000
FXUS66 KSTO 221026
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
326 AM PDT Fri Jun 22 2018

.SYNOPSIS...
Hot and dry weather through the weekend. Temperatures returning to
near normal next week.

&&

.DISCUSSION...
Beginning of a relatively modest heat wave over Norcal today and
through the weekend as 5H heights rise to around 590 dam, then
lower slightly on Sat as low pressure passes to the N, and then
rise again on Sun behind the low pressure system. This is a
relatively modest heat wave in looking at the +1 temp anomaly, as
the +2 anomaly generally stays to our W, and a 5-10 year return
interval. This will be the 2nd time this month the max temps at
the major climo sites will exceed triple digits since June 12-13
when most of the readings reached the low 100s. Max temps during
this heat wave are expected to peak out between 105-110, with the
hottest expected in the Nrn Sac Vly, RBL/RDD.

As the low pressure system passes to our N and NE later tonight and
Sat, northerly pressure gradients are forecast to increase to 11-12
mbs at times, through 06 Sun, before weakening on Sun, and turning
onshore/up valley by the end of the weekend. The synoptic pattern is
conducive to the development of a northerly barrier jet in the
Sacramento Valley. Staudenmaier (1994)and Mathews & Juskie (2005)
have documented this phenomenon (in WRH TA-Lites) and its impact
on wind advisories/red flag warning considerations. The one
noticeable difference is the more easterly track of the digging
low pressure system (into the central Rockys) in contrast to
autumn when the low pressure systems have a tendency to dig into
the Great Basin, farther W than this current system. One of the
effects of this Nly wind is the adiabatic warming/drying of the
katabatic winds which elevate temps and desiccate humidities both
overnight and during the day.

One potential stumbling block is the timing of the return of the
Delta Breeze and its impact on max temps on Sun. With the upper
ridge axis building/moving inland Sat nite/Sun, the warmest air is
expected to be over the CWA and a very warm nite/and hot day are in
store for most of the CWA. The heating of the N end of the Sac Vly
should create a large temp/density gradient between the land and the
ocean, resulting in a strong onshore pressure gradient by Sun
afternoon or evening. This should cause at least a moderately
strong Delta Breeze which should cool the Delta influence areas
quite rapidly. Sun could see a wide range of temps between the
Carquinez Strait and the Ern Sacramento Suburbs and foothills.
Since the marine layer will be relatively shallow ("squashed") by
large scale subsidence, the cooling effects may be limited away
from the immediate Delta Areas and temps in the upper 90s to
around 100 are forecast for SAC/DTS on Sun. However, the Delta
area should be much cooler and have removed zone 18 from the Heat
Advisory on Sun.

Seasonable wx returns to the CWA on Mon as another Pac NW trof
provides onshore flow and some cooling.   JHM

&&

.EXTENDED DISCUSSION (Tuesday THROUGH Friday)

Minor model differences through the extended forecast period but
general consensus is towards broad upper troughing. This will help
to keep temperatures only slightly above normal. Dry weather
expected through next week.

&&


&&

.AVIATION...

VFR conds ovr Intr NorCal nxt 24 hrs with W-NW flow alf. Sfc wnds
genly blo 12 kts.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon today to 8 PM PDT Sunday for Central
Sacramento Valley-Clear Lake/Southern Lake County-Motherlode-
Northeast Foothills/Sacramento Valley- Northern Sacramento Valley-
Northern San Joaquin Valley-Southern Sacramento Valley-Western
Plumas County/Lassen Park.

Heat Advisory from noon today to midnight PDT Saturday night for
Carquinez Strait and Delta.

Red Flag Warning from midnight tonight to 8 PM PDT Sunday for
Carquinez Strait and Delta-Central Sacramento Valley in Glenn,
Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-
Eastern Mendocino NF-Eastern Portion of Shasta/Trinity NF-Lake
County Portion of Lake-Napa-Sonoma Unit-Northern Motherlode From
1000 to 3000 Ft. Includes portions of Nevada-Yuba-Placer-Amador
and ElDorado Units-Northern Sacramento Valley to Southern Tehama
County Line Below 1000 Ft-Northern San Joaquin Valley in San
Joaquin and Stanislaus Counties Below 1000 ft-Northern Sierra
Foothills from 1000 to 3000 Ft. Includes portions of Shasta-
Trinity and Butte Units-Southeast Edge Shasta-Trinity NF and
Western Portions of Tehama-Glenn Unit-Southern Motherlode From
1000 to 3000 Ft. Includes portions of Calaveras-Tuolumne Unit-
Southern Sacramento Valley in Yolo-Sacramento Far Western
Placer, southern Sutter and Solano County Below 1000 Ft.

&&

$$