Area Forecast Discussion
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FXUS62 KRAH 101838
Area Forecast Discussion
National Weather Service Raleigh NC
140 PM EST Sat Dec 10 2016
High pressure will settle overhead through tonight, then shift
offshore Sunday. A warm front will push northward through the area
Sunday night, and then a cold front will move through the region
Monday night, before stalling out across the Carolinas through mid
.NEAR TERM /THROUGH TONIGHT/...
As of 140 PM Saturday...
Another quiet and cold night ahead as a portion of arctic high
pressure slides across the Mid Atlantic region tonight. While the
vast majority of the column is very stable and dry, areas of high
level clouds from the mid Miss Valley will track within fast zonal
steering flow eastward across VA and northern NC this evening into
the overnight hours, yielding fair to briefly partly cloudy skies
across the northern forecast area tonight. Some of these clouds may
exhibit a period of orographic enhancement, although the moisture
aloft may not be sufficient, and the upper level wind direction is a
bit more westerly than is ideal. Otherwise, these high clouds should
be mostly thin with limited coverage, and as such will have minimal
impact on radiational cooling with otherwise mostly clear skies and
very light winds. Lows 18-25, coldest in rural Piedmont areas. -GIH
.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 300 AM Saturday...
Sunday, sfc high will drift offshore, leading to a sly low level
return flow regime by late in the afternoon. this flow, originating
offshore of Georgia/South Carolina will increase the presence of low
level moisture. This should result in the formation of a low level
cloud deck, spreading over the south half of central NC prior to
sunset. Isentropic upglide increases appreciably bu sunset which
should lead to a few patches of light rain over sections of the
Sandhills and southern coastal plain. This upglide increases Sunday
night, leading to a better chance for patchy light rain and/or
drizzle over roughly the eastern half of the forecast area. With the
lift and moisture confined to the lowest 10k ft of the atmosphere,
expect rainfall to be very light, totaling no more than a few
Max temperatures Sunday dependent on some degree of sunshine,
especially across the northern counties. If thicker cloud cover
occurs sooner than expected ( by mid day or early afternoon versus
later afternoon), then high temps may end up being 3-4 degrees
cooler than currently forecast. High temperatures Sunday mid 40s
north to around 50 south. Sunday night, expect temps to cool
initially after sunset. After midnight, should see temperatures
stabilize or slowly rise as a low level sly jet strengthens overhead
and low clouds become thicker. Low temperatures mid-upper 30s north
to the lower 40s southeast.
.LONG TERM /MONDAY THROUGH SATURDAY/...
As of 240 AM SATURDAY...
The general upper level patter in the GFS and ECMWF are very
similar, however there are continued differences between the two
with respect to precipitation chances and timing.
Monday to Wednesday: Monday, an upper level shortwave will traverse
the Great Lakes while the associated cold front will approach
central NC from the north or northwest. Southwest flow ahead of the
front will result in warm advection into the area during the day.
The result will be fairly mild/above normal highs in the mid 50s NW
to mid 60s SE. The front is expected to get hung up in the vicinity
of the NC/VA border Monday Night through Tuesday Night as the parent
surface low moves away to the northeast. Meanwhile, a strengthening
low aloft will move eastward through Central Canada, while the flow
over the Eastern U.S. will become more zonal but slightly troughed.
This will contribute to the stalled southward progression of the
front. There is still a bit of uncertainty regarding the southward
progression of the front and thus the temperatures, particularly
across the north, during this time. As a result, confidence in
temperatures is below average. Will hold off on moving the front
through until late Wednesday or Wednesday night, which will result
in gradually lowering highs in the mid 50s to around 60 degrees
Tuesday to low to mid 50s Wednesday. Lows Monday and Tuesday nights
will be similar, upper 30s north to mid 40s south.
Wednesday Night through Saturday: As the aforementioned upper low
strengthens and slides further to the east-southeast, over Southeast
Canada by Wednesday Night, the trough over the Eastern U.S. will
become more amplified. The cold front will finally push through
Central NC Wednesday Night and subsequent high pressure will move
through the OH valley and into New England through Friday and ridge
southward into NC. Latest model runs indicate strong CAD setting up
for Friday Night into Saturday. The problem comes Friday night as
moisture advecting into the region in southwest flow aloft may
result in some p-type issues. For now will keep precipitation
chances just below slight until there is a bit more model
consistency and agreement, however wintry precipitation is not out
of the question at the end of the period. Temperatures through the
extended will be below normal with highs in the low to mid 40s
Thursday and Friday, potentially dropping into the mid 30s to low
40s for Saturday. Lows will generally be in the mid 20s to low 30s.
.AVIATION /18Z Saturday through Thursday/...
As of 100 PM Saturday...
High confidence in VFR conditions through at least 15z Sun. High
pressure will settle over the region today into tonight, before
shifting off the Mid Atlantic coast on Sunday. Deep dry air remains
in place, and any clouds through daybreak Sunday will be very high
(above 15,000 ft AGL) with unrestricted vsbys and light surface
winds. Then, as a warm front begins to push northward into the
region, MVFR clouds will start to spread into NC from south to north
after about 15z. Cigs are expected to drop to MVFR at FAY near the
very end of the TAF valid period, but cigs should stay VFR elsewhere
through 18z Sun.
Looking beyond 18z Sun, MVFR cigs will continue spreading northward
through NC Sun afternoon. Cigs should then drop to IFR after sunset,
with a good chance for low level wind shear developing after
midnight, as 1500-1800 ft AGL winds will be from the SW at 35-40 kts
but under 10 kts at the surface. Areas of light rain will also
develop overnight, with period MVFR vsbys along with the IFR cigs,
as the warm front stalls over the area. Unsettled sub-VFR conditions
should dominate from Mon into Wed as the front stalls out over the
Carolinas with weak waves of low pressure tracking along it,
although the details on timing of such adverse conditions are highly
uncertain. The front should finally push back well to our south
early Thursday, with a trend back to VFR as high pressure pushes in
from the north. -GIH