Weather in Tri-Cities in May

Prime time. If you get to pick your dates, May is the one. Highs average 24.5 °C, lows 10.9 °C, and rain falls on 7 days — nothing in the month is working against you.

May ranks 2 of 12 in Tri-Cities. Only September scores clearly higher, and the difference is small enough to be settled by price rather than weather.

Rain on 7 days, 0 of them heavy. Enough to need a plan B, not enough to need a plan around it. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: 5 days top 30 °C — hot spells arrive, but they break. Across the twenty years measured, the hottest May day reached 38.9 °C and the coldest night fell to 1.9 °C.

May is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest May on record still delivered 48 mm against 8 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 27 mm average is a reasonable planning figure, not a promise.

Wind is light at 9.4 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 52%.

How May sits in the year

The month is on the way up: 5.6 °C warmer than April, and June adds another 4 °C. Late in the month feels noticeably different from the start of it, which is worth knowing if the trip is short.

Daylight in May

14.9 hours of daylight, gaining 1.2 hours across the month. That is between Tri-Cities's extremes of 15.8 and 8.6 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 34.6 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

May in Tri-Cities versus nearby

If Tri-Cities is one option among several, the nearby comparison is worth making. Spokane is close enough to be a coin toss — 4.5 °C cooler, 3 days more rain. Portland is the weaker option in May — 5.3 °C cooler, 6 days more rain.

So: May is effectively as good as it gets here — 4 points behind September, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Tri-Cities

See all twelve months in Tri-Cities, or where else to go in May.