CW3E Precipitation Outlook: 12 September 2024

Septebmer 12, 2024

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Remnants of Tropical System Forecast to Bring Precipitation to Interior Western US

  • A tropical depression (TD 9E) currently located south of the Baja Peninsula is forecast to strengthen into a tropical storm and track northward through the Gulf of California during the next several days.
  • Tropical moisture associated with the tropical cyclone (TC) is forecast to expand northward into the interior southwestern US this weekend, setting the stage for showers and thunderstorms that could produce flash flooding.
  • Meanwhile, a deepening mid-level trough near the US West Coast is forecast to move eastward and bring widespread light-to-moderate precipitation to the Great Basin and Northern Rockies.
  • As this trough moves onshore, it will interact with the remnant TC moisture, leading to a broad region of enhanced moisture transport over the Colorado River Basin.
  • The Global Ensemble Forecast System (GEFS) is showing a high likelihood (> 85% probability) of atmospheric river (AR) conditions (IVT ≥ 250 kg m−1 s−1) in southern AZ on 15–16 Sep.
  • The NWS Weather Prediction Center (WPC) is forecasting 0.5–1.5 inches of precipitation in portions of central and southeastern AZ, southwestern CO, northern NV, and northern UT during the next 5 days.
  • The NWS WPC has issued a marginal risk of rainfall exceeding flash flood guidance in central and southeastern AZ Saturday into Sunday morning, expanding to much of AZ and western NM Sunday into Monday morning, expanding further northward into southwestern CO Monday into Tuesday morning.

    • Click images to see loops of GFS IVT and IWV forecasts

    Valid 1200 UTC 12 September 2024 – 1200 UTC 17 September 2024

    Summary provided by C. Castellano, S. Bartlett, and J. Cordeira; 12 September 2024

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    *Outlook products are considered experimental

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