-- Discussion containing changed information from previous version are highlighted. --
350
FXUS62 KRAH 261918
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
316 PM EDT Sun May 26 2024

.SYNOPSIS...
A cold front will approach late today and move through the region
Monday night. Dry high pressure will settle into the region toward
the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 245 PM Sunday...

...Marginal (level 1) to Slight (level 2) risk of severe
thunderstorms late this afternoon and tonight.

Weak shortwave ridging and sunny skies have been observed over
central NC at mid-afternoon. A rather moist and increasingly
unstable air mass is expected this afternoon and evening. It will be
characterized by dew points in the mid 60s NW ranging into the lower
70s SE, and MLCAPES of 1000-1500 J/kg increasing to nearly 2000 J/kg
by late afternoon. Highs will reach the upper 80s to lower 90s.
Little more than isolated (20 percent chance) of
showers/thunderstorms expected this afternoon until attention then
turns upstream to the mature MCS moving ESE KY/TN.

The latest data analysis and hi-res guidance shows a favorable
environment for MCS maintenance into the evening hours as it rides
along a CAPE gradient into the central Appalachians and NW North
Carolina, with some development of scattered strong-severe
thunderstorms out ahead of this system by 300 to 500 PM over the
northern Foothills, and toward 500 PM to 600 PM for Winston-Salem.
The main hazard will be damaging wind gusts.

As this system moves ESE through NW and north central NC,
uncertainty increases and will depend on the maturity of this system
as MLCIN begins to increase as pushes through the Triad toward the
Triangle. A mature, well formed system will be able to overcome the
weak boundary layer stability and tap into increased 500mb flow and
MUCAPE around 1500 J/kg to persist and bring a damaging wind threat
through midnight (represented by 17z HRRR and 12z HRW-ARW). The
alternate scenario would feature a less mature and broken line of
storms as it progresses through the Triad that will struggle persist
after sunset and show a weakening trend as it progresses through the
Triangle and points south and east. Regardless, there is a chance of
severe wind gusts with these storms late afternoon into the evening.
Overnight lows under variable cloudiness and light stirring will be
well above normal and settle in the upper 60s to lower 70s.

Yet, another line of thunderstorms should affect the western
Piedmont late tonight per the latest HRRR and hi-res models with
heavy rain and gusty wind threat. This should not be severe
winds given the late night timing (after 300 AM) and lack of
instability.

&&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
-- Changed Discussion --
As of 316 PM Sunday...

There is decently high uncertainty wrt to thunderstorms on Monday.
An upstream MCS is forecast to interact with the mountains early
Monday morning. Most guidance suggests the mountains should eat this
up before reaching our western areas. However, there is will still
likely be some ongoing showers (and perhaps a little thunder)
through about mid-morning across the western to central Piedmont
associated with this decaying MCS. Lingering cloudiness may persist
through late Monday morning, however clouds should clear enough in
the afternoon to support the development of scattered thunderstorms.
The spatial extent for afternoon showers/storms will largely depend
on 1) where outflow boundaries set up from the upstream morning
convection and 2) where mid-level vorticity/MCV features traverse.
The recent RAP runs suggest mid-level features could maximize along
and south of the NC/SC border Monday afternoon. It`s therefore not
surprising that latest HRRR runs tends to focus late afternoon
convection across our Sandhills/Southern Coastal Plains (and moreso
active in central SC). Additional weaker perturbations are depicted
further north into central VA maximizing over the Chesapeake Bay. As
such, some high-res guidance (eg. NamNest, ARW) depict a bit more
activity further north across our central to northern
Piedmont/Coastal Plain Monday afternoon associated with these
perturbations.

Any storms that do develop Monday afternoon will have increasing
effective shear to work with (up to 30 to 40 kts). As such, severe
thunderstorms will be possible with any stronger storms that fire. In
fact, guidance is pretty riled up about some stronger mid-level
lapse rates (~7.5 to 8 C/km) developing across our far southern
areas eastward towards the coast. Additionally, model-derived
hodographs, HREF max/min helicity neighborhood probabilities, and
model-derived STP values all support the potential for rotating
storms (and possible tornadoes) from roughly US-1 east across the
inner/outer banks Monday afternoon and evening. Given this
potentially juicy parameter space, it`s no shock that the SPC has
outlined our area in a 15% probability for severe hail and wind
(supported by strong mid-level lapse rate potential), with a smaller
area of up to 5 % probability for tornadoes across locations east of
Raleigh. The overall mean-layer flow should be strong enough to
preclude any widespread flooding concerns, however, can`t rule out
isolated urban flash flooding with any heavier downpour.

Rain chances should diminish late Monday night into the overnight
hours. Persistent swly flow will promote highs in the mid to upper
80s/lower 90s.
-- End Changed Discussion --

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
As of 155 PM Sunday...

By Tuesday morning, a cold front should be along the coastline of
the Carolinas or immediately offshore. This should keep a slight
chance of thunderstorms in the forecast along the I-95 corridor, but
by nighttime, a several day period of dry weather should begin. The
front will slowly push east, and a surface high will establish
itself over southwestern Ontario Wednesday morning. The high will
expand to the southeast through the rest of the week, with the
center reaching West Virginia by Saturday morning. An upper ridge
along the East Coast will begin to break down on Saturday, and a
shortwave could bring some isolated showers across western counties
Saturday afternoon/evening, although this scenario is only shown in
ensembles and not by deterministic models. A stronger shortwave
appears likely to move across the Appalachian mountains Sunday and
bring a chance of showers to all locations. Surprisingly, the GFS is
showing a decent cap on Saturday and Sunday, so do not have
lightning in the weekend forecast.

Temperatures will trend downward through the beginning of the
period, with highs ranging from the mid 70s to the low 80s on
Friday. High temps will then rebound for the weekend, returning into
the 80s. Thursday and Friday nights will be the coolest, with
widespread lows in the 50s.

&&

.AVIATION /18Z SUNDAY THROUGH THURSDAY/...
As of 145 PM Sunday...

A developing MCS over the Mid-MS Valley will motor through the lower
Ohio Valley and Tennesse Valley through the mid afternoon and
traverse the NC mountains during the late afternoon into the evening
hours. The terminals have a chance (40-50%) to see restrictions from
this system, but exact impacts remain uncertain until this system
fully develops. Strong to severe wind gusts, heavy rain, and
lightning will certainly be possible. The system should affect the
region between 22z and 04z.

Looking beyond 06z Mon: Another vigorous line of showers and
thunderstorms over the Ohio and Tennessee Valley early Mon morning
will weaken as it traverses the mountains and likely bring scattered
to numerous showers/storms through central NC during the day on Mon.
Additional showers/storms will be possible as the first of several
cold fronts moves through central NC Mon night. Dry and VFR
conditions will prevail through Thurs.

&&

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

&&

$$
SYNOPSIS...Badgett
NEAR TERM...Badgett
SHORT TERM...Luchetti
LONG TERM...Green
AVIATION...Badgett/Swiggett