Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 221848
Area Forecast Discussion
National Weather Service Raleigh NC
248 PM EDT FRI JUL 22 2016
A mid-level disturbance will drift across western North Carolina
this afternoon and evening. A hot high pressure ridge will then
expand from the central U.S. to the mid-Atlantic states over the
weekend and into early next week.
.NEAR TERM /THROUGH TONIGHT/...
As of 1010 AM Friday...
Convection chances remain low for much of Central NC the rest of
today into tonight, within a regime dominated by a warm cyclonic
ridge aloft resulting in stable mid levels with weak steering flow,
while low level thicknesses steadily climb. The MCV resulting from
yesterday`s Great Lakes MCS will track southward over the southern
Appalachians today as other disturbances emanating from upstream MCS
activity over the Midwest follow a similar path, likely tracking
just west of the CWA. Latest CAM runs -- as well as larger-scale
models with parameterized convection -- show good continuity with
yesterday`s model runs, suggesting that a few storms should form
this afternoon over the far western CWA, closer to the MCV tracks,
and perhaps over the far southern and SE CWA as well where low level
mass convergence along an inland-moving sea breeze should take
place. But coverage and upscale growth of any convection will be
greatly suppressed over the remainder of the CWA given the weak mid
level lapse rates (particularly during the peak heating period),
lack of a convective focus, and little to no dynamic support. PW
values are projected to rise a bit, but the 700-400 mb layer will
remain quite dry. Will restrict low chance pops to the western and
far southern CWA including the far SE this afternoon, tapering back
down in the early evening as we lose heating. High-res guidance
shows temps peaking in the 90-94 range, with dewpoints in the upper
60s and lower 70s helping to push the heat index values into the mid-
upper 90s. -GIH
Previous discussion as of 345 AM: Central NC will remain on the ERN
periphery of a strong sub-tropical ridge centered over OK, while a
surface trough will sharpen in the of the Appalachians. Within the
associated N to NNW flow aloft around the ridge, a low amplitude,
positive tilt mid-level trough, now extending from the Lower Great
lakes to the OH Valley, will drift into NC this afternoon. An MCV
evident in model analysis 700-500 mb vorticity fields and earlier
satellite imagery is embedded within the broader mid-level trough,
over ERN KY; and this feature is forecast to drift focus forcing for
ascent as it drifts into the SRN Appalachians through the same time.
While the relative highest chance of showers and storms will be
along the track of the MCV and aided by differential heating -in
the mountains- a shower or storm will also be possible in the
vicinity of the lee trough, centered over the WRN Piedmont,
despite rather dry mid levels.
Return flow around high pressure centered near Bermuda will
support slightly higher temperatures and dewpoints versus those of
Thu, with highs generally 90 to 95 degrees.
Light SSW stirring overnight should hold temperatures in the
(lower) 70s, and also preclude the development of anything more
than patchy fog, particularly given the presence of cirrus
related to the MCS upstream/over IL.
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 400 AM Friday...
Generally a persistence forecast, with a slight chance of an
afternoon storm, and higher temperatures yet, owing to a slowly
increasing influence of the sub-tropical ridge --and associated
heat beneath it-- as it builds E. Highs 93 to 97 and lows in the
middle 70s. Heat indices are expected to range from around 100
over the NW Piedmont to 105 over the ERN Sandhills and Coastal
.LONG TERM /SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --As of 245 PM Friday...
To begin the long term period, the strong upper ridge that provided
multiple days of intense heat across the Central Plains will have
dampened and became elongated in east-west fashion, extending into
the region. 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 Sunday (slightly lower than
previous runs), with similar values on Monday. 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, maybe even the upper 90s
(warmest on 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 early next week, but will
not be zero as there will be a persistent Piedmont trough that could
be a focus for convective development, as well as the sea breeze
and/or any weak disturbances that move through aloft.
The aforementioned ridge will continue to dampen and shift more
offshore through the middle of the week. Also, a shortwave trough is
progged to cross southern Canada and 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 and it will
likely stall near or just north of the area and then meander for a
few day. Another shortwave crossing the Ohio Valley will approach
towards the end of the week. Therefore, 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, especially towards the middle to end of the week. The
increased cloud cover and precip chances should allow temps to
"cool" back to the low to mid 90s (however, still slightly above
-- End Changed Discussion --
.AVIATION /18Z Friday through Wednesday/...
As of 1205 PM Friday...
High probabilities of VFR conditions persisting through the next 24
hours. Warm and dry air aloft will suppress most shower/storm
activity over Central NC this afternoon through midday Sat, with
clouds generally scattered and bases above 4 kft. Any isolated
storms would be circumnavigable. The better chances of a stray storm
would be near INT/GSO and FAY, although chances are too low to
include as a prevailing condition. As always, erratic gusty winds
and lightning can be expected in and near any storms. There is a
small chance for patchy shallow MVFR fog in low-lying areas late
tonight into early Sat morning at all TAF sites, but chances are too
small to mention at this time. Surface winds will remain light
through Sat, mainly from the southwest under 10 kts.
Looking beyond 18Z Sat: A few storms are possible late Sat afternoon
into Sat night, primarily at INT/GSO/FAY. Areas of MVFR fog may
develop late Sat night into Sun morning. Shower/storm chances will
start to improve late Sun into Sun night, with scattered daily
storms possible through Wed as the air mass moistens more deeply
over Central NC. Fog is possible early each morning Mon-Wed. -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 Mon Jul 25
RDU 105/1952 101/2011 102/2010
GSO 99/1952 99/1914 101/1914
FAY 103/2011 105/1952 103/1914