Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 201011

Area Forecast Discussion
National Weather Service Sacramento CA
311 AM PDT Fri Apr 20 2018

Dry and warm today through early next week with just a chance of
showers or thunderstorms over the Shasta County mountains on
Sunday. Isolated showers or thunderstorms over the mountains mid


Fair skies over the entire CWA this morning as upper level high
pressure develops over the west coast. A light northerly surface
gradient has developed and most locations seeing light north
winds. These north winds and warmer airmass bringing warmer
temperatures this morning on the order of several degrees. 1000
to 500mb thickness increases by 12 dm today over Thursday with 850
mb temps climbing several degrees. As a result, expect daytime
highs today to jump a good 10 degrees or more over Thursday. Even
more warming is expected on Saturday as the overall airmass
continues to warm. Highs on Saturday will reach into the 80s in
the valley with mid to upper 80s forecast for the northern
Sacramento valley. Models have been consistent in weakening the
west coast ridge a bit on Sunday as a weak upper trough moves
through the Pacific northwest. Both ECMWF and GFS continue to
paint some light precipitation over the northern mountains in the
afternoon. Stability progs indicate enough instability for a
slight threat of thunderstorms and have included them in the
latest forecast grids. For the remainder of the forecast area
Sunday will only see minor changes. Upper ridge rebuilds on Monday
bringing a bit more warming with Monday seeing some of the
highest temperatures of the season so far.



Upper level ridging will bring high temperatures about 10 degrees
above normal Tuesday and Wednesday, which means low to mid 80s for
the Valley and Delta. A closed low off the coast will gradually
approach, bringing moist southwest flow. Some instability showers
and thunderstorms in upslope flow are possible over the northern
Sierra, the mountains of western Plumas County and eastern Shasta
County afternoons/evenings Tuesday and Wednesday. These may become
more widespread Thursday and Friday, as the cool core of the low
is currently projected to move inland. Temperatures are also
forecast to drop to more seasonable levels. Model uncertainty on
timing and placement of the low remains high, though. EK



VFR conditions at the TAF sites the next 24 hours. Northerly
winds generally around 10 knots or less today. EK



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