969
FXUS66 KSTO 130819
AFDSTO
Area Forecast Discussion
National Weather Service Sacramento CA
119 AM PDT Fri Sep 13 2024
.Synopsis...
Elevated fire weather conditions this morning from locally gusty
gap/canyon winds and dry conditions. Active weather pattern
Sunday through midweek bringing scattered showers and
thunderstorms, increased moisture, gusty winds, and cooler temps.
&&
.Discussion...
Current GOES-West satellite imagery shows mostly clear skies
across interior northern California early on this Friday morning.
Temperatures are currently in the low 60s to low 70s in the
Valley and foothills, and in the 40s to 50s in the mountains,
valid at 115 AM PDT. Locally breezy conditions are being observed
in mountain and foothill gaps and canyons with a few RAWS sites
reporting gusts 15 to 25 mph along with relative humidity around
30 to 60 percent. Elevated fire weather conditions are expected
through the morning from continued locally gusty and dry
conditions.
Seasonable temperatures are in the forecast for today and
Saturday, around normal for mid-September climatology. Forecast
highs today and Saturday are in the upper 80s to mid 90s in the
Valley and lower foothills, and 70s to mid 80s in the upper
foothills and mountains, along with dry conditions.
An upper level low will drop down from the Pacific Northwest on
Sunday, bringing along scattered showers and thunderstorms,
increased moisture, and cooler temperatures into early next week.
The National Blend of Models (NBM) suggests generally a 15-25%
probability of thunderstorm development, mainly over the northern
Sacramento Valley, adjacent foothills and northern mountains
(this includes the Park Fire Burn Scar which we are monitoring
closely for potential debris flow concerns). On Monday,
thunderstorm chances look to be mainly over the Sierra Crest south
of Highway 50, around 10-20% probability. Latest guidance from
WPC generally shows storm total precipitation amounts of less
than a tenth of an inch south of Interstate 80, and up to a half
inch to an inch in the northern Sacramento Valley, adjacent
foothills, northern mountains, and Mt. Lassen area.
Increased onshore flow is expected as well, with gusty winds
returning to the forecast area on Sunday. Wind gusts of 20 to 35
mph will be possible, especially in the vicinity of the Delta and
over the Sierra Crest. The increased onshore flow is also
highlighted with a decent signature on the EC Extreme Forecast
Index (EFI) for those aforementioned locations. In addition to
the gusty winds, cooler temperatures are also in the forecast. For
much of the Valley, high temperatures are generally at or below
80 degrees on Sunday and then in the low 70s on Monday. Stay tuned
for updates as we get closer to this next weather system!
&&
.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...
Tuesday and Wednesday next week continue to see a cool, unsettled
pattern; however most of the precipitation chances are on
Wednesday (10 to 40% probability of 0.5 inches or more in 24 hours
across the area). There is an approximately 10 to 30% probability
of 0.1 inches or more in 24 hours by Tuesday afternoon/evening,
though this is limited to the northern Sacramento Valley. Snow
levels will be high enough by Tuesday and Wednesday (generally
near 9000 ft), that we likely won`t see any snow in our part of
the Sierra in the extended period, even at the peaks. Thursday and
Friday, conditions begin to warm back up closer to normal for the
time of year, as a broad ridge moves in over the west coast. By
Friday, high temperatures in the Valley will be in the mid 80s,
with 60s and 70s at higher elevations.
&&
.AVIATION...
VFR conditions prevail across interior northern California over
the next 24 hours. Surface winds generally at or below 12 kts.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
