Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
1244 am EST Wednesday Dec 2 2015
Synopsis... high pressure will weaken over the Middle Atlantic
States...but with associated in-situ cold air damming lingering
through early Wednesday. A cold front will sweep across the area late
Wednesday and early Wednesday night. High pressure will follow.
Near term /tonight/...
as of 920 PM Tuesday...
..dense fog advisory for most central NC through 1000 am
Dense fog advisory will be in effect for all areas except the far
northwest Piedmont triad zones and Person County... where rain may keep
the fog from becoming as thick in that region. However... it will
be monitored. Conditions are favorable for widespread dense fog
with visibilities to near zero locally through 1000 am Tuesday.
As generally expected...the southeast extent of the main rain area extended
from near Charlotte through The Triad and NE to Henderson. As the
middle/upper trough continues to lift NE through the central
Appalachians... the leading edge of the steady rain is expected to
halt its eastward progression... then begin to lift to the north.
This would place only The Triad region in the rain after 400 am.
This would also allow the fog in the dense fog area to linger.
Temperatures overnight will hold steady or perhaps rise a few
degrees as the initially cool damming air mass modifies up top toward
the ground later.
Short term /6 am Wednesday through Wednesday night/...
as of 410 PM Tuesday...
The in-situ wedge and associated low overcast and fog will linger
through middle-late morning Wednesday...with further thinning and erosion and
a few breaks in overcast possible...by early afternoon. Otherwise...a breezy
southwest wind will develop as the boundary layer briefly lifts and
mixing occurs...with some gusts of 20-25 miles per hour mainly in the vicinity
and east of the I-95 corridor...where warmer temperatures in the low-
middle 70s/deeper mixing are most likely. 60s should otherwise be the
rule...with perhaps a few upper 50 degree readings lingering over
the northwest Piedmont...where complete erosion of The Wedge may not occur
until cold frontal passage there between 20-22z. The front will then progress
east across the remainder of central NC through midnight...or
Regarding precipitation...the brunt will be ongoing over the northwest and
northern Piedmont to start the day...before moving east along/ahead
of the front through early evening. Ahead of the main frontal
shower band...there will be just a small chance of a few showers...so
the better part of the day may prove dry for most...until the band
of showers --in a weakening state owing to unfavorable diurnal
timing and the passage of the strongest qg-forcing for ascent
lifting to our northwest with the parent upper low-- heads east. Weak lapse
rates aloft will contribute to weak instability on the order of a
few hundred j/kg...so a few rumbles of thunder may accompany the
otherwise shrinking band of showers. While deep clearing and drying
will occur Post-frontal passage overnight...considerable high clouds in SW
flow aloft are apt to remain through early Thursday. Cold air advection-driven lows in
the upper 30s northwest to near 50 southeast.
Long term /Thursday through Tuesday/...
as of 315 Tuesday...
The long term features a departing upper trough axis on Thursday
with a split flow pattern developing over the eastern Continental U.S. During
the weekend into early next week. Not surprisingly nwp guidance
struggling with the evolution of a couple features in the pattern
including a short wave trough that drops out of the Great Lakes into
the middle Atlantic over the weekend. The GFS deepens this system
considerably and closes it off while the ec and most of its ensemble
members are much less aggressive. For now...expect little sensible
weather impacts. As this system moves offshore another short wave
trough closes off on Sunday as it crosses the Mississippi and moves
east into the Carolinas and middle Atlantic on Tuesday. The 12z GFS and
ec are more consistent with the handling of this feature and now
both advertise a close low lifting across the southern Appalachians
with a surface wave developing near the coast. Not ready to get too
aggressive in highlighting precipitation chances especially given
the pattern and with only a small number of the ec ensemble members
The sensible weather during the long term should feature a fairly
dry period with temperatures near or just below average for this
time of year.
Aviation /06z Wednesday through Sunday/...
as of 1244 am Wednesday...
24-hour taf period: with the cad wedge firmly in place...fairly high
confidence that IFR/LIFR ceilings will persist through Wednesday morning.
Dense fog will linger through daybreak for much of central NC...with
IFR/LIFR visbys. The exception will be VFR/MVFR visbys at times in
the northwest where precipitation lingers. Winds will generally be light (up to 5
kts) overnight...increasing to around 10 kts during the day and
becoming gusty during the after/evening as the cold front approaches.
Winds will be southwesterly ahead of the front...veering to north-northwest
Looking ahead: the sub-VFR conditions will improve to VFR behind the
cold front that is expected to move through Wednesday night (through
most of central NC by 06-09z thursday). Winds may be a bit breezy
out of the north-northwest initially...but should abate by late Thursday. VFR
conditions are expected to persist through the weekend as high
pressure builds into the region.
dense fog advisory until 10 am EST Wednesday for ncz008>011-