Area Forecast Discussion
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FXUS66 KSTO 192233

Area Forecast Discussion
National Weather Service Sacramento CA
333 PM 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.


Upper level ridging has brought another hot day to the northern
Sacramento Valley. As of 3 pm, Redding was 108, Red Bluff 105. A
Heat Advisory for the northern Sacramento Valley continues until
Temperatures to the south have been relatively a little less hot,
especially for areas influenced by the Delta breeze. For example,
downtown Sacramento was 97, compared to 102 yesterday.

Some showers and thunderstorms are developing over the Sierra
crest from around Ebbetts Pass southward. This is due to monsoonal
moisture and afternoon instability. This moisture will be pulled
further northward by an upper low off the coast and high pressure
center over the 4-Corners area. Showers and thunderstorms
will spread northward during the day and are expected to reach
just north of I80 by late afternoon. These are expected to spread
into the northern mountains and Coastal Range over the weekend.

The Delta breeze and onshore flow in general are expected to
increase tonight as the thermal trough shifts eastward. Cooling
will be limited, though, as the marine layer on the coast remains
rather shallow. Friday highs are expected to be 3-7 degrees lower
than today, ranging from mid 90s to lower 100s over the Central Valley,
low to mid 90s in the foothills, 80s to lower 90s in the Delta.

A fairly strong Delta Breeze is expected into the weekend, bringing
more widespread cooling across. High temperatures across the
Central 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. EK


Upper level high pressure ridging will dominate the weather
pattern over the West throughout the extended period, bringing a
return to hot weather.There remains uncertainty on the exact
location of the ridge axis due to model differences. The 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.

Continue to include 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. EK



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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