Weathercatch: Just in time for Mother’s Day – another big weather change and why

Our region’s meteorological thermostat is doing some impressive zigzagging.

Spring was running on the cool side of normal across the Inland Northwest until an abrupt surge of heat that began in late April sent temperatures into summer levels – 1½ months before the solstice. Then, as quickly as the heat and sunshine arrived, it vanished, leaving brooding clouds and a plunge in temperatures in its place into the early part of this week.

One day we were opening windows and strolling outdoors in short sleeves, the next we were turning up the furnace and stepping out in warm jackets and hats.

What caused the mercury to abruptly soar, only to suddenly nosedive?

The heat build up was caused by a stagnant ridge of high pressure, colloquially known as a heat dome, that settled over the interior Pacific Northwest, parts of the Intermountain West and all the way north into Canada’s Northwest Territories. The ridge created a pocket of sinking warm air that heated up as it compressed while approaching the ground. Meanwhile, additional heat was drawn from the south by the jet stream, a fast-moving air current in the upper atmosphere.

This atmospheric pattern brought temperatures we expect to see in late June, not in late April/early May. Much of the Inland Northwest experienced five out of six days with temperatures in the 80s.

Spokane snagged a record two days in a row, with a high temperature of 85 degrees on May 2 and again on May 3, breaking century-old records in the low 80s for both days. Coeur d’Alene, Sandpoint and Wenatchee reached 84 degrees. Missoula hit 90 degrees.

On May 4, the temperature was a toasty 78 degrees in Spokane. Then, in a remarkable turnabout, it dropped 24 degrees in a single day when the high on Friday reached only 54 degrees. A steep cooldown that included scattered showers and thunderstorms lasted through the weekend and into Tuesday. The abrupt change was instigated by a chilly trough of low pressure centered off the Northwest coast that moved inland, bringing cool, moist Pacific air with it. This, in turn, caused the heat dome to break down.

If you’re yearning for more summerlike warmth, another heat dome is building overhead, although at a slightly slower pace than the previous one. Wednesday reached near 70 degrees, Thursday will be a few degrees warmer and Friday warmer yet. Highs this weekend may climb into the mid- to upper 80s.

All of which means, Mother’s Day is expected to bear gifts of sunshine and unseasonable warmth.

Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek.