272
FXUS62 KRAH 170156
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
955 PM EDT Fri Aug 16 2024

.SYNOPSIS...
High pressure over the Eastern Seaboard will shift east and offshore
through tonight. A surface cold front and deep upper level trough
will approach our area from the west tonight through Sunday, then
move through the region late Sunday through Sunday night.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 955 PM Friday...

Flood Advisory in effect for Forsyth County as slow moving heavy
showers move across the region. Upstream from the region line of
convection along a surface boundary has continues to move east this
afternoon and into this evening. As the line continues to hold
together for the most part, it will be moving into a more stable
region with less than 1000 J/kg across the region. Some of the CAMs
show the line dissipating as it moves across the region thus, kept
some PoPs in for much of the western half of the CWA through the
night. By morning the boundary is expected to be more along the
coastal plain region with isolated to scattered showers possible
through the morning. Best chance for precip will be in the NE region
closer to the VA border. As the rain moves out of the Triad, low
level moisture will still be in place and dew points as well as
temperatures in the upper 60s to low 70s patchy fog is expected to
develop especially in the Triad area.

As of 237 PM Friday... Embedded in the W-NW flow aloft between the
upper ridge centered over the Southern Rockies and the large
troughing over the Great Lakes and Ohio and Tn Valleys, a ribbon on
higher moisture, featuring PWATs 2-2.2", will advect west to east
across central NC through night as weak perturbations traverse the
area. Steered by the W-NWLY flow, showers and storms moving into
and/or developing over the higher terrain will progress east, in
weakening fashion, into the NW Piedmont during the late afternoon
and evening. By midnight, only isolated showers are expected to
persist in the relatively stable airmass in place across central and
eastern NC.

Shear, instability and forcing are all weak. Thus, no severe storms
are expected.

The onset of SWLY low-level flow will result in continued warming
and a slight uptick in humidity levels. Lows 65-70.

&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 215 PM Friday...

A cold front will loop from Lower Michigan southeast into the Ohio
Valley and then southwest into the Tennessee Valleys Saturday
morning, slowly moving to the southeast and moving into western
North Carolina by Sunday morning. A thunderstorm cannot be ruled out
northeast of Raleigh Saturday morning left over from tonight`s
precipitation, then it appears coverage could expand a little bit in
the afternoon. Different synoptic and high-resolution models are
really all over the place with predictions for where convection will
occur. There does seem to be some broad agreement that the southern
Piedmont will remain dry Saturday afternoon, so with the
uncertainty, painted slight chance pops north of I-40 as well as
east of I-95. This is a very low confidence forecast considering the
lack of agreement from the computer models. There is slightly more
agreement in some thunderstorms moving into the region late Saturday
night as the cold front approaches, but this will also be occurring
at a time when convection is normally at a minimum, and have gone
with chance pops to the northwest of I-85. Saturday`s highs will be
within a degree or two of today`s values, generally in the mid to
upper 80s. Lows will be in the upper 60s and lower 70s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
As of 220 PM Friday...

Sun/Sun Night: The leading edge of trailing cold front from a low
over the Great Lakes will likely be pinned west of the Appalachian
mountains into Sun afternoon with a pre-frontal lee-troughing
positioned east of the Appalachians into the VA/NC Piedmont. Surface
dew points in the low/mid 70s within and east of this boundary will
contribute to 1000-2000 J/kg of MLCAPE by peak heating. The
approaching trough should help support deepening convection by early
afternoon. Some storm organization is to be expected with 20-30kts
of 0-6km shear, but flow parallel to surface boundary will prompt
congealing updrafts and linear clusters along common cold pools.
Strong winds 30-40 mph will be most common, but isolated severe
winds will be possible for well organized clusters that can take
advantage of DCAPE around 1000 J/kg, theta-e diff of 25-30K, and low-
level lapse rates > 8C/km.

A conditional threat for isolated flooding will also exist Sun
evening, mainly in urban and poor drainage locations. Storm motions
should be quick enough with 20-35kt of mid-level flow, but back-
building storms may be possible. Point soundings east of the trough
axis show a deep warm-cloud layer > 10,000 feet and strengthening
low-level jet after 21z with lingering MUCAPE of 1000-1500 J/kg.
Most likely rainfall will range from a couple tenths to around three
quarters of an inch, but where any back-building and/or training
occurs, locally higher amounts of +2" would be possible.

Mon through Fri: An effective front will slowly progress through the
area through Mon with another reinforcing front and dropping low-
level thicknesses Mon night into Tues. High pressure will continue
to build over the Northeast and extend through the Mid-Atlantic into
the Southeast through the remainder of the forecast period. Mostly
quiet through the work week with only rain chances along the
seabreeze. Highs in the upper 70s to mid 80s will become common Tues
onward with lows in the upper 50s to mid 60s.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 740 PM Friday...

INT/GSO: The Triad will see the busiest aviation weather tonight, as
isolated showers and storms skirt by to its north, most likely to
affect these sites prior to 01z, then another larger line of showers
and storms will move in from the west, impacting these sites between
02z and 05z, when a period of MVFR cigs/vsbys is expected, perhaps
dropping briefing to IFR. After a brief lull soon after midnight,
MVFR cigs are expected, developing after 08z and dominating until
14z, after which time cigs should lift to VFR. Winds will be under
10 kt from the SSW becoming SW and WSW late tonight.

RDU/RWI/FAY: The showers and storms over W NC are expected to fizzle
as they shift eastward into a less unstable environment from the E
Piedmont eastward. RDU stands the best chance of seeing a few
showers starting after 03z, however the chance of thunder is too low
to include in the TAF at this time. RWI/FAY will see an even lower
chance (but not zero) of a shower through tonight. Any showers could
briefly cause an MVFR cigs, but overall these three sites should
stay mostly VFR through Sat. There is a risk for a few storms after
18z Sat, but confidence in this is too low to include at this time.
Winds will be under 10 kt from the SSE becoming S and SW late
tonight.

Looking beyond 00z Sun, a few showers and storms remain possible at
all sites through Sat night. A high chance for some strong storms
arrives Sun afternoon, lasting through Sun night, when a cold front
will move through the area. Gusty and erratic winds, sub-VFR
conditions, and heavy rainfall may occur with any storms Sun/Sun
night. VFR conditions should return and prevail Mon-Wed. -GIH

&&

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

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...CA/CBL
SHORT TERM...Green
LONG TERM...Swiggett
AVIATION...Hartfield