214
FXUS62 KRAH 040814
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
414 AM EDT Thu Jul 4 2024

.SYNOPSIS...
A subtropical ridge will remain anomalously-strong over the Deep
South today, then gradually weaken ahead of a cold front that will
move into and stall over the southern Middle Atlantic and Carolinas
this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 230 PM Wednesday..

A 595dm upper level ridge will extend from the Gulf Coast states NE
toward the Mid-Atlantic on Thursday while surface high pressure
continues to slip further offshore and allows moist southerly return
flow to engulf the Carolinas.  With southwesterly flow and deep
mixing, dry adiabatic mixing technique yields mid to upper 90s for
highs, which is on the higher side of guidance (equivalent to the
75th to 90th percentile range of the NBM) but not out of the realm
of possibility. Thus will lean towards the higher side of guidance
for highs. Deep mixing also suggests dewpoints will be able to mix
out a little into the mid to upper 60s in a lot of areas, helping to
keep heat indices in the low 100s for the most part.  Will note that
HeatRisk suggests moderate impacts, with much greater impacts Friday
into Saturday.

Regarding any convection, the stout mid-level cap that has been
present this week will still be around early Thursday, weakening
somewhat across the north as a trough moving into the Great Lakes
tampers down the northern edge of the upper ridge.  CAPE looks
pretty limited due to the cap and mixing of dewpoints, but hires
guidance suggests some isolated development on the mtn ridges and
lee trough, perhaps migrating from SW VA toward the northern
Piedmont along loosely-consolidated outflow.  PW will also still be
less than 1.5 inches, so the number of storms should also be
limited. Thus the best chance of isolated storms should be from the
Triad to Person County later in the afternoon and evening.  Where
storms do occur, the deep mixing and dry air will favor damaging
winds as the greatest threat.

Without better moisture available, convection is expected to wane
quickly Thursday evening.  Dewpoints will continue their background
rise with the return flow, creeping into the lower 70s and keeping
overnight lows in the low to mid 70s as well.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 410 AM Thursday...

...Hot and humid conditions bring the risk for heat related
illnesses Friday and Saturday...

A mid-level subtropical ridge centered over the GOM states will
extend up through the southern Mid-Atlantic in between broad
troughing over the central CONUS and a closed low drifting by
Bermuda through Sat. At the surface, an occluded low over the Upper
Great Lakes will slide ENE into southern Quebec by Sat evening as a
compact shortwave lifts through the eastern edge of the longwave
troughing. Within the deep tropospheric southwesterly flow, low-
level thickness steadily rise to around 1445m (30m above normal) and
850mb temperatures soar to 21 to 23 C Fri afternoon. In the absence
of showers and convective outflow during the afternoon, this pattern
will support well above normal temperatures into the upper 90s and
low 100s with heat index values ranging from 100 to 107 degrees.
Little overnight recovery is expected Fri night as continued humid
airmass and lingering cloud cover will keep lows in the mid to
potentially upper 70s in spots. This would result in heat illnesses
likely for anyone without access to effective cooling and/or
adequate hydration. Some afternoon relief will be possible on Sat
especially over the western Piedmont mid/upper level clouds spread
in from the west ahead of trailing cold front. The cooler and drier
air behind the cold front will likely struggle to traverse the
mountains with another night of mid 70s expected.

As for convective potential, on Fri greatest coverage of
showers/storms will likely originate over the NC mountains in the
vicinity of the lee trough and slowly shift eastward through the
afternoon into the evening hours. The airmass within and ahead of
the storms will be characterized by around 2000 J/kg of MLCAPE and
20 kts of 0-6km shear. Little storm organization is expected given
the weak deep layer shear, but isolated strong to potentially severe
wet downbursts and isolated congealed clusters could certainly be
possible with above normal moisture and DCAPE around 1000 J/kg. By
Sat, the mid/upper trough will sag farther southeast and direct more
perturbed 500mb flow into the western Piedmont and combine with lee
trough and/or differential heating boundaries to develop more
widespread showers/storms. Deep layer shear will again be weak, but
closer to 15-25 kts (highest NW) and may result in some cold pool
organized clusters resulting in mostly a wet downburst threat as
well. Confidence on Sat is low given it will likely depend on the
prior day activity.

&&.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 410 AM Thursday...

Overall a stagnant pattern will exist over Southeast and the Mid-
Atlantic through the remainder of the forecast period. Central NC
will be tucked between broad reinforced troughing through the
central CONUS with the stationary sub-tropical high broadly draped
across the western Atlantic in the eastern GOM. At the surface a
diffuse pressure gradient will feature a lee-trough redeveloping
over the region each afternoon with unseasonably moist deep layer
moisture in place as PWAT values remain at-or-above 2 inches.

This pattern will favor continued above normal temperatures with
highs in the mid 90s in the urban areas and overnight lows only
reaching into the mid 70s. With continued heat related stresses heat
related illnesses will be possible especially among individuals
sensitive to heat and do not have access to effective cooling and/or
adequate hydration. Diurnally favored showers/storms and storms will
also be possible each afternoon into the evening, likely focused
along the lee-trough and any subsequent outflow boundaries
thereafter. Organized convection appears to be at a minimum with
deep layer shear remains weak around 10 to 20 kts, strongest across
the NW Piedmont, and result in mostly pulse summer-time
showers/storms. Greatest coverage could be Tues into Tues night with
proximity of mid/upper troughing swings through the Great Lakes
region.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
As of 200 AM Thursday...

VFR conditions, influenced by high pressure extending from just
offshore the Middle Atlantic coast southwestward into the Carolinas,
will continue through at least mid-afternoon. An Appalachian-lee
surface trough and/or outflow from upstream convection will provide
foci for shower/storm development that will probably affect INT/GSO
and surrounding vicinity across the nw NC Piedmont this afternoon-
evening. Some of that gusty outflow, and focus for additional,
isolated to widely scattered showers/storms, may drift to near RDU
and RWI through 00-03Z, before dissipating.

Outlook: A chance of showers/storms will exist Fri and especially
Sat through Mon, as a pre-frontal trough and surface front move into
and stall over cntl NC. Late night-early morning stratus and fog
will also be possible this 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...BLS
SHORT TERM...Swiggett
LONG TERM...Swiggett
AVIATION...MWS
CLIMATE...RAH