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New climate dataset (CMIP6) keeps warming projection but shows stronger late-summer heat and seasonal shifts
Summary
The forecast's climate module compared CMIP6 with CMIP5 and found roughly 1.6°C (about 3°F) average warming statewide, stronger late-summer warming (about 2.1°C), modest change in annual precipitation (~+1%), drier summers and more intense wet storms in some regions—next step: run these projections through hydrologic models.
Sasha McLarty summarized a comparison between the climate dataset used in 2021 (CMIP5) and an updated CMIP6-based dataset. "This new dataset continues to predict significant warming across Washington with little change in annual precipitation," she said, noting that the statewide mean annual temperature rise is about 1.6°C (≈3°F).
The module found seasonal shifts: spring warming is milder (~1°C) while late-summer warming is stronger (about 2.1°C in the dataset). Annual precipitation changes are small on average (≈+1%), but seasonal patterns indicate drier summers (particularly in Western Washington) and slightly wetter other seasons. Extreme wet events intensify modestly; heavy five-day storm totals are expected to increase, with absolute increases larger in Western Washington but larger proportional increases in many parts of Eastern Washington.
Presenters noted they have not yet run these updated temperature and precipitation projections through the forecast's hydrology models; doing so is the next step to estimate how changes in precipitation and temperature will translate into snowpack, streamflow, and water availability across basins.
