FOUS30 KWBC 130826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 AM EST Fri Dec 13 2024

Day 1
Valid 12Z Fri Dec 13 2024 - 12Z Sat Dec 14 2024

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

Maintained the Slight Risk area over portions of northwest
California with only minor adjustments needed based on latest
deterministic and ensemble guidance. Rainfall should be growing in
both areal coverage and intensity today as a plume of moisture is 
directed from the eastern North Pacific into northwest California. 
Event total rainfall amounts through early Saturday morning are 
still forecast to be in the 3 to 5 inch range across the Slight 
Risk area. By late tonight/early Saturday morning the heavier rain 
will shift southward as a strong mid level shortwave approaches the
region. This feature will act to increase large scale ascent, 
while also cooling the mid levels enough to allow for some weak 
instability to develop within the IVT axis. The 13/00Z HREF 
neighborhood probabilities of rainfall exceeding 0.5" in an hour 
are over 50% across most of the Slight risk...both across the most 
favored upslope areas and also within a narrow southward shifting 
axis of stronger convergence. This does not appear to be a high end
event given the progressive nature of the system...although some 
creek and stream flooding and a few mudslides will be possible.

Bann


Day 2
Valid 12Z Sat Dec 14 2024 - 12Z Sun Dec 15 2024

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

Rainfall associated with an atmospheric river will be on-going as
the Day 2 period begins at 14/12Z...with the plume of deepest
moisture continuing to be directed in to parts of northwest
California although the axis of heaviest rainfall rates/amount will
be gradually be easing eastward in time with the main shortwave
while being shunted southward ahead of the surface cold front. 
southward with time. The higher rates should quickly diminish with 
the departure of the shortwave moves...with the risk of heavy rain 
over by 18z. Thus this Slight risk is really only for the first few
hours of this day 2 period.

Bann

Day 3
Valid 12Z Sun Dec 15 2024 - 12Z Mon Dec 16 2024

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

Bann
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