Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
FXUS62 KRAH 200620
Area Forecast Discussion
National Weather Service Raleigh NC
215 AM EDT Thu Apr 20 2017
A cool wedge of high pressure extending into the Carolinas early
today will give way to a surge of warmer air this
afternoon. A cold front will approach from the northwest late
Friday, then stall over North Carolina on Saturday. A strong storm
system will move across the Carolinas on Sunday.
.NEAR TERM /THROUGH TONIGHT/...
As of 1025 PM Thursday...
The strong surface high to the north will continue to lift off to
the north and east tonight. However, a lingering CAD air mass
remains over the Piedmont of central NC this evening, with the most
notable presence across the NW Piedmont where low stratus and temps
in the upper 50s still rule. While the CAD has generally weakened
this evening with the CAD boundary slowly retreating north and
westward, we still expect it to linger over at least the NW Piedmont
tonight, with renewed low stratus and/or fog developing after
midnight in areas that have cleared out some. However, the main
concern overnight is the potential for areas of fog (some possibly
dense), primarily in the lingering CAD wedge over the NW Piedmont,
where the HRRR has shown the potential for dense fog to develop
(with cigs lowering to the surface... thus fog). For now will
mention areas of fog in the NW Piedmont and patchy fog elsewhere.
Expect low temps in the heart of the CAD to move little overnight,
maybe lower 2 to 4 degrees. Expect low temps will range from the mid
50s NW to the lower 60s SE/far E.
.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 240 PM Wednesday...
Southwest flow at the surface and a little more westerly aloft, will
result in a rapid dissipation of the CAD early Thursday. The ridge
will be replaced by a surface lee trough of low pressure in the lee
of the Mountains Thursday afternoon. Models suggest that the chance
of showers and thunderstorms will be limited to the Mountains and NW
Piedmont Thursday afternoon as weak instability develops along with
surface moisture convergence along the trough. With heating, expect
a chance of showers and thunderstorms, mainly west and north
Piedmont zones. Much warmer conditions will advect into the region
on the mean SW flow. Highs in the 80s are expected, except some
upper 70s NW.
The chance of showers/storms will diminish within a few hours of
sunset Thursday evening, otherwise partly cloudy and warm conditions
will exist in the developing warm sector of the next approaching
front. Lows should stay 60+ Thursday night.
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 245 PM Wednesday...
Fri: An approaching front will slow and become increasingly WSW-ENE
oriented over the Mid-Atlantic by Friday as the parent cyclone
becomes vertically stacked and temporarily stalls over the Great
Lakes. As a result, southerly flow /above normal temps/ are expected
to persist on Friday, albeit with an increasing potential for
convection in the N/NW Piedmont during the late afternoon/evening.
Sat-Wed: Potent shortwave energy moving ashore the Pacific coast
tonight is progged to amplify into an upper low over the lower
Midwest by Friday, track eastward through the TN valley on Saturday
and progress across the Southeast CONUS on Sun/Mon, with shortwave
ridging in the wake of the upper wave as it progresses offshore
Tue/Wed. Confidence remains lower than average w/regard to forecast
specifics (precip amounts, severe weather potential, temperatures)
given that the aforementioned wave has yet to move ashore the
Pacific coast. Until this feature is well sampled by the RAOB
network over the western US, model guidance is likely to be in error
w/regard to the evolution of the upper wave as it traverses the
CONUS this weekend and early next week. Broadly speaking, expect
mostly cloudy skies, cooler temperatures, and increasing chances for
convection over the weekend, particularly on Sunday. Chances for
precipitation will diminish from west-east and skies will clear
early next week as the upper level wave progresses offshore, though
confidence is low w/regard to when this will happen (as mentioned
above), especially given potentially complex interaction with
northern stream shortwave energy over the weekend. Some severe
weather threat may exist over the weekend, however, it is difficult
to ascertain whether or not such a threat will materialize at this
range, let alone the extent/mode thereof. -Vincent
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
As of 215 AM Thursday...
Areas of IFR and LIFR ceilings and some fog across much
of the western and northern Piedmont including the KGSO terminal
will persist overnight and expand east and southeast. VFR and MVFR
conditions across the remainder of the Piedmont and the Coastal
Plain including the KRDU, KRWI and KFAY terminals will
deteriorate as low clouds and fog expand into the area overnight.
Widespread IFR and LIFR conditions are expected during the few
hours around daybreak. Light mainly southwest winds will weaken
further and become calm in many locations providing additional
support for fog development.
Aviation conditions will improve between 13Z and 16Z as
increasing sunshine and a westerly component to the low level flow
results rising ceilings and erosion of the fog with the most
aggressive improvement arriving after 14Z with just about all
locations reaching VFR conditions by 16Z with SCT clouds at 4-5kft
and periods of BKN clouds at 10-15kft. Southwesterly winds will
increase to 7 to 10 kts this afternoon. Isolated showers and
thunderstorms will develop across the NC mountains during the
afternoon and push east possibly affecting the western Piedmont
between 19Z and 23Z. Coverage and confidence in the amount of
convection prohibits inclusion in the TAF at this time.
Looking further ahead... A cold front will approach the region on
Friday and then stall across northern NC Friday night and
linger into Saturday and Sunday. A storm system will sweep
east across the Carolinas late Sunday. These features will result in
increased chances of adverse aviation conditions with sub-VFR
ceilings with scattered showers and thunderstorms through much of
the weekend. Improving conditions are expected on Monday. -Blaes