875
FXUS66 KSTO 222241
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
341 PM PDT Tue Oct 22 2019


.SYNOPSIS...
Strong winds Wednesday into Thursday when elevated fire weather
concerns are expected. Dry conditions with above average
temperatures forecast through the remainder of the week.

&&

.DISCUSSION...
Warm and dry conditions continue today and through the rest of the
week as an upper level ridge remains centered over the eastern
Pacific. Daytime temperatures will reach the mid to upper 80s for
the Valley and 50s to 60s for the mountains this week, around 10
to 15 degrees above normal for late October. Overnight lows will
be mild across windier portions of the valley and in the foothills
thermal belts, but will be close to normal elsewhere.

The main concern this week is critical fire weather conditions
tomorrow and Thursday as an upper level shortwave digs into the
Great Basin region. Today, north to northeast pressure gradients
have tightened slightly resulting in gusts around 15-25 mph range
across the northern Sacramento Valley. Pressure gradients will
continue to tighten tomorrow as the shortwave deepens to the east
and the ridge deepens to the west. Strongest winds will begin in
the Valley and northern foothills tomorrow morning, becoming
strong over the northern mountains Wednesday night. Sustained
winds 15 to 30 mph are possible with gusts 35 to 45 mph, locally
higher over more wind prone areas. A Wind Advisory has been issued
for the northern Sacramento Valley Wednesday morning through
evening. Gusty winds will continue through Thursday.

Extremely dry conditions will persist through Friday. Daytime
humidity levels will be in the teens to 20s with extremely poor
overnight recoveries Wednesday night only reaching the teens to
30 percent. The above normal temperatures and northerly winds will
enhance the drying. Fuels in the Sacramento Valley also continue
to dry, all of which combined create a critical fire weather
situation, resulting in a Red Flag warning. Those who live in the
area of concern should be preparing now for critical fire weather
conditions.

Lighter winds forecast to return later evening Thursday and
continue Friday as the shortwave moves east and the upper ridge
moves over California. HEC

&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)...

Models are in good agreement an upper level trough originating over
Western Canada will drop into the Northern Great Basin on
Saturday. Impacts on Saturday will be minimal with daytime highs
likely to still be several degrees above normal. Northerly flow
will help to cool down the area starting Sunday.

On Sunday, the GFS and ECMWF model projections could not be more
different. The ECMWF is now digging the upper trough further
southwest with even tighter gradients with the center of low
pressure tracking south over Nevada. Meanwhile, the GFS broadens
the trough and tracks it much farther east into the central U.S.
during the exact same timeframe. The impact of these model
projections would be dramatically different. If the GFS ultimately
verifies, we would likely see minimal impact to our area.
However, if the ECMWF solution ends up verifying, we will see
another round of strong northerly to northeasterly winds over
most of the CWA with the potential for enhanced fire weather
concerns. Models do agree on cooler temperatures early next week
with much of NorCal forecast to come in a few degrees below
average for this time of year. High pressure is expected to build
in over our area early next week.

&&

.AVIATION...

VFR conditions the next 24 hours at TAF sites. Generally
northerly sustained winds 5 to 15 knots, increasing after 12z
to 10 to 20 kts with gusts up to 35 kts for Sacramento Valley and
mountains.


&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 8 AM Wednesday to 4 PM PDT Thursday 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-Northern Sierra Including Lassen NP and
Plumas and Lassen NF/S West of the Sierra Crest (West of Evans
Peak-Grizzly Peak-Beckworth Peak)-Northern Sierra Including the
Tahoe and ElDorado NF/S West of the Sierra Crest-Southeast Edge
Shasta-Trinity NF and Western Portions of Tehama-Glenn Unit-
Southern Sacramento Valley in Yolo-Sacramento Far Western
Placer, southern Sutter and Solano County Below 1000 Ft-
Stanislaus NF West of the Sierra Crest.

Wind Advisory from 11 AM to 8 PM PDT Wednesday for Central
Sacramento Valley-Northern Sacramento Valley.

&&

$$