One of the most remarkable aspects of Northwest weather is the rapid turn-on of significant precipitation in November.
October is often a decent month, with substantial sunshine. But not November. The master switch really gets pulled sometime during the first week of the month, with the third week often being the wettest of the entire year.
To illustrate this, here are the climatological probabilities of getting a tenth of an inch of rain in a day in Seattle. The probabilities sneak up in October, but there is a huge jump during the middle weeks of November (see red arrow)
This year will not disappoint rain lovers and ducks.
The highly skillful European Center model predicts substantial rainfall through November 7th….some locations (mountain slopes) will enjoy as much as 8 inches of rain.
The higher resolution WRF model describes the first pulse of rain late Wednesday and into Thursday, with substantial soakings in the Olympics and Cascades. Even eastern Washington gets notable rain.
This rainy period will be associated with a moderate atmosphere river….a plume of moisture out of the tropics/subtropics…that will be aimed directly at our region (see the forecast for tomorrow at 5 PM of the amount of atmospheric water vapor in a vertical column of air).
To evaluate the confidence in this forecast, meteorologists review ensembles of many forecasts. For Seattle, the National Weather Service global ensemble shows a rapid precipitation turn-on tomorrow after roughly 6 PM, a wet night following, and then lots of rain over the subsequent week. All the ensemble forecasts indicate wet conditions….you can take this prediction to the bank!
Many Northwest Rivers are now experiencing below-normal flows. This will not be the case in one week. Reservoirs should start to fill
Furthermore, we have been experiencing far cooler-than-normal temperatures over the past several days. The cold period will end with the precipitation, as warm moist air sweeps into the region.
