Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 200900

Area Forecast Discussion
National Weather Service Raleigh NC
400 AM EST Sat Jan 20 2018

High pressure will drift across the southeastern United States
through the weekend.


As of 350 AM Saturday...

WV satellite imagery and 00Z upr air depict a split flow pattern
across the CONUS, with the main nrn stream jet extending from a
trough along the West Coast, ewd across the nrn tier of the country.
A formerly nrn stream trough has separated from that flow and become
a closed mid-upr low over the lwr MS Valley. Meanwhile, the srn
branch of the jet extends from cntl Mexico newd across cntl FL, and
the presence, proximity, and influence of this jet will cause the
mid-upr low to shear ewd and become an open wave over srn GA/nrn FL
by 12Z Sun. A thin veil of cirrus associated with this wave may
consequently skirt srn NC tonight.

At the surface, 1026 mb high pressure analyzed at 09Z over the FL
panhandle will drift slowly newd, into the Savannah basin by 12Z
Sun, while a lee trough remains in the immediate lee of the
Appalachian. Modification of the high and the associated air mass
will yield warmer conditions over cntl NC today, with highs mostly
in the mid-upr 50s.

Strong radiational cooling conditions tonight will favor lows mostly
in the lwr-mid 30s, though if any snow cover remains after another
mild day, then those locations are apt to dip into the upr 20s.
Areas of fog will be possible late, mainly over the Piedmont, where
near surface moisture, especially from recently melted snow, will be


As of 359 AM Saturday...

The trough aloft now along the West Coast will migrate ewd, to the
Plains, with an associated exit region of a strong, ~130 kt upr jet
forecast to nose into the cntl Appalachians by 12Z Mon. The surface
ridge initially over the sern US will migrate across the Carolinas
and off the srn middle Atlantic coast. Temperatures will
consequently continue to modify, with a scattering of stratocumulus,
~850 mb, that will have spilled east of the Appalachians by that
time. Highs are expected to climb into the lwr-mid 60s. Lows, with a
good chance of radiation fog, and associated low overcast by Mon
morning, mostly in the mid-upr 30s.


As of 200 AM Saturday...

Monday and Tuesday: Fairly high confidence in the low pressure
system approaching and moving through Central NC as all medium-range
models are in good agreement. An upper low will develop off the
Rockies on Monday, progressing east-northeastward through the
Midwest and into the Great Lakes region through Tuesday. Meanwhile,
the surface cold front will move eastward toward the Mid-Atlantic.
With the increasing southerly flow over Central NC Monday into
Tuesday, high temperatures will range from mid 50s NW to mid 60s SE.
Lows Monday night in the mid 40s NW to low 50s SE. Of bigger concern
than temperatures is the chance for precipitation and possibly some
thunderstorms as the line of pre-frontal convection moves into and
through the area. As of the latest model runs, MUCAPE appears to be
less than 500 J/Kg and the surface low is displaced well to the
north over the Great Lakes. There are still slight timing and
intensity/amount of precip differences between the models, which
will play a role in forecast for possible thunder. For now, given
the uncertainty, will keep mention of thunder out of the forecast.
Both models do indicate precipitation exiting the area by Tuesday
night, with cold air starting to filter in behind the front. As a
result, Tuesday night will likely be dry and temperatures quite a
bit lower than the previous night, in the low to mid 30s.

Wednesday through Saturday: This part of the forecast is likely to
be dry, with a reinforcing dry cold frontal passage on Wednesday
night/Thursday. Surface high pressure is expected to build into the
area in the wake of the secondary cold front and remain over the
area into Saturday. Chances for precipitation will increase over the
weekend, but details are still far from nailed down. Highs will be
generally in the 50s and lows in the upper 20s to low 30s Wednesday
and Thursday night, increasing into the 30s Friday night.


As of 1235 AM Saturday...

High pressure over the southeastern US will result in mainly VFR
conditions through the weekend. The exception will be a good chance
of fog and associated ceilings/visibility restrictions between 05Z-
14Z Sun, with some lingering sub-VFR ceilings possible through the
midday hours on Sunday, as that moist layer lifts and disperses with
diurnal heating.

Outlook: Sub-VFR conditions, and showers, are expected to affect
cntl NC along and ahead of a cold front Mon evening through early




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