Intense, severe storms pelted sections of southern California on Sunday with massive amounts of rain, causing severe local flooding and damage in eastern Los Angeles county.
Most severely affected were inland empire locations and adjacent mountain locales stretching across the San Gabriel and San Bernardino ranges.
More than four inches of rain fell in about an hour at Mt. Baldy, and 2.36 inches were recorded in nearby Claremont during the preceeding 24 period. It is not clear yet whether or not this is a record; most likely it will verify as record rainfall for the date. Flash flood warnings Sunday afternoon covered nearly all mountain areas, and nearby by areas including Cajon Pass and San Bernardino. Travel was impacted on several freeways, including the 215, 210 and Interstate 15.
Flooding and devastation were reported, roads were impassible throughout the Angeles National forest, causing closures, necessitating rescues and evacuation. There was one reported fatality in the Mt. Baldy area. One resident there stated it the worst flooding since 1969.
And there may be more in the coming months, according to long range assessments.
At fault: a combination of meteorological elements. Starting with a persistent pocket of unusually warm sea water surrounding the Baja California penninsula, this alone has contributed to an unusually active summer monsoon season across the entire Southwest. Sunday's violence was further accelerated by the presence of an unusual combination of an upper level low and an easterly or tropical wave disturbance drifting in from the southeast, as is typical several times each summer. Conditions were ripe for unusually powerful lift, and an abundant moisture field was present. Moisture laden southerly winds were jacked up over Southland mountain ranges, and these storms were able to spread out in all directions, while remaining nearly stationary.
The storms gradually diminished overnight, with associated energy expected to shift north into Nevada, and Utah where more flash flooding was possible today (Monday).
Latest long range forecast data continues to suggest the development of significant El Nino conditions this autumn, and updated rainfall projections in July had predicted above average precipitation across the entire southwestern U.S. beginning in August, and continuing into next Spring.
Oceanic temperatures across almost the entire eastern Pacific Ocean are running significantly above average, this could result in a weakened or absent blocking eastern Pacific high pressure system in the coming months, allowing for more moist and persistent active low pressure disturbances to impact the southwestern United States.