NWS Area Weather Forecast Discussion
County Warning Area [CWA]: STO Regional NWS Weather Office: Sacramento, CA
FXUS66 KSTO 182119
Area Forecast Discussion
National Weather Service Sacramento CA
219 PM PDT Wed Sep 18 2019
Showers and storms are expected to continue across the region this
afternoon and evening as a weather system moves through. Showers
linger across the mountains Thursday, with dry and mild weather
returning through the early weekend. Another system skims the area
Sunday possibly bringing additional chances for mountain
precipitation. Breezy north winds may be seen across the Valley
early next week.
Early afternoon analysis shows a line of showers mainly just south
of the I- 80 corridor slowly moving southeast as the surface
front pushes across the area. To the north, showers and storms
have begun to push inland into far northern California with this
activity expected to continue through the afternoon and evening.
The upper trough will continue to move inland across NorCal this
afternoon with increasing thunderstorm activity ahead of this
feature. The best chances for storms still looks to be north of I-
80, with the HREF targeting the best areas for stronger storms and
heavier rainfall mainly in the foothills near Butte/Yuba Counties
and further north in the Shasta/Tehama County area. Soundings
continue show weak rotation in the low levels near the Chico area,
and a funnel cloud or two cannot be ruled out. The main hazards with
any storms will be heavy rain, small hail, and lightning.
As storms move from the foothills into the mountains, there is a
chance for the heavier cells to lower snow levels and produce brief
periods of heavier snowfall across Sierra passes. Overnight,
lingering showers may produce continued light snow across the
highest peaks and passes of the Sierra.
As for overall precipitation totals, rain will generally be light
(around and below 0.30 inches), expect where thunderstorms form and
locally heavy rainfall of up to an inch may occur. The Valley should
expect to see much lighter amounts with precipitation ending by the
late afternoon for most locations.
Besides some lingering showers in the Sierra tomorrow, dry weather
is expected to return to NorCal Friday into the weekend. Northerly
winds return Thursday and Friday in the Sacramento Valley, but look
relatively light at this time. As ridging builds back in Saturday,
temperatures rise to near average with Valley temperatures ranging
from the mid 80s to around 90 degrees, and mountain temperatures
generally in the 60s.
.EXTENDED DISCUSSION (Sunday THROUGH Wednesday)...
A trough is forecast to influence the region starting Sunday. A
few scattered showers will be possible over the mountains of
northern Shasta County extending into western Plumas County as
well the northern Sierra crest Sunday night. This region of low
pressure is expected to work its way south along the Sierra Crest
and become a closed low pressure. There is some disagreement
between models as to the location of this low as we go into next
week. Downsloping northerly flow and potentially gusty conditions
could lead to some elevated fire weather concerns on Monday.
The front has passed through the region leaving partly to mostly
cloudy skies overhead. Most TAF sites are reporting VFR conditions
which will likely be the case for most areas through the evening
hours; however, lingering showers and thunderstorms will be
possible. Thunder activity should remain confined to the mountains
and KRDD and KRBL areas, while showers remain scattered.