Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
754 PM EST Thu Nov 20 2025

Day 1
Valid 01Z Fri Nov 21 2025 - 12Z Fri Nov 21 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF 
CENTRAL AND NORTHEAST TEXAS INTO CENTRAL ARKANSAS...

...Central and Southern Plains into the MS Valley...
Convection over TX is moving eastward at a steadier pace this
evening, which should limit the areal extent and magnitude of the
flash flood risk going forward. However, rainfall rates are still
intense, so where we are able to get some brief training an 
isolated to scattered flash flood risk still exists. One corridor 
to keep an eye on is northeast TX into southwest AR where a more 
organized MCS is tracking. There are some signs that enhanced 
southerly flow ahead of this feature will continue to allow for 
convective development downstream of this MCS. If this downstream 
activity is able to grow in both coverage and intensity enough, 
then we will see a more pronounced training risk as the MCS moves 
across tonight. 

Also keeping an eye on redevelopment closer to the cold front over
central TX, as some of the areas hard hit earlier today could see 
another round of convection. Fortunately it looks like this 
activity will probably not increase in intensity/organization until
after it passes east of the hardest hit portions of south central 
TX...but it will be a close call. Either way this activity should 
stay progressive, but even a quick 1-2" of rain could cause flood 
concerns if its over areas recently saturated by rainfall earlier 
today.

Over portions of central and eastern KS 1-3" of rain is expected
through 12z. Lower instability here will generally keep rainfall
rates lower, although strong lower level convergence could still 
help locally push rainfall over 1"/hr. In general the lower rates 
are expected to reduce the flash flood risk, but areas of slower 
responding areal flooding are possible.

...Southern California... 
We maintained a Slight risk across portions of southern CA for the
overnight period. Thus far rainfall rates have not been that high,
although we do expect to locally see an uptick in rainfall rates 
late this evening as some weak instability moves onshore just ahead
of the surface low. Overall this is a lower end Slight risk, as 
any flash flood impacts are expected to stay pretty localized. 
However, recent HRRR runs indicate that shallow convection getting 
into the immediate coast could produce up to 1" of rain in an hour 
in and around the Las Angeles area. Rates this high should stay 
very localized, but if they occur over an urban area then isolated
flash flooding is possible.

Chenard


Day 2
Valid 12Z Fri Nov 21 2025 - 12Z Sat Nov 22 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHEAST California AND SOUTHWEST ARIZONA...

20Z Update: Little to no changes to the previous forecasts as the
overall synoptic pattern maintains continuity with little run-to-
run variance in both the QPF presentation and evolution.

Kleebauer

..Previous Discussion..

Model guidance continues to lift the Plains system northward into
portions of the Ohio Valley. Above normal levels of moisture being
transported into the region from the south and encountering an east
to west oriented boundary...there is still the possibility for
isolated areas of moderate to heavy rainfall that leads to spotty
problems from run- off. However...the flow aloft becomes
increasingly flat and confluent during the day which will reduce
the risk of any excessive rainfall.

In California...we will carry a Slight risk across portions of the
desert areas of southeast CA into southwest AZ. Lobes of vorticity
east of the closed low will produce periodic rounds of showers and
embedded thunderstorms. Instability looks pretty weak, which will
likely be a limiting factor, however some brief heavier rates are
still possible from short training segments within the deep layer
southerly flow.

Bann/Chenard

Day 3
Valid 12Z Sat Nov 22 2025 - 12Z Sun Nov 23 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann/Kleebauer


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