Frost/Freeze in Blue Mountain Foothills, Washington

The mesonet station K7DTF Walla Walla reported at or below freezing temperatures between 0103 to 0651. The Washington DOT station TDELA reported at or below freezing temperatures between 2338 to 0738. Several other stations across the area reported temperatures at or below freezing for several hours the morning of the 19th.

Clear skies in combination with dry flow regimes aloft resulted in good radiative cooling taking place at the surface. Temperatures in the morning had dropped to or below freezing for several hours in lower elevation locations between April 18th to the 20th.