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Area forecast discussion 
National Weather Service San Francisco Bay area
439 am PDT Tuesday Sep 23 2014

Synopsis...near seasonal conditions will continue across the San
Francisco and Monterey Bay area today. Cooler weather and chances for
rainfall are then expected starting Wednesday as an upper level system
impacts the region.

&&

Discussion...as of 3:00 am PDT Tuesday...satellite shows fewer
clouds early this morning compared to previous mornings with much
of our County Warning Area seeing clear skies. Surface for low still from the northwest
and with some clouds over our northwest outer waters will need to see if
they are able to advance to the coast or not. Temperatures are
running within a few degrees of yesterday, and highs are expected
to be close to Monday -- middle 60s to middle 70s at the coast with middle
70s to middle 80s inland.

All attention continues to be focused on a storm system around
45n/140w (or 1100 miles northwest of san francisco) that will advance to
first to eh pacnw coast late today and then down to norcal/sf Bay
region for Wednesday into Thursday. Rain will advance down the
coast as an associated cold front approaches. Timing continues to
suggest on Wednesday afternoon/evening for the far northwest portion of the
North Bay...into the sf Bay region Wednesday night...and down to
Monterey Bay area on Thursday. The vast majority of the moisture
will be focused to the north of our area with smaller amounts
forecast as you progress to the south. Rainfall totals by Thursday
evening still look like locally more than 1/2" over the North Bay
with generally 1/10" to 1/4" around sf Bay plus the Santa Cruz
Mountains. Other sports will likely pick up even less with
interior Monterey County and San Benito counties expecting very
little rainfall.

Models have backed off a bit from the convective parameters and
agree with the previous shift that removing them from the forecast
for late Wednesday into Thursday was the right call.

Behind the frontal passage the longwave trough and main upper level
low will move overhead on Friday. This will lead to scattered
showers across at least the northern half of our area. Synoptic
setup would also suggest the possibility of thunder so will need to
see what the higher resolution models say as it gets a little
closer. Additional rainfall amounts for Friday should be under
1/10" in almost all spots. The low is expected to slowly depart to
the east late on Saturday.

For next week...the storm track is forecast to shift back well to
the north as a ridge builds near the West Coast. Temperatures will
average out a bit above normal.

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Aviation...as of 4:35 am PDT Tuesday...late developing stratus
across much of the region this morning. Ceilings are generally
1000-1500 feet...but the marine layer is patchy in nature.
Therefore...expecting a relatively early burn off. Expecting VFR
this afternoon with some ceilings returning late tonight. Conf is
medium.

Vicinity of ksfo...MVFR ceilings across the East Bay and over ksfo.
Expecting early burn off and will currently forecast 17z...but it
could be earlier. VFR this afternoon with gusty west winds.

Ksfo bridge approach...at this time...the approach is mostly
clear...but ceilings are on the fringes. Patchy ceilings will likely
impact the approach...but it may not be constant.

Monterey Bay area terminals...IFR ceilings through 17-18z. VFR this
afternoon.

&&

Marine...as of 04:14 am PDT Tuesday...light to moderate northwest
flow will continue along the central coast as high pressure
remains over the eastern Pacific. A cold front will move through
the region Wednesday bringing a chance for rain and increasing
northwesterly swell.

&&

Mtr watches/warnings/advisories...
...

$$

Public forecast: Bell
aviation/marine: mm

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