Early September Climate Outlook
The Climate Prediction Center issued a La Niña Watch in August. This watch means that La Niña conditions are likely to develop over the next several months, but that La Niña conditions are not currently in place. If La Niña develops in fall or early winter, it is likely to be mild and brief, returning to neutral conditions by late winter or early spring. According to the official CPC ENSO Forecast, there is a 50-60% chance of La Niña conditions this cool season.
The 1-Month September outlook indicates generally low predictability for both precipitation and temperature as we transition into fall. Fall is typically a tough time for accurate seasonal predictions. That being said, there is a slight tip in the metaphorical seasonal climate scales toward wet conditions across western Washington (33-50% chance) and warmer than normal conditions across far northeastern Washington, including Spokane (33-40% chance). This outlook is largely based on extended-range numerical weather prediction (NWP) model simulations made in late August.
Similarly, the 3-Month outlook (September-October-November) also shows fairly low predictability for temperature and precipitation. There is a 33-40% chance of above normal precipitation across the western half of the state including the Cascades, Puget Sound, and Pacific Coast. As for temperatures, there is a slightly elevated 33-40% chance of above normal temperatures statewide. Given these slight changes across the board, conditions over the next several months are difficult to predict at the moment and will largely come down to specific weather patterns and how quickly La Niña may develop.