CW3E Precipitation Update: 9 October 2025 Outlook

October 9, 2025

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Multiple Precipitation Events to Impact the Western US Through Early Next Week

Forecast Details:

  • A predecessor rain event (PRE) driven by Tropical Storm Priscilla is forecast to impact the Southwest through Sat 11 Oct, with potential for ≥ 2 in. across the region.
  • In addition to the anomalous moisture provided by Tropical Storm Priscilla and its remnants, a mid-level trough and an upper-level jet entrance region will provide forcing for ascent to enhance precipitation amounts across the region.
  • Moisture from a second tropical system, Tropical Storm Raymond, is forecast to spread north into the region late on Sat 11 Oct, potentially extending the precipitation over Arizona and New Mexico.
  • The remnants of the Tropical Depression are forecast to influence a second precipitation event for Arizona and New Mexico on Mon 13 Oct and Tue 14 Oct.
  • At the same time, a mid-level trough is forecast to become cut-off and propagate down the US West Coast, bringing precipitation to the Pacific Northwest and California.
  • CW3E’s West-WRF ensemble is showing multiple episodes of elevated moisture transport over Central Arizona in association with the moisture from both tropical systems, with ~40% of members forecasting AR3 conditions for Thu 9 Oct through Sun 12 Oct for a location just south of Phoenix.

Impacts:

  • The PRE is forecast to bring 1.5–3.0 inches to portions of Arizona, New Mexico, Utah, and Colorado through Sun 12 Oct, with localized totals exceeding 4.0 inches. The second event over the Southwest is likely to bring an additional 1-2 inches to Arizona and New Mexico.
  • The trough digging south along the US West Coast is forecast to bring 0.5–1.5 in. of rain to the Pacific Northwest, 1.0–2.0 in. to much of Northern and Central California, and <0.5 in. to Southern California. The highest precipitation totals are forecast over terrain in the Sierra Nevada and Coast Ranges.
  • The NWS Weather Prediction Center (WPC) has issued a moderate risk excessive rainfall outlook (ERO) for central Arizona and slight and marginal risk EROs for the rest of Arizona and much of New Mexico, Utah and southwest Colorado with the PRE.
  • Slight and marginal risk EROs were also issued for the second event in Arizona and New Mexico early next week as well as a marginal risk ERO over Northern California for the trough precipitation.
  • Precipitation from these storms will likely bring some drought relief to the Colorado River Basin. Some watersheds in Arizona are forecast to receive as much as 20-30% of normal annual precipitation.

Click images to see loops of CW3E West-WRF 500-hPa Vorticity and IWV forecasts

Valid 1200 UTC 9 October 2025 – 1200 UTC 14 October 2025

Summary provided by M. Steen, C. Castellano, and S. Bartlett; 9 October 2025

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*Outlook products are considered experimental

For any unfamiliar terms, please refer to the American Meteorological Society Glossary.