Area Forecast Discussion
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FXUS66 KSTO 191007

Area Forecast Discussion
National Weather Service Sacramento CA
307 AM PDT Thu Jul 19 2018

Temperatures will gradually decrease late this week, with the
potential for afternoon thunderstorms in the mountains. Hot
weather returns next week.


Strong upper level ridge continues to bring fair weather across
interior Northern California this morning. A few high level
clouds have started to move across the region as this upper ridge
slides eastward. Extensive marine stratus continues along the
California coast, and even though a good onshore gradient exists
through the Delta, these cooling effects have not been felt
across the interior yet. Temperatures as of this writing are still
in the upper 60s to 80s with strong thermal belts in the Sierra

Another hot one is in store across much of the forecast area
today. The thermally-induced trough, which was situated over the
Central Valley the last couple of days, will shift east into the
Great Basin today and allow stronger onshore flow to reach the
interior later this afternoon and evening. These cooling effects
will likely be limited to areas adjacent to the Delta today,
whereas the rest of the Valley will still be in triple-digit
territory. The northern Sac Valley near Redding in particular
could once again approach 110 degrees this afternoon. A Heat
Advisory will remain in place into this evening for that local

A weak upper disturbance currently off the Baja California coast
will gradually move northward the next few days. While it is
projected to remain off the CA coast, it will help to draw
subtropical moisture northward. Expect a modest increase in cloud
cover Friday into Saturday, with perhaps a few afternoon
thunderstorms over the mountains. There appears to be enough
elevated instability for isolated thunderstorms even across lower
elevations, but forcing is weak at best.

A healthy Delta Breeze will continue into the weekend, eventually
bringing more widespread cooling across the interior. High
temperatures across the Valley will be in the 90s to lower 100s,
with 80s to 90s over the mountains. These weekend forecast high
temperatures will be within a few degrees of normal.



An upper level high pressure ridge over the westerly U.S. will
dominate the weather pattern throughout the extended period.
Daytime high temperatures will remain several degrees above normal
each day with only minor variations depending on the location of
the ridge axis which models differ on slightly. Main impact of
these differences will be location of any afternoon and evening
thunderstorm activity. GFS has a slightly more west position on
the upper ridge axis than does the ECMWF. A more south or
southeast flow aloft modeled by the GFS would bring a better
threat of afternoon convection. The ECMWF solution of a more
southwest flow aloft would be more conducive to a quieter more
stable solution.

Have compromised for now by including a slight threat of
afternoon or evening thunderstorms over the northern Sierra and
leaving remainder of the forecast area clear. Both GFS and ECMWF
have upper ridge east enough by the end of the week to keep any
thunderstorm activity east and south of the forecast area. In
short for most areas, look for hot and dry pattern to continue
through the extended period.



VFR conditions the next 24 hours across TAF sites. Winds generally
below 15 knots except west gusts to 30 kt near the Delta.


Heat Advisory until 8 PM PDT this evening for Northern
Sacramento Valley.


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