Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 100802

Area Forecast Discussion
National Weather Service Raleigh NC
300 AM EST Sat Dec 10 2016

Cold high pressure will build across the area through tonight, then
shift offshore Sunday.  A cold front will approach from the west
late Sunday and move through the area on Monday.


As of 300 AM Saturday...

Cold start to the morning as Canadian high pressure noses into
central NC, proving clear skies and a near calm sfc wind. Most
places will start the day in the low-mid 20s with upper teens likely
at the normally colder locations. Westerly flow aloft will
eventually advect high level moisture into central NC later today,
and more so tonight, leading to patches of cirrus. Still, expect
plenty of sunshine today. Afternoon temps should recover into the 40-
45 degree range.

Under clear-partly cloudy skies this evening, temperatures should
cool off appreciably due to the relatively dry air mass and near
calm winds. Overnight temps in the low-mid 20s will be common.


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.


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.


As of 1230 AM Saturday...

High confidence that VFR parameters will persist across central NC
through 12Z Sunday as high pressure at the surface will be the
dominate weather player. Westerly flow aloft will advect high level
moisture across the area later today an tonight in the form of
patchy cirrus.

The high will shift offshore Sunday. the return flow on the backside
of the retreating high will advect low level moisture into central
NC late Sunday and Sunday night, resulting in MVFR, and eventually
IFR ceilings. In addition, patches of light rain should develop
Sunday night. An increasing low level jet may produce marginal low
level wind shear parameters Sunday night, mainly in the form of
speed shear rather than directional shear, as wind speed 35-40kts
probable between 1500-2000ft.

Variable aviation conditions expected Monday through Wednesday as a
series of low pressure systems cross the southeast U.S. This will
result in periods of MVFR or IFR parameters due to adverse ceilings.





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