Hot temperatures likely next week

After a very warm May, the weather has changed for the first half of June with periods of cooler temperatures, rain showers, and thunderstorms. Computer models have remained fairly consistent over the past several days showing strong high pressure developing next week which could bring an extended period of much above normal temperatures. The latest image showing U.S. risk of hazardous temperatures says it all.

This experimental product from the Climate Prediction Center issued today (Jun 11th) shows a high risk (60%) of excessive heat across the Columbia Basin on June 19th and 20th, with a moderate risk (40%) over this same area June 21st and 22nd.  The remainder of Central and Eastern Washington is in a moderate risk June 19-22nd. 

But before the heat, let's talk about the weather this upcoming weekend and how quickly the weather pattern transitions next week.

Here is the pattern for Saturday and Sunday:

12z/June 11th GFS model forecast of 500mb heights and 700-500mb Relative Humidity (image) valid 5 PM PDT Saturday June 16

12z/June 11th GFS model forecast of 500mb heights and 700-500mb Relative Humidity (image) valid 5 PM PDT Sunday June 17

Not good if you have outdoor plans.  A low pressure system moves little, bringing the potential for showers each day and maybe even a few thunderstorms.  Previous model solutions were quicker to move the low out, but now the weekend looks showery.  Note the images above depict relative humidity with the green colors over our region indicating high values of moisture.

After that, models show a quick transition in the weather pattern. The low over Idaho takes a quick jaunt to the southwest, setting up off the California coast with strong high pressure over the Inland NW. 

12z/June 11th GFS model forecast of 500mb heights and 700-500mb Relative Humidity (image) valid 5 PM PDT WED June 20th.

This results in a hot/dry conditions over our region while the low off the California coast possibly draws in much needed precipitation into the southwest.  A large area of heat expands into much of the west as the image below shows.

12z/June 11th GFS model forecast of 500mb heights and 850 mb temperatures (image) valid 5 PM PDT WED June 20

The European model shows a similar pattern

00z/June 11th ECMWF model forecast of 500mb heights and 850 mb temperatures (image) valid 5 PM PDT WED June 20

How hot will it be?  Well it's too far out to narrow down the numbers, but 90s are a good bet for many valleys, possibly touching close to 100° in the hottest locations.  Note that this event is still 8-10 days out, and the details will probably change.  But, don't be surprised by an extended spell of heat starting around Tuesday, June 19th.

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