363
FXUS66 KSTO 152007
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
107 PM PDT Sun Sep 15 2024

.Synopsis...
Cooler and more unsettled weather thru mid-week with a chance of
showers and thunderstorms tonight into tomorrow morning. Dry and
warmer weather returns late in the week.

&&

.Discussion...
Satellite this morning shows some a line of cumulus and high
clouds over Northern CA, ahead of the weather system moving down
from the Pacific NW. Radar returns showed some virga over the
northern half of the CWA, evident of the increasing moisture
moving into the area.

Chances for showers and thunderstorms are projected to begin over
the northwestern portions of the CWA near the Coastal Range and
adjacent are this evening before another push of rain over the
Sierra late Monday morning through Monday evening. Showers will
be scattered in nature with best chances for thunderstorms across
the Coastal Range and the western portions of Shasta, Tehama, and
Glenn counties from this evening to Monday morning (15-30% chance
of thunderstorms). The 12z HRRR run shows showers tapering off by
early Tuesday morning. For total rain amounts from this evening to
Monday night, NBM probability shows a 40-75% chance of amounts
greater than 0.25", highest over the Southern Cascades.

With this, there is also the potential for some snowfall at the
higher elevations of the Sierra above 7000 feet. Warm roads may
mitigate any significant accumulations and is not expected to
impact major roadways.

After Tuesday morning, things quieten with a brief reprieve from
active weather before another weather system moves in from the
northwest Tuesday evening through Wednesday night. This will bring
another round of scattered showers and isolated thunderstorms
with breezy winds near storms. NBM forecasts 0.50-1.00" over the
Sierra and 0.10-0.50" elsewhere with a 15-25% chance of
thunderstorms over the Sierra. There is a 40-70% chance of amounts
over 0.50" across the Sierra north of I-80 on Wednesday.

Temperature highs will continue its cool trend with highs in the
upper 70s to low 80s through Wednesday before temperature begin to
warm back to normal.

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...
Ensembles continue to vary slightly on the timing and movement of
an upper level low as it progresses through interior NorCal. The
NBM still favors the slower EC ensemble, which will keep shower
chances in the Sierra Nevada throughout the day on Thursday. The
best chances will be along and south of I-80, with the NBM
advertising around a 10-40% chance of rainfall totals greater than
0.25" inches on Thursday. Locally breezy to gusty northerly winds
may develop Thursday as well as the trough continues to slide off
towards the east and ridging builds in the eastern Pacific.
Friday, ridging continues to move inland and as a result high
temperatures will climb into the low to mid 80s and continue to
warm as we move into the weekend. Ridging may also inhibit the
Delta breeze from cooling Delta breeze influenced areas over the
weekend as well, with high temperatures climbing into the low 90s.
As we warm, the area should also be free from any precipitation
chances Friday through Sunday.

&&

.AVIATION...
MVFR/IFR conditions spreading across interior NorCal through the
forecast period . Isolated tstms possible N of I-80 aft 21z. In
Central Vly, areas of Sly sfc wind up to 15 kts. Vcnty of Delta,
SWly sfc wind 15-25 kts with local gusts to 35 kts. Over hyr trrn,
areas of SWly sfc wind gusts 30-40 kts.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$