Friday, October 29, 2010

Data Review Reveals Midwest Cyclone Missed All-Time Record by 0.01"

A review of the observations from Tuesday's intense cyclone and historical records by the National Weather Service (NWS) and National Climatic Data Center (NCDC) has determined that the current storm's low pressure missed the all-time Continental U.S. record by the smallest possible margin, 0.01". The 28.20" altimeter setting reported at Bigfork, Minnesota (station ID KFOZ) has been corrected to 28.21" (955.2 mb), based on a more accurate adjustment of the raw observed station pressure to sea level. The more precise calculation takes into account the actual observed temperature, as opposed to an assumed U.S. standard atmosphere.

Also, NCDC has found 2 verified observations at 28.20" (955.0 mb):
     13 January 1913 at Canton, New York
7 March 1932 at Block Island, Rhode Island
(Note, however, that Block Island is located a little more than 10 miles off the coast of Rhode Island, so it doesn't strictly meet the definition of mainland Continental U.S.)

On the other hand, a lower reported reading of 951.6 millibars at Bridgehampton, NY on March 3, 1914 cannot be confirmed by the NCDC (although that, too, is technically not a mainland reading, since it's on Long Island).

The current storm is clearly the record-holder for lowest pressure in an extratropical storm away from the Atlantic or Pacific coasts. The previous record was held by the Great Lakes storm of January 26, 1978. That storm had a reading of 956.0 mb at Mount Clemens, Michigan, which exceeded the frequently-reported 957.7 at Cleveland. According to the NWS, "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."

The report goes on to cite record lower pressures elsewhere in the U.S.:
  • For a tropical cyclone: "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'."
  • Beyond the Continental U.S.: "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."
Image (click to enlarge): Minimum sea level pressure reported October 25-26, 2010; annotations indicate location of observations; from NWS

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