067
FXUS62 KRAH 051830
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
230 PM EDT Wed Jun 5 2024

.SYNOPSIS...
A series of mid-level disturbances will move east and interact with
an unseasonably moist airmass over NC through Thursday. A pre-
frontal trough and cold front will move across the area Thursday
evening through early Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1100 AM Wednesday...

Forecast seems to be on track, thus no major updates needed with the
morning update. Adjusted PoPs slightly to blend in the latest Hi-Res
guidance which kept the NW Piedmont in a slight chance for the rest
of the morning and then increasing to chance PoPs for areas along
and west of the US1 corridor. Scattered showers and storms are
expected to be pulse-type again today with the best chance for
storms over the western and northern Piedmont regions. The Coastal
Plain could also see some showers and storms but the timing would
most likely be later in the evening. Highs temps today are on track
to be in the low to mid 80s NW to upper 80s SE with a few of the hot
spots hitting 90 degrees.

As of 420 AM Wednesday... Although it will again be seasonably hot,
with above average chances of showers/storms, confidence in timing,
coverage, and intensity of that convection remains low.

The basal portion of a synoptic trough, now stretching from a
cyclone over the cntl SK/MB border ssewd through the upr/mid MS
Valley then swwd into the srn Plains, will move ewd in positive tilt
fashion and reach the cntl/srn Appalachians and TN Valley by 12Z
Thu. Preceding that trough and more influential for cntl NC this
period, a couple convectively-generated mid-level troughs and
vorticity centers/MCVs will move generally enewd across the Middle
and South Atlantic states. The first/lead one stretched this morning
from a well-defined MCV over ern KY ssewd across the w-cntl
Carolinas and should move ewd across cntl NC through early this
afternoon. The second, centered over the TN Valley and which
includes a couple of equally as prominent MCVS over wrn TN and w-
cntl AL, should extend from the OH Valley to the srn Appalachians by
this evening and move across the srn Middle Atlantic and Carolinas
overnight. Net, ~20-30 meter mid-level height falls will become
maximized over cntl NC tonight. Upstream VWP data this morning
depict modest, 25-35 kts of 700-500 mb mb flow centered over the TN
Valley; and this enhanced flow should move downstream and across
the srn Middle Atlantic/Carolinas later today and tonight.

At the surface, high pressure will persist and extend from near and
south of Bermuda wwd and across the South Atlantic states, while a
differential heating zone preceding the lead mid-level vorticity
lobe and associated cloud canopy, and a loosely-organized outflow
boundary from related rain/storms ongoing from the wrn NC Piedmont
swd into ern GA, will move east across cntl NC through early this
afternoon.

Given generally poor representation of the ongoing convection in
CAMs, generally non-existent in the HRRR, it remains unclear to what
degree this ongoing convection now moving across the srn and wrn NC
Piedmont will be maintained or intensity as it moves ewd through the
morning and early afternoon, and subsequently how unstable the
environment over cntl NC will be ahead of the trailing mid-level
trough/MCVs later this afternoon-tonight. It seems plausible that
this convection will increase in intensity as it, and its associated
differential heating zone and frontal-like circulation, encounters a
partly sunny and quickly, diurnally-destabilizing environment over
the NC Sandhills and Coastal Plain through early afternoon, with a
secondary instability maximum developing in its wake today over the
srn and wrn Piedmont and ahead of the trailing mid-level trough. The
relative greatest coverage and intensity of convection would then be
maximized over those wrn counties this evening. On the other hand,
the CAMs generally depict little coverage with this lead, ongoing
activity and dissipates that which it is initialized, and instead
tends to focus scattered to locally numerous showers/storms over the
wrn half of cntl NC this evening, with very little in the ern
Sandhills and Coastal Plain. Regardless, the aforementioned modest,
wly/wswly mid-level flow will favor clustering and preferential
multi-cell development on the ern flank of outflow, with an
associated risk of strong to severe outflow wind gusts.

It should otherwise be persistently hot in the mid 80s to around 90
F ahead of the differential heating zone, and up to several degrees
cooler to its west (ie. most likely the srn/wrn Piedmont and perhaps
wrn Sandhills). Given the uncertainties in convective evolution
described above, a broad, slight to low chance of convection will
be maintained overnight, with low temperatures again in mainly the
mid-upr 60s.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 230 PM Wednesday...

...There is a Level-1/Marginal Risk For Severe Storms mainly along
and north of HWY 64...

Central NC will lie along the southern fringes of a mature mid-
latitude cyclone that will traverse along southern Ontario and the
Upper Great Lakes. Meanwhile, the associated belt of enhanced
westerlies will dip down into the Ohio Valley and northern mid-
Atlantic states with the trailing surface front crossing the area
Thursday night.

The day should start start out mostly dry with a near repeat
performance of gradual lifting of the overnight/morning stratus
layer through the late morning/midday.

Thereafter, a loosely organized line of showers and storms, likely
focused along the H8 trough/front, will move east off the mtns and
foothills and into the western Piedmont between 18-21z. The
convection is expected to move east through the remainder of the
afternoon and evening hours, before exiting the eastern/coastal
plain counties ~03z. It is unclear how the line will evolve as it
moves eastward. However, there is a increasing signal in the latest
hi-res model guidance that the line could weaken significantly after
sunset, especially across the southern and southeastern portions of
the forecast area.

Deep layer shear over NC has also trended weaker in recent runs,
with some of the guidance indicating a slight increase to 25-30 kts,
in a narrow belt extending along the NC-VA late towards sunset. If
there is chance for any isolated strong to severe storm, it will
likely be across the northern tier counties between 4-8 pm. Damaging
wind gusts are the primary threat.

Highs will be warmer than today, especially across the eastern half
of the forecast area where the later arrival of showers and storms
should allow for some strong heating. Highs ranging from mid 80s NW
to lower 90s SE.

Some isolated showers will be possible overnight/predawn hours
Friday morning as the lagging cold front crosses the area. Lows 65-
70.
&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 200 PM Wednesday...

Friday and Saturday: Aloft, an upper low will meander slowly
eastward through southern Ontario/southern Quebec, Canada Fri and
Sat. The attendant trough will progress eastward through the East
Coast states Fri as a s/w passes over central NC within the trough.
The trough will continue offshore Fri night. Nearly zonal flow
should prevail Sat/Sat night, with a weak s/w or two passing
overhead. At the surface, the cold front should be through central
NC Fri morning and continue eastward offshore through the aft/eve.
Cool high pressure centered just west of the southern Appalachians
will ridge eastward into the area Fri night. A trough may develop
over the area Sat and amplify Sat night, while the high weakens. For
now the forecast remains dry. Highs Fri ranging from low/mid 80s NW
to mid/upper 80s SE, with lows ranging from mid 50s north to mid 60s
south. Temps should be similar Sat/Sat night, highs a degree or two
lower and lows a couple/few degrees higher in some spots.

Sunday onward: There is still some uncertainty in this part of the
forecast, so confidence is on the low side. Aloft, as the parent low
swings through Quebec, Canada and the Northeast US a potent s/w will
drop south out of central Canada, through the northern Plains/upper
MS Valley Sat night/Sun, then continue around the parent low through
the Great Lakes/OH Valley Sun, amplifying the attendant trough in
the process. As the low lifts northward Sun night/Mon, the trough
should swing eastward into (GFS)/toward (ECMWF) the mid-Atlantic.
The s/w should move through central NC Mon night or Tue/Tue night.
At the surface, with the trough over central NC, a warm front may
briefly lift through the area Sun aft/eve, before another cold front
pushes through the area Sun eve/night. The front should stay east of
the area, with high pressure over the Plains/MS Valley through Mon
night. Beyond that, the medium-range guidance varies greatly, with
the ECMWF showing a low tracking along the Southeast US/Carolina
coast Mon night and Tue, while the GFS slowly develops a westward
retreating, inverted coastal trough Tue/Wed. The best chances for
showers/storms will largely be tied to the initial s/w sometime
between Sun eve and Mon night. Additional showers/storms will be
possible through mid-week, but confidence is low at this time.
Temperatures should be within a category or two of normal.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 200 PM Wednesday...

MVFR conditions have lingered in the NW Piedmont for most of the day
and expected to become VFR later this afternoon. Although VFR
conditions may not last very long at the NWern terminals as isolated
to scattered thunderstorms could produce sub VFR conditions at
anytime. While the rest of the terminals are currently VFR, Hi-Res
models do suggest that a period or two of TSRA could be in the
vicinity of the terminals through the afternoon and early evening.
Generally ceiling are expected to be 2k ft in the NW and 3k to 4k
feet elsewhere overnight before another round of low stratus
develops over much of the region. Conditions are expected to improve
by mid morning to VFR conditions before the next chance of storms
move into the area ahead of an advancing frontal passage.

Outlook: Showers and storms associated with a cold front that is
expected to come through the region late Thursday will result in
flight restrictions of MVFR or lower in some areas. VFR conditions
are expected to return Friday through the weekend before another
disturbance moves into the region early next week.

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...CBL
LONG TERM...KC
AVIATION...CA