Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 201507
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1010 AM EST Sat Jan 20 2018

.SYNOPSIS...
High pressure will drift across the southeastern United States
through tonight, then offshore on Sunday. A cold front will approach
from the west Monday, and cross central NC on Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1010 AM Saturday...

Little change required to the near term forecast.

12Z upper air analysis depicts a deep westerly flow over the
Carolinas thanks to high pressure positioned across the eastern Gulf
and the FL peninsula, and an elongated west-to-east trough over the
Great Lakes into New England. This mild flow will aid to push
temperatures back to or slightly above normal across most of central
NC this afternoon. The exception will be where a snowpack of several
inches still exists, which will deter/slow temperature recovery.
Seeing evidence of this at mid morning as temperatures in the
snowpack hovering close to freezing while locations with bare ground
reporting temperatures in the upper 30s to the lower 40s. Will
likely see a similar disparity this afternoon as temperatures will
generally be in the 55-60 degree range except the lower 50s where
snow depth of more than 2 inches exists. ~WSS

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
maximized. ~MWS

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
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.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
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.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
As of 720 AM Saturday...

High pressure over the southeastern US will result in mainly VFR
conditions through the weekend. The exception will be a medium
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: The threat of persistence fog and low ceilings will exist
for Sun night-Mon morning. Sub-VFR conditions, and showers, are
expected to affect cntl NC along and ahead of a cold front Mon
evening through early Tue.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...WSS
NEAR TERM...WSS/MWS
SHORT TERM...MWS
LONG TERM...KC
AVIATION...MWS



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