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FXUS66 KMTR 170459

Area Forecast Discussion
National Weather Service San Francisco Bay Area
959 PM PDT Tue Oct 16 2018

.SYNOPSIS...Seasonably warm days followed by mostly clear and cool
nights will continue the rest of the week and into the weekend.
The forecast remains dry through the middle of next week.

&& of 9:21 PM PDT Tuesday...Just some minor 
forecast updates this evening to account for low cloud formation 
over the ocean. So far only Watsonville and Half Moon Bay are 
reporting some clouds with vsby 4 miles at Half Moon Bay. Earlier 
we talked to observers at the Farallones and they indicated no 
fog. In fact cloud heights are surprisingly high at Half Moon Bay 
around 2000 feet. Often when the stratus returns after offshore 
flow its very shallow. It was another sunny a pleasant October day
across the Bay Area with lots of highs in the 70s and 80s.

We've still got large scale offshore flow from the Nevada deserts
at nearly 10 mb with the local sfo-sac 1.5 mb onshore. So we 
continue to see warm/dry conditions in the hills with light 
offshore winds while some local onshore breezes squeeze through 
the valleys and coastal gaps. 

Latest 00z nam shows 500 mb ridge building to our north with a
weak low to our south that will keep warm and dry weather at least
through Friday with 70/80s days and 40s/50s at night.

No big changes through the weekend. Continued dry and seasonable.


.PREV of 1:52 PM PDT Tuesday...The upper level 
pattern over the region will change little through midweek as 
mid/upper level high pressure over the eastern Pacific extends 
inland over the Pacific Northwest and an upper level low remains 
over the Desert Southwest. This will keep light offshore winds 
across the interior and result in seasonably warm conditions each 
afternoon. Mostly clear conditions are likely overnight with 
seasonably cool temperatures in the lower elevations while mild 
temperatures persist in the hills/mountains with continued 
offshore winds. 

By late in the week, weak onshore flow will potentially develop 
as the upper level low slowly moves to the northeast and high 
pressure builds further inland across the West Coast. This may 
allow for a shallow marine layer to develop with the development 
of coastal stratus during the late night and early morning hours. 
However, confidence is low at this time and widespread cloud cover
is not currently expected through late week. This too may cool 
conditions a bit near the coast as offshore flow remains confined 
to the inland areas. This will likely lead to pleasant fall 
weather conditions over the region through the upcoming weekend.

The medium range models continue to suggest a possible pattern
shift early next week as an upper level trough approaches the
Pacific Northwest. This would likely at least result in a cooling
trend region-wide with rain chances increasing over northern
California late Monday into Tuesday. Unsettled weather conditions
look to linger into late next week as well with precipitation
dropping as far south as the North Bay. However, confidence
remains low on widespread rainfall actually developing over our
region late in the forecast period. Will need to monitor in the
coming days.

&& of 10:00 PM PDT Tuesday...Satellite image shows 
areas of stratus over the waters. Stratus is filling MRY Bay and
should spread into MRY and SNS. Latest NAM guidance shows cigs
into SFO and OAK early morning so have added that into the TAFs.

Vicinity of KSFO...Occasional MVFR cigs between 12Z and 16Z. 

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...IFR cigs after 07Z clearing after 17Z.

&& of 09:33 PM PDT Tuesday...High pressure over the
Eastern Pacific coupled with a thermal trough along the coast will
maintain light northwest winds  through Sunday. A long period
northwest swell will arrive on  Wednesday bringing an increased
risk of rip currents and sneaker waves. Swell period will decrease
Wednesday night and Thursday.





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