Dust Storm — Sw S.j. Valley, California

2009-10-13 · Sw S.j. Valley, California

Wider weather episode

A deep low pressure trough tapped into quite a bit of moisture from the remnants of Super-Typhoon Melor, bringing as much as around 2 inches of rain to the central and southern San Joaquin Valley on the 13th-14th. Much higher amounts fell in the Southern Sierra Nevada. Dinkey Creek received the most precipitation from this storm, with a storm total was just over 13 inches (about 9 inches of this fell in 12 hours on the 13th). Wishon Dam recorded a storm total of around 10 inches by the 14th. At the onset of this storm during the morning of Oct 13th, quite a bit of snow fell over the crest of the Sierra Nevada. Once the precipitation began in earnest by the afternoon of the 13th, snow levels actually rose to over 10,000 feet, so most precipitation was falling as rain by the end of the event on the 14th. Rock and mud slides were reported on Highway 198 in Sequoia National Park. A Flash Flood Warning was issued for the Dinkey Creek area due to the very heavy rain. A hydrograph showed a sharp rise in the stream flow due to rainwater runoff, indicative of a flash flood event in the creek which normally does not reach such high levels.

In addition to the near-record (and in a few locations, record) rainfall, the storm brought high wind gusts that toppled trees, downed utility lines, and created areas of blowing dust with near-zero visibility. Wind gusts to 58 mph were recorded at both Castle Airport near Atwater (in Merced County) and Crane Flat in Yosemite National Park. Gusts to 60 mph developed at the south end of the San Joaquin Valley near the base of the Grapevine, and 77-mph gusts occurred over the Temblors in western Kern County. High winds in the Buttonwillow area caused a chain-reaction vehicle pileup on Interstate 5 around 515 pm on October 13th, where 3 people were killed in traffic collisions. The California Highway Patrol reported several areas of wind damage to trees and powerlines in the Merced area on the 13th.

On the 15th another high pressure ridge began to build over the area with light surface winds. The lower levels of the atmosphere had abundant moisture as a result of the recent rain, with high dewpoints for at least the next three mornings. Patchy dense fog developed over the southwestern portions of the San Joaquin Valley on the morning of the 15th, with more widespread dense fog, with visibilities below a quarter of a mile, throughout much of the valley on the mornings of the 16th and 17th.

Source: NOAA Storm Events Database, event_id 284670. Narrative written by the NWS forecast office that issued the report.