A Wild Ride on the Barometer

I noticed something interesting on the atmospheric pressure graph on my home weather station yesterday. We fell to extremely low readings (29.18") when that big storm came by the Northeast last week. But yesterday we had that large high pressure system over us and we were at extremely high values (30.57"). Both of these readings are fairly extreme here in Pennsylvania, and it's even more unusual to have them occur so close together. You can see both extremes on the graph below (click to enlarge).

Grand Isle, Maine fell to 28.72" that day last week and Alberta, Virginia rose to 30.67" yesterday. It's fairly rare to see readings below 29.00" or above 30.70" in the Continental United States, especially in the South. Where I used to live in North Carolina, you didn't have pressure below 29.30" unless there was a hurricane; up here in the Northeast, it's not uncommon as major winter storms dip down.

Here are some U.S. pressure records, according to Chris Burt, author of "Extreme Weather", a comprehensive guide to which I frequently refer:

Overall U.S. Highest Pressure: 31.42" (MT)
Highest in Pennsylvania: 31.10"
Highest in North Carolina: 30.95"

Overall U.S. Lowest Pressure: 26.35" (FL)
Lowest in Pennsylvania: 28.43"
Lowest in North Carolina: 27.97"

Barometers were the only meteorological instruments which still have a scale which includes the most extreme readings. Plotting those Pennsylvania records along with my readings from the last week, we can see where we stand: