Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 232048

Area Forecast Discussion
National Weather Service San Francisco Bay Area
148 PM PDT Wed May 23 2018

.SYNOPSIS...Seasonably cool weather conditions along with overnight
and morning low clouds will continue to impact the region through
late week. An upper level system will then approach the coast late
Thursday and bring a chance of rain showers to much of the region
into Friday. Showers may linger into Saturday morning before a
warming and drying trend returns late in the holiday weekend.

&& of 01:46 PM PDT Wednesday...Low clouds continue
to impact the northern two-thirds of the region this afternoon
with persistent onshore flow. This has resulted cooler conditions
compared to yesterday over portions of the North Bay while areas
further south are a few degrees warmer. In addition, seeing breaks
in the cloud cover over the Pacific this afternoon.

With all this, expecting little change overall in the pattern
heading into tonight and Thursday morning ahead of an approaching
mid/upper level low pressure system. Look for coastal drizzle to be
a bit less widespread overnight into early Thursday morning with
continued cool weather conditions. Low clouds will likely fill back
in over the ocean and spread inland during the overnight hours as

Rain showers are forecast to develop late Thursday night and spread
inland Friday as the mid/upper level system pushes inland. There is
also a non-zero chance of high-based thunderstorms across portions
of the region late Thursday night into Friday morning as moisture
and instability increases in the 500-700 MB layer. However, have
left out mention of thunderstorms in the forecast as confidence is
low at this time and will needed to be monitored in the next 24
hours. Showers will remain possible into Friday night before
diminishing Saturday morning as the upper level system shifts inland.
Overall, rainfall amounts will range from a few hundredths to one-
tenth of an inch in most locations. Locally higher amounts will be
possible in any heavier showers that develop while the showery
nature of this system may leave some areas with no measurable
rainfall at all.

A warming and drying trend is then forecast into Sunday with
temperatures back to around seasonal averages by the Memorial Day
Holiday. This will be the result of a building ridge of high
pressure along the eastern Pacific. Another mid/upper level trough
is then forecast by the middle part of next week that would cool
temperatures once again and potentially enhance overnight/morning
coastal stratus.


.AVIATION...As of 10:41 AM PDT Wednesday for 18Z TAFs...Most of
the region has been inundated with stratus all morning. Satellite
imagery is showing the stratus beginning to dissipate over inland
areas. The SF and Monterey Peninsulas may remain IFR/MVFR through
the period with occasional clearing this afternoon. The rest of
the taf sites are expected to see VFR conditions this afternoon
through the early evening before low clouds return and settle in
once again for the night.

Onshore winds will continue today becoming breezy in the afternoon
at around 15 kt. Winds however, are not expected to be as gusty
as the past few days since the SFO-SAC gradient has lessoned.

Overall forecast confidence: Low-moderate

Vicinity of KSFO...IFR to MVFR conditions remain in place with
cigs currently between 1500 and 2500 ft. Some brief clearing may
be possible this afternoon, otherwise expect low cigs to prevail.
Any afternoon clearing will fill back in tonight. Onshore winds
today increasing to around 15 kt in the afternoon with occasional
higher gusts possible.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR cigs currently at MRY and SNS at
around 2000 ft. Satellite imagery is showing stratus beginning to
clear in the Salinas Valley. VFR conditions at SNS are expected
this afternoon while MRY may remain under MVFR cigs through the
period with only sporadic clearing. Regardless, any clear skies
will be filled back in this evening. Westerly winds becoming
around 15 kt in the afternoon.

&& of 09:01 AM PDT Wednesday...Light northwesterly
winds will continue across the coastal waters today and tonight
with the exception of locally gusty winds through the Golden Gate
gap, around Angel Island, and in the West Delta from late this
morning through the afternoon. Winds across the waters will turn
southerly by tomorrow morning as an upper low and weak surface
cold front approach from the west. This will bring chances of
showers tomorrow and Friday. Long period southerly swell will
persist along with a shorter period northwest swell through the
week, diminishing by Friday.


     .Tngt...SCA...SF Bay until 3 PM




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