Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 070705
Area Forecast Discussion
National Weather Service Raleigh NC
205 AM EST Wed Dec 7 2016
Low pressure will move away from the Middle Atlantic coast tonight.
Weak high pressure will follow and settle over the Carolinas through
Wed night. An arctic cold frontal passage will occur on Thu.
.NEAR TERM /THROUGH TONIGHT/...
As of 940 PM TUESDAY...
All rain has departed the area as of 9 PM this evening, though
overcast skies remain. Canadian high pressure will start building
toward the region overnight as the surface low moves slowly away
from Central NC. The pressure gradient between the two, particularly
in the northeast portions of the area, will be a bit tight and
result in winds in the 5-10 mph range through the night and at the
start of the day Wednesday, light to calm in the west and south. The
lows tonight will bottom out in the upper 30s to low 40s. The bigger
forecast problem remains the development of fog overnight, possibly
becoming dense in the west and southwest where winds are expected
to be lightest. Patchy fog will be likely elsewhere given the very
moist boundary layer. The fog should develop during the next couple
of hours and will likely last through daybreak everywhere, except
the far northwest where the boundary layer may dry out after 09Z.
.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 230 PM Tuesday...
The leading edge of an arctic cold front diving southeast through
the TN/OH valley begins to ooze across the Appalachians by 12Z
Thursday morning. The front will be progressing slowly as it aligns
with predominantly westerly flow, which will also serve to limit
moisture advection available for precip. Forcing aloft will be
limited as well in relatively broad cyclonic flow and channeled
vorticity, with models squeezing out less than a tenth of an inch of
rain with the system. As such will maintain only a small chance for
PoPs as the front moves through during the day. Skies should be
clearing from the northwest by mid to late afternoon. Cold air
advection will be underway for much of the day across the northern
tier with northwest winds 10 to 15 mph gusting 20 mph. This produces
a low level thickness fall of ~20 meters across the north...
indicative of 5-6 degrees cooler temps...resulting in highs from the
low 50s across the north to upper 50s in the south. Pressure
gradient relaxes overnight, but not enough to decouple and fully
realize the airmass` potential for cooling. Mins should bottom out
in the mid to upper 20s.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --As of 205 AM Wednesday...
Expect cold/brisk conditions on Friday with highs in the upper 30s
to lower 40s and a brisk NW breeze assoc/w strong cold advection as
1040 mb arctic high pressure builds eastward from the central plains
toward the Appalachians in the wake of the cold frontal passage late
Thu/Thu night. Expect chilly lows in the upper teens to lower 20s
Sat morning as the arctic high settles over the Carolinas from the
west Friday night, with highs on Sat similar to Friday albeit a few
degrees warmer. Forecast confidence decreases significantly in the
Sun-Tue time frame when the GFS/ECMWF differ by as much as ~24 hours
with regard to the timing/evolution of the next upper wave/cold
front approaching from the west. The GFS indicates a weaker, more
progressive wave with an attendant cold front moving offshore Sun
night. The ECMWF, however, indicates a more potent upper level wave
/attendant sfc low/ and suggests the associated cold front will
cross central NC Monday afternoon, exiting offshore late Monday
evening into Monday night. With the above uncertainty in mind, will
make little change to the prior forecast Sun-Tue. -Vincent
-- End Changed Discussion --
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As of 1245 AM WEDNESDAY...
In the wake of the low pressure system moving off the Mid-Atlantic
Coast, drier air will filter into the area from the west, leading to
scattering out of the IFR ceilings across central and eastern NC.
However, light to calm winds in conjunction with wet soil, will lead
to the development of fog. The lowest visibility/ceilings appear
most likely to occur at INT and GSO, where restrictions could fall
to LIFR. Any fog and low clouds will quickly disperse by 13 to 14z
with VFR conditions expected through the afternoon.
Outlook: A warm front will lift into NC and result in a good chance
of MVFR ceilings Wed night-early Thu, especially at Ern TAF sites,
followed by a small chance of a shower along an arctic cold front
during the Thu, and following blustery NW winds late Thu afternoon-