Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Sacramento California
802 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
Update (8:02 am pdt)...
Lower level onshore flow from the southwest continues this morning
bringing marine clouds and breezy cool winds. Pressure gradient
trends are dropping slightly this morning, which is resulting in
slightly lower wind speeds at Travis AFB and in the Sacramento
area as compared to overnight. Fort Ord profiler continues to show
a somewhat deep marine layer, which in combination with the lower
level orientation of the winds, will continue to bring some clouds
into the area ending by early afternoon.
Forecast continues to be on track; no changes made.
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.
Temperatures are running much cooler this evening at 6 to 20
degrees cooler. The marine layer has increased to around 2500 feet
this evening and the likelihood of marine stratus spreading into
the southern Sacramento Valley has increased. Breezy conditions
for parts of the Sacramento Valley are expected through at least
midnight if not longer. Temperatures will be even cooler for
Thursday ranging from the mid 70s to mid 80s in the Central Valley
with parts of the Delta likely to only warm into the upper 60s.
The trough will deepen overnight bringing more synoptic cooling
and linger through Friday so not much change is expected in
temperatures between the two days. A deep marine layer is expected
Thursday night and may lead to more low clouds spreading into the
interior by Friday morning. The latest NAM is indicating isolated
convective activity along the northern coastal range each of the
next two days while the GFS is dry on Thursday and indicates some
possible activity along the crest and over the northern mountains.
Extended discussion (monday through thursday)
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 for the next 24 hour period. Gusts to 30 kts in the
Delta and up to 25 kts for Sacramento area tafs. Morning stratus
intrusion should diminish with cloud deck becoming few/scattered
by this afternoon. Wind gusts over the Sierra could reach 20 kts