Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco Bay Area

359 am PST Fri Jan 18 2019

Synopsis

Shower chances will continue across the North Bay on Friday and Saturday as the storm track shifts north. A weak boundary will move into the SF Bay on Saturday morning, bringing a chance of showers to most of the Bay Area. Dry conditions are anticipated elsewhere through Saturday. More widespread light rain is forecast for Sunday as a Pacific storm system moves through the area. Dry and mild weather is expected to develop on Monday and continue through the remainder of next week.

Discussion

As of 03:20 AM PST Friday, KMUX radar indicates a few light showers over the coastal waters, which appear to be dissipating before they move inland. These showers are not being resolved by models but expect any showers which manage to reach land to be light. Extensive cloud cover has kept temperatures fairly mild with current temperatures in the mid 40s in the North Bay valleys to the mid 50s near the SF Bay shoreline. Cloud cover is preventing fog from forming apart from isolated locations.

An upper level ridge forming just offshore will build along the California Coast on Friday. This will shift the storm track to the north with heavy rainfall expected in Oregon and far northern California Friday through Saturday. Moisture will move far enough south to bring scattered light showers to the North Bay for much of Friday. A weak boundary is then forecast to move southeast into the greater Bay Area Saturday morning before dissipating. This will bring a chance of light rain as far south as San Jose. Light showers will continue across the North Bay through Saturday. Up to a half inch of rain is anticipated through Saturday night in portions of the North Bay, tapering to only a few hundredths around the Golden Gate. High temperatures Friday and Saturday will be slightly above normal in our southern regions with low to mid 60s expected. Thicker cloud cover and light precipitation will keep the North Bay cooler with highs in the upper 50s to near 60.

An upper level trough will push the ridge east and bring a chance of rain to the entire area on Sunday. A cold front will push through the area Sunday morning into Sunday afternoon, with precipitation along the front. The front is expected to weaken as it passes through the area, and moisture appears limited with PWAT remaining under an inch. Showers will continue behind the front as the cold core of the upper low moves overhead. Rainfall totals with this system will be light, with an additional half inch possible in the North Bay with less than a quarter inch elsewhere. Behind the cold front, northwest winds could become breezy near the coast and in the higher terrain as surface high pressure builds to the west and the surface low deepens over the Great Basin.

The pattern will transition to much drier beginning on Monday. High pressure will strengthen over the East Pacific and gradually shift east. By Thursday, the ridge will become highly amplified with the storm track shunted north into Alaska and the ridge axis along the coast. Models are in excellent agreement about the ridge remaining anchored in place through at least the end of next week. This will result in no chance of precipitation during the extended. Dry weather and mostly clear skies will create seasonably cool nights, while high temperatures will be above normal.

Aviation

As of 4:00 AM PST Friday, for 12Z TAFs. Light and variable winds are expected today. A weak weather disturbance will bring shower chances to the Bay Area north this afternoon and overnight. Conditions will be VFR most of the day with MVFR cigs overnight.

Vicinity of KSFO, VFR cigs expected through tonight. SE winds around 5 kt. PROB30 showers over OAK/SFO this afternoon.

SFO Bridge Approach, Similar to SFO.

Monterey Bay Terminals, VFR conditions expected through the period. Light winds.

Marine

As of 2:09 AM PST Friday, A very large long period west swell will continue to impact the coastal waters and the Monterey Bay today. While swells will continue to diminish today, squared seas will maintain hazardous conditions across the coastal waters, especially near harbor entrances and the San Francisco Bar. Conditions will improve tonight and into the weekend as the swells continue to diminish.

Beaches

As of 4:00 AM PST Friday, The large long period westerly swell will continue to decrease today. Breaking waves of 20 to 30 feet are possible today. A High Surf Warning remains in effect until 5 PM today. These large breaking waves will lead to increased wave run-up on beaches with waves topping and washing over large rocks and jetties. These conditions may also produce localized coastal flooding of vulnerable locations, especially early this morning during high tide. Use extreme caution near the surf zone as these large waves will be capable of sweeping people into the frigid and turbulent ocean water. Cold water shock may cause cardiac arrest, and it also can cause an involuntary gasp reflex causing drowning, even for a good swimmer. The surf zone will be very dangerous due to strong currents and powerful breaking waves.

Watches, Warnings, Advisories

Today, high surf warning, caz006-505-509-529-530 sca, mry bay sca, pt arena to pt reyes 0-10 nm sca, pt reyes to pigeon pt 0-10 nm sca, pigeon pt to pt pinos 0-10 nm sca, pt pinos to pt piedras blancas 0-10 nm sca, pt arena to pigeon pt 10-60 nm sca, pigeon pt to pt piedras blancas 10-60 nm sca, rough bar advisory for sf bar

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