Name: Heavy Rain in California, May 1, 2018
Start: 2018-05-01T12:30
End: 2018-05-01T12:44
Location: California

Where it happened

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 1

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.

What happened

The episode as NWS HNX wrote it up.

A cold upper trough moved across Central California on May 1. While it produced only light precipitation over the area during the morning, thunderstorms broke out during the afternoon in the cooler and unstable post-frontal airmass. Thunderstorms produced moderate to locally heavy rain across portions of the Southern Sierra Nevada and adjacent foothills as well as across the Kern County Deserts where up to six tenths of an inch of rain fell. Very little measurable fell over the San Joaquin Valley from this system as only a few stations reported a few hundredths of an inch of rainfall.

What forecasters said that day

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 Hanford, CA wrote its last area forecast discussion before the first event at May 1, 3:10 AM PST, 9 hours 20 minutes earlier.

Area forecast discussion, May 1, 3:10 AM PST, 9 hours 20 minutes before

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
410 AM PDT Tue May 1 2018

.SYNOPSIS...An upper level trough over the west will continue to
provide for unsettled conditions with cooler than normal
temperatures through Wednesday. There is a chance of showers today
and Wednesday mainly in the mountains with isolated thunderstorms
possible in the afternoon and evening hours. Dry weather and a
warming trend are expected starting Thursday and continuing
through the weekend.

&&

.DISCUSSION...Broad upper trough persists over the western CONUS.
This feature will provide for a continuation of cooler than
normal temperatures across our area along with a chance of showers
mainly over the mountains today as vort energy rotating around
the main upper low to our east will provide enough moisture and
dynamics for convection to take place. Isolated thunderstorms will
be possible across much of our area this afternoon as well as
sufficient instability and CAPE are progged. SREF indicating the
trough will slowly eject eastward tonight and Wednesday which will
allow for height rises and a slight warming trend, but there will
still be enough wrap around moisture for a chance of showers over
the mountains and the Kern County Deserts with isolated
thunderstorms possible once again during the afternoon and early
evening hours.

By Thursday, a dry upper ridge will build inland into California
and bring a noticable warming trend to the area with temperatures
expected to be several degrees above seasonal normals by Friday.
Dry conditions are also expected to prevail Thursday through the
weekend.

The medium range models are in fairly good agreement with an upper
pushing across the PAC NW Sunday Night and Monday which will bring
some high clouds to our area along with a cooling trend although
temperatures will remain above normal for our area early next
week.

&&

.AVIATION...Periods of upslope cloudiness in the Kern and Tulare
County mountains will cause areas of IFR/LIFR conditions with
local terrain obscuration. Slight chance of showers and
thunderstorms in the Sierra Nevada through 18Z Tuesday. From 18Z
Tuesday until 06z...showers and thunderstorms increasing in
coverage and spreading over the Sierra and the Kern County
mountains and desert areas. A few showers and thunderstorms may
drift over the southern half of the San Joaquin Valley. Otherwise,
VFR conditions will prevail across the Central CA Interior during
the next 24 hours.

&&

.AIR QUALITY ISSUES...None.

&&

.CERTAINTY...

The level of certainty for days 1 and 2 is medium.
The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.php for additional information
an/or to provide feedback.

&&

.HNX Watches/Warnings/Advisories...NONE.

&&

public...DS
avn/fw...Andersen
synopsis...DS

weather.gov/hanford

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

1 heavy rain. Local standard time, as filed.

Heavy Rain, Kern

When: May 1, 12:30 PM PST to 12:44 PM PST
Where: Kern County, North Edwards
Reported by: ASOS
Coordinates: 35.020, -117.770

The ASOS at North Edwards reported 0.37 inches of rain in 14 minutes from a brief heavy thunderstorm.

What these are

Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

More

Every storm in California in 2018 Every state in 2018 This day in weather history Warnings in California, May 2018

Sources

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: 748136.