NWS Forecast Area Discussion - San Francisco Area

FXUS66 KMTR 252355

Area Forecast Discussion
National Weather Service San Francisco Bay Area
455 PM PDT Mon May 25 2020

.SYNOPSIS...Very warm to hot temperatures will persist across the
interior through Thursday while coastal areas will be relatively
mild by comparison. 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. Cooler temperatures and unsettled conditions
return to the region this upcoming weekend.

&& of 2:28 PM PDT Monday...An 587dm 500mb ridge
off of the southern and central California coast continues to
strengthen as it slowly shifts toward the coastline this
afternoon. This has resulted in a robust warming trend with
temperatures around 5 to as much as 15 degrees warmer compared to
24 hours ago. Downtown San Francisco has reached 81 deg F with
many other locations away from the immediate coastline also in the
80s. With that said, those areas along the immediate coast remain
in the 60s. Interior locations have already warmed into the 90s
and will likely top out in the mid/upper 90s. Meanwhile, onshore
flow has kicked in and will likely keep coastal areas from warming
much more this afternoon. One example is at KSNS (Salinas
Airport) where the temperature in the past hour has already cooled
8 degrees in response to an increase in WNW winds.

Under a mainly clear sky, temperatures will cool modestly tonight
near the coast and adjacent valley locations while mild conditions
will persist in the hills and far inland valleys. Thus, relief from
today`s heat will be limited for interior locations tonight. The air
mass aloft will continue to warm into Tuesday and Wednesday as the
aforementioned mid/upper level ridge axis shifts over the region and
850mb temperatures peak between 23-25 deg C. This will result in
another couple of days of very warm to downright hot temperatures
across the interior where widespread 90s to around 103 deg F
(region`s warmest locations) will be possible. Thus, a Heat Advisory
remains in effect for just about all interior locations as hot
daytime and mild overnight temperatures produce moderate to high
heat risks. While daytime temperatures on Tuesday may be as warm if
not slightly warmer than today near the coast, an afternoon onshore
breeze is again expected to inhibit heating. Some cooling is likely
on Wednesday near the coast as onshore continues to increase while
inland areas remain very warm to hot.

The forecast models typically try to cool conditions too soon, yet
there is good consensus among the models and ensemble members that
even inland temperatures will begin to cool on Thursday. This
cooling will be the result of the ridge shifting further inland and
the approach of a mid/upper level cut-off low currently on the
western flank of the Omega Block aloft. Thus, the current Heat
Advisory`s extent in time may need to be adjusted in the coming
days. Regardless, temperatures will remain well above seasonal
averages across the interior and to a lesser extent near the coast
on Thursday.

A more robust cooling trend is likely to occur on Friday as the
aforementioned mid/upper level low beings to approach the central
California coast. This system will not only cool conditions region-
wide but also bring the potential for unsettled weather as it pushes
into northern California late Friday into Saturday. Thus, there will
be a slight chance of rain showers and even the potential for an
isolated thunderstorm or two. While confidence remains low at this
time regarding the details, we will need to monitor for
thunderstorms as dry lightning and potential fire starts would be of
concern given the prolonged period of hot and dry conditions. Stay

&& of 4:55 PM PDT Monday...For 00z TAFs. Skies will
remain clear this evening and overnight. Strong 7 mb northerly
gradient in place with high pressure overhead. Local onshore
gradients will produce some moderate west winds this evening.

Vicinity of KSFO...Clear skies overnight into Tuesday. West winds
to around 15 kt this evening and again Tuesday afternoon.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Clear skies this evening and overnight.
Evening northwest winds then light overnight with westerly
seabreeze developing around 20z Tuesday.



Record highs        May 25            May 26            May 27
Santa Rosa          96/1951           96/1974           94/1984
Kentfield           92/1992           99/1951           99/1919
Napa                98/1951           98/1896          102/1984
Richmond            92/1951           87/1996           98/1984
San Francisco DT    87/1951           91/1896           85/1933
SFO Airport         87/1951           89/1974           97/1984
Redwood City        99/1982           98/1974           98/1984
Half Moon Bay       78/1975           78/1951           72/1982
Oakland DT          90/1975           94/1974          100/1984
San Jose            95/1982           95/1951          101/1984
Gilroy              98/1982           98/1979          101/1974
Santa Cruz          95/1896           94/1896           93/1984
Salinas             96/1951           94/1974           84/2003
King City          102/1951          104/1974          104/1984

&& of 04:42 PM PDT Monday...Weakening high pressure over
the eastern Pacific will keep northwesterly winds light to
moderate across much of the coastal  waters. Locally breezy
conditions will persist over the northern  waters through much of
the week. These winds will generate steep  fresh swell resulting
in hazardous seas conditions for smaller  vessels. 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.


     .Tday...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




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NWS MTR Office Area Forecast Discussion