Area Forecast Discussion
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FXUS66 KSTO 182111

Area Forecast Discussion
National Weather Service Sacramento CA
211 PM PDT Tue Sep 18 2018

Below average temperatures continue today, then warmer weather
returns for the second half of the week. Enhanced fire weather
concerns Wednesday evening through Thursday. Patchy smoke and
haze will continue, mainly locally over northern portions of
Shasta County.


A weak upper level trough is moving over the forecast area today.
Today`s temperatures will be similar to yesterdays with Valley
highs in the high 70s to mid 80s and mountains in the 60s. Upper
level ridging builds through the rest of the week over California,
allowing temperatures to warm to near or few degrees above normal
Wednesday through Friday. However, a weak impulse moves along the
large scale flow over NorCal Wednesday night through Thursday
night. Gusty northerly winds are expected to return overnight
Wednesday into Thursday, with the strongest winds expected
Thursday afternoon. The warmer temperatures and northerly winds
will lower humidity levels over the northern and northwestern
portion of our forecast area. This has increased fire weather
concerns, and as such a fire weather watch has been issued for
this time period. HEC



Upper trof moves through the Pac NW on Sat with Wly flow bringing
seasonably warm temps to our CWA. Any precip from the trof is
forecast to remain N of CA. Medium range models in decent agreement
in moving this trof through the Nrn Rockys this weekend and into the
Nrn Plains early next week before some model differences arise
Mon/Tue and into mid week. The GFS digs some secondary energy from
the Canadian Rockys into the Nrn Rockys Mon/Tue, in contrast to the
ECMWF which is more progressive with the trof. This results in the
GFS having a more Wwd (offshore) displacement of the W Coast ridge
than the ECMWF, and a cooler, breezier scenario for our CWA than
the ECMWF.

With the WR ModTrend tool showing higher 5H heights over the NErn
Pac/B.C./PacNW and Norcal region, we are inclined to trend the
latter half of the EFP to the warmer, less windy ECMWF. This will
moderate the "cooling" trend with max temps trending a little above
normal by Tue. Dry, warm ridge expected to prevail through the
middle of next week. JHM



Dry/stable air mass over interior Norcal through Wed with VFR/SKC
conditions except for local MVFR/IFR VSBYS due to smoke near the
Delta fire in Shasta Co. Winds generally below 10 knots with weak
to modest Delta Breeze. Less of a marine influence over the
inland areas is expected Wed morning (than this morning) as the
marine layer is eroding from the N and is becoming elevated this


Fire Weather Watch from Wednesday evening through Thursday
afternoon 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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