Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 190500

955 PM PDT Sat Apr 18 2015

Very warm weather continues across the region into early next
week. Isolated late day showers and thunderstorms will be possible
over the mountains. Another low pressure system will move into the
region by the middle of next week bringing cooler temperatures and
continuing the threat of mainly mountain showers and thunderstorms.


Diurnal convection has ended over interior Norcal although upper
trof lingers over the far Nrn zones and weak closed mid/upper level
low drifts off the far northern California coast. Cloud cover from
afternoon convection forecast to erode/dissipate overnight. Still
mins will be seasonably mild overnight especially in the thermal
belt areas due to warm air aloft. However...pressure falls from
heating in the valley have initiated a nearly 3 mbs SFO-SAC gradient
and a Delta Breeze.

Today was quite warm with max temps some 10-22 degrees warmer than
normal. RDD boasts a record max of 92 breaking the RDD AP (87 in
2009) and City records (90 in 1945).  JHM

.Previous Discussion...

The closed low over far northern California is forecast to drift
back to the southwest on Sunday as strong ridging over the eastern
Pacific moves closer, evolving into a Rex Block. This may cap off
deeper convection for a day across the northern mountains while the
focus of late day thunderstorms shifts to the Sierra to the south of
Lake Tahoe.

Temperatures will likely be the warmest of the past week on Sunday
as northerly/northeasterly flow briefly reinvigorates. Readings
through much of the Central Valley will likely climb into the upper
80s to lower 90s. These readings may flirt with records in the RDD
area again on Sun...especially the AP reading of 91 in 2009 while
the City record is 93 in 1945. The exception to the warming temps
may be in the Delta where a trickle may keep Fairfield in the lower

Diurnal mountain showers and thunderstorms are forecast to be on
the upswing again across NorCal on Monday as the ridge weakens
and a little more mid-level moisture is forecast to entrain up
from the southeast ahead of the weak low off the Central
California coast.

More widespread showers and thunderstorms along with cooler
weather will be possible beginning Tuesday as a stronger trough
moves into the region.


.Extended Discussion (Wednesday through Saturday)...
The longwave trough will dominate through the early portions of
the extended period, keeping temperatures moderated. Showers and
thunderstorms still look like a pretty good for the mountains
Tuesday through Thursday, and possibly into Friday. A few of these
showers may make it down to the Valley as well, though timing and
location of these showers could be tricky.

Significant model differences arise by the end of next week. The
ECMWF and GEM both show a trough moving through Northern
California next Friday, whereas the GFS keeps a drier, broad
westerly flow solution. With no inkling toward any solution, our
forecast Friday and beyond leans heavily on climatology. Expect
temperatures to remain around or slightly warmer than normal. Dang


.Aviation...VFR conditions next 24 hours. Light winds will continue
except in vicinity of Sun afternoon thunderstorms over Mtns.


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


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