Severe Thunderstorm Warning 1, NWS San Francisco Bay Area, CA

658 
WWUS56 KMTR 161043
SVSMTR

Severe Weather Statement
National Weather Service San Francisco CA
343 AM PDT Sun Aug 16 2020

CAC001-053-069-075-081-085-087-161115-
/O.CON.KMTR.SV.W.0001.000000T0000Z-200816T1115Z/
Alameda CA-San Mateo CA-Santa Cruz CA-San Francisco CA-San Benito CA-
Santa Clara CA-Monterey CA-
343 AM PDT Sun Aug 16 2020

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 415 AM PDT
FOR ALAMEDA...SAN MATEO...SANTA CRUZ...SAN FRANCISCO...NORTHWESTERN
SAN BENITO...SANTA CLARA AND WESTERN MONTEREY COUNTIES...

At 342 AM PDT, severe thunderstorms were located along a line
extending from 31 miles southwest of Point Reyes Station to 17 miles
southwest of Patterson, moving north at 55 mph.


HAZARD...Erratic outflow wind gusts up to 60mph. Frequent lightning.

SOURCE...Public and Doppler Radar.

IMPACT...Expect damage to roofs, siding, and trees.  Wildfires may 
         start in remote areas due to the lightning.

Locations impacted include...
San Jose, San Francisco, Oakland, Fremont, Salinas, Hayward,
Sunnyvale, Santa Clara, Daly City, San Mateo, San Leandro, Livermore,
Redwood City, Mountain View, Alameda, San Ramon, Pleasanton, Union
City, Milpitas and Palo Alto.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Continuous cloud to ground lightning is occurring with these storms.
Move indoors immediately. Lightning is one of nature's leading
killers. Remember, if you can hear thunder, you are close enough to
be struck by lightning.

&&

LAT...LON 3587 12142 3630 12198 3663 12204 3669 12187
      3680 12185 3693 12193 3694 12216 3724 12250
      3752 12261 3777 12261 3785 12278 3771 12292
      3772 12294 3786 12279 3772 12156 3754 12156
      3739 12141 3725 12146 3715 12140 3716 12126
TIME...MOT...LOC 1042Z 177DEG 46KT 3779 12325 3727 12133 

HAIL...<.75IN
WIND...60MPH
 
$$

DRP

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1056 PM PDT Sat Aug 15 2020

.SYNOPSIS...Hot temperatures and thunderstorm chances continue
tonight into Sunday. Any thunderstorms will end by Sunday
afternoon but hot weather continues into next week with little
relief through midweek.

&&

.DISCUSSION...as of 9:15 PM PDT Saturday...Active weather
continues at this hour with most of the activity remaining just
east of our area. With that being said models continue to suggest
the possibility of thunderstorm development overnight with
moisture streaming in from the south and moderate instability over
the region. We are currently monitoring a patch of clouds located
just off the Southern California coast that is gradually making
its way northward toward Santa Barbara. Models suggest this area
of moisture will continue northward across the Monterey and San
Francisco Bay Area overnight into Sunday morning. The trajectory
of the moisture coupled with the instability over the region has
the potential to trigger thunderstorms and dry lightning over our
area. This may result in additional fire starts overnight. As a
result the Red Flag Warning remains in effect.

The only significant change that was made to the forecast this
evening was the extension of the Heat Advisories through tonight
and Sunday. Overnight temperatures will provide limited and
short-lived relief with lows only expected to drop into the 60s
in the valleys and 70s and 80s in the hills and mountains.
Temperatures are forecast to ramp up rapidly once again on Sunday.
While temperatures will be slightly cooler than what we saw
today, the prolonged duration of this record breaking event will
increase the potential for heat related illnesses, particularly
among vulnerable populations.

A list of todays records is located in the Climate section below.

From previous discussion...Two main items of focus for the
current forecast:

1) Red Flag Warning and thunderstorms: Fire weather watches have
been upgraded to Red Flag Warnings. About 36 hours ago the models
started picking up on a monsoon push for today into Sunday. This
morning after 7 am the first lightning strikes occurred over Santa
Barbara county. This initial shortwave has kept most of the
convection over San Luis Obispo county but several strikes and
t-storms have made it into extreme southern Monterey county with
some action now shifting into Kings county. There are numerous
confirmed small fires in southern Monterey county and into San
Luis Obispo county and now one near Avenal. Even though the
storms are creating some rain drops the fuels are so dry there
is a high ignition efficiency. As always t-storm forecasts remain
difficult around the Bay Area for summertime events. In the short
term the Red Flag Warning is focused on Monterey and San Benito
counties. Expect more activity across this region through this
evening.

Earlier model runs showed good agreement that a second round of
activity would fire somewhere between the Santa Cruz mtns and Mt
Hamilton after dark tonight and then shift northward overnight.
The more recent runs of the hrrr/rap/nam have changed slightly.
However rather than chasing models decided to keep the forecast
idea the same. The 12z gfs seems to capture a shortwave currently
near the CA/Mexico border and rotate it northward overnight. The
18z gfs and short terms mesoscale models now show the better
chances for convection by morning somewhere around Pt Reyes and up
into Sonoma/Napa. Will continue to monitor short term convective
trends closely this evening and overnight. Main concern will be
any new ignitions. Any storms should end by midday Sunday across
the Bay Area and shift northward by Sunday afternoon. Must be
stated that most areas will not seeing thunder and lightning but
any new ignitions will be problematic.

2) Heat: Hot temps continue this afternoon with record high temps
falling once again. No changes to inland excessive heat warning
which goes through Weds evening. Heat Advisories remain in effect
around the Bay through 9 pm this evening. Idea remains that we
will do targeted advisories for those locations closer to the
water based upon what is reported for highs today. But either way
it will be another hot day on Sunday with record or near record
warmth. Not much time spent analyzing the long range but ecmwf
still showing a strong ridge at least through midweek.

&&

.AVIATION....as of 10:50 PM PDT Saturday...Models suggesting an
increase in mid level moisture coming from the south tonight.
Lightning strikes have been observed in a mass of clouds off Point
Conception. Cannot rule out the possibility of an isolated strike
somewhere in the area through Sunday morning as these clouds move
north. Midlevel moisture decreases Sunday morning but another
slug of mid level moisture may arrive Sunday evening. Some early
morning low clouds possible near the Big Sur and MRY Bay coast.

Vicinity of KSFO...VFR with increasing mid level clouds after
12Z. Bases 12000 ft or higher. Isolated thunderstorms are a
possibility Sunday morning when the midlevel moisture will be at
its highest.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR with increasing mid level clouds
after 03Z. Isolated thunderstorms are possible overnight when the
mid level moisture is at its peak. Also a possibility of low
clouds over the bay which may impact MRY between 12Z and 15Z but
confidence is low.

&&

.CLIMATE...

RECORD HIGH TEMPERATURES SATURDAY, AUGUST 15, 2020

LOCATION                    HIGH           PREVIOUS RECORD
-----------------------------------------------------------------
SANTA ROSA                   103    TIED    103 IN 2019
NAPA                         103            102 IN 1906
LIVERMORE                    108    TIED    108 IN 1967
SFO AIRPORT                   94    TIED     94 IN 2019
REDWOOD CITY                 100    TIED    100 IN 2019
OAKLAND DOWNTOWN              93    TIED     93 IN 2015
GILROY                       108            104 IN 2019
MONTEREY                      91             90 IN 2015

Record High Temperatures for Sunday.
			    August 16
------------------------------------------------------
Santa Rosa		100 in 2019
Kentfield		101 in 2015
Napa			104 in 2015
Richmond		 94 in 2015
Livermore		105 in 1951
San Francisco	 90 in 2015
SFO				 90 in 2015
Redwood City	101 in 2015
Half Moon Bay	 72 in 2015
Oakland Dtown	 92 in 2015
San Jose		 97 in 2015
Gilroy			107 in 2019
Santa Cruz		 94 in 1983
Salinas			 94 in 1933
Monterey		 83 in 2015
King City		103 in 2015

&&

.MARINE...as of 10:54 PM PDT Saturday...Monsoonal moisture
wrapping around an upper high over the southwest will bring a
slight chance of thunderstorms tonight and Sunday morning. Light
west to northwest winds will continue over  the coastal waters
through the weekend. Northwest winds will  increase early next
week as high pressure builds off the  California coast. Mixed seas
will persist with a short period  northwest swell and a couple of
longer period southerly swells.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Excessive Heat Warning...CAZ507-510-511-513-516>518
             Red Flag Warning...CAZ516>518-528-530
             Red Flag Warning...CAZ006-505>513-529
             Heat Advisory...CAZ006-506-508-512-528>530

&&

PUBLIC FORECAST: CW
AVIATION: W Pi
MARINE: W Pi

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Special Weather Statement
National Weather Service San Francisco CA
142 AM PDT Sun Aug 16 2020

CAZ509-512-516>518-528>530-161015-
Northern Salinas Valley/Hollister Valley and Carmel Valley CA-
Mountains Of San Benito County And Interior Monterey County Including
Pinnacles National Park CA-San Francisco Peninsula Coast CA-
Southern Monterey Bay and Big Sur Coast CA-Santa Cruz Mountains CA-
Santa Lucia Mountains and Los Padres National Forest CA-
Southern Salinas Valley/Arroyo Seco and Lake San Antonio CA-
Northern Monterey Bay CA-
142 AM PDT Sun Aug 16 2020

...A LINE OF THUNDERSTORMS WILL LEAD TO FREQUENT LIGHTNING WHICH MAY
LEAD TO WILDFIRES...

At 140 AM PDT, doppler radar and trained weather spotters reported
strong thunderstorms along a line extending from 46 miles west of
Del Monte Forest to 6 miles south of Gorda. Movement was north at 40
mph.  Expect these thunderstorms to move across the areas of Big
Sur, Monterey Peninsula, Santa Cruz, and Santa Cruz mountains over
the next two hours.

The main threat is frequent lightning from this line of
thunderstorms. This lightning may ignite wildfires where it strikes.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3579 12146 3583 12152 3611 12174 3629 12199
      3660 12207 3670 12199 3671 12190 3681 12188
      3689 12195 3688 12208 3697 12228 3716 12248
      3729 12249 3728 12248 3696 12163 3689 12158
      3692 12154 3681 12126 3579 12135
TIME...MOT...LOC 0840Z 180DEG 37KT 3634 12273 3584 12144

DRP