The Upcoming Cool Down

During the past week we have experienced a few warmer than average days, although none pushed temperatures into the 90s over the Puget Sound region (see Sea Tac temperatures below, with average max and min values in red and blue).

The recent warmth has been associated with a broad upper level ridge of high pressure over the West Coast and eastern Pacific, as illustrated by the upper level map at 5 PM Thursday below.

However, the hallmark of this summer has been the transient nature of West Coast high pressure, with the tendency to have periods in which troughing (low pressure) has developed over the region.    Such troughing will be happening in spades during the next week, as illustrated by the upper level map for Saturday at 5 PM:  a low is centered over British Columbia, with a trough over the Northwest.

 Subsequently, the trough moves out and is replaced by a strong, small-scale, low centered over NW Washington (see below for 11 PM on Monday).  This will bring both cooler temperatures and some precipitation.

 Fast forward to Thursday at 5 PM. Another low is moving into our area.

This time of the year it is hard to get heavy rain even with weak troughing.   Thus, the 24-h precipitation forecast ending 4 PM on Tuesday shows some light rain over western WA, but modest wetting over British Columbia.

Turning the National Weather Service GFS model, here is the accumulated forecast precipitation over the next 10 days.  The West Coast is starkly drier than the rest of the continent, with Oregon and coastal CA being dry.  In contrast, the East Coast is soaked.

With much cooler and wetter conditions over the Northwest, the number of wildfires has been minimal.  With the upcoming cooling, one should expect the continuation of the benign fire season.