FOUS30 KWBC 052011 CCA
QPFERD

Excessive Rainfall Discussion...CORRECTED
NWS Weather Prediction Center College Park MD
311 PM EST Mon Jan 5 2026

Day 1
Valid 16Z Mon Jan 05 2026 - 12Z Tue Jan 06 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE CENTRAL
TO NORTHERN CALIFORNIA COAST AND NORTHERN CALIFORNIA...

...16Z update...

The forecast reasoning in the previous discussion remains valid and
only minor adjustments were made to the existing Marginal Risk
across north-central California. The primary shortwave embedded
within the longwave trough in the eastern Pacific was centered near
128W and will advance closer to the north-central California coast
between Point Arena and San Francisco Bay through 00Z. After 00Z,
the closed mid-level low will elongate and weaken as it moves
southward offshore of the coast. There is good model agreement in
this forecast and the corresponding low level wind field becoming
largely parallel to the central California coast overnight while
weakening.

The main concern for heavy rain related impacts will be prior to
03Z Tuesday where isolated hourly rainfall of 0.50 to 0.75 inches
primarily focused along the Coastal Ranges toward the San Francisco
Bay region later today with isolated hourly totals near 1 inch
possible. East of the Coastal Ranges, peak hourly rainfall up to
~0.50 inches is expected. Additional peak rainfall through 12Z
Tuesday will be in the 2-4 inch range

Otto

...previous discussion follows...


Upper disturbance off the California coast will meander to the
southeast closer to the coastal plain, eventually pinching off the
mean trough centered to the north and closing off into an ULL as it
migrates down near the latitude of the Bay area. Proximity of the
disturbance and prevailing flow will send a modest IVT pulse
(300-400 kg/ms) crashing into the northern CA coastal plain with
some minor protrusion of the IVT signature inland with a secondary
QPF maxima forecast around the Trinity Mountains over into Shasta
National Forest domain. Hi-res deterministic output is pretty
consistent with the axis of heaviest precip focused from the King
Range down towards Santa Rosa, north of the Bay area with the
latest HREF EAS probs for 1" running between 60-90% for much of
that location with another prob max focused near Mount Shasta.

The main threat for this setup is easily over any urbanized zones
and remnant burn scars across northern CA leading to mainly a
lower-end flash flood concern in the grand scheme of the setup. IVT
signature is one that historically yields more isolated flash flood
threats with the primary focus typically aimed at that coastal
urban centered from the Bay area up towards Eureka, and over the
northern valley locations like Redding. This is where the MRGL
risk was maintained during the forecast as the trend for the
southern edge of any heavy rain prospects south of San Jose has all
but disappeared on guidance. It's still something we'll monitor
for any last minute trends back, but guidance favors mainly the
area north of the Bay at this time. Total QPF for the impacted
areas will be between 1.5-3" with a max between 4-5" for the
coastal ranges north of the Bay area, and over the Shasta National
Forest.

Kleebauer


Day 2
Valid 12Z Tue Jan 06 2026 - 12Z Wed Jan 07 2026

The probability of rainfall exceeding flash flood guidance is=20
less than 5 percent.

Fracasso


Day 3
Valid 12Z Wed Jan 07 2026 - 12Z Thu Jan 08 2026

The probability of rainfall exceeding flash flood guidance is=20
less than 5 percent.

Fracasso


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!6iQ4L-UbvWDSw4dGlZLIfuz2wLaBHsz6i675pOOl0HeF= nq7UiRCdn2XTQTHlvTZRPJiEnuuUJnUpGJUOw-ddO03kBpQ$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!6iQ4L-UbvWDSw4dGlZLIfuz2wLaBHsz6i675pOOl0HeF= nq7UiRCdn2XTQTHlvTZRPJiEnuuUJnUpGJUOw-dduFdKZ8M$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!6iQ4L-UbvWDSw4dGlZLIfuz2wLaBHsz6i675pOOl0HeF= nq7UiRCdn2XTQTHlvTZRPJiEnuuUJnUpGJUOw-dd2gUpZv8$=20

=3D =3D =3D
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