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Here's What We Know About The Pressure Records From October 26, 2010

The low pressure rapidly deepened on October 26, 2010, leading to several pressure records being broken. Here are some facts about those pressure records:

  • Bigfork, MN (KFOZ) had a minimum sea level pressure of 955.2 millibars (28.21") at 5:13 pm CDT
    This is recalculated slightly from the lowest altimeter reading of 28.20" that was initially reported for this storm. Both altimeter readings and sea level pressure are derived from the station pressure. Although the altimeter reading is a sea level reduction as well, it uses a US standard atmosphere assumption. The sea level pressure factors in observed temperatures. Therefore, the altimeter and sea level pressure readings are often very slightly different.
  • 955.2 millibars is now the Minnesota state record for lowest observed sea level pressure
    The previous record was 962.7 millibars (28.43"), set on November 10, 1998 at both Albert Lea, MN and Austin, MN.
  • Superior, WI had a minimum sea level pressure of 961.3 millibars (28.39") at 11:15 am CDT
    This is now the Wisconsin state record for lowest observed sea level pressure

    The previous record was 963.4 millibars (28.45"), set on April 3, 1982 at Green Bay, WI.
  • Our two climate reporting sites set low pressure records as well
    Duluth, MN had a minimum sea level pressure of 960.2 millibars (28.35") at 11:15 am CDT. This broke the old record at Duluth which was 964.3 millibars (28.48"), set on November 10, 1998. International Falls, MN had a minimum sea level pressure of 956.0 millibars (28.23") at 3:45 pm CDT. This broke the old record which was 971.9 millibars (28.70"), set on October 10, 1949.


Was This Any Kind Of National Record For Lowest Pressure?

The bottom line, is that Bigfork, Minnesota did not set the CONUS record for lowest extratropical sea level pressure. Here are the details:

  • The lowest sea level pressure recorded at any United States certified observing station was 892 millibars (26.34"), recorded at Matecumbe Key, Florida on September 2, 1935 in the "Labor Day Hurricane". Therefore, the reading at Bigfork on October 26th was not the lowest pressure in the entire United States.
  • The lowest sea level pressure recorded in a non-tropical (extratropical) storm at any United States certified observing station was 927 millibars (27.35"), recorded at Dutch Harbor, Alaska on October 25, 1977. Therefore, the reading at Bigfork on October 26th was also not the lowest pressure in the entire United States for a non-tropical storm.
  • Many storms have been discussed as potential record holders for the lowest recorded sea level pressure in a non-tropical storm at a land-based observing station in the Continental United States (CONUS). The lowest that has been mentioned was 951.6 millibars at Bridgehampton, NY on March 3, 1914. However, this value cannot be confirmed by records held at the National Climatic Data Center (NCDC).
  • The lowest CONUS, land-based, non-tropical, sea level pressure that can be confirmed by NCDC is 955.0 millibars (28.20"). This occurred twice in United States history. The first time was on January 3, 1913 at Canton, NY. The second was on March 7, 1932 at Block Island, Rhode Island. These were verified by NCDC using archived climate data publications.


How Does This Rank Amongst Storms Away From The US Coasts?

  • If you only consider extratropical lows that tracked between the mountain ranges (Rocky Mountains on the west, Appalachian Mountains on the east) - the Central US - the lowest sea level pressure on record appears to be at Mount Clemens, Michigan at 13Z on January 26, 1978. A 956.0 millibar value was recorded there and is supported by NCDC data. This was related to the same storm that produced a 957.7 millibar sea level pressure at Cleveland, Ohio. The lowest value for the central US is sometimes reported as the reading in Cleveland, however, that was superseded by the value in Mount Clemens.
  • The January 26, 1978 storm later went on to produce lower sea level pressure readings in Ontario, Canada, including a 955.5 millibar reading at Sarnia. However, these are not in consideration as we are only discussing the United States.
  • Therefore, the 955.2 millibar value that was recorded in Bigfork, Minnesota on October 26, 2010 appears to be the lowest extratropical sea level pressure on the record books in the mainland United States, excluding the west and east coasts.


What Should I Take Away From This?

The bottom line is that the storm that struck the Upper Mississippi River Valley on October 26-27, 2010 was a very intense and rare storm, something that is not seen in this part of the country very often. While the minimum sea level pressure may not necessarily be the lowest on record, the storm was undoubtedly one of the most intense on record in the continental United States.

In fact, with the storms on January 3, 1913 and March 7, 1932 tied for first place at 955.0 millibars, the October 26, 2010 storm would be the second lowest recorded sea level pressure at 955.2 millibars. NCDC was also able to confirm a 956.3 millibar reading at Eastport, Maine on December 16, 1916.

It is also worth noting that lower pressures have likely been attained off the coast of the Pacific Northwest (Oregon and Washington) or perhaps even just off shore of the New England States (Maine, New Hampshire, Massachusetts). However, given that there are very few reliable observing stations offshore, especially dating back many decades, these low pressures may not have been sampled by our observing network.


Caveats About The Pressure Value At Bigfork

Bigfork (KFOZ) is an AWOS (automated weather observing system) station, which is completely automated. Unlike an ASOS (automated surface observing system), an AWOS does not automatically report a sea level pressure value. Therefore, it was necessary for us to calculate the sea level pressure from the reported station pressure. As we continue to evaluate these calculations, the lowest sea level pressure at Bigfork may fluctuate slightly. However, any slight calibrations in the equation and constants that we are using would not allow the Bigfork reading to break any other records.


Pressure Graphs

Here are a few pressure graphs. The procedure was to evaluate the lowest pressure at each individual time in the day across the Upper Midwest, and then to plot the data on a graph to assess the trends in the minimum pressure at the center of the low. The data was adapted from information provided by Daryl Herzmann.


Fig. 1: minimum observed sea level pressure on October 26, 2010 across the Upper Midwest. Fig. 2: as in fig. 1, except the previous Minnesota state low pressure record is annotate in a horizontal red line.



Fig. 3: as in fig. 1, except individual sea level pressure values are annotated on the graph. Fig. 4: as in fig. 1, except with a trend line showing the rapid deepening of the low on October 26th.


Finally, here is a graph with different sea level pressure trends plotted at different observation sites across the NWS Duluth county warning area. The data from Hibbing and Duluth are 1 minute data downloaded from the ASOS.