Multiscale Interactions and Extreme Rainfall

What can subseasonal predictability tell us about rainfall extremes in the midlatitudes?

Atmospheric river (red) propagation, MJO convection (orange), total precipitable water (grayscale), and vertically integrated vapor transport vectors (blue).

The Madden-Julian Oscillation (MJO) and Predictability

You've probably seen NOAA's three-month outlook for temperatures and precipitation for the United States. I'm sure you've wondered how during some years the three-month outlook can deviate so strongly from what you experience on the ground. NOAA's seasonal outlook is based on the expected state of the climate, and those expectations are strongly predicated on El Niño and La Niña. Climate conditions—like El Niño and La Niña—can take place over the course of years. This is far longer than the timescale of a storm that can throw off a seasonal prediction by precipitating a month of rain or snow in a few days. To more accurately predict natural disasters that can upend seasonal predictions, researchers need a bridge that connects shorter-term weather and longer-term climate. In my work, I use the Madden-Julian Oscillation (MJO) as that bridge.
The MJO is an eastward moving disturbance of clouds, rainfall, winds, and pressure that often moves through the tropics (often from the Indian Ocean into the Pacific Ocean) roughly every 30 to 60 days. In doing so, the MJO can kick off (or teleconnect) to a variety of other phenomena, potentially making them worse. MJO activity has been linked to everything from wildfire activity to atmospheric river activity. The atmospheric river connection is key to my research.

MJO and Atmospheric Rivers

There has been a library of studies written about the connections between the MJO and atmospheric rivers (ARs). The MJO has been found to change everything from AR severity to frequency (see this article I wrote about the MJO and ARs from 2024). Much of this work, however, uses statistical methods to locate the MJO, as opposed to identifying its precipitation directly to track its location. My research, thus far into my PhD, investigates whether MJO precipitation can be a water source for ARs in a way that might make their precipitation more intense (spoiler: it does).

Relevant Publications

  1. Small, C. A., S. S. Chen, and B. W. Kerns, 2026: Madden-Julian Oscillation and Atmosphere Rivers: New Insights on Water Source and Transport for Extreme Rainfall Over the Western U.S.. J. Geophys. Res., Atmospheres, 131. https://doi.org/10.1029/2025JD045573. (PDF)