Wednesday, September26, 2018

Marine Weather and Tides
Point Arena, CA

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9/17/2018 XTide broke when 1and1 "upgraded" my server. It has been esculated. I am sorry for the problem.

Sunrise 7:00AMSunset 7:00PM Wednesday September 26, 2018 4:09 AM PDT (11:09 UTC) Moonrise 7:36PMMoonset 7:42AM Illumination 97% Phase: Waning Gibbous; Moon at 16 days in cycle
NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION.
Marine Forecasts
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7 Day Forecast for Marine Location Near Point Arena, CA
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location: 36.95, -126.32     debug

Area Discussion for - San Francisco/Monterey Bay Area, CA
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Fxus66 kmtr 261036
area forecast discussion
national weather service san francisco bay area
336 am pdt Wed sep 26 2018

Synopsis Seasonably warm today and Thursday. Cooling trend
starts Friday as an upper trough passes north of the golden gate
with a slight chance of a north bay shower Saturday. Dry and
seasonable Sunday. Then a slight chance of rain by early next

Discussion As of 3:36 am pdt Wednesday... Marine layer is
around 1000 feet but showing signs of compressing. Given the
shallow depth its only filled into the salinas valley and locally
through the golden gate and petaluma gap. Dense fog reports are
showing up at santa rosa and half moon bay as well as around
monterey bay as the moisture gets compressed under the high
pressure and offshore flow. Large scale gradients from the deserts
of nevada to our coastline show about 8-9 mb so a moderate
offshore pattern but most of that gradient is actually over the
sierra so we are not seeing much wind in the hills. Vertical temp
and moisture gradients are impressive with 3 am readings showing
mid 70s in the hills with continued dry rh readings of 10-30%
while much cooler and more moist conditions persist in the
valleys. The warm air aloft suggests that today will be our
hottest day with inland areas warming into the 90s with widespread
upper 70s and 80s throughout the bay area. The coast will stay
cool with continued local onshore gradients.

Right now were not forecasting much change in the pattern for
Thursday but afternoon winds may trend onshore as an upper low
approaches and we lose our offshore tendencies. So if anything
there may be a few degrees of cooling Thursday but temps still
above normal overall.

Large upper low will approach the north bay coast by Friday and
all areas will notice a cooling trend with inland areas back into
the 70s due to airmass cooling and onshore breezes. The core of
the upper low looks to move onshore near CAPE mendocino. The
structure of this low suggests we'll only see showers right under
the core of the upper low which will probably be mendocino county
northward. However its close enough to keep the slight chance of
Saturday showers for the north bay.

That feature will eject inland on Sunday and leave a dry and
seasonable weather pattern in place for the last day of sept.

The extended forecast is quite interesting. Will be watching
tropical storm rosa which is currently getting itself organized
way down in the tropics west of central america. Latest forecasts
bring the feature northward to west of baja california as a
hurricane by later Sunday Monday. Meanwhile a longwave trough will
be developing off the california coast. Models are struggling
with the interaction of this trough and the tropical system
forecast to approach northern baja. We've seen some pretty drastic
run to run variations for the last few days and the euro GFS are
at odds with each other. There are scenarios where the mid-latitude
trough by-passes us and moves onshore over socal while interacting
with rosa while other scenarios suggest the potential for some
early season soaking rains over norcal by early next week.

Given all this believe its still prudent to just keep the low end
pops going in the forecast until some of the model uncertainty
gets more clear in the coming days. There are plausible scenarios
where much of the district sees little or no rain and vice-a-versa.

Aviation As of 10:24 pm pdt Tuesday... For 06z tafs. Marine
layer remains at around 1000 to 1200 feet in depth with stratus
along the coast and moving down the salinas valley. Given similar,
if not more extensive, cloud cover than this time last night
sticking with a persistence forecast. Low CIGS expected at most
sites aside from ksjc and klvk with patchy fog in the north bay
and reduced visibility possible at the monterey bay sites.

Generally light winds overnight becoming onshore in the afternoon
10-15 kt.

Vicinity of ksfo...VFR with light winds. Possible MVFR ifr cigs
late tonight 10z-12z.

Sfo bridge approach... Similar to ksfo.

Monterey bay terminals... Ifr lifr CIGS through 16z-18z tomorrow
morning with possible ifr lifr vis.

Marine As of 02:46 am pdt Wednesday... A trough of low pressure
along the coast will keep light west to northwest winds through
Friday. Winds will turn southerly on Saturday as a low pressure
system develops off the pacific northwest.

Mtr watches warnings advisories
Tday None.

Public forecast: rww
aviation: W pi
marine: W pi
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Wind Forecast for San Francisco/Monterey Bay Area, CA (7,2,3,4)
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Ground Weather Radar Station San Francisco Bay Area, CA
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