FOUS30 KWBC 080758
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
258 AM EST Fri Nov 8 2024

Day 1
Valid 12Z Fri Nov 08 2024 - 12Z Sat Nov 09 2024

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

The upper level low over the Southwest and its attendant surface
low will continue moving northeast across the Plains on Friday. 
With a continued influx of Gulf moisture with precipitable water
values of 1.5-2.25" expected near the cyclone's cold front, the 
typical comma shaped precipitation footprint will develop farther
up the warm conveyor belt from Texas to Oklahoma which should occur
with precipitable water values at or above an inch. Out west in 
Colorado and New Mexico the precipitation will be mostly in the 
form of snow. Where it remains all rain, the heaviest rain will be 
from north Texas across Oklahoma and into south-central Kansas. 
Instability should be sufficient for heavy rain-related issues.

While somewhat lesser amounts of rain are expected overall for 
southern Oklahoma and Texas...greater instability there as high as
1500 J/kg of MU CAPE will favor at least some storms capable of 
heavy rainfall in that area, with hourly rain totals to 2.5" and 
local amounts as high as 6" where cells train. Meanwhile, north of
Oklahoma City, expect a much longer duration rainfall as the 
surface low takes its time getting its act together. So while 
hourly rain totals will likely be lower than further south, perhaps
1" where slantwise convection/frontogenesis aloft forces greater 
precipitation efficiency, it will be made up for by the longer 
duration of the rain.

Roth/Wegman


Day 2
Valid 12Z Sat Nov 09 2024 - 12Z Sun Nov 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSISSIPPI VALLEY...

An upper level low will move faster towards the northeast. As 
Rafael moves west over the central Gulf, a plume of moisture with
precipitable water values of 1.5-2" gets drawn north ahead of the 
surface low's strong cold front. The front will likely be the 
dominant forcing for storms in this region. As on Friday, the 
southern areas of Louisiana and Mississippi will have the greater 
moisture. MU CAPE rises towards 1000 J/kg across parts of LA/MS/TN.
Areas further north have soils which are more saturated/flash 
flood guidance is lower. The front should progress slow enough that
training storms tracking north along the front could still cause 
flooding problems, especially over portions of LA, MS, and TN. 
Hourly rain totals to 2.5" and local amounts of around 6" appear 
likely. Lingering disagreement on exactly where the maxima are 
expected kept the risk level from being raised to Moderate, though 
an upgrade remains possible in future updates should this placement
issue resolve itself and model QPF magnitudes don't back off. 

Roth


Day 3
Valid 12Z Sun Nov 10 2024 - 12Z Mon Nov 11 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST, LOWER MISSISSIPPI VALLEY...TENNESSEE VALLEY... 
AND UPPER OHIO VALLEY...

Central Gulf Coast northeast towards southwest Pennsylvania...
Moisture and instability from the Gulf gets advected from the
vicinity of Raphael northeast across portions of the Central Gulf
Coast through the Tennessee and Upper Ohio Valleys. The forward
progress of the front across much of the East should keep any
excessive rainfall concerns minimal -- some of the risk area from
eastern AR to the east-northeast just south of the OH river
accounts for recent rains/some soil saturation. The latest NCEP 
and CMC guidance suggests that Raphael gets much closer to the Gulf
Coast than the NHC forecast, which led to avoiding use of the GFS,
NAM, and Canadian guidance explicitly. Since the distance of the 
storm from the region at this time frame is unclear, it's also 
unclear how high precipitable water values get, though they should 
rise above 1.5", particularly in the southern portion of the area
near the coast, which should be enough for heavy rain concerns. It
appears that enough instability could be available along the 
immediate Gulf Coast for convection with heavy rainfall. Hourly 
rain totals to 2" with local totals to 5" appear achievable along
or near the immediate Gulf coast. Whenever better agreement 
amongst the guidance on the future of Rafael as well as the 
placement any rainfall maximum near the coast occurs, a Slight 
Risk could prove useful at that later time. To the north, hourly 
totals up to ~1" with local totals to 2" appear to be the maximum 
potential.

Pacific Northwest...
Precipitable water values rise to 0.75-1" with a front moving into
the area. Inflow from the Pacific rises to 50-60 kts from the
south-southwest near the front. In the wake of the front,
instability moves in due to colder air aloft. Hourly rain totals
exceeding 0.5" appear likely here, which would be most problematic
in burn scars. Left the Marginal Risk area intact though simplified 
the area's appearance.

Roth

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