A Dynamical View of the Record Heatwave of June 2021 in Western North America - PV

During the last week of June 2021, an unprecedented heat wave engulfed the US Pacific Northwest and adjacent province of British Columbia (BC), Canada. The highest ever recorded temperatures were reported in Portland, OR, on June 26, and in numerous other locations as the heat spread up the Western States. On June 28, the temperature reached 49.2° C in Lytton, BC: this is the highest value ever recorded in Canada.

Meteorological fields at 2100UT (Universal Time), which is locally near noon on the West Coast of North America, on June 30, 2021. The purple dots show hot surface air temperatures (exceeding 30°C, or 86° F) on a meshed grid. These high pressure ridge, or omega blocking structure, over Western North America is depicted by the high geopotential height fields (white contours) at 200hPa (near 12km altitude) in the atmosphere. The shading shows the Ertel’s potential vorticity (PV) field, also at the 200-hPa pressure level, with low values, associated with subtropical air, in cool colors and high values, associated with polar air which rotate more vigorously, in warm colors. Read More.