295
FXUS66 KSTO 191957
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1257 PM PDT Sun May 19 2024


.SYNOPSIS...
Seasonable temperatures will continue today and into early next
week. Mostly sunny and dry conditions with periods of breezy winds
expected through the next 7 days, strongest winds expected
tonight-Monday.

&&

.DISCUSSION...

Afternoon GOES-18 Satellite analysis reveals some passing mid and
upper level clouds across interior NorCal, mostly in the central
Sacramento Valley. Locally breezy winds have been observed
this morning, with some 10-20 mph speeds reported across the
Valley. The strongest winds are expected to begin later tonight
and last through Monday.

A trough is currently digging through northeastern WA and will
continue to dig into the Great Basin region through Monday, where
it will phase with a closed low in SoCal. As the trough and closed
low phase together, our current northwesterly flow will transition
into a northerly component, and pressure gradients will increase
setting up for gusty northerly winds tonight and tomorrow, mainly
in the wind prone areas of the western Sacramento Valley along
the I-5 corridor. Wind gusts of 30-35 mph are anticipated, along
with sustained winds of around 20-25 mph. Strongest winds are
expected to develop just after sunrise tomorrow morning, around
7am and last through the evening. The National Blend of Models
(NBM) continues to show roughly 50-80% probabilities that there
could be local gusts greater than 40 mph during the timeframe of
peak winds. At this time, we are not expecting widespread wind
gusts greater than 40 mph, however some areas between Red Bluff
and Arbuckle could experience local wind gusts of 40 mph. Minimum
Relative Humidity (RH) values will fall, with widespread less than
15% RH values forecast for much of the Sacramento Valley tomorrow.
As such, with low RH values and breezy/gusty northerly winds,
locally elevated fire weather conditions will exist tomorrow
across the western Sacramento Valley.

Tuesday we will see some relief from the gusty northerly winds as
northerly flow will weaken as the trough translates to the east.
Our upper level pattern will transition into a northwesterly flow
again, and pressure gradients will weaken as a result.
Temperatures will climb on Tuesday into the mid 80s to low 90s
across the Delta and Valley and upper 60s to low 80s for the
Foothills and mountains. While we remain in northwesterly flow
aloft, another shortwave is progged to dig into Washington and
Oregon on Wednesday, which will bring another round of northerly
winds and cooler temperatures. There is very limited moisture
associated with this system, so we are not anticipating any
precipitation chances for the area.

&&

.EXTENDED DISCUSSION (Thursday THROUGH Sunday)...

On Thursday, an upper level closed low is forecast to develop
over Idaho and place our area under upper troughing. Right now,
main weather impacts from this troughing will be cooler
temperatures and breezy northerly winds for the western Sacramento
Valley. Friday and Saturday, another trough in the PacNW begins
to dig southward and keep the area under the influence of upper
troughing extending through SoCal, again keeping temperatures
cooler. The NBM introduces slight precipitation chances in the
northern and eastern foothills and mountains Saturday afternoon,
however current probabilities of seeing a trace of rainfall are
below 25%, which highlights some of the uncertainty with exact
track, strength, and timing of the system. Cluster analysis
reveals general agreement that the area will be under the
influence of troughing, however the uncertainty lies on the exact
track/location.

High temperatures on Saturday will struggle to reach 80 for the
Valley, with cooler low 50s to upper 60s for the mountains and
Foothills. Sunday, we will warm up slightly as upper level heights
are projected to flatten into a more zonal component, with highs
reaching the 80s for the Valley and 60s to upper 70s for the
foothills/mountains.

&&

.AVIATION...

VFR conditions prevail over interior NorCal through the forecast
period. Light to breezy surface winds, 12 kts or less, expected
through 06z. Winds then shift to a predominantly northerly
direction overnight, with gusts increasing to 20 to 30 kts within
the Sacramento Valley after 09z.

&&

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

$$