in assoc/w insolation and strengthening SW
low-level flow in advance of a shortwave trough /DPVA/ approaching
the Mid-Atlantic from the W/NW. Overcast skies should thin and may
become broken this afternoon, though current trends would suggest
breaking out entirely is unlikely except near the NC/SC border. As
such, expect highs ranging from the upper 50s to ~60F in the North
to mid 60s in the far SW Piedmont. Forcing this aft/eve will be
limited to weak low-level warm advection, primarily in the NW
Piedmont and VA border counties where a few periods of light rain
will be possible through this aft/eve. Precipitation chances
overnight remain difficult to ascertain. Low-level forcing will
largely be absent overnight, with central NC in a relatively
homogeneous warm sector characterized by unidirectional /SW/ flow.
As a result, expect dry conditions with the best chance of rain
between 06-12Z to the north in southern VA. Broken to overcast cloud
cover and a 10-15 mph SSW/SW breeze should result in mild
temperatures tonight, i.e. little diurnal variation from this
.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 115 PM Tuesday...
Expect some chance for showers along the cold front progressing into
central NC Wed morning given a modest plume of SFC-925 mb moisture
in the presence of low-level convergence within the low-level
trough. In the immediate wake of the front late Wed morning through
early Wed afternoon, strong DPVA progged to track ESE through VA
into northeast NC may encounter lingering low-level moisture across
central/eastern NC. As a result, a period of anafrontal
precipitation will be possible in central NC, primarily from the
Triangle east into the Coastal Plain. Expect a clearing trend
mid/late afternoon in assoc/w subsidence in the wake of the
shortwave and the onset of low-level cold advection in the wake of
the front. Given the timing of the front and the potential for
precipitation /evap cooling/ late Wed morning through early Wed
afternoon, high temps on Wed will vary little from overnight lows
except perhaps in the far S/SE where temps may reach the mid 60s
prior to cold advection post-fropa. Lows Wed night will be driven by
a combination of cold advection and radiational cooling, ranging
from near 40F at the VA border to the mid 40s SC border. -Vincent
.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 244 PM Tuesday...
There is fairly good model agreement through this period. The
general pattern is a series of weather systems swinging through the
region, resulting in alternating wet and dry periods.
Thursday through Friday Night: Thursday will be largely dry with a
surface high briefly moving over and away from the area and an upper
level ridge over the Southeast U.S. Meanwhile, an upper low that
developed over the Southwest U.S. will lift northeast and get
absorbed into the northern stream. This low will then transition
into a shortwave trough extending southeast into the Carolinas from
the Plains. A warm front will lift northward through Central NC
Thursday night into Friday. Strong southerly flow advecting warm
moist air into the region, combined with the upper forcing from the
s/w aloft, will result in a period of rain moving through the area
Friday aft/eve and clearing out Friday night. Highs will increase
slightly from Thursday (mid to upper 50s) to Friday (mid 50s north
to mid 60s south), but lows will be mainly in the mid to upper 40s.
Saturday through Monday: Saturday should be dry with highs in the
low to mid 60s with continued advection of warm air into the region.
The weather gets increasingly more interesting for the rest of the
weekend and model agreement remains above normal, especially for
this far out in the forecast period. A strong low pressure system
moves off the Rockies Saturday night and quickly moves east through
the ARKLATEX on Sunday. With continued advection of warm moist air
off the Gulf ahead of the low, PWATs and precip chances will
increase Saturday night. The trough will become increasingly
negatively tilted Sunday night into Monday as the upper low swings
toward and along the Appalachians. This system will bring our first
chance for potentially strong storms to move through the area,
though for now will indicated the chance for some isolated
thunderstorms until it gets closer in time we get a better handle on
the instability, shear, and lapse rates that will largely determine
what type and strength of convection we can expect. Temps will
increase Sunday through Monday, especially across the southeast,
before decreasing again Monday night on.
The weather should dry out on Tuesday, though the negatively tilted
trough will remain over the Mid-Atlantic as the low lifts northward
through NY into Canada. Highs in the mid 50s and lows in the upper
30s to mid 40s expected.
.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
As of 100 PM Tuesday...
24 Hour TAF period: IFR ceilings are expected to improve to MVFR
this afternoon. Any improvement in conditions this aft/eve should be
short-lived, however, as conditions are expected to deteriorate from
N/NW to S/SE (earliest at Triad and latest at FAY) tonight/Wed
morning as an upper level disturbance tracks through the central
Appalachians into the Mid-Atlantic and an attendant cold front /low-
level trough/ progresses east of the mountains through VA/NC. Expect
the best potential for rain and low ceilings between 09-17Z Wed as
the front progresses SE through central NC. Breezy SW flow in
advance of the front tonight and early Wed will give way to breezy
NW flow in the wake of the front Wed aft/eve.
Looking Ahead: Expect a clearing trend in the wake of the front with
a brief return to VFR conditions Wed night/Thu. A pattern similar to
the one affecting the region today is progged to develop over the
region again late this week. With this in mind, expect ceilings to
begin deteriorating Thu night/Friday. -Vincent