Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Sacramento California
310 am PDT Mon Jul 24 2017
a slight chance of afternoon and evening thunderstorms across
norcal mountains through Wednesday. Near normal temperatures through
Tuesday, warming back up mid to late this week.
the primary weather feature impacting northern California this
morning is a very slow-moving upper shortwave currently situated
just off the northern California coast. Southerly flow aloft out ahead of
this system has advected subtropical moisture northward, and even
at this hour showers and thunderstorms are being detected just
east of the Sierra crest. The marine layer has also steadily
increased in depth over the last 24 hours, and is now nearly 2000
ft deep at Fort Ord. Locations near the coast have begun to feel
the effects of this greater marine influence, though these cooling
effects haven't penetrated farther inland yet.
High temperatures will trend closer to normal today and Tuesday as
the aforementioned system slowly moves inland. Convective activity
will be on the rise this afternoon, mainly along and east of the
Sierra Cascade crest.
The upper low is forecast to very slowly lift across the region
Tuesday and Wednesday. As such, thunderstorms chances will remain
in similar areas both of those days as they are today. The system
should fill and shift eastward by Thursday...which will bring
warmer and drier weather.
extended discussion (friday through monday)
Upper ridge rebuilds across interior norcal late this week into
the weekend. This will result in daytime highs about 5-10 degrees
above normal. There are model differences in terms of the
position and strength of this ridge. At this point, the European model (ecmwf)
is the farthest westward and strongest solution. Thus, how much
warming will occur over the weekend remains in question given
model uncertainty. Dry weather is expected across interior norcal
during the extended period. However, the GFS is indicating an
embedded disturbance in the upper flow that could trigger some
afternoon shower activity near the Sierra crest on Sunday. Have
kept the area dry for now given model uncertainty.
VFR conditions the next 24 hours across interior norcal. Winds
will remain light today, except gusts to 25 kt near the Delta and
over higher terrain.