Valid 071200Z – 081200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
NORTHERN CALIFORNIA…
…SUMMARY…
A few strong thunderstorms are possible across portions of northern
California Saturday afternoon.
…Northern CA…
Upper trough off the Pacific coast is forecast to shift east during
the day1 period. As a result, 500mb speed max will translate into
northern CA by 08/00z which should encourage surface confluence zone
across the Sacramento Valley during the afternoon. While the primary
surface front should hold offshore through sunset, some instability
is expected to materialize across the Sacramento Valley due to weak
boundary-layer heating. Latest RAP guidance is more buoyant than the
NAM across this region with forecast instability that could allow a
few robust updrafts. RAP 23z forecast sounding at BAB exhibits 800
J/kg SBCAPE with deep-layer shear supportive of rotating updrafts;
although, NAM displays considerably less instability. If surface
temperatures can warm into the upper 50s/near 60F, convection that
develops north of the 500mb jet will have a tendency to rotate. As a
result, a few weak supercells may ultimately evolve which would pose
a risk of producing a brief weak tornado.
..Darrow/Squitieri.. 12/07/2019
$$