National Weather Service Raw Text Product

766 
FXUS66 KMTR 020423
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
923 PM PDT Fri Sep 1 2017

.SYNOPSIS...Dangerous heat is forecast to continue across our 
entire forecast area through Saturday. A region-wide cool down is 
forecast to begin on Sunday, especially near the coast, but very 
warm to hot conditions will continue over inland areas through 
Monday. Moisture increasing from the south later in the weekend 
will result in a slight chance of thunderstorms south of Monterey 
Bay by Sunday evening. 

&&

.DISCUSSION...As of 9:10 PM PDT Friday...An oppressively hot
airmass descended across the entire forecast area today.
Afternoon high temperatures exceeded 100 at nearly all reporting
locations, even close to the ocean. Downtown San Francisco's high
of 106 today was the hottest temperature ever recorded in the
City. San Francisco's temperature records date back to 1874 (more
than 140 years). In addition to Downtown SF, three other climate
stations either tied or set all-time temperature records today, 
including San Francisco Airport (104), Moffett Field (106) and the
Salinas Airport (105). In addition, eight climate stations set 
monthly temperature records today and 17 locations set daily high 
temperature records. For a complete list of today's record heat, 
see the Record Event Report (RERMTR).

The strong upper ridge over northern California responsible for
our current record-shattering heat event will continue to maintain
a very hot airmass over our region and compress the marine layer
to near the surface through Saturday. In addition, light offshore
flow is expected to continue through at least midday Saturday. 
What this means is that temperatures tomorrow will likely be 
similar to what they were today in most locations. There is some 
indication that surface pressure gradients will trend a bit more 
onshore by Saturday afternoon which may result in slightly cooler 
temperatures near the immediate coast tomorrow. In any case, 
temperatures will remain dangerously warm regionwide. Adding to 
the heat risks going into tomorrow will be the lack of significant
cooling overnight tonight. 8 pm temperatures were still mostly in
the upper 80s and 90s. Overnight lows tonight are forecast to 
range from the mid 60s to mid 70s at lower elevations and from the
upper 70s to near 90 in the hills. In addition, heat risks 
increase the longer a heat event persists and so a second 
consecutive day of oppressive heat will create high risk for heat 
related illnesses across our entire region through Saturday 
evening. Emergency management officials with the city of San 
Francisco reported that an excessive number of heat related 
illnesses occurred in the City on Friday and that hospitals were 
overwhelmed. This is ample proof that people throughout the region
should take this heat seriously and take action to remain cool 
and hydrated. Remember to check in on the sick and elderly, 
especially those without air conditioning. An excessive heat 
warning remains in effect for our entire forecast area through 9 
pm Saturday.

The upper level high is forecast to shift to our east by Sunday
which will allow for at least light onshore flow. Modest cooling
is forecast for most of the region on Sunday, with most cooling
expected near the coast where highs will be as much as 10 to 15
degrees cooler compared to Saturday. However, inland cooling on
Sunday and Monday is not expected to be enough to significantly 
reduce heat risks away from the coast. Therefore, the Excessive
Heat Warning for inland areas remains in effect until Monday
evening. 

Air quality will also be a concern over the next few days as
easterly flow aloft advects smoke from Sierra Nevada wildfires
across our region.

As the upper ridge shifts to our east over the next few days, the
upper flow will turn more southerly across California. This
southerly flow will then advect subtropical moisture northward
into California, including moisture from Tropical Storm Lidia 
which is currently centered over the Baja Peninsula. Most of the 
moisture from Lidia will likely remain offshore, but there could 
be sufficient mid/upper level moisture for isolated showers and 
thunderstorms to develop across Monterey and San Benito Counties 
by Sunday evening. Another pulse of subtropical moisture could 
then arrive by the middle of next week as the upper flow remains 
out of the south. 

The models agree that a region-wide cooling trend will continue
through most of next week and that temperatures in all areas will
return to near normal by Wednesday or Thursday. 

&&

.AVIATION...As of 4:30 PM PDT Friday...Upper level high over
northern California bringing easterly flow over the area. Warm
airmass will keep the area free of clouds tonight. The easterly
flow is bringing in some smoke aloft from the Sierras which may
reduce visibilities down to 4-6 miles at times. Generally light
winds. 

Vicinity of KSFO...VFR. Periods of smoke may reduce vsbys to 4-6
miles at times. West winds to 15 kt through 04Z. 

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. 

&&

.FIRE WEATHER...As of 9:20 PM PDT Friday...Strong high pressure
will remain over the district through Saturday, continuing to 
produce very hot and dry conditions. Temperatures on Saturday are
expected to be similar to Friday when widespread highs of over 
100 occurred, even coastal areas. Daytime relatively humidity 
values will be as low as the single digits and teens. Also, 
nighttime humidity recoveries in the hills tonight will be very 
poor with relative humidity values not expected to rise above 30 
percent for most elevations above 1000 feet. In addition, 
temperatures in the hills will remain very warm overnight, with 
lows expected to range from the upper 70s to near 90. Finally, 
moderate northeast winds are expected in the hills tonight and 
then become moderate and gusty northwesterly winds by Saturday 
afternoon. These weather factors will result in the potential for 
rapid fire spread, especially in the hills. The Red Flag Warning 
for elevations above 1000 feet has been extended through Saturday 
evening. This Red Flag Warning is for the North and East Bay 
Hills, the Santa Cruz Mountains, the Diablo Range, the Santa Lucia
Range and the interior mountains of Monterey and San Benito 
Counties. 

A gradual cooling trend is forecast to begin on Sunday and
continue through next week. However, hot and dry conditions will
persist inland, especially in the hills, through at least Monday. 

Subtropical moisture is forecast to increase from the southeast 
by late in the weekend, resulting in a slight chance of showers 
and thunderstorms across the southern portion of the district by 
Sunday evening. Thus, the Red Flag Warning may need to be extended
further if there is evidence that dry lightning may be possible 
by later on Sunday. 

&&

.CLIMATE...The following is a list of daily record high 
temperatures for the next 3 days at the selected cities.

San Francisco Bay Area....Fri Sep 1...Sat Sep 2...Sun Sep 3
..........................Temp/Year...Temp/Year...Temp/Year
...............Kentfield   103/1955    104/1955    104/1950 
..............San Rafael   103/1955    101/1955    104/1950
....................Napa   107/1955    109/1955    105/1950
......San Francisco Dtwn    90/1952     94/1991     92/1961
...San Francisco Airport    94/1955     93/1950     93/1961
.........Oakland Airport    99/1952     97/1950     95/1961
................Richmond    93/1955     89/2008     89/2004
...............Livermore   109/1952    111/1952    115/1950 
...........Moffett Field    93/2002     93/2002     93/1961
................San Jose   101/1950    102/1950     99/1950
..................Gilroy   102/1976    104/2002    104/2002
Monterey Bay Area.......
.................Salinas    91/2010     90/2008     94/1961
.........Salinas Airport    96/1952     90/2008     94/1961
...............King City   108/1955    113/1955    103/1955 

The following is a list of All-time record high temperatures for 
the selected cities. Note the period of record for each individual
site will vary from one to the other.

San Francisco Bay Area....All-Time Record High
..........................Temp  Date
...............Kentfield   112  Jul 11 1913  
..............San Rafael   110  Jun 15 1961
....................Napa   113  Jun 14 1961
......San Francisco Dtwn   103  Jun 14 2000
...San Francisco Airport   103  Sep 14 1971
.........Oakland Airport   104  Jun 14 1961
................Richmond   107  Sep 15 1971
...............Livermore   115  Sep 03 1950
...........Moffett Field   106  Jun 14 2000
................San Jose   109  Jun 14 2000
..................Gilroy   115  Jun 15 1972
Monterey Bay Area.......
.................Salinas   106  Sep 14 1971
.........Salinas Airport   105  Oct 05 1987
...............King City   113  Sep 02 1955

&&

.MARINE...as of 01:18 PM PDT Friday...Look for light to moderate
northerly winds through the day, occasionally breezy along the
immediate coast. Light seas are  forecast to persist through the
period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Excessive Heat Warning...CAZ506>508-510>513-516>518-528
             Excessive Heat Warning...CAZ006-505-509-529-530

&&

$$

PUBLIC FORECAST: Dykema
AVIATION: W Pi
MARINE: BAM
CLIMATE: Rowe/Dykema/BAM
FIRE WEATHER: Dykema

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea