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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1155 AM EDT Fri Nov 1 2024

Day 1
Valid 16Z Fri Nov 01 2024 - 12Z Sat Nov 02 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A SMALL PORTION
OF SOUTHEASTERN NEW MEXICO...

16Z Excessive Rainfall Outlook Discussion...
No changes needed to either the Slight/Marginal risk areas
southeast New Mexico and adjacent portions of the Texas/Oklahoma
panhandles or with the Marginal risk area along the immediate Gulf
coast. With trough amplification over the western United States now
underway...flow across the Gulf coast region should begin to
back...allowing for moisture to return northward/westward leading
to expanding coverage over the southern High Plains late tonight.
Dry antecedent conditions should mitigate the risk of excessive
rainfall in most areas...with the biggest exception being in
southeast New Mexico which remains hydrologically sensitive
following significant flash flooding less than 2 week ago. So made
no changes to the Slight Risk area that was already in place...and
only minor nudges to the perimeter of the Marginal risk area.
Farther east...the HREF continues to suggest additional convection
is possible later today that will have the potential for isolated
rainfall rates of 1 inch per hour...and even a low probability of 2
inch per hour rates immediately west of Lake Pontchartrain late 
this afternoon/early evening. So no significant change made with 
that Marginal risk area.

Bann

...New Mexico and the TX/OK Panhandles...

A digging trough over the intermountain west will begin to tap into
building Gulf moisture across eastern New Mexico and the Texas and
Oklahoma Panhandles. With interactions with upper level energy,
CAMs guidance is highlighting the Slight risk area from the
Sacramento Mountains to the Texas state line for the heaviest
rains. The whole area has been very dry in recent weeks (as has
most of the country), so that should greatly mitigate the flash
flooding threat. Further, the guidance isn't in perfect agreement
on where the heaviest rains will occur...though the Slight risk
highlights where most of the guidance is. Thus...the threat is most
certainly still on the lower end of the Slight risk scale.

The storms that form over New Mexico will train northeastward
across the Panhandles. Where repetitive training can occur,
isolated flash flooding is possible, but the storms will be
stronger further south and west.

...Louisiana/Mississippi...

A convergence zone is likely to set up across the Mississippi Delta
Friday night. Slow moving convection is expected, though that
convection would likely need to move over an urban or flood
sensitive area to cause localized flash flooding. With HREF
probabilities for 3 inches of rain Friday night over 50%, a
Marginal Risk area was added with this update.

Wegman

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...

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...

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
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