000
FXUS66 KSTO 292048
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
148 PM PDT Mon May 29 2023

.SYNOPSIS...
Isolated to scattered shower and thunderstorm chances continue
for the mountains, portions of the foothills, and northern half
of the Sacramento Valley through Tuesday, then thunderstorm
chances mainly in the mountains the rest of the week.
Temperatures will remain near or slightly below normal through mid
week, followed by slight warming late-week into the weekend.
Periods of locally breezy onshore winds.
&&

.DISCUSSION...Today through Thursday.

Latest satellite imagery and observations shows the upper-low
circulating off the central CA coast. This low will slowly track
southeast over the next few days, keeping southerly flow across
interior northern CA. Continued anomalous PWAT (100-200% of normal)
over the region through Tuesday will continue to allow for afternoon
showers and thunderstorms to develop primarily over the Sierra,
southern Cascades, and portions of the Coastal Range. Instability
is primarily over the mountains this afternoon, with mesoanalysis
showing 400-700J/kg SBCAPE over the Sierra and southern Cascades.
Mean wind around 10 knots today across northern portions of the
CWA is mostly east-southeast, allowing for storms across the
southern Cascades and Coastal Range to move west-northwest. As
storms drift off the mountains, they will quickly weaken with lack
of forcing and decreased instability. Overall, thunderstorms
today and tomorrow will be of the garden-variety; capable of heavy
rain, gusty winds, frequent lightning, and small hail.

By Wednesday, weak shortwave over the PacNW will usher in drier air
across the northwest CWA, limiting thunderstorm development to
mainly the Sierra and southern Cascades. By Thursday, a weak,
shortwave will brush far northern CA, bringing dry, westerly flow to
the region, further limiting thunderstorm development, with only
isolated (15-30%) chances in the Sierra.

Temperatures will remain slightly below seasonal normals through mid-
week, but will slowly start to increase Wednesday. Temperatures will
reach near normal by Thursday, with Valley temperatures in the mid
to upper 80s.
//Peters

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)...

Ensemble guidance and cluster analysis continue to indicate that
weak ridging will develop Friday-Saturday, allowing for warmer,
slightly above normal temperatures. The National Blend of Models
(NBM) advertises a 50 to 90+ percent probability of portions of
the Sacramento Valley to reach 90 degrees for the daytime high on
Friday/Saturday with the best chances in the Northern/Central
Sacramento Valley, and a 50 to 95 percent probability on Sunday
for most of the Valley. Areas of moderate heat risk are currently
forecast to return this weekend, mainly in portions of the
northern and central Sacramento Valley.

By Sunday, ensembles and cluster analysis indicate another weak,
upper- level trough will begin to influence southern CA, leaving
northern CA with weak northeasterly flow. Even though the
placement of the weak low to our south is still uncertain, the
general pattern will allow for renewed thunderstorm chances in the
Sierra.
//Peters

&&

.AVIATION...

VFR conditions are generally forecast to prevail over the next 24
hours. Local MVFR conditions associated with showers and/or
thunderstorms in the afternoon and evening hours, mainly over
mountains. Gusty and erratic winds expected near thunderstorms.
MVFR/IFR conditions possible in stratus vicinity of Delta after
06Z Tuesday. Low stratus may push eastward into the Sacramento
area terminals between 10Z-16Z Tuesday, with local MVFR/IFR
conditions. Surface wind generally at or below 15 kts except
vicinity of Delta with southwesterly wind up to 25 knots.
&&

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

$$