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fxus66 kmtr 201200 
afdmtr

Area forecast discussion
National Weather Service San Francisco Bay area
500 am PDT sun may 20 2018

Synopsis...a deep marine layer will allow for continued overnight
and morning clouds along the coast the next few days. Temperatures
will remain seasonably cool this week and into next weekend.

&&

Discussion...as of 2:53 am PDT Sunday...infrared satellite
imagery reveals low clouds blanketing much of the San Francisco
Bay area and central California coast this early morning. An upper
level trough axis that has sagged over the California coast since
yesterday has allowed the marine layer to balloon in excess of
2,500 ft, according to the ft. Ord profiler. This upward trend in
the marine layer depth has also been captured in the Oakland
soundings over the past day and a half. Locations that have been
spared from the overcast skies so far this early morning include
the North Bay interior valleys, which has been the case for the
last few nights through this time. Temperatures are generally
running within a degree or two from what they were at this time on
Saturday morning. Breezy conditions have persisted past midnight
for parts of the region as a 2.8 mb onshore surface pressure
gradient has held from San Francisco to Sacramento. For example,
San Francisco International Airport continues to gust to 26 kt as
of 1:56 am PDT.

Synoptically, a longwave trough axis extends from the Gulf of Alaska
south through California. Over the next 24 hours, an upper low
will develop and drop south and set up residence over the
southern half of the state as a cut-off low for a few days. This
low will aid in reinforcing the cooler than normal conditions for
the San Francisco Bay area, and will likely allow for continued
overnight/morning low clouds along the coastline. The best
convective potential over the next few days will remain outside
our County Warning Area in the Sierra Nevada, Klamath Mountains,
and the northern coastal range peaks from Trinity to lake
counties. The 06z NAM does bring some minor surface-based
instability to extreme northern Napa and Sonoma counties on both
Monday and Tuesday afternoons, with the best potential looking to
be on Tuesday. With this in mind, did introduce a slight chance of
thunderstorms to these locations for Tuesday, closely aligning
with the latest storm prediction center's day 3 convective
outlook.

Models suggest the cut-off low will gradually lift northeast into
the Great Basin late Tuesday or Wednesday, and gradually fill
(weaken) in the process. There should be a brief period of weak
ridging aloft for Thursday before models advertise an another
approaching upper level low in the eastern Pacific. The GFS lifts
the low's center north toward the Oregon/Washington border by the
Memorial Day weekend, while the European model (ecmwf) takes a different track by
bringing the low onshore near Point Reyes. It's still 5-7 days
out, but if the low takes the southern Route, this could bring an
increased chance of showers and possible convection to the area
for the Holiday weekend.

&&

Aviation...as of 4:59 am PDT Sunday...for 12z tafs. Generally
MVFR cigs across the region, per 11z surface obs. Fort Ord
profiler and fog product satellite shows a very robust and deep
marine in place. The thick marine layer and the decent onshore
gradient will likely keep stratus over all taf terminals through
the majority of, if not all, the day today. Perhaps some clearing
possible at some terminals for a few hours in the afternoon. Winds
will be on the breezy/gusty today, into this evening, sustained
around 15 kt by this afternoon, with gusts exceeding 20 kt at
times.

Moderate forecast confidence.

Vicinity of ksfo...MVFR cigs through at least 20-21z, with the
possibility of not clearing at all. Westerly breezy/gusty winds
will continue through the day and evening.

Sfo bridge approach...similar to ksfo.

Monterey Bay terminals...thick marine layer will likely keep
MVFR cigs over the Monterey Bay terminals all day/evening. Slight
chance of clearing at ksns this afternoon, but not confident
enough to include in taf. IFR cigs possible by tonight. Breezy
onshore winds, occasionally gusty this afternoon and evening.

&&

Marine...as of 2:42 am PDT Sunday...a tight north to south
pressure gradient along the California coast will continue to
produce moderate to strong northwesterly winds across the coastal
waters through Monday. As a result, steep wind waves will produce
hazardous conditions for small crafts. A long period southerly
swell will increase and mix with northwesterly swell by Monday
morning, gradually increasing through much of the week.

&&

Mtr watches/warnings/advisories...
... Bay from 12 PM
Small Craft Advisory...mry Bay from 12 PM
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm from 12 PM
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm

&&

$$

Public forecast: Rowe
aviation: BAM
marine: BAM

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