Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco Bay Area

454 am PDT Mon apr 24 2017

Synopsis

A weak weather system approaching from the northwest is expected to bring light precipitation to the North Bay this morning, and may generate scattered showers farther south this afternoon and evening. Periodic rain chances will continue in the North Bay through Wednesday, with dry and seasonably cool weather expected elsewhere. Dry weather along with a warming trend is forecast across the region from Thursday through the weekend as high pressure builds in. Locally breezy conditions are likely from Thursday through Friday.

Discussion

As of 3:15 AM PDT Monday, Clouds have been on the increase overnight as a weak weather system approaches from the northwest. Models show light precipitation developing across portions of the North Bay from about sunrise through late morning. Most models also forecast widely scattered light showers south of the Golden Gate during the afternoon and early evening hours. Temperatures today will continue to be slightly cooler than normal.

At least two additional weak systems are forecast to move in from the northwest over the next few days and possibly produce local light rain at times in the North Bay through Wednesday. From San Francisco southward look for dry and seasonably cool conditions on Tuesday and Wednesday.

A more amplified weather pattern is forecast to develop during the second half of the week, with a deep trough forming over the Intermountain West while a ridge builds offshore. In between, across our area, a dry and brisk northerly flow will develop which will likely result in gusty north winds from Thursday through early Saturday, especially in the hills. A warming trend will begin on Friday and continue into the weekend as the upper ridge offshore edges eastward and over California.

The longer range models diverge somewhat after the weekend. The GFS maintains a ridge and warm temperatures over California early next week. The ECMWF retrogrades the ridge offshore, resulting in some cooling. But both models maintain dry conditions into next week.

Aviation

As of 4:53 AM PDT Monday, For 12z Tafs. Mid and high clouds will continue to stream across area terminals ahead of an approaching weather system. Light rain showers expected after 15z across the North Bay and will spread south through the day. Showers will taper in the afternoon. Light to moderate west winds will ramp up in the afternoon becoming moderate and locally gusty.

Vicinity of KSFO, VFR through much of the period. Light showers will reach area terminals around 20z this afternoon and taper after 00z. West winds around 15 kt anticipated to strengthen in the afternoon to 15 to 20 kt with gusts to 25-30 knots possible.

SFO Bridge Approach, Similar to KSFO.

Monterey Bay Terminals..VFR through much of the period. Light showers will reach area terminals around 19z-20z this afternoon and taper after 03z. Southwest winds around 5 kt will strengthen to around 10-15 kt with gusts to 15-20 kt in the afternoon.

Marine

As of 04:35 AM PDT Monday, Moderate northwesterly winds will prevail through much of the forecast period with strongest winds confined along the coast south of Pt. Sur. Winds and seas will increase Wednesday night into Thursday as high pressure strengthens over the Eastern Pacific resulting in a tighter pressure gradient across the coastal waters.

Watches, Warnings, Advisories

Today, sca, pt pinos to pt piedras blancas 0-10 nm

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