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Area forecast discussion 
National Weather Service San Francisco Bay area
454 am PDT sun Jul 24 2016

Synopsis...modest cooling is forecast for inland areas today and
Monday as high pressure over California weakens slightly. Warmer
weather is then forecast for Tuesday and Wednesday before a
cooling trend develops late in the week and into next weekend.

&&

Discussion...as of 3:35 am PDT Sunday...patchy low clouds began
to develop along the coast shortly after midnight as northwest
winds eased over the coastal waters and the low levels became
more stable. Expect low clouds to become somewhat more widespread
in coastal areas prior to sunrise. However, little inland
development of low cloud cover is expected given that the marine
layer remains shallow with a depth of 1000 feet or less.

Early morning water vapor satellite imagery shows that a weak
upper level shortwave trough has settled in across the Pacific
northwest and northern California, weakening the upper ridge
slightly. However, this has not resulted in any notable
modification of the airmass over our area which remains very warm
and dry. Early morning temperatures in the hills are in the 70s
and lower 80s with relative humidity values as low as the single
digits above 2000 feet. So it's likely that very warm and dry
conditions will persist in the hills today. However, some cooling
is expected at the lower elevations today. This is because the
relatively strong north-to-south surface pressure gradient we
have seen along the northern California coast during the past few
days is beginning to wane. And short-term forecast models indicate
this trend will continue today...which will allow for stronger
onshore flow by afternoon and thus modest cooling. The inland
cooling trend will continue into Monday as the low level flow
takes on a southerly component which will enhance the inland
influx of marine air. Inland high temperatures by Monday are
forecast to be as much as 10 to 15 degrees cooler compared to
Saturday, especially in the North Bay valleys.

Temperature trends are expected to reverse on Tuesday as high
pressure strengthens over California once again and the surface
thermal trough migrates close to the coast during the late night
and morning hours, thereby reducing onshore flow. Locations near
the coast are expected to warm into the 70s on Tuesday and
Wednesday while the warmest inland areas will see highs up near
100 again.

The longer range models agree that gradual cooling will begin late
in the work week, but for the most part very warm conditions will
persist inland through Friday. More significant cooling is then
expected next weekend as an upper trough settles in along the West
Coast.

Monsoon moisture is forecast to increase across far Southern
California by late in the week as the upper flow turns to the
southeast. But the arrival of the upper trough by next weekend
will turn the upper flow to the southwest and likely prevent that
monsoon moisture from making it anywhere near our area.

&&

Fire...as 3:30 am PDT Sunday...high pressure aloft remains strong
enough this morning to confine marine air to a shallow layer near
the coast. Above the marine inversion the airmass remains very
warm and dry with early morning temperatures in the hills in the
70s and lower 80s. Humidity recoveries have been poor above 1500
feet. In fact, early morning relative humidity values are in the
10 to 20 percent range at some of the higher peaks and as low as
the single digits at chew's ridge in Monterey County. One bright
spot is that winds have generally been easing in the hills and
should remain relatively light through this morning. Winds are
then expected to turn to the west and southwest and increase this
afternoon. Winds on Monday are forecast to turn more southerly and
this may be accompanied by a modest increase in the depth of the
marine layer, allowing for cooling and better humidity recoveries,
at least below 1500 feet. Warming is then expected to occur
Tuesday and Wednesday as high pressure strengthens over our area.
However, winds on Tuesday and Wednesday should be relatively
light.

&&

Aviation...as of 4:53 am PDT Sunday...shallow marine layer this
morning near 1k feet. Low clouds and patchy fog have develop near
Half Moon Bay southward through Monterey Bay. Impacts this morning
will likely be confined to kmry and ksns. Given the shallow nature
and moderate north-S gradient clouds inside sf Bay seem less likely.
VFR this afternoon. More widespread stratus seems likely tonight.

Vicinity of ksfo...VFR.

Sfo bridge approach...similar to ksfo.

Monterey Bay terminals...IFR/LIFR cigs this morning with clearing
17-18z timeframe. VFR this afternoon with cigs returning early
this evening.

&&

Marine...as of 02:24 am PDT Sunday...strong high pressure off
the coast and low pressure inland will continue to produce gusty
northerly winds along the coast. The strongest winds will be over
the outer waters and locally nearshore north of Point Reyes and
south of Point Sur. Steep wind waves will be possible due to the
gusty winds. Gusty winds will continue into early next week.

&&

Mtr watches/warnings/advisories...
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...sf Bay from 2 PM
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm

&&

$$

Public forecast: dykema
aviation: mm
marine: mm
fire weather: dykema



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