Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 230740
Area Forecast Discussion
National Weather Service Raleigh NC
340 AM EDT Thu Mar 23 2017
Continental polar high pressure will continue to modify over the Srn
Middle Atlantic states through tonight. A warm front will retreat
north across the region on Fri, as the high drifts east toward
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
As of 945 PM Wednesday...
Forecast is on track. The opaque high clouds which covered the
southern half of the forecast area for much of the afternoon have
been shunted southward with the push of deep dry air into the area.
Skies should remain clear for the next several hours, although high
level moisture to our NW (evident on upstream soundings) should lead
to increasing high clouds late, and these may be orographically
enhanced yielding thicker cloud cover over the western CWA. Temps
are running a degree or two warmer than the forecast pace, although
as northeasterly surface winds die off later tonight, readings
should plunge given the low dewpoints and expectation of good
radiational cooling. Lows in the upper 20s to lower 30s. -GIH
Earlier discussion from 250 pm: An upper level ridge over the
central U.S. and a l/w trough along the eastern seaboard will funnel
cold dry air into central NC tonight. This drier air already made
evident by sfc dewpoints in the teens across the western Piedmont at
18Z. This drier air will continue to spread south and east through
Orographic induced high clouds will slowly fade/dissipate through
early evening as the atmosphere aloft dries out and the winds field
weakens. Sfc winds will remain 4-8kts after sunset, though should
decouple after midnight. With the cold dry air mass in place and
near calm sfc winds, should see temperatures drop into the upper 20s-
lower 30s overnight. Patchy frost possible in the well sheltered
areas though most places will see little if any frost due to the dry
low level air mass.
.SHORT TERM /6 AM THIS MORNING THROUGH TONIGHT/...
As of 250 PM WEDNESDAY...
Thursday, 850mb thermal trough overhead signals a day of well below
normal temperatures. While skies will be sunny, the cold dry air
mass deposited by the high pressure system will yield max temps in
the low-mid 50s, a solid 10-12 degrees below normal.
Thursday night, l/w trough will lift to the ne while the upper ridge
will extend across our region. This set-up will maintain mostly
clear skies and chilly overnight temperatures. Under clear skies and
a light wind regime, temperatures will quickly fall after sunset
with overnight temperatures generally near 30 to the lower 30s with
the coldest temperatures across the far northeast Piedmont and the
northern coastal plain.
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --As of 320 AM Thursday...
The extended will primarily feature a Bermuda high and warm
southerly flow, with highs in the 70s, at least 5-10 degrees
Continued moistening Friday night may lead to some stratus near
and west of the Yadkin River Saturday morning, and a pronounced
cap will likely trap this moisture and yield partly to even
mostly cloudy by Saturday afternoon. Meanwhile, and upper low
over the Deep South will lift west of the mountains Saturday
night, providing a glancing blow of DECENT height falls that
should erode the cap and permit showers and storms, mainly west
on Sunday. Current timing suggest early day clouds and showers,
an extension of upstream convection on Saturday, may impede
warming and destablization enough in the west to limit any
severe with potential, though an axis of instability between the
morning convection and the stronger cap to the east could
support an isolated severe threat given 30-40kt bulk shear.
The cold front associated with Sunday`s lifting upper low looks
as though it will stay well west of the mountains and NC will
stay in the warm sector, with another, less amplified system
progged to cross the area on Tuesday. The latest ECMWF is much
less amplified with this wave that it`s previous run, as well as
the 00Z/23rd GFS runs. This system could be interesting given
the potential for decent destablization in the warm sector on
Tuesday and possibility of locally enhanced shear associated
with the shortwave. For now, chance POPs still look most
appropriate. After that, a backdoor cold front is forecast to
sink south into NC by mid to late week, though the presence of
the sub-tropical ridge makes frontal passage much less certain.
-- End Changed Discussion --
.AVIATION /07Z THURSDAY THROUGH MONDAY/...
As of 230 AM Thursday...
Continental polar high pressure will result in VFR conditions
through the TAF period. Surface winds around the high will
generally be light and gradually veer from NEly/ENEly this morning
to Ely/ESEly by this afternoon. The exception will be at FAY and RWI
for a few hours mid to late morning, when winds may briefly increase
to around 10-15 kts, with occasional gusts between 15-20 kts. Skies
will be clear, aside from periods of thin cirrus.
Outlook: There will be a chance of MVFR-IFR visibility restrictions
in radiation fog in SErn NC (FAY and possibly RWI) Fri morning, then
with patchy coverage throughout central NC Sat morning. A chance of
showers and storms and sub-VFR conditions mainly at Piedmont TAF
sites will follow for Sun.