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California is currently experiencing unusually warm winter weather, with temperatures approaching 80 degrees—typical for late spring in Southern California. In February 2022, snow covered the city of Rialto, and nearby mountains were fully blanketed in snow. Fast forward to February 2025, and there is barely a cloud in the sky. But why is this winter so much warmer than it was three years ago?

A simple explanation could be changes in weather patterns. Climate change increases the frequency of extreme weather events, such as unusually warm winters. One common weather pattern shift is known as the “El Niño” effect, which causes Pacific Ocean temperatures to rise above normal and impacts global weather patterns. For example, a strong El Niño in one year can lead to a warmer winter in the following year for nearby regions.

What Exactly Is El Niño?

This phenomenon occurs when the surface of the Pacific Ocean becomes unusually warm. It disrupts atmospheric circulation and alters typical weather patterns by releasing warmer air into the atmosphere. El Niño also affects jet streams—fast-moving air currents that significantly influence weather. During El Niño, jet streams are guided northward, leaving southern regions with warmer air.

Some regions affected by El Niño include the Midwest and Southern U.S., Europe, and Asia. While El Niño is currently inactive, the most recent event occurred from late 2023 to early 2024. This may explain why the winter of 2025 is warmer than usual.