441
FXUS66 KSTO 190414
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
914 PM PDT Thu Jun 18 2026

Evening Update:
Confidence has increased in thunderstorm probabilities and
coverage for Friday morning through afternoon. Red Flag Warning
has been issued for portions of Shasta County for lightning
outside the main precipitation core in wet thunderstorms, isolated
dry thunderstorms and gusty outflow winds. The rest of the AFD is
unchanged, see WWA section at the bottom for updated RFW details.
We have also added in shower/thunderstorm chances for Valley,
foothills, and mountain areas north of Interstate 80 for this
evening into the late night due to observed conditions.

For additional details on weather and expected impacts over the
next 7 days, please visit weather.gov/sto/briefing.


.KEY MESSAGES...

 - Cooler and more seasonable weather through Saturday before a
   return to hot and dry conditions Sunday through next week.

 - Elevated fire weather conditions are anticipated due to the
   potential for elevated mountain thunderstorms and gusty
   thunderstorm outflow winds.

&&

.DISCUSSION...
Conditions across the area this afternoon show mostly sunny skies
with temperatures in the 80s to mid 90s for daytime highs.
Warmest temperatures are expected in the northern Sacramento
Valley. Upper level pattern has a weak shortwave moving along the
California coast and shifting inland through the early part of the
weekend. Moisture influx and instability increase as the
shortwave moves onshore. HIRES guidance has indicated the
potential for isolated thunderstorm activity within the Sierra for
this afternoon and evening (along and south of I80), with
soundings indicating modest moisture in the low levels along and
west of the crest. There is a potential for a few isolated dry
thunderstorms mainly in the Sierra and along the crest this
afternoon/evening. Probabilities are 20 percent for occurrence as
the soundings indicate sufficient moisture content. None the less,
this brings the elevated fire weather concerns for today.

Chances for continued isolated showers and thunderstorms overnight
and into Friday, with coverage increasing along the northern and
northeastern section of the forecast area Friday morning. This
would include the southern Cascades into portions of the coastal
range near Shasta county. As the center of shortwave moves
onshore, initiation of thunderstorms start in the southern
Cascades and coastal range through Shasta county. Some dry air is
noted in the latest HIRES atmospheric soundings showing slight
inverted V structures at times. Elevated fire weather concerns are
anticipated from isolated to scattered dry thunderstorms during
the morning and afternoon hours on Friday. Main threats from the
dry thunderstorms would be new fire starts and gusty outflow
winds.

Uncertainty arises with the coverage of the dry thunderstorms and
how much dry air is near the surface through 700mb. As of right
now the probabilities of thunderstorms is around 30 percent with
the highest in the southern Cascades. This is where the CAMS have
picked up the highest chances for initiation of thunderstorms as
the short wave moves onshore. Because of the remaining uncertanity
in coverage and nature of thunderstorms, we do not anticpated the
need for a Red Flag Warning at this time. We will conitnue to
monitor the latest trends and if the need arises for the increased
messaging for fire weather concerns.

Around the mid to late afternoon hours, chances for storms begin
to dwindle as the wave moves further east. Concerns for fire
weather start to dwindle by the evening and overnight hours.

Moving into the weekend and beyond we will start to heat back up
into the 90s across the area, with the potential for lower 100s as
we move into the new work week. Conditions will start to dry out
quickly and RH values begin to drop. Confidence is increasing in
the potential for breezy conditions at times next week on top of
the drier conditions. We will continue to monitor the fire weather
conditions for next week.

&&

.AVIATION...
VFR conditions are expected through the TAF period. Winds are
light and variable, but increase out of the west for the
Sacramento sites this afternoon and evening. Sustained winds up to
15kts are possible. Periods of gusts of 20-25kts for Sacramento
sites this evening. RDD and RBL will see southerly winds this
afternoon and evening, while SCK and MOD see WNW to NW winds.
Winds do go light and variable overnight and into tomorrow
morning. Otherwise, higher terrain isolated showers and
thunderstorms will be possible this afternoon and evening.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 5 AM to 7 PM PDT Friday for Burney Basin-
E. Shasta /S. Cascades Above 3000 ft-Shasta County Foothills
1000-3000 ft-Shasta Lake Area & 1-5 1000-3000 ft-Shasta Metro-W.
Shasta County 1000-3000 ft-W. Shasta County Above 3000 ft.

&&

$$