Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 171600

900 AM PDT Thu Apr 17 2014

Weak low pressure system will bring a slight chance of showers over
the mountains this afternoon and into Friday and over the Northern
Sacramento Valley Thursday evening. Temperatures will continue above
normal through Sunday...then are forecast to cool to near normal to
below normal early next week. An unsettled weather pattern moving
over the region will bring a chance of showers over interior
Northern California Monday night into Tuesday night along with a
slight chance of thunderstorms in the Valley Tuesday.


.Short Term Discussion...
Upper level trough off the Pacific Northwest coast and a disturbance
moving into Southern California will bring increasing cloud cover
over Interior Northern California today. The southern disturbance
is bringing some mid and high clouds to the Northern San Joaquin
Valley and adjacent foothills and mountains this morning. The
trough to the north is expected to deepen today pushing the other
one farther south. The trough is expected to move through Northern
California late this afternoon into Friday. Cooler temperatures
are expected today with synoptic cooling especially across the
north and areas in the delta will have additional cooling with
onshore flow. Max temperatures are expected to be in the low to mid
70s near the Delta and upper 70s to low 80s in the Valley and mid
50s to low 70s in the mountains which is about 6 to 12 degrees
above normal for mid April. Precipitable water around an inch with
this system for some moisture but dynamics fairly weak so
precipitation amounts will generally be less than a tenth of an inch.
Showers are possible over the Coastal Range and Shasta and Western
Plumas County this afternoon and spread southeast late this
afternoon into tonight for a slight chance for the Valley from
north of Marysville to around I-80 in the mountains. Showers and
possibly isolated thunderstorms from Western Plumas County and
down the Sierra on Friday. Snow levels are expected to be around
9000 ft. Temperatures will be similar to a little cooler on Friday
with high temperatures in the mid 70s to around 80 in the Valley
and 50s and 60s in the mountains. The instability moves to the
Central sierra and east on Saturday but may still see some cumulus
development in Alpine and Tuolumne counties near the instability.
Another trough moves through the Pacific Northwest on Saturday but
looks like it may stay dry in Northern California. Temperatures
will be similar on Saturday. Weak shortwave ridging on Sunday
ahead of a stronger and deeper low for a little warmer
temperatures and dry weather. The deeper low will bring cooler and
wetter weather for early next week.

.Extended Discussion (Monday through Thursday)

Pattern change starts Monday with cooler and wetter weather on the
way. The ECMWF, GFS, and GEM models are finally trending toward a
consensus for the main arrival of a large upper low from the Gulf
of Alaska. Although light mountain showers could start Monday
morning, the brunt of this system will start impacting NorCal
Monday evening. Showers will spread southward across our CWA
Monday into Tuesday. Have kept the mention of slight thunderstorm
chances Tuesday as forecast instability appears favorable for the
valley. Cooler temperatures will be noticeable as valley highs go
from the low 80s on Sunday cooling to mid-upper 70s on Monday and
mid 60s-low 70s by Tuesday. Those cooler temps on Tuesday will
continue into Wednesday with lingering showers.  JBB



VFR conditions will continue today for TAF sites. Winds will be
light this morning into early afternoon, but onshore flow will
develop later in the afternoon into early evening. This will bring
some moderate winds to the delta region while also bringing local
gusts of 15-18 kts to KSMF, KSAC, and KSCK between 22-03z today.


.STO Watches/Warnings/Advisories...

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