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We predict the coolest October in five years in Washington with plentiful rainfall

Temperatures should end up close to normal but with a lot of volatility.

Fir tree needles exhibit some early fall color. (Fred Cochard/Flickr) (Picasa/Fred Cochard)
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After a fast shift to autumn in September, we anticipate the coolest October since 2015 along with a healthy dose of rainfall.

Our forecast is for Washington’s average October temperature to fall within 2 degrees of normal. Remarkably, the past four Octobers have each been at least 3 degrees above normal, all ranking in the top 20 warmest on record.

We don’t see the streak of abnormally warm Octobers continuing.

We predict 2020′s temperature will fall somewhere between 57.5 and 61.5 degrees, whereas the normal is 59.5 degrees. The last time the average temperature was below normal was in 2015, when it was 58.9 degrees.

We doubt we’ll have any concerns with drought or dryness in the upcoming month. We predict between 3.2 and 3.8 inches of rain, compared with the average of 3.6 inches. The month’s first substantial rainfall could occur Monday.

This October will attempt to depart some from the pattern of the past 10 years, which has featured overwhelmingly warmer-than-normal temperatures, while our prediction of somewhat above average rainfall would more fit the mold.

Expect volatility

While the average temperature and precipitation for the month may end up near average, daily weather is likely to frequently stray far from the norms. We expect the September narrative of volatility to continue, featuring both cool periods and then occasional warm/muggy intervals.

For example, the first seven days of October should lean to the cooler side with highs mostly in the 60s to low 70s and lows in the 40s and 50s, while the second week of the month trends warmer with highs rising through the 70s with lows mainly in the 50s. Whether in the 60s or 70s, the month promises to offer a refreshing reprieve from this summer’s punishing heat.

The NOAA CFS model agrees with our forecast for near normal temperatures but projects below-normal precipitation:

While La Niña patterns in the tropical Pacific Ocean, as we see presently, usually mean drier-than-normal weather in Washington, that is not usually the case in October. Already, models are starting to converge on a rainy forecast for early next week, bringing a coastal low pressure system close to the region.

Here are the latest rainfall forecasts from the National Weather Service for the period of Oct. 3 to 6:

Unlike the past two years when summer extended into October, we should continue to see more typical autumn variability in the Mid-Atlantic with plenty of nice days to talk about.