FOUS30 KWBC 100720
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 AM EDT Mon Mar 10 2025

Day 1
Valid 12Z Mon Mar 10 2025 - 12Z Tue Mar 11 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Chenard


Day 2
Valid 12Z Tue Mar 11 2025 - 12Z Wed Mar 12 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Chenard


Day 3
Valid 12Z Wed Mar 12 2025 - 12Z Thu Mar 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHERN CALIFORNIA...

A deep mid level trough and cold front will move across CA
Wednesday into Wednesday night bringing widespread rain and
mountain snow to the region. The IVT axis is rather narrow and
quick moving and only forecast to peak around 400-600
kg/m/s. When combining this modest strength and lack of longevity
of these higher values...this event will likely only reach weak 
atmospheric river levels. This limitation will be partially offset
by the strength of the cold front and deep layer forcing 
associated with the synoptic scale trough and upper jet. Even so, 
rainfall totals over much of the state are unlikely to be enough to
cause much of a flood concern. Mainly looking at a beneficial 
rainfall, although some locally higher rates near the front could 
be enough to result in generally minor and localized flooding 
within urban and other prone low lying areas.

More flood impacts are possible over southern CA, specifically 
portions of Santa Barbara, Ventura and Los Angeles counties. South 
to southwesterly upslope flow into the Transverse range will likely
help enhance rainfall over this area late Wednesday night into 
Thursday morning. Also will likely have a bit better large scale 
forcing overrunning the front at the base of the mid level trough, 
helping steepen lapse rates and increasing rainfall rate potential.
Most of the weak instability is currently forecast to be post- 
frontal, but could see just enough destabilization work into the 
front to produce some localized convective elements within the 
southward shifting rainfall axis. It does seem probable that some 
0.5"/hr rainfall will accompany this front, and while any heavy 
rates will only last for an hour or two, this could be enough to 
locally increase the flash flood threat over the more sensitive 
burn scars and any flood prone urban areas. The quick shot of 
potential high rainfall rates, combined with the sensitive burn 
scars over this area, warrants a Slight risk upgrade, and localized
significant impacts are possible.

Chenard

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