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

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FXUS66 KMTR 241149

Area Forecast Discussion
National Weather Service San Francisco Bay Area
449 AM PDT Tue Apr 24 2018

.SYNOPSIS...A cooling trend is forecast from Tuesday through the
end of the week as an area of low pressure offshore slowly
approaches the coast. This low pressure may produce widely scattered
showers from late Friday into Saturday, mainly from the San
Francisco Bay north. Temperatures will be cool through the weekend
and early next week.

&& of 3:00 AM PDT Tuesday...An upper level trough
that moved inland north of the state on Sunday has brought onshore
flow to the area which has allowed low clouds to spread around the
bay this morning. Forecast high temperatures have been adjusted
lower around the Bay Area for today to account for the 1500 foot
marine layer and the onshore gradients. Wednesday should be a
continuation of today with more night and morning low clouds
around the bay.

An upper level low currently near 40/137 will drift slowly
eastward over the next few days. This will deepen the marine layer
even more Thursday and Friday resulting in a cooling trend for all
areas including the interior valleys. Models are indicating
stratus may spread into the North and East Bay interior valleys
Thursday night and Friday morning. The marine layer will
eventually mix out but cooler air will continue to advect into the
area as the low gets closer to the coast. There is remarkably
good agreement with the GFS ECMWF and Canadian models in bringing
the low into northern California Friday night and Saturday.
Showers will be limited due to lack of moisture so the main
effects will be the cool temperatures. The forecast mentions a
slight chance of showers from the Bay Area north Friday night and
Saturday. Highs Friday and Saturday only in the 60s in the Bay
Area and low 70s in the inland valleys.

As the low moves inland models indicate a secondary upper level
disturbance pinwheeling around the upper low and racing through
the area on Sunday. Again shower chances will be very minimal but
it will keep the cool temperatures going into Monday.

Temperatures will start to warm back up the middle of next week as
an upper level ridge builds along the west coast.


.AVIATION...As of 4:45 AM PDT Tuesday... Stratus deck w/ cigs
400-1200 ft this morning as thermal trof lingers inland tightening
the onshore gradient. Gradient will weaken into the sunrise hours
allowing for a gradual burn off from the edges by 16-18Z depending
on location. Otherwise, light to locally breezy (near coastal
gaps) onshore winds today with passing high clouds at or around
20000 ft. Another round of stratus, possibly thicker/lower,
anticipated to begin again overnight tonight.

Vicinity of KSFO...Borderline IFR/MVFR thru 16z posbl with some
SCT- BKN clouds impacting approach into the 17Z hour. Breezy PM
W-NW wind with a few more gusts to 20 knots possible later today.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...IFR/LIFR into sunrise hours with a few
areas of lingering stratus into the mid morning around the lip of
the MOnterey Bay. Light onshore winds this afternoon and evening.
Stratus and fog are likely to roll back inland early Tuesday

&& of 04:42 AM PDT Tuesday...Generally light onshore
winds through the work week, with locally breezy to gusty winds
near coastal gaps or prominent points such  as the Golden Gate
bridge and Point Sur. Light to moderate seas  will prevail through
the forecast period with a mixed southerly  and northwesterly
swell developing late this week.





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