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739
FXUS62 KRAH 090510
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
110 AM EDT Wed Jul 9 2025

.SYNOPSIS...
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Disturbances in unseasonably moist, southwesterly flow aloft will
interact with a surface trough over the Middle Atlantic and
Carolinas through Thursday.
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&&

.NEAR TERM /THROUGH TONIGHT/...
As of 249 PM Tuesday...

* Heat Advisory remains in effect for portions of central NC, where
  heat index values will range from 105 to 109 degrees

* Slow moving showers and thunderstorms possible this afternoon and
  evening.

Early afternoon satellite imagery and surface obs reveal broad
southwesterly flow at the surface (and aloft) across the area. The
combination of weak surface high pressure parked off the Southeast
coast, along with a 595dm H5 ridge near Bermuda has allowed for a
continued influx of deep level moisture into the area. PW`s range
from around 1.75 inches across the western Piedmont, to just over 2
inches across the Coastal Plain. A similar distribution is noted in
surface dewpoints, where much of the region is seeing readings in
the mid to upper 70s while the western Piedmont is lingering in the
upper 60s.  Not surprisingly, this has yielded dangerously high heat
index values across the area, with readings consistent at or above
105 degrees throughout much of central NC. The Heat Advisory remains
in effect until 8 pm tonight, although showers and thunderstorms may
provide some degree of relief beforehand. Look for daytime highs to
climb another 1-3 degrees, ultimately topping out in the mid to
upper 90s.

In terms of shower/storm chances this afternoon and evening, we are
already seeing the first hints of storm development in the mountains
as well as the Sandhills. Taking the CAMs at face value during weak
forcing regimes such as this is a challenge, as several hi-res
models are struggling to catch on to the present situation. While
individual runs of the HRRR are largely absent of convection today,
the 12Z HREF does paint a picture showing convection across the
Sandhills, southern Coastal Plain, as well as the western Piedmont
later today. This certainly makes sense given MLCAPEs up around 2500-
3000 J/KG today and a maturing cu field in satellite imagery. Going
to maintain relatively high PoPs in these areas with the inclusion
of at least some 30 PoPs everywhere later today to account for
colliding outflows and new cell development. DCAPEs are fairly high
today with values around 1000 J/KG across the western Piedmont.
While any storms that form today should be short lived given weak
steering flow aloft, they will be capable of strong winds especially
in the west. Meanwhile, steadily increasing PW values suggests that
storms will be efficient rain producers as well, and locally heavy
rainfall is a possibility today as well.

As for temperatures, it was remarkably mild this morning with many
locations only dipping into the upper 70s (RDU hit 80 which if it
stands, would tie its all time record warm minimum temperature), and
I would expect similarly warm conditions tonight, perhaps just a bit
lower given the presence of rain cooled air. Mid 70s in most
locations looks to be a reasonable forecast.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 249 PM Tuesday...

* Flood Watch in effect for portions of central NC

* Slight Risk (Level 2 of 5) of severe weather along with a Slight
  Risk (Level 1 of 5) of excessive rainfall

* Areas that saw heavy rainfall from Chantal will be the most
  susceptible to additional flooding and runoff

The large scale synoptic pattern should be relatively unchanged on
Wednesday with broad southwesterly flow remaining in place. The
surface trough should sharpen up a bit throughout the day and
convection should have a decent triggering mechanism in the form of
a weak H5 wave that is forecast to move through the western Piedmont
tomorrow afternoon. Meanwhile, continued southwesterly flow aloft
will allow PW`s to increase further, with mid afternoon values
forecast to range from 2 to 2.25 inches area-wide. Convection should
initiate by early afternoon across the area, with the western
Piedmont being the particularly favored area for development. This
area has been highlighted by SPC within a Slight Risk, with damaging
winds as the primary threat.

At the same time, 00Z and 12Z HREF have both been strongly hinting
at the potential for locally heavy rainfall across the western
Piedmont tomorrow afternoon and evening, with Local Probability
Matched Mean (LPMM) values over 3-4 inches in spots. In addition,
HREF continues to suggest some 30-50 percent probabilities of more
than 3 inches of rain in 3 hours. What`s particularly worrisome is
that some of these values are co-located in spots that saw
tremendous rainfall from Chantal on Sunday. Given the overall
synoptic setup, including anomalously high PW`s, increased areal
coverage of showers and storms, widespread saturated soils and very
low Flash Flood Guidance values, issuing a Flood Watch for portions
of central NC seems prudent. The Watch goes as far west as the Triad
and as far east as Warren Co, leaving out Wake Co and points east.
While rainfall is certainly possible (and expected) from Wake Co
eastward, these areas haven`t seen anywhere near the magnitude of
rain over the past week and soils should be able to accept a decent
amount of rain before it becomes problematic. The Watch can
certainly be expanded if there is an eastward shift in the axis of
heaviest rainfall from newer model runs. Peak timing for convection
and flood threats will be from early afternoon through early
overnight (18Z-06Z).

Now it is important to note that this setup is very different from a
tropical system moving through the region. Primarily convective
events are difficult to predict where these consecrated areas of
higher rainfall will occur and may fall outside of the more
sensitive areas altogether. Additionally, these setups more likely
result in localized areas of enhanced rainfall rather than large
swaths of flash flooding from tropical events. There are still a lot
of details to be worked out, but the pattern and ingredients appear
to be in place.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 125 PM Tuesday...

The chance of showers/storms will continue to be high in the
extended forecast, although a wash-out over several days is not
expected. Coverage should be the greatest on Thursday as an upper
trough is over the Ohio Valley, with 80-90% chances of storms across
all locations. After this, the upper flow becomes a bit more zonal
in nature, which should help to decrease the chances of
showers/storms each afternoon/evening. Once an upper high begins to
develop over the eastern Gulf Sunday into Monday, this will pump
additional moisture into the area, resuming the higher chances for
showers/storms.

Thursday remains under a marginal (level 1 of 5) severe thunderstorm
risk from the Storm Prediction Center - despite meager wind shear,
there should still be warm and moist enough conditions to prompt
some isolated severe thunderstorms. As for temperatures, values
should be relatively close to seasonal values, with highs in the
upper 80s/lower 90s and lows in the low to mid 70s..

&&

.AVIATION /05Z WEDNESDAY THROUGH SUNDAY/...
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As of 105 AM Wednesday...

Minor tweaks were made to the 06z TAFs. VFR conditions begin the
forecast period with SCT MVFR beginning to develop in between the
FAY, RDU, and RWI terminals. This appears co-located where the
heaviest rain fell this past afternoon. How this expands is
uncertain, but a slow development of MVFR to IFR cigs is expected,
especially around sunrise. Slow improvement through the morning
hours with scattered to locally numerous showers/storms expected to
develop over western NC by early afternoon (16-18z) and slowly shift
eastward through midnight. Timing of TEMPOs at GSO, INT, and RDU for
storms was tweaked based on latest hi-res guidance timing.

Outlook: Scattered storms are expected each afternoon and evening
through Fri, as a weak upper trough slowly approaches from the west;
greatest coverage through the outlook period may be Thurs. Early
morning fog and/or stratus will also be possible. Storm coverage
decreasing a bit this weekend as westerly flow aloft takes hold.
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&&

.HYDROLOGY...
As of 249 PM Tuesday...

River Flood Warnings remain in effect for a few locations across
central NC. As of this afternoon, this includes the following:

Little River at Manchester
Cape Fear at Fayetteville

Additional rainfall is expected this afternoon, but especially
Wednesday through Friday when slow moving thunderstorms are forecast
across the western Piedmont. Naturally, given the heavy rainfall
from Chantal on Sunday, soils are saturated across portions of
central NC and it won`t take anywhere near as much rainfall as it
normally would to produce additional flooding. Flash Flood Guidance
from the River Forecast Center suggests that only 1.5-2.0 inches of
rain in a 1 hour period could lead to additional flooding, which is
certainly in the realm of possibility given the synoptic
ingredients in place through the end of the week. The Flood Watch
may ultimately need to be expanded in both time and space depending
on where new rainfall occurs.


&&

.RAH WATCHES/WARNINGS/ADVISORIES...
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Flood Watch from this afternoon through late tonight for NCZ007>010-
021>025-038>040-073>076-083>086.
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&&

$$
SYNOPSIS...MWS
NEAR TERM...Leins
SHORT TERM...Leins/Swiggett
LONG TERM...Green
AVIATION...Swiggett/MWS
HYDROLOGY...Leins