Intense Atmospheric River Storm to Drench California with Four Days of Rain

An intense atmospheric river storm is set to impact California this week, bringing substantial rainfall and severe weather conditions. The storm will arrive in Northern California on Wednesday and progress southward, reaching Southern California by Thursday. It is expected to linger through Saturday, creating the potential for heavy rainfall, flooding, and debris flows, especially in areas affected by previous wildfires.

Storm Forecast and Rainfall Expectations

Forecasters predict that downtown Los Angeles may experience the highest rainfall in recent weeks, possibly exceeding amounts recorded since February. Rose Schoenfeld, a meteorologist from the National Weather Service in Oxnard, warned about the risk of flash floods and debris flows in burn areas.

• Rainfall Totals:
  • 1-2 inches in coastal and valley areas of L.A.
  • 2-4 inches in mountain and foothill regions.
• Specific Rainfall Projections:
  • Long Beach: 1.08 inches
  • Downtown L.A., Redondo Beach, Pomona, Pasadena: ~1.3 inches
  • Oxnard: 1.51 inches
  • Santa Clarita: 1.75 inches
  • Westlake Village: 1.98 inches
  • Santa Barbara: 2.22 inches
  • Ojai: 2.88 inches

The storm is expected to produce widespread rainfall at rates of 0.25 to 0.5 inches per hour. Mountain areas may see rates increase to 0.5 to 0.75 inches per hour, raising concerns for debris flows, particularly in burn areas.

Wind Conditions and Impact

Winds accompanying the storm could pose additional hazards. Peak gusts may reach up to 50 mph in certain areas, particularly along the Grapevine section of the 5 Freeway and in the Antelope Valley. Conditions could disrupt traffic, especially during evening commutes on Thursday and Friday.

• Wind Forecast:
  • Downtown L.A.: 21 mph
  • Long Beach: 24 mph
  • Santa Clarita: 26 mph
  • Redondo Beach: 32 mph
  • Lancaster: 39 mph

Effects on California’s Fire Season

This storm may signify the end of California’s autumn fire season. David Gomberg, a fire program manager at the NWS, indicated that if projected totals are accurate, they could reflect a significant change in vegetation conditions. A cumulative 3 to 4 inches of rain is typically needed to mark the official end of fire season.

As temperatures are expected to drop dramatically due to the storm, many areas will see a marked decrease from earlier highs. For instance, temperatures in downtown L.A. are predicted to drop from 92°F to 61°F between Monday and Friday.

Forecasted Weather Across California

Rain should begin to ease by Friday, but there could be further rain showers on Saturday. Uncertainty remains regarding the expected precipitation on Saturday due to a developing cut-off low pattern. Thunderstorms may also be possible, bringing gusty winds and small hail.

• Key Locations Affected:
  • San Francisco Bay Area: Late Wednesday through Thursday.
  • Sierra Nevada: Heavy snowfall expected, up to 18 inches in some regions.

Travel between Thursday and Friday may encounter difficulties due to hazardous conditions, especially over mountain passes. Chain requirements are anticipated for motorists traversing the Sierra Nevada.

The upcoming storm represents a critical weather event for California, with implications for both water supply and fire season management. Residents are encouraged to prepare for possible flooding and difficult travel conditions as the atmospheric river approaches.