Cool and Damp for the Foreseeable Future

Welcome to autumn everybody! The equinox occurred at 12:50 this morning, and our days will continue to get shorter and shorter until the winter solstice. Interestingly, the equinox has slightly more day than night for two reasons: first, the sun is a disc and not a point, and two: Earth’s atmosphere refracts light, making the sun appear higher in the sky than it actually is. The date with equal night and day is known as the equilux, and for Oregon and Washington, it will occur on Wednesday the 25^th.

We’ve had an extremely wet September thus far, with 3.22 inches of rain through the 22^nd. High temperatures have also been well-below average thus month, but with ample cloud cover at night and the “Blob” still remaining offshore, lows continue to be above-average. I think it’s safe to say that our sticky nights are over for 2019, though.

A look at the current 500mb heights and satellite shows a large ridge in the Eastern Pacific and trough in the Gulf of Alaska driving strong zonal flow into British Columbia. This ridge will strengthen through midweek and give us partly cloudy skies with highs near 70 on Tuesday and a few degrees warmer Wednesday.

However, 60s will return Thursday as this ridge begins to weaken, and a stronger trough will arrive Friday, potentially bringing another shot of rain to the Portland metro area Friday night and Saturday and even some snow to the mountains above 6,000 feet.

Models show this trough deepening over the weekend, giving us dry but chilly, northerly flow. If the models were showing this setup two months from now, I’d be talking about the potential for snow in the lowlands.

The ensembles continue to show below-average temperatures and above-average precipitation persisting for the first week of October. Anything past two weeks is outside the realm of the “foreseeable future,” so I’ll play it safe and won’t make any guesses on what the rest of October will be like.

El Nino Update

The Tropical Pacific is currently in a “Neutral” (neither La Nina or El Nino) state. El Nino/La Nina are by far the most reliable indicators of what type of weather we can expect for the winter – El Nino winters are generally warmer-than-normal with fewer large storms, while La Nina years tend to be cooler and snowier-than-normal. By contrast, Neutral winters can be highly variable and haven’t fit a general pattern within our period of record, though they tend to give us near normal precip/temperatures on average.

The Climate Prediction Center is calling for a 75% chance of Neutral conditions this autumn, with a 55-60% chance of Neutral conditions persisting through winter and spring. Given this outlook, I’d expect this winter to have near-average precipitation/temperatures, but there is above-average uncertainty. Spoken like a true meteorologist!

Have a great week,
Charlie