TeamPlayersBlue wrote:1989 - Phase 7 entering the month of Feb lead to VERY cold air into the Pacific NW. -40 C 850 temps into Montana, eventually, -30C 850 temps creep into Nebraska with energy coming out of the SW. Phase 7 didnt last long with this example but this air was historically cold.
February (not December) 1989 was a near miss glancing blow. Yet it was a spectacular blast in these parts. DFW got down to 10F after being entombed in ice. Much forgotten event because of what happened later that year.
In fact Feb 1989 holds the North American high pressure record 1079.6mb of that outbreak. Alaska had 1078.6mb which is a US record. The 500mb pattern did not allow the full crushing blow of this HP as it weakened in the north rather than hold its strength southward. Still what was left, was quite a show.
The 500mb flow is not always representative of the HP strength, though there is some correlation. Density of the cold air matters too.