Mesoscale Precipitation Discussion 0006
NWS Weather Prediction Center College Park MD
156 PM EST Mon Jan 05 2026

Areas affected...north-central CA

Concerning...Heavy rainfall...Flash flooding possible

Valid 051854Z - 060400Z

SUMMARY...Isolated flood/flash flood impacts will be possible
across portions of central to northern CA through the late
evening. Peak hourly rainfall of 0.50 to 0.75 inches and peak
additional total rainfall of 2 to 3 inches (locally higher
possible) can be expected through 06Z.

DISCUSSION...GOES West 6.9 micron imagery showed a mid-level
vorticity max/closed low centered near 36.6N 127.0W at 18Z,
embedded within a larger scale trough axis off of the West Coast.
At the surface, low pressure was located ~70 miles northwest of
Point Arena, with a cold front extending south and southwest. Over
the past few hours bands of moderate to heavy rain have been
observed moving across the northern CA Coastal Ranges with current
radar imagery showing an axis of locally heavy rain oriented SSW
to NNE into the North Bay region of San Francisco. In addition,
infrared imagery showed a band of colder cloud tops just ahead of
the cold front where weak MLCAPE values up to ~250 J/kg were
estimated by short term RAP forecasts and SPC mesoanalysis data.

850-700 mb winds were from the southwest at 30 to 40 kt ahead of
the offshore trough axis into north-central CA with PWAT values
ranging from 0.6 inches within the northern Sacramento Valley to
about 0.9 inches just west of San Francisco Bay. Short term
guidance is in good agreement with the track of the mid-level
vorticity max/closed low slowly advancing toward the CA coast
between Point Arena and San Francisco through about 03Z at which
point stalling and eventual southward translation are forecast.
The effect of these larger scale features will translate at the
surface to a SSW to NNE band of heavy rain advancing eastward
toward the central CA coast with embedded peak hourly rainfall
between 0.5 and 0.75 inches (locally higher possible) through the
afternoon and evening. Hourly rainfall up to about 0.5 inches in
an hour will be likely for the northern Sacramento Valley where
weak MLCAPE values up to 250 J/kg area forecast by the RAP from
about 00Z-04Z.

Recent heavy rainfall has left this region of CA more susceptible
to heavy rainfall compared to normal, and there will be the
typical enhancement of heavy rain impacts in and around the San
Francisco Bay region to contend with. Within areas of higher
terrain, localized landslides/rockslides will be possible and
flooding of creeks, streams, urban areas and other
low-lying/flood-prone locations will remain possible through about
04Z. Beyond 04Z, low level winds are likely to weaken and orient
more parallel to the coastline, diminishing the potential for
flooding impacts across the region.

Otto

ATTN...WFO...EKA...MTR...STO...

ATTN...RFC...RSA...NWC...

LAT...LON   41122240 41062196 40692174 40362164 39812141
            39542172 38992204 38132212 37402214 36942223
            36952281 37572330 38122362 38962364 39842330
            40422311 40932275