347
FXUS62 KRAH 091741
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
140 PM EDT Thu May 9 2024

.SYNOPSIS...
A series of upper level disturbances will interact with an
unseasonably moist airmass over North Carolina through early Friday,
bringing unsettled weather. A cold front will move across the region
on Friday, ushering in drier and less humid air for the weekend.

&&

.NEAR TERM /TODAY THROUGH TONIGHT/...
As of 1025 AM Thursday...

The severe threat for today has lowered, particularly across the N.
Recent update included a reduction in convection coverage today, esp
across the N and NE, along with timing adjustments according to
trends and new high-res model runs. The latest surface map shows a
trough/outflow across our extreme E and SE, with the showers and
isolated storms that crossed our far S into SC overnight having
dissipated and moved well to our E. We`re left in a weakly unstable
environment, with marginal SBCAPE in our E but plenty of SBCINH. The
next area of rain/storms is now moving into our W, although all of
the lightning so far has held S of the NC/SC state line. The
northern end of the strongest line of convection is holding just S
of CLT, and while this more robust convection is likely to scrape
across our far S and SE sections through the afternoon, the greatest
buoyancy and deep layer shear, and thus the greatest severe threat,
will hold to our S across GA/SC. The latest few RAP/HRRR runs latch
onto the scenario of the stronger convection across our S, perhaps
into the central Coastal Plain, with limited recovery potential
overall, esp across the NW where stabilizing low clouds remain
locked in. Highs were nudged down slightly in a few spots, esp W,
where diurnal heating will be minimal. Highs in the upper 70s to
lower 80s. -GIH

Earlier discussion from 225 AM: An upper level shortwave is
supporting a MCS that is just about to enter the forecast area.
While the nocturnal timing will help to limit overall instability,
the line of thunderstorms is expected to hold together through most
of the forecast area. High-resolution models are not in total
agreement as to the evolution, but with greater instability to the
south, the odds of the line holding together across the forecast
area will be higher across the south. The bulk of the rain appears
to be near the I-95 corridor around sunrise and pushing east of the
area by mid-morning. Unfortunately, models diverge as to the
evolution of precipitation for the rest of the day. Will go with
scattered thunderstorms through the afternoon, but models might have
a better handle on the environment across the area once the current
line of showers/thunderstorms moves through. The entire forecast
area is under a slight (level 2 of 5) risk for severe thunderstorms,
with the primary threat coming from damaging wind gusts. The
greatest threat is likely to come in the morning with the overnight
line of thunderstorms departing the region, but the scattered
thunderstorms in the afternoon could also generate strong winds.
Model guidance has come in a few degrees cooler than the previous
forecast, which removes the 90s from the forecast, but still has
highs in the 80s everywhere.

Scattered thunderstorms could continue east of US-1 into the
evening, but conditions should dry out overnight. Lows will range
from the upper 50s to the upper 60s.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 300 AM Thursday...

A positively-tilted shortwave trough will approach from the TN
Valley on Friday, becoming more neutrally-tilted as it crosses
central NC on Friday evening. An MCS will also be moving east across
GA and SC early in the day, and while the exact location it will be
is still unclear, most high-res guidance keeps it to our south as it
exits into the Atlantic. At the surface, a cold front will begin to
cross through central NC as a wave of low pressure rides along it,
but exactly how far south and east it gets is a bit uncertain. The
aforementioned shortwave will provide some upper forcing for ascent,
so scattered showers will be possible anywhere on Friday afternoon
and evening, but the main threat of storms will be along and ahead
of where the front sets up. The 00z HREF has CAPE values around 500-
1000 J/kg across our southernmost tier of counties, which is where
the SPC expanded a marginal (level 1 of 5) risk of severe storms.
Damaging straight-line winds and hail are the main threats.
Instability and moisture will not be as high as today or yesterday
even down there, so convective coverage doesn`t appear great enough
to justify likely POPs anywhere, but they are still around 50% in
the far south. Forecast highs range from mid-70s far north to lower-
80s far south. Any precipitation will come to an end Friday night as
the cold front sweeps off the coast and lows turn slightly below
normal (upper-40s to mid-50s).

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 345 AM Thursday...

NW flow will dominate this weekend between broad troughing over the
Northeast US and mid-level ridging over the southern Plains and
lower MS Valley. A shortwave will move across the OH Valley and
northern Mid-Atlantic on Saturday, which could bring weak height
falls and forcing for ascent across northern portions of central NC
in the afternoon and evening. This will help increase moisture
around 700 mb, but model soundings indicate dry air in the low
levels from the NW flow and PW values only around 0.5-0.75 inches
(50-75% of normal). So any precipitation would be very light and
likely just some sprinkles across the far north if anything.
Otherwise it will be a very pleasant weekend with temperatures
remaining slightly below normal. Forecast highs are lower-to-mid-70s
on Saturday and mid-to-upper-70s on Sunday, with lows remaining in
the upper-40s to mid-50s. Dew points will only be in the 40s.

The surface high will move offshore on Monday and turn the flow
southerly, which will help increase high temperatures back to near
normal (upper-70s to lower-80s). Meanwhile a closed mid/upper low
will move into the southern Plains on Monday, becoming more of an
open wave as it traverses east into the mid-MS and TN valleys. SW
flow ahead of this system will increase moisture across our region
once more. However, models continue to differ significantly on how
quickly it will move east, with the GFS still much faster and the
ECMWF and Canadian holding it back. This affects when we would begin
to see any precipitation from this system. The earliest we see
anything should be Monday night, with POPs increasing to high chance
to likely through Tuesday and Wednesday, maximized during time of
peak diurnal heating (afternoon and evening) both days. The
deterministic GFS depicts a quick exit of the system with a mostly
dry Wednesday, but this appears to be an outlier as even most of its
ensembles are wet. The widespread clouds and precipitation may keep
temperatures down on Tuesday, as the raw GFS, ECMWF and CMC are only
indicating highs in the 60s to lower-70s. Models indicate a warmer
and more unstable air mass in place on Wednesday with highs in the
mid-70s to lower-80s.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 140 PM Thursday...

The coverage of showers and storms has trended much lower than what
we expected earlier, as the stronger storms have held south of the
NC/SC border, leaving central NC with just isolated showers at most.
Earlier IFR to MVFR cigs over the Piedmont terminals (INT/GSO/RDU)
has lifted and mixed to scattered, and we should see scattered 2-
3kft clouds plus a mix of scattered higher base cu with patchy mid
and high level clouds for the next 24 hours. Another round of
scattered showers and storms is expected across the S and SE Fri,
but this risk will be limited to near FAY and most likely after the
end of the TAF valid period. Surface winds will be around 10 kts or
less from the SW through tonight and from the W Fri, with a few
gusts to 15-20 kts possible this afternoon.

Looking beyond 18z Fri, S and E sections including FAY may see a
storm pass nearby during the mid to late afternoon Fri. Otherwise,
VFR conditions are expected through at least Mon, with a cooler and
less humid air mass moving in starting late Fri. Rain and isolated
storms are expected to move in Tue morning, with an increasing
chance of sub-VFR conditions. -GIH

&&

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

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...Hartfield/Green
SHORT TERM...Danco
LONG TERM...Danco
AVIATION...Hartfield