Grimes, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

509
FXUS66 KSTO 191011
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
311 AM PDT Thu Sep 19 2024

.Synopsis...
Warmer temperatures today compared to yesterday, with chances for
scattered showers and thunderstorms along the Sierra mountains south
of I-80, with a few lingering cells in the higher elevation
foothills. Warm and dry weather returns Friday into next week,
with areas of moderate HeatRisk and elevated fire weather
conditions Monday & Tuesday across the Delta, Valley, and
foothills.

&&

.Discussion...
Today`s thunderstorm threat will remain confined to the Sierra
mountains and higher elevation foothills south of I-80, where NBM
probabilities show a 30-40% chance of development. The center of
the low pressure system will gradually move across Southern
California later today, drawing in moisture across the Sierra in
an east to west orientation. A few scattered showers developing
during the late morning hours will precede afternoon thunderstorm
initiation along the foothills. East-southeasterly steering flow
aloft will allow storms to propagate downslope of the Sierra
shortly after their initiation. Storms will generally weaken as
they move downslope, but more robust cells will hold together
longer bringing potential thunderstorm impacts further into the
Sierra foothills where only a 20-25% chance of thunderstorms
exists. Remnants of these storms have the potential to bring light
showers/virga to eastern portions of the Valley, particularly the
eastern portions of the northern San Joaquin Valley. Dry
conditions are expected everywhere else. A few light showers may
reach the Park Fire burn scar, but no debris flow impacts are
expected today.

High pressure begins to build in Friday as eastern Pacific ridging
builds eastward. Temperatures begin to warm to near normal by
Saturday, with highs above normal on Sunday. The NBM shows a 60 to
90% chance of high temperatures greater than 90 deg F on Friday
over the central and northern Sacramento Valley. Probabilities
extend into the Delta, southern Sacramento Valley, and northern
San Joaquin by Saturday and Sunday. This warming trend continues
into early next week, accompanied by a drying trend.

As the previous system propagates eastward, a steepening pressure
gradient develops as ridging begins to move over Northern
California. As a result, periodically breezy north winds will
permeate throughout the Valley and easterly/downslope winds over
the Sierra over the weekend and into early next week. Gusts will
generally be 15-20 mph with daytime relative humidities will be in
the mid teens to mid 20s, initially over the northern Sacramento
Valley and adjacent foothills Sat-Sun resulting in localized
elevated fire weather conditions. &&


.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Warmer and dryer weather is expected Monday and Tuesday, as we
see the return of Moderate HeatRisk throughout the Valley and
foothills. The NBM is also showing a 20-50% of high temperatures
greater than 100 degrees around the Greater Sacramento Metro Area.
Alongside these warmer temperatures, daytime relative humidities
in the mid teens to low 20s will be present throughout the Valley,
Delta, foothills, and mountains. This is also when were seeing
indications of breezier northerly flow across the more wind-prone
areas of the Sacramento Valley (i.e. the northern Sac Valley and
along the I-5 corridor in the Sacramento Valley) on Monday with
gusts 15 to 25 mph. On Tuesday, increased flow will be located
along the Sierra foothills and mountains where breezy
downslope/easterly winds and gap winds gusting 20 to 30 mph will
be present. These conditions look to bring more widespread
elevated fire weather conditions to the region, especially in the
Valley and foothills where RH values will be lowest.

By Wednesday and into Thursday, troughing begins to develop
offshore resulting in increased onshore flow and higher humidities
through the Delta and Sacramento area. However temperatures will
still be 5 to 10 degrees above normal for this time of year.

&&

.AVIATION...
Exiting weather system will keep MVFR/IFR conditions along the
foothills and Sierra/Nevada Mountains near showers and
thunderstorms for the next 24 hours. Gusty and erratic winds near
storms should be expected. Elsewhere VFR conditions with variable
winds 12kts or less is expected.

&&

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

$$