Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 200236
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
930 PM EST Fri Jan 19 2018

.SYNOPSIS...
High pressure will remain over the southeastern United States
through Saturday, then drift offshore Sunday. This will promote a
mild westerly flow over central NC through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 930 PM Friday...

Just minor updates required with this evening update, mainly
matching up temperature trends which were slower than expected
across portions of the Triad and a bit faster across the sandhills
of North Carolina. Still some concern with isolated fog development
tonight, especially across the sandhills where the surface dewpoint
depression is only 5 degrees in spots. Confidence is low
though, mainly due to the high overhead and the dry airmass aloft,
so have continued to leave it out of the weather grids for now.

Previous Valid Discussion...

Deep westerly flow over the eastern U.S. coupled with a sfc high
anchored over the Deep South will maintain a weak lee side trough
over the Piedmont tonight. While sfc winds will likely decouple
around sunset, this sfc feature should induce a weak south-sw flow
over central NC overnight just above the surface. Thus, should see
overnight temperatures a few degrees warmer. Some members of the NAM
hinting at possible low cloud/fog development above the snowpack as
warmer air just above the surface overrides the colder air at the
surface. Will continue to monitor but believe tomorrow night may be
a better set-up for low clouds/fog. Still expect to see a disparity
between locations where snow covers the ground and where snow is
absent. Minimum temperatures should range from 17-21 where the snow
depth is several inches deep, to the mid-upper 20s elsewhere.

&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 235 PM Friday...

The atmosphere will continue to warm as the deep wly persists and
the sfc high remains positioned over Southern GA/north FL. The
relatively dry air mass will continue to promote wide diurnal
temperature swings from sub freezing early morning lows to mild
afternoon temperatures. Under sunny skies, expect afternoon temps in
the upper 50s to around 60. The exception will be where snow several
inches deep remains. The snow pack of this depth will continue to
have an influence on the air temps, so afternoon temps in the lower
50s will be more likely.

Saturday night, a moistening atmosphere aloft coupled with a
persistent low level warm air advection should promote the
development of fog or low clouds late Saturday night/early Sunday
morning, primarily across the Piedmont where recent heavy snow fell.
If the fog does develop, areas of freezing fog may occur as early
morning temperatures will be slightly below freezing. Min temps 29-
33.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 220 PM EDT Friday...

Southern stream shortwave trough traversing the northeastern GOM and
Florida Peninsula will provide little more in the way of some thin
high clouds across central NC on Sunday. Meanwhile, sfc high over
the SE US will eventually shift offshore Sunday night/early Monday.
This will translate into a continuation of dry and moderating
conditions, with highs Sunday afternoon ranging from mid/upper 50s
NW to to lower/mid 60s SE. Milder min temps Sunday night as well,
owing to strengthening southerly return flow and extensive high
level cloud spreading east of the mountains, well downstream of the
closed low and highly amplified trough advancing east through the
nation`s mid-section.


The closed low will track NE from the Upper MS Valley to SE Canada
by Tuesday, which is coincident with the timing of the trailing cold
frontal passage through the region. Models currently indicate a band
of showers will accompany the frontal passage, but given how far
removed central NC is from the better forcing, expect precipitation
amounts to be on the light side, driven primarily by the WCB. Highs
Monday, just ahead of the front, will be similar to Sunday`s mild
temps, followed by a brief cool done behind the cold front Wednesday
and Thursday. Temperatures will begin to moderate on Friday, with
the approach of yet another amplified long wave trough advancing
east into the Central US.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 600 PM Friday...

With high pressure in control and a dry airmass in place, there is a
high likelihood of VFR parameters over the next 24 hours. In
general, expect good to excellent aviation conditions, with light
surface winds and mostly clear skies prevailing. Similar to last
night, the only uncertain part of the forecast remains extremely
isolated fog development overnight, potentially sneaking into
KINT/KGSO. The likelihood of this is low, so have left mention out of
the TAFs during this round. This may need reevaluating, especially
if dewpoints inch up overnight in these areas.

In the long term, expect mainly VFR parameters through Monday
afternoon, aside from the chance for late night/early morning fog
early Sunday morning. An approaching frontal system may bring enough
moisture to lower ceilings into the MVFR category Monday night
through early Tuesday morning along with a few rain showers.
Otherwise VFR parameters anticipated Tuesday afternoon through
Wednesday.

&&

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

&&

$$
SYNOPSIS...WSS
NEAR TERM...JJM/WSS
SHORT TERM...WSS
LONG TERM...CBL
AVIATION...JJM/WSS



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