San Francisco Bay South of the Bay Bridge Marine Forecast
|Today...N Winds Up To 10 Kt, Becoming Nw This Afternoon.|
|Tonight...Nw Winds Up To 10 Kt.|
|Sun...Nw Winds Around 5 Kt.|
|Sun Night...W Winds 5 To 10 Kt.|
|Mon...W Winds 5 To 10 Kt.|
|Mon Night...Nw Winds Up To 10 Kt.|
|Tue...N Winds Around 5 Kt.|
|Wed...Ne Winds Around 5 Kt.|
| 230 AM PST Sat Nov 28 2020 |
Synopsis for the Central California Coast and Bays Including the Monterey Bay, Greater Farallones and Cordell Bank National Marine Sanctuaries - PZZ500
High pressure covers the coastal waters and the Great Basin. This will keep light northwest winds through Wednesday except for locally gusty winds along the coast south of Pigeon Point. The next long-period northwest swell arrives next Monday into Tuesday with another swell train late in the week.
| Area Forecast Discussion|
National Weather Service San Francisco Bay Area
401am PST Sat Nov 28 2020
High pressure over California will result in sunny, mild days and clear, cool nigheights through this weekend. Slight cooling is expected on Monday, followed by a gradual warming trend through the remainder of next week. Dry weather is expected to continue through next week.
As of 3:05am PST Saturday...Water vapor imagery this morning shows an elongated plume of moisture stretching from the center of a low pressure system at 145W to the PAC NW. While some of this moisture has made it into portions of far northwestern California, the vast majority of the State is under a very dry air mass regime. Winds are also much lighter this morning when compared to what was observed yesterday morning, especially over some of our historically windiest locations (e.g. Mt. St. Helena and Mt. Diablo). The culmination of clear skies and calm/light winds regionwide has resulted in some North Bay locations like Santa Rosa and Napa running 10-15 degrees F cooler than this time yesterday morning.
Short and Medium-term guidance both paint a rinse-and-repeat pattern for tomorrow and Sunday, with cold temps by daybreak in much of the region and some of our coldest locations in the interior North Bay valleys followed by rapid daytime warming and much milder temps in the 60s F for today and tomorrow. Given the perseverance of this upper-level ridge, can expect slightly warmer daytime highs in the upper-60s F by Sunday, especially in the interior. Nonetheless, dry and clear sky conditions will result in rapid overnight radiational cooling over the next couple of days. Winds will also remain rather light regionwide. Offshore flow will be near null as the SFO-WMC gradient will continue to decrease over the next couple of days. The only major variance for the next couple of days is the passage of a weak shortwave trough over the PAC NW through Monday. Can expect slightly cooler temps Monday as its axis moves ashore and an increase in the possibility for some isolated locations to wake up to some morning frost. Will depend largely on how much moisture manages to move into our CWA over the next couple of days, as GFS does bring the current moisture plume over the PAC NW slightly closer to NorCal and the Bay Area through Monday morning. It should be noted, however, that the upper-level ridge overhead and the fragility of the plume makes it unlikely that much, if any, moisture makes it that far into Northern California this weekend. Moreover, even if some moisture does make it into portions of the North Bay, will at most see patchy frost. Not expecting any sort of precipitation out of this.
The latest GFS and ECMWF (European Centre for Medium-Range Weather Forecasts) runs paint a disheartening picture for next week. Following the dissipation of the PAC NW moisture plume, a much more amplified pattern will develop between the Northeastern and Northcentral Pacific. Essentially, the current upper-level ridge over California looks set to expand farther north, with 580dm 500hPa building up to the Washington/British Columbia Border. This will be in sharp contrast to the 500-520dm 500hPa heigheights that are forecast to continue over much of the open waters of the North Pacific Ocean. The repercussions of this synoptic-scale setup will be two-fold. First, the upper-level ridge will help to maintain the widespread subsidence over our area, so will see a gradual warming trend, along with sharp variations between daytime max and nighttime min temps. Second, storm systems that develop over the North Pacific will now be diverted even farther north than what has been observed in recent weeks, impacting portions of Central and far Northern British Columbia and leaving much of the West Coast bone dry. There is some potential that we may still receive moisture from the tail-end of some of these storm systems, with the ECMWF ENS members taking a more aggressive approach to the intensity of these storm systems. That being said, the odds are not in our favor for moisture next week, as the most likely scenario is that these systems will not be able to overcome the strength of the upper-level ridge and thus high- confidence that dry conditions will prevail next week.
As mentioned in the previous AFD, the latest CPC 8-14 day outlook calls for dry conditions through at least the first half of December.
as of 03:47am PST Saturday...High pressure covers the coastal waters and the Great Basin. This will keep light northwest winds through Wednesday except for locally gusty winds along the coast south of Pigeon Point. The next long-period northwest swell arrives next Monday into Tuesday with another swell train late in the week.
.MTR WATCHES/WARNINGS/ADVISORIES... .Tday...None.