Temperatures in May across the region were slightly above normal.
That headline is a bit misleading as temperatures when one looks beyond monthly summaries. The first half of the month was incredibly warm with 7 consecutive days at or exceeding 80F in Spokane, Pullman and Moscow from the 6-12th with a similar warm spell for Missoula. These spells of warm weather so early in the year have only been seen 1-2 times on record for some of the stations that go back 100 years or so. Somewhat curious was that the warmest “location” in the contiguous US on four consecutive days in May occurred in Washington state thanks to a Rex blocking pattern.
However, the latter half of the month featured a more progressive weather regime that allowed some very cool and unsettled conditions including wintery mix on the Palouse on the 22nd of May. Several days set record low highs (coldest daytime high temperature), and temperatures the morning of the 23rd (28F in Moscow) forced folks who had planted tomatoes during the warm conditions earlier in the month to hit the replay button on the home gardening adventure game.
This upside down sequence is somewhat fortuitous from the perspective of early season wildfire potential which you can read more about on my outlook posted here.
May was the fifth consecutive month of below normal precipitation for much of the inland Northwest sinking most spots further in water debt. The drought monitor has much of the region in some form of drought, including 80% of Idaho and 90% of Oregon as of the end of May.
A few stations in the western Columbia basin including Yakima picked up a decent amount of precipitation of convective variety around mid-month and ended with one of the wettest May’s on record. Of course, it doesn’t take too many rouge precipitation events to top a monthly normal of just over a half-inch of precipitation.
In the wake of a lame precipitation showing since the new years, streamflow is pretty low across the upper and middle Snake River basins.
The lack of precipitation resulted in an earlier start to irrigation season across much of the region, but in particular the Snake River Plain. The lack of spring rains and low soil moisture actually required some cases growers to use irrigation to encourage their crops to emerge. In what is likely to be a summer that taxes water users and keeps the threat for wildfire high across much of the region, we will be keeping a keen eye on the skies. Chances for any useful precipitation climatologically dwindle substantially around mid-June and the next 10 days don’t look like they’ll help much.