Area Forecast Discussion
Issued by NWS Sacramento, CA

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457
FXUS66 KSTO 012150
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
250 PM PDT SUN MAY 1 2016

.Synopsis...
Threat of afternoon showers and thunderstorms continues over the
mountains into Tuesday then a more widespread chance Wednesday
into Friday. Cooling to near normal midweek.

&&

.Discussion...
Thunderstorms and showers have developed along the western Sierra
slopes this afternoon. Current radar shows that most of the
thunderstorms are in El Dorado county and southward along the
Sierra. Latest HRRR run is showing that showers/thunderstorms will
gradually spread northward along the Sierra...reaching up to
around the Quincy-Chester area. HRRR also shows that
showers/thunderstorms could move into the foothills, especially
the Motherlode region along with some showers possible in the
Northern San Joaquin Valley this evening around Stockton and
Modesto. All shower activity should diminish by 9-10 pm tonight.
In the meantime, if you hear thunder, stay indoors for shelter to
avoid dangerous lightning and possible hail.

Meso low weakens over NorCal Monday although some lingering
chances for showers/thunderstorms possible along the higher
elevations of the Sierra. By Tuesday, a deep upper trough over the
Eastern Pacific Ocean will move into the West Coast which will
continue the threat of afternoon mountain showers and
thunderstorms. High temps trend down slightly on Tuesday as
synoptic cooling and onshore flow gradually increase over Interior
NorCal.

More notable cooling (5-10 degrees) on Wednesday as the
center of the low gets closer to interior NorCal. Valley highs
will be around the mid 70s with 50s and 60s along foothills and
mountains. Chance of showers will become more widespread on
Wednesday, covering much of our CWA. Instability with this low
will keep a slight chance of thunderstorm development in the mix,
too. JBB

&&
.EXTENDED DISCUSSION (Thursday THROUGH Sunday)

Forecast models are in decent agreement as to the position and
timing of the upper level low track and progression starting at the
beginning of the long term forecast period.  The high amplitude
trough of low pressure is a bit quicker as advertised by the GFS
heading into late Wednesday night to early Thursday morning, while
the ECMWF has the arrival into NorCal more into the early to mid
morning hours on Thursday. In either scenario, the incoming storm
system will bring the needed lift behind enough moisture to bring
showers and thunderstorm chances for the entire forecast area. The
system will not move very quick, and cool temperatures along with
chances for showers and thunderstorms will continue through next
weekend.

A cool down of temperatures is expected with a return to near normal
high temperatures in the low to mid 70s in the valley, 50s to 60s in
the foothills, and the low to mid 40s in the higher elevations on
Thursday and Friday.  Temperatures should return to slightly above
normal temperatures in the valley next weekend.
&&

.AVIATION...

VFR conditions are expected at the terminals for the next 24
hours. Thunderstorms over the Sierra Cascade range this afternoon
and evening. Light winds.

&&

.STO Watches/Warnings/Advisories...
None.
&&

$$



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