Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 222008

Area Forecast Discussion
National Weather Service Raleigh NC
308 PM EST Thu Feb 22 2018

An anomalous sub-tropical ridge aloft situated off the coast of the
Carolinas, and related Bermuda surface high pressure, will weaken
while drifting southwest toward the Bahamas through Friday night.
Meanwhile, a back door cold front will settle south through central
and southern VA today, and into north-central NC late tonight and
early Friday. That front will become quasi-stationary over northern
NC through Friday night, then retreat north as a warm front on


As of 250 PM Thursday...

Continued record-smashing sub-tropical high pressure centered near
31N/71W will remain influential throughout the southeastern U.S.
through tonight.

At the surface, a backdoor front has stalled this afternoon over
cntl VA, directly over the Richmond metro area, as 3-hrly pressure
changes on both sides of the boundary over nrn VA/MD and NC,
respectively, have been nearly identical. Near term model guidance
indicate the front will begin moving swd once again after nightfall,
which seems reasonable given higher surface pressures observed now
over PA, and a continued accumulation of cold air/mass there and
east of the Appalachians, which will have nowhere to go but south
(geostrophic adjustment). The previous thinking remains relatively
unchanged, with the front expected to stretch by 12Z Fri along an arc
from near INT, to RDU, to PGV, to the srn Outer Banks.

So for tonight, it will be continued unseasonably mild with
generally upr 50s to lwr 60s and the redevelopment of low stratus
and fog in the warm sector, with the latter most prevalent again
over the Sandhills and srn Coastal Plain. Meanwhile, CAA behind the
front will cause temperatures to fall through the 50s, and with a
slight chance of post-frontal rain/drizzle, from a deeper,
synoptically-driven low cloud layer over the nrn Piedmont and nrn
Coastal Plain.


As of 305 PM Thursday...

Principle forecast challenge remains how far into n-cntl NC the cold
front moves, then to what degree it retreats nwd during the
afternoon and evening hours. Forecast confidence is relatively high
for the srn half of cntl NC, with persistence lifting and scattering
of morning low cloudiness and fog, with with temperatures again in
the upr 70s to around 80 degrees. Forecast confidence is similarly
high that nrn locations from near Roxboro to Henderson to Lake
Gaston and Roanoke Rapids Kerr will remain cool, in the 60s, with
some upr 50s possible, amidst CAD and continued post-frontal low
cloudiness, and a chance of light rain and drizzle in the morning.
The greatest uncertainty and 10-15 degree bust potential will exist
roughly along and just north of Highway 64, including the major
metro areas along I-40. There will be a sharp gradient in
temperatures in this corridor separating the two regimes noted
above. The front will remain quasi-stationary and become
increasingly diffuse Friday afternoon and evening, with an otherwise
persistence forecast of continued mild conditions, with yet another
round of late night low cloudiness and areas of fog owing to the
persist unseasonably humid conditions in place.


As of 225 PM Thursday...

The subtropical ridge hangs tough through the weekend and looks like
we will remain in the warm sector, with highs well into the 70s
Saturday and Sunday. A cold front will be edging east as the ridge
retrogresses slightly southwest, but the front`s progress will be
glacial and the front will be basically stalled in the vicinity
through Monday. Will have likely PoPs in the West on Sunday,
transitioning slowly across the area to the east on Monday, which
looks to be our best chance for rain as a surface wave lifts
northeast along the boundary. The persistent subtropical ridge will
weaken/dampen as a vigorous mid level short wave lifts out of the
midwest, hammering the ridge further south and interrupting our warm
spell. Highs Monday will be limited to low and mid 60s by cloud
coverage and potential for some cool air advection as the surface
front reaches the Coastal Plain late in the day.

Drier and seasonable high pressure will build in on Tuesday through
Wednesday, with copious sun and highs mostly from 60 to 65 after
morning lows from 40 to 45. The ridging hasn`t finished with us yet,
as it will be re-amplifying northward up the eastern CONUS on
Wednesday, lifting a warm front north into the area with associated
rain on Wednesday night into Thursday. Highs Thursday will be mostly
low and mid 60s.


As of 115 PM Thursday...

Continued strong sub-tropical ridging off the coast of the
Carolinas, and related Bermuda surface high pressure, will result in
a mainly persistence forecast through the next 24 hours. Associated
unseasonably humid conditions, on the wrn periphery of the ridge,
will favor the redevelopment of low stratus (LIFR-IFR), and fog
mainly at FAY, late tonight-early Fri. The low clouds, and fog
mainly at FAY, will then lift and scatter to high MVFR or low VFR
between 14-18Z. The exception will be mainly at RWI, where the IFR-
MVFR stratus may linger throughout the day, and with a chance of
light rain/drizzle in the morning, owing to the passage of a back
door cold front in the few hours centered around 11Z, and following
cool/saturated, post-frontal air mass. There is a slight chance that
the front may pass through Piedmont sites and result in similar
conditions there, but it is more likely the boundary stalls just
north and northeast of INT/GSO/RDU.

Outlook: The aforementioned ridge will weaken and drift south, but
maintain influence over the Carolinas; and as such, a persistence
forecast of late night-morning stratus and fog, lifting and
scattering to high MVFR-low VFR each afternoon, will generally
continue through the weekend. Otherwise, the next chance of rain
will accompany a frontal zone that will settle into, and possibly
stall over the Carolinas, late Sun into early next week.



RDU Records:

Date     |  High  Year  |  High Min  Year
02/22       75    1897        60     1897
02/23       79    1980        57     1962
02/24       81    1982        58     1985

GSO Records:

Date     |  High  Year  |  High Min  Year
02/22       74    1925        57     1980
02/23       74    2017        52     1922
02/24       79    1982        55     1985

FAY Records:

Date     |  High  Year  |  High Min  Year
02/22       77    2003        56     1989
02/23       80    1922        55     1922
02/24       83    1930        60     1975




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