267
FXUS62 KRAH 030826
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
425 AM EDT Wed Jul 3 2024

.SYNOPSIS...
Canadian high pressure centered just offshore the Middle Atlantic
coast will linger over the Carolinas through tonight. A subtropical
ridge will otherwise extend across the South Atlantic states through
the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 350 AM Wednesday...

Around an anomalously-strong (+3 sigma), 500 mb anticyclone centered
at 596 dam over the Deep South, a subtropical, mid-level ridge will
continue to extend from the srn Plains to the South Atlantic coast.
In wswly flow poleward of the expansive subtropical ridge,
convectively-generated disturbances will develop and move from the
cntl Plains and mid MS Valley ewd and across the OH Valley and lwr
Great Lakes/nrn Middle Atlantic. While associated height falls will
be maximized across the OH Valley and nrn Middle Atlantic, 10-20
meter/12 hr falls will support some gradual weakening, as far south
as cntl NC later tonight, of a preceding strong subsidence inversion
evident in regional RAOB data the past couple of days. Some mid/high-
level moistening and cloudiness may result especially across nrn NC
tonight, after high-based, diurnally-enhanced stratocumulus become
scattered to broken this afternoon (with greatest coverage over the
wrn Piedmont) and dissipate through the evening. Otherwise,
temperatures will moderate to slightly above average, with highs in
the upr 80s to lwr 90s and lows in the mid 60s to lwr 70s, as
Canadian surface high pressure, which will extend from just offshore
the Middle Atlantic coast southwestward into the Carolinas, becomes
increasingly-modified and gradually loses influence.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 420 AM Wednesday..

Much hotter, but with seasonable humidity characterized by
mixed/afternoon surface dewpoints in the upr 60s to around 70 F.

A subtropical ridge over the Deep South will weaken and retreat
slightly, as a mid-level cyclone develops and deepens from the nrn
Plains to the upr MS Valley. In the intervening wswly flow between
the two, a corridor of convectively-amplified disturbances will sag
sewd and extend from the Middle Atlantic to the srn Plains by 12Z
Fri. Weak mid-level height falls and associated adiabatic cooling
will cause initially weak mid-level lapse rates to steepen to 5.5 to
6 C/km over the srn Middle Atlantic by Thu afternoon.

At the surface, very warm-hot sswly flow will expand throughout the
Southeast, equatorward of a convective outflow-modulated frontal
zone that will settle to a similar position as the corridor of mid-
level disturbances noted above (ie. from the Middle Atlantic to the
srn Plains). Meanwhile, an Appalachian-lee trough will become
established across the Foothills and wrn Piedmont of the srn Middle
Atlantic/Carolinas.

The influence of the subtropical ridge and sswly low-level flow will
allow heat to expand newd and across cntl NC once again, with
forecast high temperatures in the mid 90s to around 100 F and around
daily records at all three climate sites. Mixed/afternoon surface
dewpoints mostly in the upr 60s will somewhat temper associated heat
index values that are expected to peak in the upr 90s to near 105.
Thu night will be very mild and muggy, with lows centered in the
middle 70s.

While the intersection of the lee trough and convectively-modulated
frontal zone will likely focus the greatest concentration of
diurnally-maximized convection across n-cntl VA, isolated cells will
be possible swwd in the vicinity of the lee trough over the wrn NC
Piedmont during the afternoon. Additionally, some outflow from
upstream convection may outpace the main baroclinic zone and move
into the nrn NC Piedmont during the evening, during which time
scattered, multi-cell development will be possible. An isolated
strong to damaging wind gust will be possible with any afternoon
cells owing to strong diabatic cooling potential in the strongly-
heated boundary layer characterized by 9.5 C/km lapse rates and 25-
30 degree dewpoint depressions, after which time nocturnal cooling
and stabilization will limit convective intensity.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 225 AM Wednesday...

Aloft, a potent northern stream s/w will move through the Great
Lakes Fri/Fri night, as the longwave trough amplifies southward
through the Plains and MS Valley. As the trough amplifies, the high
over the Southeast US will be gradually pushed southeastward off the
Southeast US coast Fri night/Sat. Another northern stream s/w will
drop into the northern Plains and track eastward along the US/Canada
border Sat/Sat night as the initial s/w lifts newd into Canada. As
this second s/w moves through the Great Lakes Sun/Sun night, another
disturbance will quickly drop ssewd through the northern Rockies and
into the central Plains, helping further amplify the longwave trough
through the southern Plains/lower MS Valley by Mon morning. All the
while, central NC will remain situated between the trough to the
west and the high to the east, with deep southwesterly flow
prevailing. The fly in the ointment is the medium-range guidance
picking up on a possible tropical low approaching the Carolina coast
over the weekend. There is some uncertainty wrt this feature for Mon
and Tue. Also on Sun/Sun night, Beryl is expected to make landfall
along the western Gulf Coast, however exactly where that happens and
when will determine what happens to the system as/where it moves
inland early next week. There is still a lot of uncertainty in the
forecast for Mon/Tue, but for now, it appears the longwave trough
axis will generally remain west of the Appalachians through Tue,
while s/w disturbances move through it. At the surface, a lee trough
will remain in place through Sat, when a cold front will approach
from the west. As of the latest model solutions, the front still
appears to get hung up and generally wash out along the Appalachians
Sat night, as Bermuda high pressure ridges westward. An area of low
pressure will sit off the Southeast US coast Fri/Fri night, then
weaken on Sat before the remnants of the low lift newd off the
Carolina coast Sat night/Sun. possibly laying W-E through WV/VA Sun
as high pressure lifts newd through the OH Valley and Northeast, but
the front appears to stay north of central NC. Expect swly flow and
the advection of warm, moist air into the area to take over once the
ridge moves out Thu morning and prevail through at least Sat. The
lee trough should once again strengthen over the area early next
week.

Temperatures will be above to well above normal through Tue. Latest
forecast heat index values of 100-106 are expected across much of
central NC for Fri and Sat. Sun and Mon heat index values max out
around 100, mainly across the south, but may creep upward again on
Tue.

As for rainfall, the weather seems to be turning a bit wetter. As
the mid-level ridge gradually gets suppressed south and the lee
trough strengthens, expect more diurnally driven convection Fri
through Tue, with higher chances/amounts as s/w disturbances clip
the area.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As of 210 AM Wednesday...

The presence and influence of Canadian high pressure that will
extend from just offshore the Middle Atlantic coast southwestward
into the Carolinas will favor mostly VFR conditions in cntl NC
through Thursday morning. While a brief period of visibility
restrictions cannot be entirely ruled out at RWI around daybreak,
the likelihood seems relatively low given the foregoing
Canadian/continental air that would favor more dew than fog, should
surface temperatures even radiationally cool sufficiently amid areas
of ~ 6 thousand ft AGL stratocumulus that are apt to persist there.

Outlook: A chance of showers/storms will exist over the wrn NC
Piedmont (INT/GSO) Thu afternoon-evening and throughout cntl NC Fri
through the weekend.

&&

.CLIMATE...
Record High Temperatures:

July 4:
KGSO: 98/1970
KRDU: 101/2012
KFAY: 98/2019

July 5:
KGSO: 98/2012
KRDU: 102/1999
KFAY: 101/2002

July 6:
KRDU: 102/2022
KFAY: 99/1990


Record High Minimum Temperatures:

July 4:
KGSO: 73/2018

July 5:
KGSO: 74/1999
KRDU: 78/1902
KFAY: 77/2005

July 6:
KGSO: 76/1999
KRDU: 79/1900
KFAY: 76/2017

July 7:
KGSO: 73/2019
KRDU: 77/1900
KFAY: 78/2017

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...MWS
LONG TERM...KC
AVIATION...MWS
CLIMATE...RAH