May 2018 Recap & Summer Outlook

May 2018 brought above normal temperatures, with some new records, to much of the eastern half of Washington and the Idaho Panhandle. Wenatchee, WA; Winthrop, WA; Mazama, WA; and Bonners Ferry, ID all experienced their warmest May on record. Spokane, WA and Lewiston, ID also had some of their warmer Mays on record; it was in the top 5 warmest Mays for both cities. It was not the typical wet and cool May that we are used to. Many locations received below normal precipitation, but did not reach any new record low totals. However, due to the above average temperatures and remaining snow pack, some lakes and rivers rose to significant heights. Numerous lakes and rivers experienced flooding. The Kettle River, near Ferry, reached a historic crest of 22.54 ft. on May 11^th. 

Monthly Weather Summary - May 2018

Table 1. Average May temperatures with their rank when looking at the previous/current May records

*It is important to note that due to long periods of record, sites of observations may have changed.

Table 2. May 2018 high and low temperatures with date and total monthly precipitation

Temperature and Precipitation Anomalies

When looking at May mean temperature anomalies above, much of Washington east of the Cascades, the Idaho Panhandle, and northwestern Montana had the biggest warm-anomalies in the western United States.

A closer look at May percentile rankings shows that some record warm mean temperatures occurred in the Eastern slopes of the Cascades, which is where you can find record setting Mazama, Winthrop, and Wenatchee in Washington. Most of the Pacific NW was much above normal.

In the Pacific Northwest, the map of May precipitation anomalies displays the drier than normal conditions in much of the region. 

Looking closely at Spokane

For the entire month of May, there were no days with temperatures below 40°F at Spokane Intl. Airport. 

xmACIS Plot showing number of days in May with min temperatures below 40°F (1947-2018)

There have only been two previous years where Spokane's low temperature has failed to fall below 40° F in the month of May: 1957 & 1980. The last time the temperatures dropped below 40°F this year was April 23^rd with a low of 34°F.  This year had the second warmest May low temperature, just below 1957’s record of 42°. 

Summer Outlook

CPC summer temperature outlook issued May 17, 2018

CPC Summer precipitation outlook issued May 17, 2018

The Climate Prediction Center (CPC) outlook is favoring elevated odds of a warmer than average and drier summer (June-July-August) this year for the Northwest. However, this does not mean there will not be periods of cooler weather and precipitation, like we will be seeing this weekend.

Please monitor our website for all of the latest updates: https://weather.gov/spokane