Why is Snoqualmie Pass WARMER than the lowlands?

SEATTLE -- It's not often that a mountain pass in the Cascades is warmer than the lowlands.

Q13 News Meteorologist M.J. McDermott explained why Monday morning and what it means for air quality in the Pacific Northwest:

"Snoqualmie Pass is already at 70 -- warmer than the lowlands (except for Seattle at 71 on this map). It's called an "inversion" when there are warmer temps aloft and it causes the air at the surface to be trapped, so we can have air quality issues," M.J. said.

Air temperatures the morning of Monday May 14, 2018.

"Sure enough, air quality is at "moderate" in King County this morning (the yellow dots)," she said.

Air quality map for Monday, May 14, 2018.

"Not a big deal, because this "air trapping" weather isn't lasting long. But it can be a big deal especially in the summer. Remember last year when we had that bad smoke from fires?"