FARGO — Fargo and Grand Forks reached their highest temperatures on record for June 1 on Monday, with both cities breaking their records set in 1933, according to WDAY Cheif Meteorologist John Wheeler.

Fargo reached a high of 97 degrees and Grand Forks reached a high of 94 as an advancing cold front pushed a mass of hot air into the Red River Valley, Wheeler said.

Some mobile phones may have shown users higher temperatures, Wheeler said, but it is impossible to verify if these numbers are accurate because they are based on models, not physical measurements.

Temperatures on mobile phone applications are based on models and are estimates based on area measurements, he explained. So if a phone showed the temperature had reached 100 degrees in West Fargo, that number was likely based on a calculation — not any instrument.

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Monday's high temperatures were the result of a phenomenon called compressional heating, which Wheeler likened to a compressor in a refrigerator or air conditioner.

High pressure in the upper atmosphere causes air to expand. When this air reaches lower altitudes, increasing air pressure in the lower atmosphere causes it to compress and warm.

Clear blue skies across the Red River Valley were also a consequence of the compressional heating, Wheeler said.