502
FXUS62 KRAH 200602
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
201 AM EDT Sat Jul 20 2024

.SYNOPSIS...
A series of convectively-amplified disturbances in moist,
southwesterly flow aloft will overspread and interact with a surface
front that will remain nearly stationary over central NC through the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1015 PM Friday...

Amid swly flow downstream of a shortwave perturbation that will
pivot from sern MO/nrn AR newd and across the mid-South, a series of
convectively-amplified disturbances will be directed from the lwr MS
and TN Valleys to the srn Middle Atlantic. The most notable and
probably influential of these features for the sensible weather in
cntl NC was well-defined in regional radar data over n-cntl SC this
evening, including in KCAE velocity data that depict a deep
circulation from around 3 to 25 thousand ft ARL in wrn Chester and
Fairfield Co. SC. This feature will continue to move generally newd
and across cntl NC overnight. As it does so, it will encounter an
environment characterized by only weak instability from widespread
outflow and surface cooling from prior convection and otherwise
weak, 5-5.5 C/km lapse rates upward through 500 mb. As such, it
seems most likely that a mix of stratiform rain immediately
surrounding the approaching MCV, and occasional weak cellular
development preceding it, will spread newd into/across cntl NC
overnight. Hourly rainfall amounts in the stratiform rain have
generally been light, from several hundredths to a quarter inch over
nrn SC in the past couple of hours. Given that the stratiform rain
shield will likely continue to diminish in the absence of
additional, concentrated deep convection, beyond the sporadic/
isolated cellular development like that which has recently developed
from near FAY to CTZ to GSB, the risk of flooding overnight appears
low.


.PREV DISCUSSION... /ISSUED 318 PM EDT Fri Jul 19 2024/

The cold front is now a stationary front as it has moved little
since this morning. The best estimate position of the front, mindful
of an outflow boundary sagging south from the boundary, stretches
from Davidson/Randolph east into southern Wake and into Wilson
County. An outflow boundary exists south of this tied to convection
from Wayne to Lee counties. The front arcs to the southwest to near
CLT and into northern SC/GA/AL.

Since the front has not made any southward progress the main showers
and storms have occurred along and south of the boundary, along US-
64. Storm chances are thus highest over the next few hours in this
area. With time, southward movement of the outflow from convection
should aid increased coverage of storms in the southern Piedmont,
Sandhills, and southern Coastal Plain by early evening.

While convection along and north of the boundary should weaken near
sunset with loss of heating, additional convection is forecast to
move into the southern and western Piedmont later tonight and
overnight into early Sat. This would be tied to mid-level energy
from MS/AL and upstream convection that may congeal over GA/SC and
track ENE. Isentropic ascent could also favor showers over the Triad
and western Piedmont overnight. Guidance also suggests perhaps an
MCV may track into the Triad early Sat, which could also touch off a
few isolated showers/storms along and north of the boundary in the
Triangle and northeast Piedmont early Sat morning. How much of this
convection survives with nocturnal stabilization is unclear, but
have 30-60 percent PoPs mainly US-1 westward.

Outside of convection, low stratus is forecast to envelope the area
overnight, especially along and north to northwest of the boundary.
Overnight lows are expected to be in the upper 60s to low 70s,
coolest across the north.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 230 PM Friday...

The damp pattern will persist through the weekend, including above-
normal cloud cover and rain chances, and near to slightly below
normal highs. A marginal severe threat persists for Sat, and locally
heavy rainfall will remain possible throughout the weekend.

Sat/Sat night: Rain chances will be high amidst PWs of 2.0-2.3", but
the highest pops are likely to be skewed to earlier in the day than
usual, morning through mid afternoon, as indicated by the HREF local
probability matched mean output. Southwesterly mid level flow over
the region will draw MCVs from the current Gulf Coast convection
northeastward across the western and central Carolinas starting Sat
morning. It`s tough to tell exactly where the weak surface boundary
will be, but the latest RAP runs depict it sitting nearly W-E over
NC as the low-mid level perturbation lifts northeastward. Light low
level winds will limit mass convergence, but this may still play a
role in focusing locally heavy downpours and slow-moving storm
clusters. The RAP output also favors warm rain processes, with an
LCL-0C depth over 4 km, and slow MBE movement will increase the risk
of localized flooding. The risk of strong to severe storms is
supported by an uptick in mid level flow from 15-20 kts to 25-35 kts
Sat, within persistent moderate SBCAPE and beneath a modest upper
divergence max. After high morning-through-midday pops, we may have
a relative lull period for a portion of the afternoon until we see a
redevelopment of scattered convection late in the day and into the
evening, perhaps lasting into the early overnight with at least
marginal elevated CAPE lingering amidst growing CINH. Expect highs
to range from the 80s to lower 90s, with lows in the upper 60s to
mid 70s.

Sun/Sun night: Attempting to pin down convection details (both
location and timing) becomes more difficult by Sun, but we`ll still
be in a regime featuring weak Gulf-source southwesterly low-mid
level flow, between baggy troughing over the E Plains/Miss Valley
and a strong NW Atlantic ridge extending WSW toward FL. Both PWs and
the vertical thermal/moisture profile will likely exhibit little to
no change, although mid level flow will once again weaken, leading
to a reduced threat of strong storms. See no reason to change from
the good chance/likely pops, with continued variably to mostly
cloudy skies. We should see highs in the 80s to near 90 and lows
mostly in the low-mid 70s. -GIH

&&

.LONG TERM /MONDAY THROUGH FRIDAY...
As of 300 PM Friday...

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

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 moisture-laden plume of 120-140% percent of
normal PWATs 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 above normal
rain chances and associated increase cloud cover and will result in
seasonable to slightly below-normal high temperatures and mild above
normal min temps. Highs generally 85-90. Lows in the 70s.

The super ensemble mean average cumulative rainfall during the long
term period is between 1-2", with higher amounts possible within any
heavier convection.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
As of 201 AM Saturday...

MVFR to IFR ceilings will continue to fill across central NC this
morning, persisting through mid to late morning.  Additional showers
and a few storms will be possible later this afternoon which could
produce brief sub-VFR conditions at all terminals. A few stronger
thunderstorm gusts could also be possible especially at KRDU and
KRWI.  Otherwise, expect MVFR to IFR stratus to sock back in later
tonight.

Beyond 06Z Sunday: Showers and storms will continue Sunday into
early next week.  Early morning fog and stratus will be possible
each day as well. The wet pattern will continue into middle of next
week.

&&

.CLIMATE...
Record High Minimum Temperatures:

July 19: KGSO: 75/2016 KFAY: 77/2023

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

July 21: KGSO: 76/2011 KRDU: 78/1932 KFAY: 80/2017

July 22: KRDU: 78/2011

July 23: KRDU: 78/2011

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

&&

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

&&

$$

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