Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 211843
Area Forecast Discussion
National Weather Service Raleigh NC
243 PM EDT THU JUL 21 2016
Surface high pressure will build across the mid-Atlantic states
today, then move offshore tonight. A strong high pressure ridge will
expand from the central U.S. across the Carolinas through the
weekend, bringing hot and humid conditions.
.NEAR TERM /THROUGH TONIGHT/...
As of 950 AM Thursday...
Convection chances still appear quite low and confined to the SW
CWA. Latest surface map shows the weak surface ridge nosing in from
the NNE, poised to build overhead today as it weakens further.
Humidity will remain elevated today as surface dewpoints drop
minimally from their current readings in the upper 60s to lower 70s,
and the lack of clouds currently overhead and upstream combined with
dry air aloft as noted on the water vapor imagery (and likely to dry
further with acceleration of the NNE-erly upper jetlet over the
Delmarva/SE VA/NE NC today) should lead to no worse than partly
cloudy skies today, boosting isolation and causing surface temps to
peak in the upper 80s to lower 90s. Latest CAM runs including the
HRRR/RAP and SPC`s SSEO favor a storm-free day for much of Central
NC, with the exception of the far W and SW near the old boundary
where low level mass convergence will take place, and perhaps just
off the higher terrain which will be subject to differential
heating. Convection over Central NC should be further smothered by
slow steady warming aloft, with gentle but persistent mid level
height rises continuing into tonight, leading to low CAPE values.
Will limit pops to isolated thunder in the extreme west / SW. -GIH
Previous discussion as of 355 AM Thursday... WV imagery and model
analysis PV fields depict a couple of perturbations in NW flow aloft
over the DelMarVA and Lower OH Valley. The models indicate the
former will amplify off the VA/NC coast through 18Z, while the
trailing one will dive across west-central NC, to NERN SC, through
the same time. The tail end of the lead perturbation over the
DelmarVA has already aided in the development of a few showers over
the Shenandoah Valley, amidst an area of 6-9 thousand ft strato/alto-
cumulus centered over central and SRN VA; and the HRRR suggests a
few additional showers may develop over the NC Piedmont during the
morning to midday hours, presumably as the strongest QG-forcing for
ascent accompanying the trailing Lower OH valley wave moves SEWD.
Otherwise, 1025 mb surface high pressure now over WV will build
east across and offshore VA today, in the subsident wake of the
aforementioned perturbations aloft. The surface ridge axis and
associated NE low level flow around it, over the ERN half of NC,
will result in temperatures AOB those of Wed, with generally
upper 80s to around 90 degrees anticipated. To the west of the
ridge axis, a light SLY return flow will develop across WRN NC,
including the SRN and WRN Piedmont; and an associated 925-850 mb
theta-e ridge there warrants a continued slight chance of an
afternoon shower or storm.
Light return flow will envelop all of central NC tonight, once the
aforementioned surface ridge migrates offshore, with dry and
mainly clear conditions. Lows in the upper 60s to lower 70s.
.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 410 AM Thursday...
A strong sub-tropical ridge centered over OK at 500 MB and AR at
700 mb, will gradually expand EWD this period, and more so this
weekend. Warmth beneath the ridge will likewise expand EWD, with
highs in central NC mainly in the lower 90s. Lows 70 t0 75. Associated
warm and dry mid levels will limit the chance of showers and
storms to differential heating boundaries in the mountains and
along the coast.
.LONG TERM /SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --As of 240 PM Thursday...
To begin the long term period, the strong upper ridge that provided
multiple days of intense heat across the Central Plains will dampen
some and start to spread east. As it does, heights will rise over
central NC through the weekend. As such, max low level thickness
values are progged to top out in the low to mid 1440s on Saturday
(slightly lower than previous runs) and the mid to upper 1440s on
Sunday. This combined with mostly dry conditions and temps not
cooling off much as night, temps will be able to rise well into the
mid 90s and even the upper 90s by Sunday. This combined with a moist
air mass may necessitate the issuance of a heat advisory, most
likely across at least the eastern half of the forecast area, where
heat index values will approach or exceed 105 degrees. With regards
to precip chances, overall they will stay rather low through the
weekend, but will not be zero as there will be a persistent Piedmont
trough that could be a focus for convective development, as well as
any weak disturbances that move through aloft.
The aforementioned ridge will dampen and shift even more over our
region into early next week and eventually offshore, after another
rather warm day on Monday. Also, a shortwave trough is progged to
cross the Great Lakes Monday into Tuesday. This will propel a cold
front towards the region Tuesday into Wednesday, but as can be
expected this time of the year, there is disagreement with just how
far south it will make it. Regardless, with us gradually losing the
influence of the upper ridge and with a cold front in the vicinity,
precip chances will start to increase, at least back to the normal
diurnal range. The increased cloud cover and precip chances should
allow temps to "cool" back to the lower 90s, especially Tuesday
-- End Changed Discussion --
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 1210 PM Thursday...
High probabilities of VFR conditions persisting through the next 24
hours. Weak high pressure over the region combined with warm and dry
air aloft will suppress most shower/storm activity over Central NC
this afternoon through much of Friday, with clouds generally
scattered at most with bases above 4 kft. Any isolated storms would
be circumnavigable and be very unlikely to affect a TAF site. There
is a small chance for patchy shallow IFR fog in low-lying areas late
tonight into early Fri morning, and if it occurs, it would be most
likely to affect RWI. Surface winds will remain light/variable
through daybreak Fri, then be from the southwest under 10 kts.
Looking beyond 18Z Fri: Chances for storms Fri afternoon/evening
will remain low. VFR conditions are expected to dominate through at
least Sat, as the warm/dry air aloft persists. A few storms are
possible late Sat into Sat night, but coverage will not be
widespread. Areas of sub-VFR fog may develop late Sat night into Sun
morning. Shower/storm chances will start to improve late Sun into
Sun night, growing through Tue as the air mass moistens more deeply
over Central NC. Fog is possible early Mon and Tue mornings. -GIH
Record high temperatures and the year in which the record was most
recently set at Raleigh, Greensboro, and Fayetteville.
Sat Jul 23 Sun Jul 24 Sat Jul 23
RDU 105/1952 101/2011 102/2010
GSO 99/1952 99/1914 101/1914
FAY 103/2011 105/1952 103/1914