NATIONAL WEATHER SERVICE FORECAST DISCUSSION
Area Forecast Discussion
Issued by The National Weather Service
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000
FXUS66 KSTO 200953
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
253 AM PDT Thu Sep 20 2018



.SYNOPSIS...
Breezy north winds and low humidity will bring increased fire
danger Sacramento valley and coast range today. Remaining warm on
Friday then cooling to near normal by the end of the weekend.
Warming slightly again early to middle of next week. No
precipitation expected interior Norcal through extended period.

&&

.DISCUSSION...
A northerly surface gradient has developed in the wake of an
upper trough that moved through norcal on Wednesday. Currently
the surface gradient from MFR to SAC is over 9 mb. Breezy north
winds have developed over the northern Sacramento valley and along
the coast range this morning. Upper level flow a bit more
northwest so upper level support is limited. Therefore breezy
north winds will be spotty. RH values in these windier areas have
shown fairly poor recovery this morning and minimum RH expected
to drop down to as low as single digits some areas this afternoon.
Therefore a Red Flag warning for the western portions of the CWA
will remain in place. Upper level ridge amplifies over the west
coast by this afternoon bringing a few degrees of warming today.
Daytime highs are expected to come in a few degrees above normal.
Upper level ridge slides quickly across the west coast on Friday
bringing decreasing winds and similar airmass on Friday.
Therefore, expecting daytime highs Friday remaining a few degrees
above normal. An upper trough is forecast to move into the Pacific
Northwest on Saturday bringing more onshore flow and cooler
temperatures. RH values should see some increase as well. Overall
airmass cools a bit more Sunday as the upper trough swings across
the north state and into the Great Basin. Daytime highs Sunday
should come in right around normal for this time of year.
Precipitation and even significant cloud cover from this system
should remain well north of the forecast area.

&&
.EXTENDED DISCUSSION (Monday THROUGH Thursday)

Warm and dry weather is expected through the extended period as a
Rex Block pattern develops over the eastern Pacific, and high
pressure builds over California. The latest ECMWF model would
suggest a period of gusty north winds Sunday into Monday as an
upper trough drops into the Great Basin, but the GFS is much
weaker and farther east with this system. Regardless, look for
Valley high temperatures generally in the 90s through the extended
period, with 70s and 80s over the mountains.

Dang

&&

.AVIATION...

Mainly VFR conditions the next 24 hours, except local MVFR
conditions due to smoke near the Delta Fire in Shasta County.
Northerly winds will increase to 5-15 kt today, with local gusts
up to 25 kt near KRDD-KRBL.

Dang

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 7 PM PDT this evening for 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 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-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.

&&

$$
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