Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco Bay Area

826 am PST Tue Feb 19 2019


Cool, dry weather conditions are forecast to persist along with cold overnight temperatures through Wednesday morning. Another cold weather system is forecast to bring light rain showers to the region Wednesday into Thursday morning with snow likely in the higher elevations. Dry conditions return late Thursday and persist into at least Friday.


As of 08:25 AM PST Tuesday, Clear sky conditions prevail over the region this morning with only very localized fog showing up along some of the region's rivers, especially along the Russian River around Guerneville. This is likely occuring as air temperatures are in the 30s for much of the region while 20s are being reported in the higher terrain. Meanwhile, current temperatures around San Francisco are in the low/middle 40s. Overall, expect today to be a near repeat of yesterday with mostly sunny conditions and temperatures warming into the 50s for most urban areas. The ongoing forecast remains on track at this time and no updates are needed. Please see the previous forecast discussion below for additional details.

Previous Discussion

As of 3:00 AM PST Tuesday, Overnight satellite imagery reveals mostly clear skies across the entire state of California thanks to high pressure. A quick look at many automated sensors around the Bay Area also indicated rather light winds overnight. The exception are the hills where some gusts of 25-35 mph remain. The combination of light winds and clear skies set the stage for excellent radiational cooling. Temperatures early this morning will be rather cold with lows in the 20s (interior valleys) to 30s and 40s (urban areas and coast). The cold temperatures will likely lead to frost and some window scraping for morning commuters. It should also be noted that if any continued water runoff from the recent rains occurs on some roads black ice would be possible in the hills/coldest valleys.

After a cold start, today will feature another sunny day with highs in the 50s for most locations and colder in the hills/mts 40s.

The next weather item of note is currently dropping south along the British Columbia Coast. High pressure currently over the region will weaken as this disturbance moves in from the north Wednesday and Wednesday. Latest forecast models indicate it will be another cold system with 1000-500mb thickness levels/700mb temps puts snow levels back to 2500-3000 feet. Unlike some of the previous systems from the past few weeks this system appears to be more moisture starved leading to scattered showers. Nonetheless, forecast will bring scattered showers down the coast early Wednesday and spreading more inland Wednesday afternoon. Rainfall amounts will be on the order of a few hundredths to a few tenths at best or a dusting in the hills.

Drier northwest flow returns Thursday as any lingering precip ends from N-S. Dry weather returns completely Thursday night and Friday as shortwave ridging develops overhead. Next weekend looks to start off dry then another round of precip will be possible by Sunday. A very broad upper level trough sweeps through the region Sunday into Monday with scattered showers. Additional rain chances will be possible next week, but details vary from model to model.

Simply put, the storm door remains open.


As of 03:45 AM PST Tuesday, For 12Z TAFs. Widespread except chance of very localized patchy fog around STS thru sunrise hours. Otherwise, increasing high clouds with generally light offshore winds through the morning, becoming onshore by the afternoon and evening. Approaching system will bring gusty winds overnight with VCSH by sunrise Wednesday.

Vicinity of KSFO, VFR. Increasing high clouds through the day. Generally light offshore am winds becoming 8-12kt onshore by the mid afternoon through evening. Winds increase to become gusty onshore overnight. VCSH around Wednesday morning.

SFO Bridge Approach, Similar to SFO.

Monterey Bay Terminals. VFR. Light offshore winds in morning become light onshore winds in the afternoon and evening. Onshore breezy to gusty winds overnight with VCSH later tomorrow.


As of 03:47 AM PST Tuesday, Northerly winds steadily increase through the day today and will persist across the waters through midweek. A series of northwest swells will impact the region through the rest of the week.

Watches, Warnings, Advisories

Today, sca, pt arena to pt reyes 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, pt reyes to pigeon pt 0-10 nm from 3 pm

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