Summary:
- Much of Washington, Oregon, coastal California and the Bay Area and delta region had a cooler than average September. This was largely the result of the blocking ridge over Alaska that keeps much of these areas with relatively cool air flow. Points to the south and east were flipped with much warmer than average temperatures. Even with some rain in western Oregon and Washington, dry conditions persisted in the western US in September continuing long-term drought concerns.
- The major change over the short term (10-14 days) is a turn to colder than average over much of the entire western US. The pattern shift is the result of what is happening in Alaska, one of the warmest and driest falls ever seen. The greatest likelihood of precipitation for California and the desert southwest may have already occurred over the last couple of days, while more northern areas have some coming over the next few days.
- The seasonal forecast balances the current cool conditions with expected warmer conditions into early winter. The forecast continues to point to a dry period through the end of the year for the PNW, and other regions to likely see average precipitation. Heading into the final weeks of the season heat accumulation is likely to end up slightly below average to close to the average heat accumulation of the last five years.
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