000
FXUS66 KSTO 102129
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
229 PM PDT Fri Jul 10 2020

.SYNOPSIS...
Dry weather with seasonably hot temperatures are forecast this
weekend and into next week.

&&

.DISCUSSION...
Aside some passing high clouds, mostly sunny conditions continue
to dominate the skies across central and northern California this
afternoon. Current temperatures are generally running at or
several degrees warmer compared to this time yesterday. Friday
afternoon highs will peak in the upper 90s to low 100s.

Main message for the weekend and into next week will be the heat.
A broad upper level ridge located in the Southwestern US will be
largely responsible for the widespread and persistent above normal
temperatures for much of the Golden State. The strength and scale
of this ridge is impressive; most forecast models are advertising
geopotential heights at 500 millibars maxing at 600 decameters
over New Mexico, and heights at/above 590 decameters over nearly
all of California by Saturday. The hottest days for the southern
Sacramento Valley will likely occur on Sunday and Monday while the
northern Sacramento Valley will peak a day or two later. Overall,
temperatures will be around 5 to 10 degrees above normal. Heat
risk will be limited to the moderate category as most communities
will see overnight lows cooling to the 60s. Some locations will
struggle to drop below 70, but this appears to be limited at this
point to the northern Sacramento Valley and the adjacent
foothills.

The afternoon/overnight Delta breeze will bring locally gusty
winds to the Delta region over the next several days. These
winds combined with the hot and dry conditions will lead to
several hours of elevated fire weather concerns each day this
weekend. //Rowe

&&
.EXTENDED DISCUSSION (Tuesday THROUGH Friday)...

The 5H Cluster analysis indicates anticyclonic flow from the
strong high pressure cell over the Ern Pac will prevail over
Norcal, lessening the influence of the Desert SW high. This will
maintain a dry, subsiding air mass over Norcal. Tue and Wed appear
to be the hottest days in the EFP with a +1 to +2 temp anomaly
from 850 mbs to 500 mbs. The 850 mbs temp anomaly favors the Nrn
half of the Sac Vly and surrounding higher terrain where 850 mbs
temps are forecast to be in the 26-29 deg C temp range. Dry
adiabatic descent from 850 mbs supports max temps in the 105-111
deg F range with a 17% chance of hitting 110 at RDD on Tue and 28%
on Wed. The percentages drop off significantly at RBL and
elsewhere due to onshore/up valley flow in the afternoons/evenings
instead of the warming/katabatic winds. However, this pattern
will result in strong thermal belts overnight and elevated min
temps in those areas. Fortunately we are not anticipating much
wind during the period, except in the Carquinez Strait/Delta
region with the typical Delta Breeze.

A cooling trend is anticipated Thu/Fri as a relatively weak trof
moves through the Pac NW. Deterministic runs vary as to the amount
of cooling with the GFS (ECMWF) basically warmer (cooler) than the
ECMWF (GFS). The 5H EOF monopole suggests uncertainty in the amplitude
of the Pac NW trof so we relied on the NBM max forecast which showed
about a 5-6 degree F drop in max temps from Wed over the
Nrn/central Sac Vly, and a trend to normal max temps in the Srn
Sac Vly, foothills and marine/Delta areas.   JHM

&&

.AVIATION...

VFR mostly SKC conditions through 00z Sun. Winds remain under 10
kts except through the Carquinez Strait and Delta with gusts to
20-25 kts at times.

&&

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

$$