Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 251056

Area Forecast Discussion
National Weather Service Sacramento CA
356 AM PDT Thu May 25 2017

Cooling continues into Friday with near to below normal
temperatures. Slow warming trend this weekend into early next
week. Isolated afternoon showers or thunderstorms possible over
the northern Sierra through the weekend. Afternoon thunderstorm
threat spreading to northern mountains early to middle of next


Upper trough axis now stretching across northern California has
deepened the marine layer to near 3000 feet this morning. Delta
breeze continues strong with gusts to over 30 knots at Travis AFB.
Marine stratus has already moved through the delta with patchy low
clouds being reported at the Sacramento airport. Much of the
Sacramento region will likely wake up to low clouds this morning.
Meanwhile, just about all areas seeing cooler temperatures this
morning with stations in the central Sacramento and northern San
Joaquin valleys showing over ten degrees of cooling compared to
Wednesday morning. Cooler airmass will bring still cooler high
temperatures today down to near or a little below normal for this
time of year. Upper troughing remains across northern California
on Friday so not expecting much change in overall temperatures or
marine layer with morning stratus likely again through the delta
and Sacramento region. GFS and NAM models both showing some
instability over the northern Sierra in the afternoon and evening
hours with GFS painting in some precipitation south of about
Tahoe. Will therefore keep a slight threat of afternoon and
evening thunderstorms in the forecast for this region. Upper ridge
pushes back over the west coast on Saturday bringing the start of
a warming trend. Lighter onshore flow and a squashed marine layer
will likely keep morning stratus from making it past the delta.
GFS showing some instability over the northern Sierra in the
afternoon and evening so left in slight threat of thunderstorms
there. Warming continues on Sunday under upper ridging. Daytime
highs are likely to reach several degrees above normal. Enough
southerly flow and instability to keep afternoon thunderstorm
threat over the northern Sierra.


Hot weather continues into early next week as strong ridging
remains over the area. Highs for Memorial Day will top out near
the century mark across the northern Sac Valley, low to mid 90s
elsewhere in the Valley and 60s-70s in the mountains. Those with
outdoor plans should prepare accordingly for the heat! Tuesday
will also be hot, perhaps a degree or two warmer than Monday.
Ridge begins to break down and shift to the east by Wednesday as a
weak trough approaches the West Coast. This will start a cooling
trend that may continue through the end of the week. Enough
instability present each afternoon/evening for a few thunderstorms
to fire across higher elevations. Have continued to mention in the
forecast but confidence remains low given subtle model
differences at this time.




VFR conditions next 24 hours at TAF sites. Gusts to 30 kts invof
of the Delta and 20 kts across northern Sac Valley through 12Z
Thursday. Stratus intrusion through Delta and central Sacramento
valley possible early Thursday morning. HEC



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