Area forecast discussion
National Weather Service San Francisco Bay area
1112 am PDT Tuesday may 21 2013
Discussion...as of 9:40 am PDT Tuesday...made a minor forecast
update today to show winds picking up faster than expected plus
less cloud cover than forecast. 24 hour change product shows many
locations running 5 to 10 degrees cooler than Monday morning.
Still on track to have highs mostly in the 70s for inland spots
and 60s at the coast. Did issue a graphic to facebook and twitter
showing the peak speeds over the past few hours. 925 mb speeds
off the latest NAM keep 25-40 knots across much of our area through
tomorrow although speeds are not forecast to be quite as strong.
Previous discussion...after a string of nice mild weather...much
cooler weather is in store.
An upper level low currently near 48n/131w is expected to bring a
big change to the sensible weather across the region. Latest
satellite imagery reveals widespread high clouds covering much of
the Bay area. Surface observations indicate that under the high
clouds...a few patchy low clouds exist around 1k feet. Fort Ord
profiler and sodars put the diffuse marine layer 1000-1200 feet.
Short term(today-thursday)...
a few patchy low clouds will be possible early this morning...but
ample high clouds and a moderate north-S gradient will keep widespread
stratus from forming. More importantly today will be the big cool
down and breezy to occasionally gusty winds. The aforementioned
upper low is forecast to drop S and east into the Pacific northwest
today. As a result...much colder air will filter over the region.
Comparing yesterday/S maximum temperatures to the predicted maximum temperatures for
today show a big drop. In fact...parts of the North Bay may be as
much as 20 degrees colder today. Other locations will likely see
cold down of 10 to 15 degrees compared to Monday. Generally
speaking...highs today will be in the 60s at the coast and 70s
inland...southern interior up to the upper 80s. The cold advection
aloft and increasing onshore flow will lead to stronger
winds today...but just below Wind Advisory criteria.
However...gaps and passes...like Pacheco...may see occasional
gusts to 40-45 miles per hour. Despite the approaching upper low...the Bay
area is expected to remain dry. A few showers will be
possible...but well north of the County Warning Area.
For the rest of the short term...winds will ease up a bit
Wednesday and Thursday....but seasonably cool temperatures will
remain. Some patchy night and morning low clouds will be
possible...but currently not expecting a well established marine layer.
Long term(friday-monday)...
the longwave pattern indicates an Omega block covering much of the
Continental U.S. With an upper low lingering around the Pacific northwest. 500 mb
rebound slightly on Friday producing slightly warmer 850mb temperatures.
A few shortwave troughs rotate around the Pacific northwest upper low through
next week...but with little fan fare. All that being said...dry
weather and seasonably cool conditions will continue for the
Holiday weekend.
&&
Aviation...as of 11:00 am PDT Tuesday...VFR except for a small
patch of stratus over the mry peninsula. Increasing gusty winds
today as both north south and west east gradients increase. No
stratus expected tonight due to the northerly flow.
Vicinity of ksfo...VFR. Gusty west winds sustained to 30 knots with
gusts as high as 45 knots this afternoon. Airport weather warning in
effect through 9 PM this evening.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...small patch of stratus over mry this
morning. Otherwise VFR. Gusty west winds this afternoon.
&&
Mtr watches/warnings/advisories...
... Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm until 3 PM
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm until 3 PM
glw...pt Arena to Pigeon pt 10-60 nm from 3 PM
glw...pt pinos to pt Piedras Blancas 0-10 nm
glw...Pigeon pt to pt Piedras Blancas 10-60 nm from 3 PM
glw...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...mry Bay from 3 PM
Small Craft Advisory...sf Bay
&&
$$
Public forecast: Bell/mm
aviation/marine: ac
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