S. generated a prolonged heatwave from May 5th - 10th.
Every event with a place to put it; 6 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SGX wrote it up.
A large area of upper level high pressure over the Southwestern U.S. generated a prolonged heatwave from May 5th - 10th. Deserts were quite hot with some records broken. The high temperatures at Palm Springs International Airport were 101 degrees or higher for seven consecutive days (May 4-10). Even coastal areas got in on the warm weather, with San Diego International Airport hitting 85 degrees on May 6th. Coastal areas of San Diego County also experienced some dense fog on the mornings of the 7th and 8th. An accompanying shortwave trough brought some elevated convection bringing locally up to one quarter of an inch of rainfall on May 9th and another shortwave trough brought some windy conditions to the mountains and deserts with gusts 55-65 miles per hour on May 12th and 13th.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS San Diego, CA wrote its last area forecast discussion before the first event at May 5, 8:22 AM PST, 1 hour 38 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
922 AM PDT Tue May 5 2020
.SYNOPSIS...
High pressure centered over northern Baja will continue the
warming trend with well above average high temperatures this week.
The heat is expected to peak on Wednesday and Thursday with
slight cooling for Friday and Saturday. For Sunday into early next
week, a low pressure system centered over the northeast Pacific
will bring stronger onshore flow to southern California,
spreading cooling inland and bringing a greater return of night
and morning coastal low clouds and fog.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
...Update...
The sky is clear this morning. Very patchy low clouds along and
mainly offshore the southern San Diego County coast has dissipated.
Abundant sunshine will prevail today with temps soaring into the
90s inland, except 70s to near 80 along the coast and in the
mountains, and to around 105 degrees over the lower deserts. It
gets even hotter tomorrow.
No changes were made to the forecast this morning. See previous
discussion below for more forecast details.
...Previous Discussion (Issued at 255 AM PDT Tue May 5 2020)...
.SHORT TERM (Today through Thursday)...
High pressure centered over northern Baja will continue the
warming trend with the heat peaking on Wednesday and Thursday.
High temperatures on those days will be 10 to 15 degrees above
average in the deserts, higher elevations in the mountains, and
near the coast and 15 to 20 degrees above average for the valleys,
inland coastal areas, and lower elevations of the mountains. There
may be some patchy night and morning low clouds and fog near the
coast at times.
&&
.LONG TERM (Friday through Sunday)...
For Friday and Saturday, the lower level flow will turn weakly
onshore and high pressure aloft will weaken slightly. This will
bring some very slight cooling for Friday and Saturday, but with
high temperatures remaining well above average.
For Sunday and Monday, a low pressure system centered over the
northeast Pacific will strengthen the onshore flow across southern
California. This will spread greater cooling inland and bring a
greater return of night and morning coastal low clouds and fog.
High temperatures could return to near average on Monday.
&&
.AVIATION...
051515Z...Coast...Mostly clear skies through tonight. There is a
chance of very patchy low cloud development along the coast and a
few miles inland after 06Z Wed. If clouds develop bases will be
mainly 600-1000 ft MSL with areas of vis 2-4SM. Low confidence that
low clouds and vis restrictions will impact TAF sites.
Valleys/Mountains/Deserts...Clear with unrestricted vis through
tonight.
&&
.MARINE...
No hazardous marine weather is expected through Saturday.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT Friday for Orange County Inland
Areas-San Bernardino and Riverside County Valleys-The
Inland Empire-San Diego County Valleys.
Excessive Heat Warning until 9 PM PDT Friday for Coachella
Valley-San Diego County Deserts-San Gorgonio Pass Near
Banning.
PZ...NONE.
&&
PUBLIC...Gregoria (Update)/17 (Prev Discussion)
AVIATION/MARINE...COThe national radar mosaic for the moment the first event began.
3 heat, 2 excessive heat, 1 dense fog. Local standard time, as filed.
High temperatures reached the upper 90s to 102 degrees for areas across the Inland Empire May 5th through May 8th.
Areas of the Coachella Valley saw high temperatures in the low 100s to 110 degrees from May 5th through 10th.
High temperatures across the lower deserts of San Diego County ranged from the low 100s to near 110 degrees May 5th through 10th.
High temperatures in the low to upper 90s were recorded across parts of the San Diego County valleys May 5th through 7th.
Areas of inland Orange County saw high temperatures in the low to mid 90s May 5th through 7th.
Areas of coastal San Diego County experienced patchy dense fog on the early mornings of May 7th and 8th. San Diego International Airport reported one quarter mile visibility on the 7th and Miramar MCAS reported a visibility near zero on the 8th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2020Every state in 2020This day in weather historyWarnings in California, May 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 891223, 891225, 891226, 891227, 891228, 895755.