504
FXUS62 KRAH 141152
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
750 AM EDT Wed Aug 14 2024

.SYNOPSIS...
High pressure centered over the Great Lakes will shift east and
southeast into the mid Atlantic and the eastern Carolinas through
Friday and then shift offshore Saturday. A cold front will approach
the region from the west on Saturday.

&&

.NEAR TERM /TODAY AND TONIGHT/...
As of 750 AM Wednesday...

Quick update to cancel Dense Fog Advisory as visibility restrictions
have improved to 2SM or more at all locations.

Previous discussion: Areas of fog have begun to develop in the last
hour or so, mainly across the northern/northwest Piedmont into the
northern Coastal Plain. Satellite imagery reveals much of the
mid/high clouds have exited to the south and east. This trend should
continue, although some patchy 10 kft clouds may still exist across
our southern zones. Much of these low visibilities have developed
where rain fell Tue. Based on latest observational trends and model
guidance, a dense fog advisory may be needed for portions of the
Piedmont and Coastal Plain, mainly along/north of US-64. We will
continue to monitor.

For the rest of today, northwest flow will persist through the
period. Another shortwave will dive down from OH/VA, skirting our
northeastern zones before exiting offshore later tonight. High
pressure will slowly build south from the OH valley into the Mid-
Atlantic states, resulting in a light NE flow. Highs this afternoon
should be warmer than Tue thanks to more sunshine, with low to
middle 80s. This is slightly below normal for mid-August. Afternoon
cumulus will develop at peak heating, and some CAMs still suggest a
few widely isolated showers or a storm could develop in the aftn/eve
as the shortwave aids some 250-500 J/kg of CAPE. Rain chances should
be 20-percent or less overall given lack of appreciable forcing,
with any isolated showers tapering off after sunset.

Tonight, with generally clear skies and calm winds, lows should
manage to dip some 2-6 degrees below normal in the upper 50s in
outlying areas to low to mid 60s elsewhere. This will certainly be a
comfortable night we have not seen in some time.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 220 AM Wednesday...

Ridging aloft over the Midwest and OH valley will gradually pivot
east into the Mid-Atlantic as an upper trough tracks into the Great
Lakes region. High pressure will continue to nose down into our area
from the northern Mid-Atlantic. Temperatures will be perhaps 1-2
degrees warmer than Wed owing to a slight rise in low-level
thicknesses, in the low to mid/upper 80s. This is just below
average. We will again see some afternoon fair weather cumulus.

The aforementioned trough will combine with low to mid-level WAA
across the TN/OH valleys Thu night, increasing some mid/high clouds
across the western Piedmont. The WAA will likely generate some
upstream convection as far south as the TN/KY region, but it will
not reach us due to high pressure and its stability. Lows should be
comfortable again, ranging from the low to middle 60s, lowest in the
Coastal Plain.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 400 AM Wednesday...

Dry WNW flow aloft will continue to dominate on Friday, as ridging
pivots farther east across the Carolinas and surface high pressure
extends down the Eastern Seaboard, which will help keep what is then
likely Hurricane Ernesto well to our east over the Atlantic. Enough
mixing of the dry air aloft will likely help keep dew points in the
mid-60s in the afternoon. As troughing extends down from the Great
Lakes to the TN Valley, guidance shows it pushing the ridging far
enough east for some increased moisture to spill over the
Appalachians. This may result in isolated showers or storms making
it as far east as the NW Piedmont, so carry slight to low chance
POPs there on Friday.

As the trough and associated cold front push farther east into the
Appalachians on Saturday, SW flow will increase moisture and
instability across all of central NC, with 1000-2000 J/kg of MLCAPE
and PW values reaching or even exceeding 2 inches. This looks to be
the day with greatest confidence in precipitation during the
extended period, which is backed up by the latest ensemble
probabilities. Mid-level flow doesn`t look terribly impressive,
around 20-30 kts, but a few strong to severe storms still can`t be
ruled out. Low chance POPs continue on Sunday, highest east, as the
surface trough works it way through central NC. However, drier air
beginning to work in from the west at that point may decrease
shower/storm chances a bit compared to Saturday.

Guidance depicts below-normal PW values in place by Monday and
Tuesday behind the passage of the trough/front, as the low-level
flow turns W/NW. With the mid/upper trough axis near or over the
area, diurnally-driven slight to low chance POPs linger, but
coverage does not look too impressive, and guidance actually depicts
weak mid-level height rises. The ECMWF had been depicting a
slower/wetter solution, but the 00z run looks more like the GFS with
bringing the cold front through our area over the weekend instead of
stalling it out.

The frontal passage may be more like a trough than an actual cold
front, as temperatures should be pretty consistent through the
extended period and within a few degrees of normal. Forecast highs
are in the mid-to-upper-80s each day. Lows will be in the upper-60s
to lower-70s each night, maybe a bit cooler by early next week as
drier air moves in.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
As of 610 AM Wednesday...

Fog has developed at RDU and partially near RWI. Elsewhere, VFR
conditions are largely present. LIFR fog should lift by 13-14z.
Thereafter, VFR conditions should persist for much of today with
scattered to broken cumulus in the 4-7 kft range. Winds will be out
of the ENE around 5 kt. Tonight, some model guidance shows that with
clear skies and light winds, fog could develop again in the vicinity
of RDU/RWI. Given that dewpoints will mix out today, crossover
temperatures may be more difficult to meet. Nevertheless, introduced
sub-VFR restrictions at RDU early Thu morning, where sub-VFR
probabilities are highest. Confidence was too low to mention at the
other terminals.

Outlook: Some fog may again be possible Thu morning, most favored at
RDU/RWI. VFR conditions are expected across the area otherwise into
Friday. A cold front will approach this weekend, producing a limited
threat of an afternoon or evening shower/storm across the west on
Friday with a marginally greater chance of mainly afternoon and
evening showers and storms for Saturday and Sunday.

&&

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

&&

$$
SYNOPSIS...Kren
NEAR TERM...Kren
SHORT TERM...Kren
LONG TERM...Danco
AVIATION...Kren