Area Forecast Discussion
Issued by NWS Sacramento, CA

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000
FXUS66 KSTO 192200
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
300 PM PDT Sun Apr 19 2015

.Synopsis...
Very warm weather continues across the region through Monday.
Isolated to scattered late day showers and thunderstorms will be
possible over the mountains. Another low pressure system will move
into the region by the middle of the week bringing cooler
temperatures and continuing the threat of showers or thunderstorms
into the end of the week.

&&

.Discussion...
Sunny skies and warm temperatures across the interior of NorCal
once again this afternoon. Temperatures are running a little above
readings of 24 hours ago across most of the region, except in the
Delta and northern San Joaquin Valley where a Delta trickle has
resulted in a few degrees of cooling. Current temperatures in the
valley range from around 70 at Travis AFB to about 90 at Redding
and Red Bluff.

Thunderstorms have so far been confined to the northern Sierra to
the south of Lake Tahoe this afternoon. Satellite imagery shows
some building cumulus further to the north up to around Blue
Canyon, and across portions of the Coast Range well to the north
of Clear Lake. The atmosphere further to the north is a little
drier and a little more capped as ridging builds into far northern
California, so development further north will likely be much more
isolated if something manages to pop. Similar to yesterday, the
storms will diminish rapidly by sunset with the loss of surface
heating.

Another warm day is on tap for much of the interior of NorCal on
Monday as the Rex Block moves overhead in response to the approach
of a stronger upstream trough. Most areas expected to see at least
a few degrees of cooling, but Delta Breeze influenced areas of the
valley should be down around 5 degrees or so from today. Also,
diurnal convection is expected to spread back into the northern
mountains as a little more moisture feeds up from the south and
soundings are less capped.

More substantial cooling is expected to spread across NorCal by
Tuesday as the upstream trough splits as it approaches the west
coast. It is expected to be strong enough to bring stronger
onshore flow to the region along with more widespread mainly
mountain convection, though favorable steering flow may bring
storms that form over the Coast Range down into the northern
Sacramento Valley.

Southern portion of the splitting trough is forecast to develop a
closed low as it drops south off the coast on Wednesday. Depending
on where the low tracks, the deformation zone may set up favorably
for much of the region to see at least a slight chance of showers
or thunderstorms that day with scattered showers and thunderstorms
continuing over the mountains.

&&

.Extended Discussion (Thursday through Sunday)...
A closed low that moves southward along the coast will be over
northern Baja by Thursday. However, the broad low will still
provide instability over NorCal and bring return flow moisture
from an easterly direction with thunderstorms looking like a
pretty good bet Thursday. The low will weaken and move to the east
by Friday, but the longwave trough will likely remain near the
west coast with potential showery activity through the weekend.

JClapp/Dang

&&

.Aviation...
VFR conditions for the next 24 hours. Isolated thunderstorms will
continue over the Sierra south of Lake Tahoe through 03z. Light
winds will continue except in vicinity of thunderstorms. Dang

&&

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

&&

$$




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