Scientific Forecaster Discussion
fxus62 krah 151134
Area forecast discussion
National Weather Service Raleigh NC
630 am EST Fri Dec 15 2017
an area of low pressure will develop and track NE across the area
early Friday morning, to off the srn middle Atlantic coast through
Fri. High pressure will follow and migrate across the southeastern
US through the weekend.
Near term /Friday/...
as of 245 am Friday...
WV and 00z upper air datasets continue to show a positively tilted
trough extending from the Great Lakes region south and west through
the central/Southern Plains. At the surface, the forecast area finds
itself between a building high currently situated along the Mason
Dixon line with a quasi-stationary front draped along the NC/SC
state line with a backdoor front inching south and west inland from
the Outer Banks.
A strengthening low will begin to inch northeast along the stalled
boundary before sunrise Friday, allowing a mid to upper level cloud
deck to steep north gradually during the pre-dawn hours. Isentropic
lift across the front will lead to stratus formation just prior to
sunrise, especially across portions of The Triad and northern
Piedmont counties of North Carolina. This low to mid level deck will
struggle to dissolve by mid day, with some guidance keeping the
stratus layer in place past the end of peak heating. Thus, have
trended down with temperatures for areas to the north and west with
warmer values as you travel east toward the southern coastal plains,
which should remain cloud free. Some concern with patchy fog in
these areas, but likely not dense and very brief after sunrise.
The aforementioned low will transition northeast throughout the day
Friday, with combining northern and southern streams aloft assisting
in enhancing the early stages of frontogenesis as it pushes
offshore. Guidance continues to keep any and all precipitation well
east of the area during this time period.
Short term /Friday night and Saturday/...
as of 245 am Friday...
High pressure takes over by Friday night, keeping things calm,
clear, and chilly as we progress into the weekend. Early morning
temperatures Saturday should be sub-freezing across the area, even
as low as the mid 20s across The Triad and northern Piedmont
counties. Afternoon temperatures should be a bit warmer under a
westerly breeze, settling near 50 for the northern portions of the
forecast area, with mid 50s prevalent in the south and east. Pops
should remain near zero overnight Saturday into Sunday, with
temperatures once again dipping just below freezing.
Long term /Sunday through Thursday/...
as of 235 am Friday...
The surface high will shift offshore on Sunday as a warm front lifts
northward through the area Sunday eve/night, resulting in south-
southeasterly return flow and warm advection into central NC.
Meanwhile aloft, the southeast US will be under an upper level
ridge, while a deep trough dominates over The Rockies and southwest.
A shortwave will break off from the low, migrating east-northeast
through the Midwest toward the mid-Atlantic. As of the latest model
runs, the shortwave should ride the northern periphery of the ridge
and stay north of the area Sunday/Sunday night. Temperatures will be
on the rise, with highs in the mid to upper 50s and lows in the low
to mid 40s.
Although the models are in much better agreement with the overall
upper level pattern, there are still some significant differences in
the temperature and precipitation forecasts. The closed low over the
southwest US will become more of an open trough on Monday, gradually
deamplifying as it lifts eneward into the Midwest Tuesday/Tuesday
night. The southwest flow into central NC will increase during this
time, increasing the moisture advection and thus chances of
precipitation. Meanwhile, a cold front will drop southward toward
and into central NC Tuesday/Tuesday night. The highest chances for
and amount of rain will be across the south, ahead of the front. The
weakening trough turned shortwave may enhance the precipitation
along the front Tuesday night as it passes near/over the area.
Temperatures will be unseasonably warm Monday and Tuesday, with
highs in the upper 50s to mid 60s and lows in the mid to upper 40s.
Expect a slight decrease in temperatures for mid week, albeit still
a bit above normal (highs in the mid to upper 50s and lows in the
30s Wed night and 40s Thu night).
Aviation /00z Friday through Tuesday/...
as of 630 am Friday...
VFR conditions should be prevalent throughout the taf period, with
the possible exception of brief MVFR stints in int/gso this morning
thanks to lower cigs as a stratus deck forms near the border of
VA/NC. Confidence is lower at the location of this cloud layer
formation, as some guidance keeps the lowest ceilings north of the
taf sites. Have held mention of a lower deck, but that may need to
be amended closer to 2,500 feet if stratus deck dips further south.
Also have kept short lived reduced vsbys in Fay just after daybreak,
as the site will be the first to clear out of the mid deck that was
present overnight. Otherwise, expect improving conditions as time
continues, with little changes expected through the end of the taf
Vfr+ is expected to continue through Sunday morning. The next threat
for sub VFR parameters is expected late Sunday into early next week
as a low pressure system approaches from the west-SW, introducing
rain showers back to the forecast.