Summary:
- September was a roller coaster for temperatures with recording breaking heat early and late in the month, sandwiching a very cool period in between. Overall, the month ended up warmer than average* in the west.
- Overall, a dry month over the west, although rains from the mid-month system dipping southward into California and some monsoon moisture in the Great Basin was evident but “barely enough to settle the dust.” Heat and dry conditions elevated fire activity, most notably in Southern California.
- Growing degree-day accumulations for the vintage are now higher than average over most of the west, except along some coastal zones and within some mountain-valley areas.
- The run of warm and dry days to end last month looks to continue into October with ridging dominating the west. Extreme heat all the way to the coast to start the month, then likely record breaking warmth for many. Dry conditions are likely to persist for most of the west, although the potential for a push of fall-like moisture may make its way into the PNW. But don’t expect much rain until later in the month. Elevated fire risk for now.
- Moving into the first half of winter, the long-term forecast has the majority of the country warm and dry with average precipitation. The PNW has the greatest chance of a normal start to winter rains, but amounts are iffy.
- The Tropical Pacific appears to be slowly heading to La Niña conditions, with the forecast calling for a weak event with a short duration. A weak La Niña often indicates that it would be less likely to result in conventional winter impacts over the western US and throughout the Pacific region, though predictable signals could still influence forecast guidance over the short term.
