Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 262345
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
445 PM PDT Tue May 26 2020

.SYNOPSIS...Very warm to hot temperatures will persist across the
interior through Thursday. Thus, a Heat Advisory remains in effect
across the interior. Cooling will first take place at the coast on
Wednesday before spreading inland Thursday and moreso into Friday as
onshore flow increases. There is a chance of rain showers late
Friday night into Saturday when isolated thunderstorms will also be
possible.

&&

.DISCUSSION...as of 2:29 PM PDT Tuesday...A 589dm 500mb ridge of
high pressure remains positioned just off of the southern
California coast and extends northward through the San Francisco
Bay Area. As a result, 850mb temperatures range from 21 to 23 deg
C across much of the region with interior surface temperatures
well into the 90s. Meanwhile, onshore flow near the coast has held
temperatures in the 60s (immediate coast) to lower 80s (such as
in Downtown San Francisco). Sky conditions also remain generally
clear region-wide with a few to scattered high clouds advecting
inland over northern California and small "puff" of lower
clouds/fog well offshore of the Monterey Bay.

The aforementioned ridge axis aloft is forecast to shift inland
during the next 24 hours or so yet 850mb temperatures will continue
to warm. Thus, interior locations will remain very warm tomorrow
with widespread 90s again in the interior, yet 2-5 deg F cooler
potentially.  Additional cooling is likely to occur near the coast
as onshore flow begins to increase yet temperatures will still be
well above seasonal averages.

As the ridge shifts further to the east on Thursday, cooling will
continue to occur region-wide with the most relief likely near the
coast. Will continue the Heat Advisory over the interior through
Thursday evening regardless of the modest cool down given the
cumulative impact of the prolonged very warm to hot temperatures and
limited overnight cooling.

By Friday, inland areas cool by as much as 10 degrees (about 20 from
the peak of this heat event) as the ridge moves into the Desert
Southwest and Great Basin and a mid/upper level low begins to
approach the central/southern California coast. This will help to
usher in much cooler marine air and finally put an end to this heat
event. Precipitation chances will also increase late Friday into
Saturday as the system lifts northward while advecting deeper
moisture across the region. As the core of the low moves inland over
the San Francisco Bay Area and northern California on Saturday,
there will also be the potential for isolated thunderstorm. Have
added a slight chance of thunderstorms to the forecast for locations
north of the Golden Gate as the NBM has also increased probabilities
to above 20 percent. It will be important to monitor this closely as
the development of thunderstorm may produce dry lightning as
rainfall will likely be limited. Longer range guidance indicates
continued unsettled weather and cooler temperatures through early
next week in response to a broad mid/upper level trough along the
West Coast.

&&

.AVIATION...as of 4:45 PM PDT Tuesday...For 00z TAFs. Skies will
remain clear this evening and overnight through Weds with strong
high pressure over the region. Northerly gradients of 8 mb will
support keeping any local stratus and fog formation out of
terminals. Winds are generally light with typical afternoon
seabreeze winds to around 15 kt through sunset.

Vicinity of KSFO...VFR with clear skies tonight into Weds. Evening
westerly seabreeze gusts to 15-20 kt then easing overnight.

SFO Bridge Approach...Clear skies with light onshore breezes.

Monterey Bay Terminals...VFR with clear skies forecast tonight
through Weds. Light winds, locally to around 15 kt Salinas Valley
afternoon/early evening hours.

&&

.CLIMATE...

Record highs              May 26            May 27
-----------------------------------------------------------------
Santa Rosa                96/1974           94/1984
Kentfield                 99/1951           99/1919
Napa                      98/1896          102/1984
Richmond                  87/1996           98/1984
San Francisco DT          91/1896           85/1933
SFO Airport               89/1974           97/1984
Redwood City              98/1974           98/1984
Half Moon Bay             78/1951           72/1982
Oakland DT                94/1974          100/1984
San Jose                  95/1951          101/1984
Gilroy                    98/1979          101/1974
Santa Cruz                94/1896           93/1984
Salinas                   94/1974           84/2003
King City                104/1974          104/1984

&&

.MARINE...as of 3:00 PM PDT Tuesday...Breezy northwest winds will
persist over the northern waters  through tomorrow. These winds
will generate steep fresh swell  resulting in hazardous seas
conditions for small crafts. Generally light to moderate northwest
winds are expected elsewhere with winds generally easing across
the waters late this week as an  upper ridge sits over California
and an upper low slowly approaches from the southwest. Mixed seas
will continue with a short period  northwest swell and a longer
period southwest swell. A longer  period northwest swell will
arrive later this week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Heat Advisory...CAZ506-507-510>513-516>518-528
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: RWW
MARINE: AS

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