Mesoscale Precipitation Discussion 0005
NWS Weather Prediction Center College Park MD
334 PM EST Sun Jan 04 2026

Areas affected...Southern CA Coastal Mountains

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

Valid 042030Z - 050400Z

SUMMARY...Narrow squall of heavy rain and embedded thunderstorms
may produce rainfall rates up to 1"/hr. Given the highly saturated
and sensitive soils along the Coastal Range and Santa Ynez
mountains, flash flooding and mudslides are possible again this
afternoon.

DISCUSSION...Doppler Radar showed a potent squall line approaching
Vandenberg AFB at 20Z moving east ahead of a weakening cold front.
Compared to yesterday, PWATs are generally topping out between
0.9-1.0" within the squall, a little less than yesterday. However,
these values are still above the 90th climatological percentile
and RAP mesoanalysis also shows the southern CA coast has >250
J/kg of MUCAPE at these storms disposal. In addition, these
squalls have upper-level support as the are located beneath the
right-entrance region of a 120kt 250mb jet streak located over the
central Sierra Nevada. Lastly, 925-700mb winds remain out of the
SW and generally between 20-30kts, which is just strong enough and
oriented favorably enough to support some upslope enhancement into
the Coastal Range and Santa Ynez. With anomalous moisture,
sufficient instability, beneficial synoptic-scale ascent, and
topographic enhancement, these storms are likely to produce
locally heavy rainfall as they move east.

The soil sensitivities in the region have only grown worse since
yesterday. MRMS CREST soil saturation over southern Santa Barbara
County is over 85% and most locations within the highlighted
at-risk area are over 50%. A recent FFW near Ventura referenced an
LSR that mentioned more issues along highway 101 with one vehicle
stuck in mud. That band of rainfall produced roughly 1.3" in under
3 hours near Red Mountain and prompted flash flooding/mudslide
issues. This approaching squall is more potent, however it is also
progressive, which should help limit the extent of the flash flood
potential. That said, the recent FFW near Ventura captures the
most notable concern-- soils and burn scars in the area are highly
sensitive and even hourly rates of 0.50-0.75" in an hour could
prompt flash flooding and mud slides in the Santa Ynez. Expect
rainfall totals to surpass 1" in the mountains which could be
enough to trigger more flash flooding in southern Santa Barbara
county this afternoon. Given the lingering instability and forcing
aloft, additional cells could flare up over the Santa Barbara
channel this afternoon and pose a flash flood threat into this
evening.

Mullinax

ATTN...WFO...LOX...

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

LAT...LON   35682058 35402035 35091995 34881962 34761913
            34721859 34521867 34291923 34271965 34241980
            34311997 34412060 34552073 34962083 35222099
            35542098