Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 231913
Area Forecast Discussion
National Weather Service Raleigh NC
213 PM EST Mon Jan 23 2017
A potent low pressure system over the southern Appalachians will
track east-northeast through the Carolinas today, then track off the
Mid-Atlantic coast on Tuesday.
.NEAR TERM /THROUGH TONIGHT/...
As of 1030 AM Monday...
Previous forecast is in pretty good shape. The stacked low over
southwest NC, a little further south than previously projected, will
move east across central NC today. The associated occluded front
moved north through the area this morning and has resulted in a
period of breaks in the clouds and even total clearing in the east.
Wrap around moisture will be pulled back east today and lead to
mostly cloudy skies by this afternoon. The early clearing in the
east will allow temps to reach the low/mid 60s, which combined with
a -22C cold pool at 500mb will yield a few hundred J/KG of MLCAPE
and should support scattered low-topped convection. This seems most
like to form around the leading edge of an area of stratiform
precip/low clouds and surface troughing currently pivoting up from
eastern SC, keeping POPs mainly focused in southern half of the
Coastal Plain. While instability isn`t terribly impressive, the
freezing level was between 7-10kft this morning per RAOBs and will
fall throughout this day, so some small hail or graupel may
accompany a few isolated storms. Otherwise, the wrap around moisture
may produce a few showers in the west late this afternoon, but the
trend should be for this to diminish as the flow becomes
northwesterly behind the low. Highs generally 53-63 west to east.
Tonight: Drier air filtering into the area with the departure of the
system should lead to SW to NE clearing late tonight into Tuesday
morning. Lows in the lower 40s NW to mid 40s elsewhere.
.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 400 AM Monday...
In the wake of the vertically stacked low progressing offshore the
Mid-Atlantic coast, a shortwave ridge aloft will build eastward over
the Carolinas and Mid-Atlantic Tue afternoon/evening, progressing
offshore by Wed morning as an upper level trough (moving ashore the
Pacific coast today/tonight) digs/expands across the Intermountain
west/Rockies and shortwave energy rounding the base of the trough
(in vicinity of the 4-corners region) ejects northeastward through
the Central Plains into the Upper Great Lakes, establishing
southwest flow aloft downstream along the Gulf/Southeast Coast and
Eastern Seaboard. A cold front assoc/w a sfc cyclone attendant the
aforementioned shortwave energy ejecting NE into the Upper Great
Lakes will slowly approach the Appalachians from the west Wed
aft/eve. Expect dry conditions through this period, with a breezy NW
wind gusting 20-30 mph on Tue and a breezy SW wind gusting 20-30 mph
on Wed. Highs near 60F on Tue will fall into the upper 30s to lower
40s Tue night, then rebound into the upper 60s on Wed. -Vincent
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --As of 210 PM Monday...
A transition from mild conditions to more seasonable, but generally
dry ones, will occur during the medium range.
Ridging aloft will crest over the Ern U.S. on Wed, then move
offshore in advance of a broad, positive tilt longwave trough that
will migrate Ewd and encompass the Ern two thirds of Ern North
America by the weekend.
A surface cold front --one related to the lead shortwave trough that
will initiate the Ewd progression of the longwave trough, and which
will trail a parent surface cyclone that will migrate NEwd across
the Great Lakes-- will settle across NC late Wed night-Thu. Both
moisture and lift are forecast to be limited, as the parent forcing
lifts to our NW, so rainfall chances and amounts are likewise
expected to be limited.
Behind this lead front, temperatures will cool to more seasonable/
average levels for the end of the week and weekend. The positive
tilt configuration of the trough aloft will cause surface high
pressure to sprawl into the SErn U.S. and suppress any additional
precipitation chances until Sun-Mon, at which time a Nrn stream
shortwave trough in NW flow aloft will amplify into the Middle
Atlantic region and possibly support some degree of cyclogenesis
over the Wrn Atlantic. At this time, it appears that a generally dry
reinforcing cold frontal passage will result for our region, though
the prosepcts of nearby coastal cyclogensis will be worth watching
in the coming days.
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.AVIATION /18Z MONDAY THROUGH SATURDAY/...
As of 130 PM Monday...
the passage of an occluded front early this morning helped clear
some of the low level moisture and VFR has resulted for much of
eastern NC. Clouds are beginning to fill back in this afternoon as a
low pressure system crosses the area and 1)kicks off some scattered
showers around FAY and RWI, and 2) brings wrap around moisture back
across the area this evening. MVFR is expected to redevelop this
afternoon, with a band of IFR level stratus moving west to east
across the area between 00Z and 09Z.. Confidence is fairly high at
this point. Winds will turn to northwesterly with the
aforementioned band of moisture tonight and may gust to 15-20kt as
cold advection kicks in a scours all remaining moisture. Winds
should weaken by 12Z but then increase again by 15z, with wind
gusts to around 20kt again on Tuesday afternoon.
Looking ahead: VFR conditions are expected Tuesday and Wednesday. A
cold front will cross the region late Wednesday night/early
Thursday, bringing with a chance of showers and sub-VFR ceilings to
the area. VFR conditions should return late Thursday