FOUS30 KWBC 020041
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
841 PM EDT Fri Nov 1 2024

Day 1
Valid 01Z Sat Nov 02 2024 - 12Z Sat Nov 02 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF=20
SOUTHEASTERN NEW MEXICO INTO FAR WEST TEXAS...

Training convection this evening has resulted in isolated flash
flooding across portions of central LA. HRRR guidance indicates=20
the convergence axis driving this activity should weaken over the=20
next couple hours, with convective intensity and training=20
potential expected to diminish as well. Cloud tops are beginning to
show some signs of warming, so maybe this weakening trend is=20
beginning. Nonetheless, a localized flash flood risk is possible=20
for the next several hours.

Otherwise attention turns to portions of southeast NM for the
overnight hours into Saturday morning. An increasing and robust
southeasterly low level jet is rapidly returning moisture into the
region, and convergence on the nose of this moisture transport=20
axis should help initiate convection within the next several=20
hours. Larger scale forcing in the form an an approaching longwave
trough and upper jet streak to the north should increase=20
overnight, which should help convection grow upscale in nature=20
after 06z. Some southwest to northeast training appears likely, and
as is seemingly often the case over this region, would not be=20
surprised if convective coverage ends up a bit larger than depicted
by the HRRR. Overall expect 1-3" of rainfall through 12z Saturday,
but a narrow swath of 3-6" seems possible along the convergence=20
axis where training is maximized.=20

Recent HRRR runs have trended a bit north with the maximum=20
QPF swath in recent runs, and so have also expanded the Slight risk
in this direction as well. Will not cut back on the southern=20
extent of the Slight risk as some model guidance still favors this
corridor. Overall the updated Slight risk encompasses the model=20
spread and the bit broader nature accounts for the potential of a=20
more organized convective area as the night progresses.

Chenard


Day 2
Valid 12Z Sat Nov 02 2024 - 12Z Sun Nov 03 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...

2030Z Excessive Rainfall Discussion Update...
There was a subtle westward/southward shift in the axis of heaviest
rainfall shown in the 12Z numerical suite of guidance. The axis of
the high-end Slight risk area was elongated in a similar fashion
with a more subtle shift in the axis, The expectation about the
very dry antecedent conditions helping to mitigate the overall
excessive rainfall impacts still hold.

Bann


Previous Discussion...

Additional Gulf moisture will track north on a LLJ across Texas and
into the Slight Risk area on Saturday. PWATs may exceed 1.75
inches. The trough over the intermountain west will slow to a
crawl, while much faster moving shortwaves round the base of the
trough and move north up the Plains. Multiple rounds of storms are
expected from north Texas to the Kansas City metro. The heaviest
rains are likely across central Oklahoma, where a higher-end Slight
is in place.

As on Day 1, extremely dry antecedent conditions are in place over
much of the Slight Risk area, with soil moisture levels from Nasa
Sport at under 10%. While clay soils may start out hydrophobic, for
the most part, the empty creeks and streams should work to prevent
much flash flooding. Given the available moisture for the storms to
work with, training is likely, which should raise the flash
flooding potential to widely scattered. The Slight Risk area was
expanded a bit towards the northeast and now approaches the Kansas
City metro. Meanwhile a portion of north Texas was removed based on
the latest guidance. Nonetheless a slower forward progression of
the entire pattern should concentrate the worst impacts from any
flash flooding in a smaller corridor highlighted by the Slight
Risk. No major changes were made to the inherited risk areas. The
greatest uncertainty is how well the dry soils will absorb the
sudden abundance of moisture as the drought conditions in place now
across the southern Plains will help in many cases to mitigate any
potential flooding impacts.

Wegman

Day 3
Valid 12Z Sun Nov 03 2024 - 12Z Mon Nov 04 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN OKLAHOMA AND THE OZARKS...

2030Z Excessive Rainfall Discussion Update...
The 12Z suite of guidance offered good support for the placement of
the Moderate Risk area. Uncertainty remains as to exactly how well
the dry soils will absorb the rainfall and exactly how much of an
overlap there will be with the rainfall on Saturday. The model run
to run consistency to maintain the Moderate risk outlook area.

Bann

Previous Discussion...

The inherited Moderate Risk area was shifted to the southeast a few
rows of counties in Oklahoma with this update. This is in response
to the latest guidance suggesting the heaviest rainfall will
fall more across eastern Oklahoma through the Ozarks of western
Missouri. A big factor as to the flooding potential will be
rainfall from the Day 2/Saturday period, which alone is expected to
result in a widespread 3-5 inches of rain across the Moderate Risk
area. When added to the 2-4 inches of rain expected Sunday for many
of the same areas, even the antecedent drought conditions in place
now should not be able to handle two consecutive days of heavy
rain. The primary point of uncertainty is how much overlap there
will be between the two days. The slow moving nature of the entire
system should mean much of the Moderate Risk area will be in the
overlap. Urban and flood sensitive areas are likely to have the
greatest risk of impacts from training storms, with the strongest
storms and heaviest rains expected Sunday night. The storms will
continue north and east across northern Missouri and into Iowa and
Illinois, where the Slight Risk was extended based partially on
prior days' rainfall. Regardless, outside of the Moderate Risk
area, antecedent dry conditions will have a bigger mitigating
impact on the flooding.

Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!5kmUC1SiAotJQqvC9m6TUNm7Jf4ADeIfkR2nhhQM7Ju2=
l4G2TBzZuHq_bBaqLU-8qxmrkUzUcjfhtOsvvgzzFUbXPMc$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!5kmUC1SiAotJQqvC9m6TUNm7Jf4ADeIfkR2nhhQM7Ju2=
l4G2TBzZuHq_bBaqLU-8qxmrkUzUcjfhtOsvvgzziP_rrww$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!5kmUC1SiAotJQqvC9m6TUNm7Jf4ADeIfkR2nhhQM7Ju2=
l4G2TBzZuHq_bBaqLU-8qxmrkUzUcjfhtOsvvgzz8U9ole4$=20

=3D =3D =3D
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