FOUS30 KWBC 171556
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1056 AM EST Sun Nov 17 2024

Day 1
Valid 16Z Sun Nov 17 2024 - 12Z Mon Nov 18 2024

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

1600Z Update...

The 12Z HREF guidance along with 06Z RRFS/REFS output continues to
support a locally heavy rainfall event across areas of the southern
Plains by this evening and extending into the overnight period. There
has been some shift farther west with some of the swaths of heavy 
rainfall potential across west TX as some of the individual CAMs
are supporting the heavier rainfall/convection along the immediate
cold front and in close proximity to the deepening surface low 
that will be evolving across the TX High Plains tonight. However, a
complication to the rainfall forecast is the downstream evolution 
of convection along the front ahead of the surface low involving 
areas of northwest TX through southwest to central OK. This is 
where strong moisture convergence and forcing may foster a threat 
for some training areas of convection that become aligned in a 
southwest to northeast fashion. Overall, still expecting some 
swaths of 2 to 4 inch rainfall totals, with isolated potential for 
heavier amounts and especially across northwest TX into southwest 
OK where the better convective training threat will exist. Given 
the latest CAM guidance, the Slight Risk area has been expanded
somewhat to account for the varying modes of convective evolution 
that are expected this evening and overnight.

Elsewhere, no changes have been made to the previous D1 outlook
including the Marginal Risk area across western OR where there
continues to be some lingering, but modest atmospheric river
activity.

Orrison

Previous Discussion...

...Southern Plains...

A southern stream cutoff low is expected to eject into the Plains
today with very impressive IVT and accompanying anomalous PWs and
forcing as it moves across Texas and Oklahoma by this evening into
the overnight hours. This looks to be enough to overcome the
limited forecast instability and result in deep convection and
heavy rainfall rates across portions of the Southern Rockies and
the adjacent Southern/Central Plains. Guidance continues to suggest
2-4" of rain (per latest HREF and WPC QPF), but would expect
isolated swaths as high as 4-6" within this setup (indicated by
some of the heaviest CAMs). The overall progressive nature of the
system and limited instability will cap the upper bound of rainfall
totals, but this system is dynamic enough with plentiful moisture
to suggest at least localized flash flooding is likely. A Marginal
Risk area remains in effect for central/eastern New Mexico,
northern Texas, most of Oklahoma and southern Kansas. The inherited
Slight Risk area saw only minor adjustments to reflect the latest
trends and WPC QPF and spans from northern Texas/panhandle to
western Oklahoma.

...Coastal Oregon and northwest California...

A fairly progressive, weak/moderate atmospheric river will be
ongoing across the region. Total rain of 2-4" (through 12z Mon)
and hourly rainfall rates possibly approaching 0.5" within a narrow
southward shifting axis suggest that some minor flooding issues
could arise along coastal areas/mountains. A Marginal Risk area
remains in effect along the coastline.

Churchill/Campbell


Day 2
Valid 12Z Mon Nov 18 2024 - 12Z Tue Nov 19 2024

...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST AND THE PLAINS/UPPER MIDWEST...

...Central U.S. ...

The precipitation shield will shift eastward as the cold front
advances further into the Plains. Moderate to locally heavy
rainfall is expected from northern Texas to southern Minnesota with
areal average of 1 to 3 inches. The higher amounts will likely
concentrate over eastern Kansas, eastern Nebraska and western Iowa.
A Marginal Risk area was maintained once again with only minor
adjustments for this issuance (not enough confidence for 2"+ totals
to introduce a Slight Risk).

...Gulf Coast...

A plume of enhanced tropical moisture will likely advect northward
through the Gulf of Mexico well in advance of tropical cyclone
Sara; which will increase the potential for heavy rain and
localized flooding concerns along portions of the Gulf Coast. A
Marginal Risk area is in effect from southeast Texas to southern
Mississippi (changed very little from inherited with 3" localized
totals possible).

Churchill/Campbell


Day 3
Valid 12Z Tue Nov 19 2024 - 12Z Wed Nov 20 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST AND CENTRAL GULF COAST...

...Central Gulf Coast and Southeast...

By Tuesday significantly more tropical moisture will likely advect
northward through the Gulf of Mexico in association with the
remnants of Tropical Storm Sara; which will increase the potential
for heavy rain and localized flooding concerns along portions of
the Gulf Coast. An inherited Slight Risk area was maintained for
southern AL and surrounding portions of FL/GA/MS/LA, given the
potential for localized 3-5" totals (per ensemble guidance and WPC
QPF).

...Coastal Washington, Oregon, and northwest California...

Another weak/moderate atmospheric river is expected for region for
Day 3. Total rain of 2-4" (similar to Day 1) are expected with
hourly rainfall rates possibly approaching 0.5" once again suggest
that some minor flooding issues could arise along coastal
areas/mountains. An inherited Marginal Risk area remains in effect
along the coastline.

Churchill
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