Mesoscale Precipitation Discussion 0061
NWS Weather Prediction Center College Park MD
958 PM EST Sat Feb 17 2024

Areas affected...Bay Area into the Sacramento Valley

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

Valid 180258Z - 180758Z

SUMMARY...Heavy rainfall rates are expected with bands of locally
stronger convection over the next few hours. Areas of flooding
will be possible over the next few hours.

DISCUSSION...The latest GOES-W IR satellite imagery in conjunction
with dual-pol radars from the Bay Area and the Central Valley have
been showing some uptick in small-scale bands of convection with
some some cooling cloud top activity noted as a cold front arrives
in off the Pacific Ocean.

Strong forcing aloft associated with the arrival of an upper-level
trough working in conjunction with a ribbon of modest instability
and localized orographics have been allowing for rainfall rates to
increase over the last few hours, and over the last hour, some
rates have been reaching as high as 0.5" to 1.0"/hour with the
stronger semi-organized convective cells.

Over the next few hours, some semi-organized linear bands of
convection will continue to impact areas near and a bit south of
the Bay Area, but also farther east into the Sacramento Valley
where even some brief training of convection will be likely given
the orientation of the activity with the deeper layer southwest
flow aloft ahead of the upper-level trough.

Expect rainfall rates to reach easily into the 0.5" to 1.0"/hour
range with the convection over the next 2 to 3 hours, which will
foster some additional rainfall totals of as much as 1.5 to 2.5
inches.

Already there have been some areas of flooding around the Bay
Area, and additional areas of flooding will be possible as these
additional rounds of heavy rainfall advance inland. Gradually the
passage of the cold front will allow for the deeper moisture axis
to advance well off to the east, along with the better forcing
aloft, and thus the rainfall rates should gradually wane later
this evening and overnight.

Orrison

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

ATTN...RFC...CNRFC...NWC...

LAT...LON   40472215 40372146 39562094 38392081 37262113
            36982183 37012220 37542259 38672234 39422234
            40202255