450
FXUS62 KRAH 261756
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
155 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 1122 AM Sunday...

...Marginal risk of severe thunderstorms this afternoon and tonight.

Weak shortwave ridging and sunny skies have been observed over
central NC this morning. 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 as highs 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 a
developing MCS over KY/IN morning.

Hi-Res guidance shows a favorable environment for MCS maintenance
this morning into the evening hours as it rides along the CAPE
gradient into the lower Ohio Valley into the central Appalachians
and possibly western or NW North Carolina, with some development of
scattered strong-severe thunderstorms out ahead of this system by
400 - 500 PM over the Appalachians, and toward 600 PM for Winston-
Salem. As it traverses the NC mountains during the late afternoon
into the evening hours, the environment becomes less favorable with
time, but still characterized by 1000-1500 SBCAPE and steep low-
level lapse rates around 9 C/km that would bring a risk for mainly
strong to severe wind gusts, especially to the Triad.

As this system moves ESE through central NC, uncertainty increases
and will depend on the maturity of this system as MLCIN begins to
increase. 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 06z HRRR and 00z 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 (represented by the 00z HRW-NSSL
and 06 NamNest). Observational trends will need to be watched
through the afternoon to determine the most likely scenario.

Overnight lows under variable cloudiness and light stirring will be
well above normal and settle in the upper 60s to low 70s.

&&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
As of 315 AM Sunday...

Still tough to get a handle on convection timing. We`ll likely see
the remnant wave/MCV and clouds from today`s storms over the Mid
Miss Valley and W Ohio Valley passing into the Carolinas and Mid
Atlantic during the morning hours. While this early timing and
convective debris clouds are not ideal for destabilization, we`re
still likely to have moderate MLCAPE with morning low and mid level
lapse rates of 6.5-7 C/km and improving low- and mid-level flow to
25-30 kts and 40-55 kts respectively, amid high PWs of 1.5-1.8",
exceeding the 90th percentile. The more favorable kinematics appear
to shift E into the Coastal Plain and E NC during the afternoon,
with a stark downturn in mid level flow late in the day and a dip in
CAPE that may be due to the morning showers and isolated storms.
There remains some potential for temporal and spatial overlap of the
more ideal thermodynamic environment with the better wind fields and
incoming MCVs, which would support a decent severe storm threat, but
such an alignment is far from guaranteed. The latest NCAR neural net
guidance presents two rather muted windows for potential severe
threat, one in the mid morning and the second in the mid afternoon
to early evening associated with the incoming longwave trough axis
and ahead of the incoming surface cold front, although the possible
morning cloudiness and convection may reduce this late-day threat.
Will maintain 20-30% pops in the morning, increasing to good chance
to likely in the afternoon, highest NW near the cooler mid levels
associated with the incoming longwave trough. These higher pops
should shift into our E sections after 00z, then exiting all but the
far SE overnight. Thicknesses are expected to be 10-20 m above
normal, supporting highs in the mid 80s to around 90. Lows in the
mid 60s NW, where some lower dewpoints will begin to work in just
behind the front, ranging to around 70 in the SE. -GIH

&&

.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...Kren
NEAR TERM...Badgett
SHORT TERM...Hartfield
LONG TERM...Green
AVIATION...Badgett/Swiggett