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Area forecast discussion
National Weather Service Sacramento California
855 PM PDT Tue Jun 27 2017

Synopsis...
near average temps thru mid-week followed by a warming trend.

&&

Discussion...
strong Delta breeze working tonight helping to bring cooler
air into the interior. A very weak trough remains over the
region helping to keep the stronger onshore flow. Onshore
pressure gradient is currently 3.6 mb between sfo-SAC and the
Delta breeze is expected to stay up through the night. Marine
layer is currently at around 2000 feet and models indicate a
chance for some patches of low clouds to make it into the
Sacramento area again late tonight. Generally the same locations
as this morning. Many temperatures in the region should cool into
the mid 50s by morning with the north end of the valley cooling to
the mid 60s. Mountain Valley temperatures generally cooling into
the 30s and 40s. Only slight warming expected on Wednesday above
today's highs.

Previous discussion... weaker Delta breeze today than yesterday
resulted in a few degrees of warming in the Delta influenced
areas, while temps mostly followed persistence or were just
slightly warmer elsewhere.

Yesterday's short wave trof is now over Idaho and moving farther away
allowing flat ridging to build in its wake. However, a weak trof
is moving into the pac northwest with a weak short wave moving across
norcal early this evening. Hence, the Delta breeze should increase
again, but likely not quite as strong (or to the extent) as the
recent past. That makes for a lower probability (less of a chance)
of stratus making it inland in a similar fashion than the
previous two mornings. Marginal instability is forecast over the
nrn mtns, mostly over the Trinity Alps and Siskiyous, where short-
lived convection may materialize, just north or our County Warning Area.

Warming returns Wed-Fri as ridging over the eastern Pacific moves
onto the West Coast. This will suppress the marine layer weakening
onshore flow and resulting in modest synoptic warming. 850 mbs and
low level thickness values suggest another 2-4 degrees of warming or
so over most locales each day for the next couple of days. That
means triple digit heat will likely return to the nrn SAC valley
Thu-Fri and possibly into the srn SAC Vly. The question is, will
the Delta breeze arrive on time Fri afternoon to keep Max temps
below 100 in the srn SAC vly? With the GFS/European model (ecmwf) faster with the
incoming trof than the Gem on Fri (gfs/European model (ecmwf) well east of 130w, while
the Gem is along 130w), the chances are good that a Delta breeze
will be initiated in time to provide some cooling in the Delta
influenced areas. The passing trof will promote a cooling breeze
Fri nite and its fast movement will allow heights to rebuild
rapidly on Sat. Nly flow in the wake of the trof will provide a
rapid warm-up on Sat. Jhm
&&
extended discussion (saturday through tuesday)



Forecast models indicate a weak short wave trough moving across
the forecast area on Saturday with minimal impacts. Have nudged
up temperatures on Saturday given northerly flow and a weak Delta
breeze. Therefore, a slight warm up is expected near the Delta
influenced areas, while triple digit heat could be expected over
the northern Sacramento Valley. Temperatures will remain above
normal this weekend. Otherwise, highs could return to near average
for this time of the year early next week. However, there are
model differences at this point, with the European model (ecmwf) showing increasing
heights over the Great Basin. Dry weather will continue during
the extended period.



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Aviation...



VFR conditions the next 24 hours. South to west winds 5 to 15 kt
will decrease overnight. Near the Delta...SW wind gusts up to 30
kt expected. A chance for some patches of MVFR cigs around ksac to
kmhr 11z-15z.



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