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FOUS30 KWBC 070022
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
822 PM EDT Sat Jul 6 2024

Day 1
Valid 01Z Sun Jul 07 2024 - 12Z Sun Jul 07 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
GEORGIA AND THE CAROLINAS...

01Z Update:

...Gulf Coast to the Carolinas...
Afternoon to early evening convection continues along the
stationary boundary draped along the Gulf Coast region, with a few
clusters of more organized convection across southern MS. This
activity is within the very moist airmass characterized by PWs well
above 2" based on current blended TPW products. With the loss of
daytime heating over the next few hours, this activity is expected
to diminish in coverage and intensity, but until then a few
instances of flash flooding will be possible due to localized but
intense rain rates (1-2" hourly totals).

Further east into Georgia and into the Piedmont region of the
Carolinas, a better focus of deep convection thanks to a surface
trough ahead of the stationary boundary along with the very moist
airmass is fueling more organized and intense thunderstorms. The
18Z HREF neighborhood probabilities show support for isolated 2-4"
hourly totals through about 03-04Z, particularly over east-
central GA where several colliding clusters are expected to come
together. Further north into SC/NC Piedmont, slower moving and very
efficient rain producing thunderstorms will linger into the late
evening hours. Isolated 1-2" hourly totals will be possible and
flash flooding remains a concern particularly for the urban areas
until convection diminishes after midnight. Some of the flash
flooding could be locally significant, particularly over east-
central Georgia.

...Texas...
Showers and thunderstorms, some of which are locally heavy, will
continue across portions of central Texas for a few more hours
until peak heating wanes and convection diminishes. Until then, an
isolated flash flood threat will continue for localized 2-3" totals
as supported by the 18Z HREF neighborhood probabilities.

...Plains into the Upper Midwest...
Closed 500 mb low over the eastern Dakotas within the broader
troughing will help continue showers and thunderstorms over
portions of the Upper Midwest (moving from the eastern Dakotas into
MN) where the combination of locally heavy rainfall (up to 1" in
spots) over more saturated areas due to recent heavy rainfall could
bring a few instances of flash flooding for a few more hours until
convection diminishes later this evening. To the south, a few
different complexes are organized over NE and KS. While these areas
are likely to be more progressive and limiting the flash flood
threat, the intense thunderstorms will still be capable of
producing rain rates above 1-2"/hr at times and could bring a few
instances of flash flooding.


Taylor


Day 2
Valid 12Z Sun Jul 07 2024 - 12Z Mon Jul 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
KANSAS AND OKLAHOMA AS WELL AS THE CENTRAL AND SOUTHERN COAST OF
TEXAS...

...Coastal Texas and Louisiana...

The latest (15Z) NHC forecast track for Beryl has remained
generally consistent from the 09Z forecast, which positions Beryl
just offshore the mid-Texas coast early Monday. Outer bands will
wrap into the coast from South Texas up along the coast into far
southwestern Louisiana, though the bulk of its precipitation shield
will lie in the Day 3 period. Maintained the previous Slight Risk
outline right along the coast due to the expected heavier rainfall
to be moving onshore very early Monday. Future adjustments in the
track of Beryl may shift the ERO areas a bit, depending on its
evolution in the next 24-36 hours.

...Southern and Central Plains...

Organized convection is likely over portions of KS and OK Sunday
into Sunday night. 12Z CAM guidance still shows quite the
impressive model QPF agreement/signal; thus, forecast confidence is
above average with this event. Interestingly the pattern appears
to favor a rather progressive convective complex...and PWs are not
forecast to be overly high either. The impressive QPF from the
models, while somewhat surprising, is likely indicative of the very
strong mid/upper level forcing and low level frontal convergence
in play. A look at layer IVT suggests we may start to see some low
level connection to the moisture plume ahead of Beryl, so this is
certainly something to keep an eye on and could act to enhance
rainfall efficiency. Either way this is a solid Slight risk with
higher but sub-Moderate probabilities within that outline. The
apparent progressiveness of convection keeps the risk from going
higher...but will need to continue to monitor. It has also been dry
lately in much of the region, which can increase the flash flood
threat due to hydrophobic soils. Regardless, with 12Z HREF
neighborhood probabilities of >2"/hr rainfall rates ~10-30% for
several hours Sunday afternoon and early evening, Slight Risk is
certainly warranted.

...Southeast...

With the stalled front across the region convection is expected to
persist, maintaining an isolated threat for flash flooding
concerns. PWs will remain above the climatological 90th percentile,
and layered IVT suggest we may see some mid/upper level moisture
connection to Beryl. The intrusion of tropical moisture may help
bolster rainfall efficiency in what will already be a favorable
environment for heavy rainfall rates. A Marginal Risk remains in
effect from southern Alabama to northern Florida and northward to
southeast Virginia. Some of this will be dependent on rainfall
today (Saturday) and if there is any overlap.

Fracasso/Campbell


Day 3
Valid 12Z Mon Jul 08 2024 - 12Z Tue Jul 09 2024

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF EASTERN TEXAS...

The National Hurricane Center has Beryl forecast to make landfall
during the first few hours of this forecast period somewhere up the
coast from Corpus Christi, TX (please see the NHC website for the
latest information). The guidance continues to suggest a fairly
compact storm, therefore the QPF swath is expected to be relatively
narrow and oriented N-S as the storm lifts northward across
eastern Texas. The highest QPF amounts will still follow the track
or slightly east of the path through this period. A reasonable
analog is Tropical Storm Bill (2015) which recurved a bit farther
west than what Beryl is expected to do. Max QPF with Bill was ~15"
within a broad area of 3-6" or so. Latest WPC areal average QPF of
3 to 7 inches can be expected with maximums climbing into the
double digits. The Moderate Risk was maintained for this period
from Coastal Texas into eastern Texas. A Slight Risk spans the
coastline from south of Corpus Christi to east of Lake Charles and
northward into southwest Arkansas. A Marginal Risk covers from
South Texas to central Louisiana and from the Texas/Oklahoma
Panhandles to Southern Missouri, tied to the frontal boundary to
the north. Model spread increases toward the end of this period and
the recent guidance showed a quickening trend with Beryl, but this
still fit well within the Slight Risk outline into Arkansas. Note
that the placements of the Excessive Risk areas will largely be
dependent on the NHC track so stay tuned for future adjustments.

...Southeast...

Lingering boundary in the Southeast will again act as a focus for
convection on Monday, and maintained the Marginal Risk here. With
additional showers and thunderstorms expected over recent wet
soils, the threat for isolated flooding concerns will remain
elevated for this part of the country, despite the lower QPF signal
in the guidance. Will gain more insight once we move into the CAM
window, and also with better clarity on the speed of recurvature of
Beryl.

Fracasso/Campbell


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt