822
FXUS62 KRAH 201918
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
317 PM EDT Sat Jul 20 2024

.SYNOPSIS...
The combination of a weak nearly stationary front sitting over North
Carolina and Virginia, a very moist air mass in place, and a series
of upper level disturbances tracking southwest to northeast over the
region will bring continued unsettled weather through Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 305 PM Saturday...

Fairly high pops will continue through tonight within a moist air
mass along and south of a weak quasi-stationary sfc front across far
S VA. Earlier showers over the Triad extending up into VA continue
to progress E with upscale growth back to the SW, with development
near and just south of the I-40 corridor through the southern
portions of the Triad and back into the N and central Foothills.
This activity is associated with an MCV, clearly discernible on GOES
IR and vis imagery, that has tracked from NW NC/SW VA to near the
central NC/VA border region from daybreak through the current time.
Deep moisture remains in place with above normal PWs of 2.0-2.25",
still anomalously high at 110-120% of normal but a bit below some of
the values we`ve seen in recent days. SBCAPE in the northern
Piedmont region is somewhat modest at around 1000-1500 J/kg, not bad
though considering how moist the column is (noted on the 12z GSO
sounding) with delayed heating due to morning low clouds. And while
SBCAPE is better in the SE at 2000-3000 J/kg and low level lapse
rates are reaching 7 C/km in the SE, mid level lapse rates over the
area are rather poor at just 5.5 C/km. Effective bulk shear remains
good around 25-30 kts, which may still support a few strong storms
with isolated wet microbursts, particularly as those storms progress
into the better environment in the S Piedmont, Sandhills, and the
Coastal Plain. Later tonight, our S and SE sections are likely to be
affected by the cluster of storms or resultant MCV currently over S
AL/S GA as it lifts NE, so will maintain pops there through the
night, while northern sections see pops diminishing later tonight
with the arrival of lower PW from the N as the frontal zone sags S
into our far N. Expect lows tonight from the upper 60s far N to the
mid 70s SE, with another round of low clouds developing overnight,
particularly across the W and far N. -GIH

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 242 PM Saturday...

A Marginal (level 1 of 4) risk of excessive rainfall continues
Sunday and Monday.

On Sunday, a trough will be roughly located over the Mid-Mississippi
Valley, with ridging over the southwest Atlantic. At the surface,
weak low pressure will be situated along the western TN valley. The
stationary front from today will still be present across southern
VA, although some remnant outflow boundaries from Sat will likely be
present across the region. With the front to our north, the main
forcing would appear to be from what models are showing to be
another impulse at mid-levels. This energy looks to come out of
eastern GA and SC during the late afternoon and evening hours.
Additional forcing could come from the sea-breeze interacting via
outflow boundaries. The 12z CAMs are mixed on coverage and location,
but the global models and ensembles are favoring the highest storm
chances across the southern Piedmont to southern Coastal Plain, and
expanding northward as the energy tracks through. Have kept high PoP
chances as a result, centered on the aftn/eve. Flash flooding will
again be possible with 15-20 kts of mean-layer flow and continued
anomalous PWs. Highs look to be a tad warmer than Sat in the upper
80s to around 90. A second wave of energy could favor overnight
convection into Monday so have kept chance PoPs during the latter
half of Sun night. Overnight lows to be in the upper 60s/low 70s.

On Monday, the trough from Sun will move from the OH valley into the
lower Great Lakes. Broad low pressure at the surface should be
located over the lower OH valley. The stationary front should inch a
tad further north into northern VA. With the front currently
anticipated to be well removed from central NC, forcing for
convection at the surface may be more subtle than Sun. A surface
trough appears to be in place across the southern Appalachians and
western NC. At mid-levels, guidance shows yet another impulse coming
out of the SW flow from western SC. This impulse appears as a
possible driver for afternoon and evening showers and storms once
again. A jet streak near the region could also aid divergence aloft.
Storms may additionally fire along the trough in the NC Foothills,
tracking east into the evening hours. Deep layer shear is somewhat
higher than prior days of ~30 kt, with similar or higher
instability. While we are not outlooked, a few stronger storms could
produce damaging wind gusts. On top of that, heavy rainfall
remains a threat. Convective initiation may be slower to develop
with the front removed from the area. Thus, highs may be a tad
warmer in the mid 80s N to low 90s central/south.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY...
As of 300 PM Saturday...

...Above normal rain chances will lead to seasonable to slightly
below normal temperatures next week...

...Widespread beneficial rainfall is expected to bring additional
drought improvement...

Sandwiched between persistent upper level troughing that stretches
south from the Great Lakes to the southern US Plains and a strong
subtropical ridge that extends over the western Atlantic and SE US,
deep SW flow will keep a plume of deep moisture, featuring PWATS of
2.3-2.5" (120-140% percent of normal), entrenched across the region
all next week. DPVA via shortwave impulses embedded in the SW flow,
in tandem with daytime heating and interaction with
seabreeze/outflow will lead to high/likely chances of showers and
storms each day. The super ensemble mean average cumulative rainfall
during the long term period is between 1-3", with higher amounts
possible within any heavier convection. The expected rainfall
amounts should lead to additional improvement in drought conditions
across NC.

Timing discrepancies still need to be resolved, but a frontal
passage sometime next weekend could mark an end to the convectively
wet pattern.

The above normal rain chances and associated increase cloud cover
and will keep the heat at bay, resulting in seasonable to slightly
below-normal high temperatures. Highs generally 85-90. Lows in the
lower to mid 70s.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 115 PM Saturday...

Sct-bkn MVFR clouds persist across central NC, although cigs
continue to lift, and the current pace of this lift would suggest
that all TAF sites will be VFR by 19z. INT/GSO has seen a band of
showers with brief IFR conditions pass over during the last couple
of hours, and while these particular showers are exiting, there is a
chance for additional scattered to numerous showers and storms to
develop through mid afternoon. These are most likely to impact
INT/GSO/RDU first, between 18z and 22z, before reaching RWI within
an hour later as the showers and storms increase in number, and
finally reaching FAY after 22z. Isolated wind gusts over 40 mph will
be possible in and near any storms, along with erratic speeds and
directions and brief sub-VFR cigs/vsbys. FAY will see a trend from
storms to mostly scattered showers overnight, while other sites
should trend to dry weather from mid evening onward. We should see a
redevelopment of sub-VFR conditions, mainly MVFR cigs (except mainly
IFR at INT) with patchy MVFR vsbys after 07z tonight, with the
highest confidence across the W. Cigs will again be slow to rise
Sun, likely not lifting and breaking up to VFR until after 16z.
Surface winds will be under 10 kts and mostly from the SW through
Sun.

Looking beyond 18z Sun, cigs should have lifted to mostly VFR by
18z, however another round of numerous slow-moving showers and
storms is expected across all terminals Sun afternoon through Sun
night. There will be a high chance for showers and storms each day
through Thu, as we stay in a moist and unsettled pattern. The chance
for late-night-through-mid-morning sub-VFR clouds and briefly sub-
VFR vsbys will also continue through mid week. -GIH

&&

.CLIMATE...

Record High Minimum Temperatures:

July 20:
KGSO: 75/2019
KRDU: 76/2020

July 22:
KGSO: 77/2011
KRDU: 78/2011

July 23:
KRDU: 78/2011
KFAY: 79/2017

July 24:
KRDU: 79/2011
KFAY: 79/1945

July 25:
KFAY: 78/2016

July 26:
KGSO: 76/2016
KRDU: 77/2010

&&

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

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...Hartfield
SHORT TERM...Kren
LONG TERM...CBL
AVIATION...Hartfield
CLIMATE...RAH