Area Forecast Discussion
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FXUS66 KSTO 231022

Area Forecast Discussion
National Weather Service Sacramento CA
322 AM PDT Mon Sep 23 2019

Hot and dry weather with breezy northerly winds will lead to
elevated fire weather concerns early this week. Significant cool
down with a chance of showers late in the week.


Satellite imagery indicates the upper trough is over western
Nevada early this morning and is in the process of closing off as
a strong vort drops southeastward near Lake Tahoe. Skies have
cleared behind the vort, other than some lingering low clouds
over eastern Shasta County and northern Plumas County, but remain
partly cloudy over the southern part of the forecast area.

Current temperatures are milder compared to 24 hours ago and
generally range from the upper 30s and lower 40s in the mountain
valleys, to the upper 60s across milder portions of the Central
Valley. Northerly surface gradients have already begun to tighten
(KMFR-KSAC over 8 mbs at 09Z) resulting in local wind gusts in the
teens to lower 20 mph range over the northern Sacramento Valley
and surrounding foothills.

The low will move south to near Yuma early Tuesday, and into
northern Baja by early Wednesday, allowing ridging from the
eastern Pacific to build into NorCal in its wake. Along with dry
conditions and hotter temperatures, breezy to locally windy
northerly flow will develop elevating fire weather concerns into

The strongest northerly winds for the Sacramento Valley will occur
during each afternoon and evening thru Wednesday where gusts of
25-35 mph will be possible, but the strongest winds will retreat
to the western edge of the valley each night. Locally gusty east
winds will also be likely each night across the Sierra Nevada and

Temperatures will only warm a few degrees today compared to
Sunday, but hotter weather is expected Tuesday and Wednesday when
highs warm to 5-10 degrees above average with warmest valley
readings around 100. Some cooling will be possible by Thursday as
short-waves moving through the PacNW flatten the ridge and induce
a return of onshore flow.


Anomalously deep troughing will settle over the western U.S. late
this week into early next week, bringing significantly cooler
temperatures and precipitation chances across interior NorCal. The
highly amplified setup over North America has been rather well
advertised as a powerful ridge across the Gulf of Alaska forces a
deep trough to position itself over the West. During the Fri-Sun
timeframe, forecast highs could drop 15 to 25 degrees below
seasonal normals. Valley locations should see temperatures in the
upper 60s to low 70s, while 30s and 40s would be more commonplace
across the mountains. At this point, precipitation coverage and
amounts remain uncertain, but it appears best chances will be over
higher terrain. Snow levels could lower to around 5,500 to 6,500
foot over the weekend, so cannot rule out the potential for some
snow over the higher elevations.


VFR conditions are expected over the next 24 hours. Northerly
wind gusts increase to 20-30 kts across the Sacramento Valley by
15Z-18Z Monday.


Red Flag Warning from 11 PM this evening to 11 AM PDT Wednesday
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 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.


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