Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco Bay Area

154 pm PDT Fri aug 17 2018

Synopsis

A gradual warming trend is forecast across the region through the upcoming weekend as onshore flow weakens and high pressure builds toward the coast. Look for less widespread coverage of overnight and morning clouds as well with a less defined marine layer.

Discussion

As of 01:50 PM PDT Friday, Morning low clouds rolled back to the coast by late morning. Some total clearing has occurred near the coast, but not so much north of the Golden Gate. Despite some lingering clouds along the coast the latest 24 hour temp trends does in fact show many places are running warmer than Thursday. As of 1 PM Livermore is already 9 degrees warmer than yesterday's 1 PM temp.

The much advertised longwave pattern has not really changed all that much with the current 12Z run. An upper low is currently sweeping through the PacNW as high pressure buildings over SoCal. The latest models push the upper low eastward as the ridge to the SE builds to the NW today and Saturday. For the Bay Area this will translate to continued warming and drying. In the low levels onshore flow remains, which will keep coastal temperatures in check and also keep the marine layer in place. Night and morning low clouds will continue, but just be a little more compressed. One item of note in the short term will be some weak offshore developing at 925 mb over the North and East Bay tonight. This will create dry and mild conditions with heightened fire weather concerns, but nothing critical since winds will be light to moderate.

Temperatures on Saturday will trend warmer with the building high pressure. The warmest locations will be the far interior with highs in the 90s to low 100s. As noted before, lingering onshore flow will keep most urban centers and coastal locations to seasonal levels - highs 60s/70s coast and 80s to 90s interior.

The warm up is short lived as another upper low is on track to drop southward into the Pac NW on Sunday flattening the ridge. Temperatures will moderate or possibly cool a few degrees. Further cooling is expected through early next week with a deepening marine layer due to lowering 500 mb heights from the low to the north.

Aviation

As of 10:45 AM PDT Friday, Marine layer has nearly pulled offshore leaving widespread VFR throughout all terminals. Expect to see this continue through the day and into at least the early evening. Winds generally light onshore to locally breezy near coastal gaps. For tonight, less widespread marine layer is expected with some localized tempo borderline IFR/MVFR cigs near coastal areas.

Vicinity of KSFO, VFR. West winds up to 18kt this afternoon. Tempo SCT/BKN around sunrise hours Saturday. Mixing out by 16Zish SAT.

SFO Bridge Approach, Same as terminal.

Monterey Bay Terminals, VFR. Light onshore winds. Late return of LIFR-IFR cigs, mixing out by 16Zish SAT.

Marine

..as of 10:45 AM PDT Friday, Marine layer has nearly pulled offshore leaving widespread VFR throughout all terminals. Expect to see this continue through the day and into at least the early evening. Winds generally light onshore to locally breezy near coastal gaps. For tonight, less widespread marine layer is expected with some localized tempo borderline IFR/MVFR cigs near coastal areas.

Vicinity of KSFO, VFR. West winds up to 18kt this afternoon. Tempo SCT/BKN around sunrise hours Saturday. Mixing out by 16Zish SAT.

SFO Bridge Approach, Same as terminal.

Monterey Bay Terminals, VFR. Light onshore winds. Late return of LIFR-IFR cigs, mixing out by 16Zish SAT.

as of 10:39 AM PDT Friday, Generally light to locally breezy northwest winds today and into tomorrow. The strongest winds are expected in the outer waters north of Point Reyes. Winds increase on Sunday. A small but long period southerly swell will move through the waters this weekend.

Watches, Warnings, Advisories

Tonight, sca, pt arena to pigeon pt 10-60 nm until 9 pm

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