Weather Blog

Midwest storm greatest ever? We beg to differ!

Midwest storm greatest ever? We beg to differ!

Update: After further review, the lowest pressure recorded at Big Fork, Minnesota was officially declared as 955.2 mb / 28.21" of mercury. The Minnesota State Climatology office has said this indeed appears to be the lowest pressure ever recorded in the continental U.S., exlcuding hurricanes and tornados.

What began as a little "sister" trough to the big storm that rolled through the Northwest this past weekend has grown up into a monster.

Strong winds over 80 mph are blasting the upper Midwest, along with all sorts of severe thunderstorms and tornadoes as this "monster" moves east.

But aside from keeping weather forecasters busy warning residents of the impending storm, it's also got the meteorological community quite abuzz with how strong this storm's central pressure is -- it might be the lowest on record for a non-tropical storm!

Or....is it?

NOAA put out a note Tuesday night that it indeed had the lowest central pressure recorded in the continental U.S. (So, not Alaska which has storms like this for breakfast and lunch in the winter). Then it recanted to "Top 5" while they dug through more research.

Wednesday morning, the Weather Channel Tweeted a note from NOAA that a pressure recorded at Big Fork, Minnesota on Tuesday was 954.95 milibars, or 28.20" of mercury. They think that is indeed the lowest.

But wait!

The "Great Blizzard of 1978", or alternately nicknamed the "Cleveland Superbomb" (in reference to a "bombing" storm where the pressure drops very rapidly in its core as it undergoes intensification) apparently had estimated central pressures around 950 mb -- UW assistant professor Greg Hakim had written a paper on this storm and analyzed a central pressure of 955 mb, while another researcher came up with 952. But those were calculated based on other observations, and the actual lowest pressure might have been in Ontario, meaning the "U.S." record today woudl be vaild. They're trying to go back and find decades-old data and I'm sure NOAA's research teams are hard at work to see what they can find.

So maybe this is the second-lowest storm.

But wait!

Our own local weather community is abuzz, shouting "East coast bias!" pointing out that some of the great windstorms to strike the Northwest over the years have had stronger central pressures.

UW Atmospheric Sciences Professor Cliff Mass wrote an excellent blog defending our turf. Although I think in this case, they're both right.

Our big storm in Dec. 12, 1995 might have had a stronger central pressure for a non-tropical storm -- a buoy out offshore measured a pressure of 958.8 milibars -- and the buoy was not near the center of the storm, suggesting that the storm was, in fact, stronger. Wolf Read, a local expert who has researched every windstorm to strike the Northwest, puts his calculations at 953 mb for peak strength. But read says for places closer to land -- Destruction Island which is just off the coastline had a lowest pressure reading of 961 mb.

This 1995 storm did a lot more wind damage than this current storm with peak gusts over 100 mph -- even a 112 mph reading at Cannon Beach, OR.

There is also some debate over whether our great storm of Jan. 9, 1880 (dubbed the "Storm King") had a lower pressure than 955 mb. As you can imagine, pressure recordings in 1880 were not that extensive. Read told me that the 955 mb reading came from two separate ships that were not too far from the Oregon coast at as the storm passed, but the lowest land-based reading was 967 in Portland.

But all of these might not count anyway because as far as what NOAA is saying, we are losing on a technicality. The Midwest record is the lowest pressure *recorded* over mainland United States. I can't find any actual measurement that is lower than 954.95 mb in any of our storms -- the '95 storm here set all of our pressure records, and they are mainly in the 960s (Seattle's is 965). Cape Elizabeth, which is some 40 miles offshore, recorded that 958 in 1995, but even then, technically that's not on the mainland U.S. (or is it? Not sure if that would count.)

Mass' point is that our storms have been stronger. Note that the central pressure is not the final word in how strong a storm will be, it just is a measure of potential. The real factor is the "pressure gradient" -- as in how large of a difference there is in pressure over a short distance. Air likes to flow from high pressure to low pressure, and when there is a big difference, the air flows faster.

In fact, in this sense, this storm probably won't rank near the top on a gradient level because the pressure field around the storm isn't as high, meaning you don't have as big a difference as some of the other historical national storms this current system is being compared to.

So in essence, while the Midwest can have it's fancy numbers record, that storm is not the "strongest non-tropical storm" ever to strike the U.S., if any claims are made to that effect, because the power from some of our windstorms are greater -- the Columbus Day Storm of 1962 would "blow" all those other storms away, hands down.

Check out Wolf Read's excellent "Storm King" website as he has extensive research on all of our Northwest windstorms.

P.S. I'll hope you'll forgive the blog this week. I've got some great material sent in covering how big the ocean surf was and how distinct the Olympic Rain Shadow was over the weekend and Monday. It'll be a bit old-hat by the time I post the stories this week, but I think they'll be worth the wait :)