NOAA Forecast Discussion

000
FXUS66 KSTO 171917
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1117 AM PST Sat Feb 17 2018

.Synopsis...
A cold weather system brings breezy winds and a chance of snow
showers over the mountains and foothills Sunday into Monday
followed by cold temperatures with a possible widespread freeze.

&&

.Discussion...
There were some cool morning temperatures this morning, with some patchy
frost and temperatures remaining in the 30s for many Valley
locations. This was due to light winds and clear skies, allowing
for strong radiative cooling. Temperatures are quickly rebounding,
though, and at 11 am were 1 to 5 degrees higher than yesterday.
Afternoon highs in the upper 60s are expected across the Valley
and Delta, potentially reaching 70 for the northern Sacramento
Valley.

The foothills were milder this morning due to an inversion,
generally ranging in the 40s, and should see mid 60s for afternoon highs.

A change in the pattern arrives Sunday, as upper level ridging
shifts westward. This will allow system with cold air from western
Canada to drop into the region. Temperatures on Monday morning
will be quite cold across the region. A Freeze Watch remains in
effect for Late Sunday night through Wednesday morning. The
coldest temperatures are expected on Tuesday morning. These look
to be trending a little cooler, with widespread lows in the mid to
upper 20s, and several hours of subfreezing temperatures. EK

&&
.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)

Extended period starts out dry and cool under upper level ridging
and northerly flow. Daytime highs Wednesday will push upwards to
near normal while mainly clear skies bring another morning of
below freezing temperatures in the valley. Warmer airmass finally
brings morning minimums up above freezing in the valley by
Thursday morning with minimum temperatures currently forecast in
the lower 30s. Models drop an upper trough out of the Pacific
northwest on Thursday but differ significantly on strength. GFS
more shallow with this system and would keep Norcal dry while
deeper ECMWF would bring light precipitation to much of the
forecast area. For now, have kept precipitation chances to the
mountain areas. Friday could be dry under shortwave ridging but
model timing with these shortwave systems will be difficult. Model
discrepancies continue going into the weekend. Models show
similar differences to Wednesday system with ECMWF again coming in
deeper with a shortwave dropping out of the Pacific Northwest.
For now, have kept shower threat over the mountains again with
just a bit of daytime cooling until models come into better
agreement.


&&

.AVIATION...

VFR conditions over Interior NorCal through next 24 hours except
Periods of MVFR after 06z northerly Sacramento valley as weather
disturbance drops southward. Winds below 15 knots picking up
after 00z with gusts 25 to 35 knots over higher terrain.
&&

.STO WATCHES/WARNINGS/ADVISORIES...
Freeze Watch from late Sunday night through Wednesday morning
for Carquinez Strait and Delta-Central Sacramento Valley-Clear
Lake/Southern Lake County-Motherlode-Mountains Southwestern
Shasta County to Northern Lake County-Northeast
Foothills/Sacramento Valley-Northern Sacramento Valley-Northern
San Joaquin Valley-Shasta Lake Area / Northern Shasta County-
Southern Sacramento Valley.

&&

$$

NWS STO Office Area Forecast Discussion

Information from NOAA - National Oceanic and Atmospheric Administration

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