Wildfire and Strong Wind in California, September 26 to 30, 2020

Area Forecast Discussion
National Weather Service Sacramento CA
335 PM PDT Sat Sep 26 2020

.SYNOPSIS...
Temperatures will warm over the weekend along and will be
accompanied with drier and windier conditions. This will lead to
critical fire weather conditions starting Saturday night and
continuing through Monday morning. Above normal temperatures and
dry conditions linger into late next week.

&&

.DISCUSSION...
Our weather will become more active over the next 12 to 24 hours
across NorCal. Long wave troughing is setting up over the central
part of the country and we will see an embedded short wave dig
out of western Canada into the western Great Plains. This will
increase the surface pressure gradient over NorCal as the Pacific
high continues to build into the region. We are already seeing
increased northerly flow over the area with gusts up to 25 mph.
Currently the KSAC-KMFR gradient is around 8 mb and we will see
that increase to 11 to 15 mb by the mid-morning tomorrow. We will
also see an increased gradient from KSAC-KRNO (9-11 mb) overnight
tonight. With these gradient we will see gusty north and east
winds over much of the area with the strongest winds over the
Sacramento Valley and Sierra Foothills. Wind gusts 30-45 mph,
locally higher in wind prone areas can be expected after 13z/6 am
and will continue into Sunday afternoon. We should see the winds
die down some during the evening tomorrow but they will still
remain breezy. Winds pick back up over the Sierra Sunday night as
the gradient increases and wind gusts over the Sierra and
Foothills may be a bit stronger than tonight but should be weaker
over the Valley. Winds will be diminishing during the morning and
into the afternoon Monday as the upper level ridge builds in over
us and we see the troughing push east. These downslope winds will
bring very low daytime humidity falling into the single digits
and poor to moderate overnight recoveries. The combined wind and
humidity will bring extreme fire weather concerns starting late
this evening through Monday.

The heat will be our other concern as the Pacific ridge builds in.
Temperatures are running about 5 to 10 warmer then this time
yesterday and the warming trend will continue into Sunday and for
early next week. The hottest days are expected to be Monday-
Wednesday. Moderate heat risk is forecasted starting tomorrow and
heat impacts will be possible especially for those sensitive to
the heat and those that work outside.

Smoke will also likely be a concern over the much of the region
as we see the north winds develop and the inversion increase.

-CJM

&&

.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Upper level ridge will remain parked over the West Coast through
much of the next work week. This will result in a prolonged period
with widespread 90s for the Sacramento and northern San Joaquin
Valleys, likely through the end of September and into the
beginning of October. For those keeping tally, Downtown Sacramento
has recorded 105 days this year at/above 90 deg F, ranking second
all-time. The record is 110 days, which occurred in 1984. If the
present forecast remains on track, 2020 will overtake 1984 by the
end of next week.

Dry conditions are forecast to prevail through the extended period.

&&

.AVIATION...
VFR conditions are currently forecast for the next 24 hours;
however, with increasing northerly and easterly winds, smoke from
the wild fires may bring lowered visibility and/or ceilings to TAF
sites. Expect to see increasing winds throughout the overnight
hours, with sustained valley wind speeds ranging from 15 to 30 kt.
Gusts up to 40 kt or so will be possible at times, especially for
sites north of Sacramento. For the mountains and foothills gusts
up to 40 to 45 kt may be possible, especially for wind prone
canyons, gaps, and ridgetops.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 9 PM this evening to 9 PM PDT Monday 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-
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 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-Stanislaus NF
West of the Sierra Crest.

Wind Advisory from 2 AM Sunday to 2 PM PDT Monday for Carquinez
Strait and Delta-Central Sacramento Valley-Mountains
Southwestern Shasta County to Western Colusa County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Shasta
Lake Area / Northern Shasta County-Southern Sacramento Valley-
Western Plumas County/Lassen Park.

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