The intense high pressure ridge currently residing over Alaska is by some measures the strongest on record for the month of May. Yesterday afternoon's balloon sounding at Fairbanks observed the height of the 500 mb surface at 5750 m above sea-level, compared to a previous monthly record of 5744 m on May 30, 1964. This is equivalent to saying that the pressure was the highest on record for May in the middle troposphere. The observed heights also broke the monthly records closer to the ground, at 700, 850, and 925 mb, but the surface pressure was 1 mb shy of a record.
This morning's sounding reported an even higher 500 mb height, 5760 m. The 4 am AKDT 500 mb analysis from Environment Canada is shown below.