Area forecast discussion
National Weather Service San Francisco Bay area
1023 PM PDT Sat may 25 2013
..cool Holiday weekend with light rain possible by late on Memorial
Day...
Discussion...as of 8:55 PM PDT Saturday...the upper trough that
has been parked along the West Coast for several days now
continues to produce cool conditions across our region. High
temperatures today were from 5 to 10 degrees below normal at most
National Weather Service reporting locations. Skies were mostly
sunny today except for some patchy low clouds inland this
morning...and areas of persistent low clouds near the ocean.
Water vapor satellite imagery shows a well-defined shortwave
trough dropping southeast offshore near the California/or border. As this upper
level feature swings across northern California tonight...it will enhance
onshore flow across our region...result in more widespread low
cloudiness...and perhaps produce enough lift to generate some
local drizzle near the ocean. The NAM continues to show light quantitative precipitation forecast
near the ocean from later tonight all the way through Sunday
evening. Doubt we will see such an extended period of coastal
drizzle...but patchy night and morning drizzle seems like a good
bet. Sunday will be another cool and locally breezy day. Low
clouds should clear in most areas by midday...but some low
cloudiness will likely persist through the day near the ocean where
the moist low level northwesterly flow impinges on the coastal
terrain.
A weather system over the northeast Pacific...near 150w and
between 40n and 50n...is projected to move east-southeast and into the Pacific northwest
and northern California by Monday afternoon. This system currently
has a pretty good moisture tap and should hold on to enough of
that moisture to produce rain across much of our area from midday
Monday through Monday night. There had been some disagreement
between the models as to how far south this system would produce
precipitation...but recent model runs are in pretty good agreement in
spreading light rain into the North Bay by midday on Memorial
Day...then south and east across the rest of the sf Bay area by
late Monday afternoon...and finally south into the Monterey Bay
area on Monday night. Thus...much of our area from San Jose south
is expected to remain dry for most of Memorial Day. Rainfall totals
in the coastal ranges are projected to range from a quarter to a
half inch...with perhaps a bit more across the North Bay hills.
Elsewhere...rain totals will be on the order of a tenth or two to
as little as just a few hundredths or trace amounts in the
southern interior valleys.
Some widely scattered light showers may linger into Tuesday
morning...but for the most part Tuesday looks to be a mostly dry
and cool day. Another shortwave trough may produce some additional
light rain on Wednesday. Earlier model runs indicated that only
the North Bay would have a chance of rain on Wednesday...but the
00z NAM suggests that rain could reach farther south that day.
Will need to consider extending wednesday's rain chances farther
to the south once the full compliment of 00z model data is in.
Gradual warming and drying is expected during the second half of
next week as the longwave upper trough finally moves east.
&&
Aviation...as of 10:27 PM PDT Saturday...low clouds continue to
gather over the coast. The sfo-SAC gradient is 3 mb. Onshore winds
will usher in low clouds overnight.
Vicinity of ksfo...west winds have diminished somehwat. Low clouds
will increase overnight with MVFR ceilings forecast.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...MVFR ceilings are forecast tonight.
Light drizzle is possible.
&&
Mtr watches/warnings/advisories...
... Bay until 11 PM
Small Craft Advisory...mry Bay until 11 PM
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm until 11 PM
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm until 11 PM
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm until 2 am
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm until 2 am
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm until 2 am
&&
$$
Public forecast: dykema
aviation/marine: canepa
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