UW's Neal Johnson ran the numbers and found that the sea level pressure at Seattle-Tacoma Airport today was the highest since record keeping began there in 1948. Last night at midnight Sea-Tac hit 1043.4 hPa, smashing the old record of 1043.0 hPa.
According to the Weather Underground site the highest pressure in Seattle occurred on 12/3/1921 (1043.90 hPa), but that was at a very different location (downtown Seattle, not the airport) and thus not a fair comparison.
- National Weather Service sea level pressure analysis : A very strong high pressure area is centered over the Northwest and southwest Canada, with pressures greater than 1040 hPa over much of the region and a 1046 hPa center over southern BC. 1046 hPa is equivalent to 30.89 inches of mercury. This is REALLY high sea level pressure. At Sea-Tac the 9 pm pressure was 1042.6 hPa - and it is still going up! There has been a huge pressure rise over the past 24h--roughly 20 hPa.
According to Cliff Mass Weather Blog these pressures are very unusual, it's the highest pressure in 15 years! The Portland International Airport has recorded a maximum barometric pressure reading of 30.76" (4:53am observation) which is tied for the second highest reading since records began at the airport in 1940. This push of high pressure over the Northwest is creating huge pressure gradients over the southwest U.S. The latest model prediction for tomorrow morning shows high pressure over US and a big pressure differences over Colorado, Utah, Nevada, California, and the offshore waters.