California, 1998

Flash Flooding and Damaging Winds in California, September 2, 1998

September 2, 1998 · NWS LOX · 7 events in 1 county or zone

A series of severe thunderstorms affected the San Gabriel Valley, bringing strong winds and heavy rain. The strong thunderstorm winds knocked down numerous trees and power lines across the area.

Where it happened

Every event with a place to put it; 4 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

  • Tornadoes
  • Tropical storms and surge
  • Floods
  • Wind
  • Hail
  • Winter weather
  • Heat and drought
  • Cold
  • Fire, smoke and dust
  • Marine and coastal
  • Other

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The toll

Deaths
0
Injuries
0
Property damage
None recorded
Crop damage
None recorded
Events
7

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 LOX wrote it up.

A series of severe thunderstorms affected the San Gabriel Valley, bringing strong winds and heavy rain. The strong thunderstorm winds knocked down numerous trees and power lines across the area. In Pomona, several houses had parts of their roofs blown off. Also, a helicopter pilot reported a funnel cloud near the Pomona area. The heavy rain produced widespread flash flooding across the valley. In some areas, motorists were forced to the roofs of their cars. In Walnut, the heavy rain collapsed the roof of a Von's Supermarket.

The radar

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

Open the radar archive at this moment

Event by event

3 thunderstorm wind, 3 flash flood, 1 funnel cloud. Local standard time, as filed.

Thunderstorm Wind, Los Angeles

When
September 2, 2:05 PM PST to 2:15 PM PST
Where
Los Angeles County, San Dimas
Measured
70 kt (81 mph)
Reported by
LAW ENFORCEMENT
Coordinates
34.120, -117.820

Thunderstorm Wind, Los Angeles

When
September 2, 2:09 PM PST to 2:20 PM PST
Where
Los Angeles County, Diamond Bar
Measured
52 kt (60 mph)
Reported by
LAW ENFORCEMENT
Coordinates
33.980, -117.830

Thunderstorm Wind, Los Angeles

When
September 2, 2:45 PM PST to 2:55 PM PST
Where
Los Angeles County, Pomona
Measured
52 kt (60 mph)
Reported by
LAW ENFORCEMENT
Coordinates
34.070, -117.750

Funnel Cloud, Los Angeles

When
September 2, 2:55 PM PST to 3:05 PM PST
Where
Los Angeles County, Pomona
Reported by
AIRPLANE PILOT
Coordinates
34.198, -118.261 (the zone’s center; the record gives no point)

Flash Flood, Los Angeles

When
September 2, 3:00 PM PST to 4:00 PM PST
Where
Los Angeles County, Diamond Bar
Reported by
TRAINED SPOTTER
Coordinates
34.198, -118.261 (the zone’s center; the record gives no point)

Flash Flood, Los Angeles

When
September 2, 3:00 PM PST to 4:00 PM PST
Where
Los Angeles County, Pomona
Reported by
TRAINED SPOTTER
Coordinates
34.198, -118.261 (the zone’s center; the record gives no point)

Flash Flood, Los Angeles

When
September 2, 3:00 PM PST to 4:00 PM PST
Where
Los Angeles County, Walnut
Reported by
TRAINED SPOTTER
Coordinates
34.198, -118.261 (the zone’s center; the record gives no point)

What these are

Thunderstorm Wind
Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.
Funnel Cloud
A rotating column of cloud extending from a thunderstorm that did not reach the ground.
Flash Flood
Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

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

The same day elsewhere

More

Every storm in California in 1998Every state in 1998This day in weather historyWarnings in California, September 1998

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: 5665227, 5665228, 5665229, 5665230, 5665231, 5665232, 5665233.