Image caption
A dome of high pressure squatted over Alaska July 4–8, 2019, keeping temperatures high and skies cloud-free. The 500-millibar pressure level—the altitude at which the air has thinned enough to drop the pressure to 500 millibars—was more than a hundred meters taller than average during the period. NOAA Climate.gov image, based on NCAR/NCEP Reanalysis data provided by ESRL Physical Sciences Division.