Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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518
FXUS62 KRAH 211933
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
330 PM EDT THU JUL 21 2016

.SYNOPSIS...
Surface high pressure will over the mid-Atlantic states will move
offshore tonight. A strong high pressure ridge will expand from the
central U.S. across the Carolinas over the weekend, bringing hot and
humid conditions.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 PM Thursday...

A weakening surface ridge remains over the region, with relatively
warm and dry air aloft. Isolated cells have tried to get going over
the northern Piedmont but are facing marginal mid level lapse rates,
poor deep layer shear, and insufficient moisture through the column
(PW < 1.5"), conditions that are likely to persist at least into the
evening when the loss of heating will foster stabilization. Latest
CAM runs including the HRRR/HRRRX show very little to no convective
activity in Central NC for the rest of the day, focusing instead on
areas to our south and west near the old boundary, in areas with
steeper low level lapse rates and better MLCAPE and moisture, and at
the coast with weak DPVA and sea breeze contributions to lift. Will
retain an isolated storm mention across the far west and SW CWA for
the next few hours, followed by no pops overnight. A little light
fog or shallow ground fog is possible late tonight, but should not
be widespread or dense based on the dry air just off the surface and
minor stirring near the ground overnight. High-res guidance supports
lows in the upper 60s to lower 70s. -GIH

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 330 PM Thursday...

Another fairly quiet day is expected, but with gradually building
heat, and uncertainty regarding the fate of the MCV leftover from
the complex now dropping through the Great Lakes. Models are not
doing well handling the timing/movement of this MCS (too slow), thus
their reliability is questionable. But using the timing of the SREF
mean and steering flow would suggest that this could venture into
the southern Appalachians by tomorrow, likely working with
differential heating in the higher terrain and weak mass convergence
along a lee trough to spawn scattered afternoon convection mostly to
our west, although some of this could certainly spill into our far
western Piedmont. But overall, the gradually rising warmth and dry
air in the mid levels will limit the CAPE potential with continued
poor mid level lapse rates. And the PW, while improving, should mean
greatly reduce coverage. Will have isolated showers and storms over
the NW Piedmont in the afternoon, trailing back off in the early
evening as we lose any instability. Rising thicknesses will equate
to highs in the lower 90s, even given the potential for some
convective debris cloudiness early in the day, and this combined
with dewpoints in the lower 70s and minimal reduction with mixing
will generate heat index values in the mid to upper 90s -- a prelude
to the more intense heat over the weekend. Lows in the lower to mid
70s Fri night with light fog possible. -GIH

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
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
through Thursday.

&&

.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

&&

.CLIMATE...

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


&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...Hartfield
SHORT TERM...Hartfield
LONG TERM...KRD
AVIATION...Hartfield
CLIMATE...BLAES



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