When you read about the record heat today, you might think that the high temperature record was shattered by 10 degrees in the city of Portland.   What’s true is that it did reach the 90s and as I write this Portland has just broken their record high for the date, but the record won’t be broken by 10 degrees – and here’s why.

Back in 1941 the National Weather Service moved the weather records to the Portland Jetport.  The same thing happened in Boston when they moved the records from the center of Boston to Logan Airport in the mid 1930s.  In Boston however, the National Weather Service’s records include both the database of records from downtown and Logan Airport. This gives a continuous weather picture since 1872.  This means when Boston breaks a record it includes both Logan Airport and earlier pre-1936 downtown locations.  As an aside, the Logan location is a horrible one to represent Boston because it sticks out in the ocean and no one lives there, but that’s another story.

Here in Portland, the National Weather Service believed that moving the station from downtown to the airport was too great a distance to keep the records continuous.  In other words, where the Jetport is located is too different to consider it the same as the other records.   Another reason might have been that some of the readings in the database might be off because thermometers where’s situated as accurately as we do today.

In reality, the old data is likely as good or good enough as  from other sites around the country from the late 1800s and early 1900s.   Based on this reasoning, the true record high for today in Portland was 92, set back in 1936.  Portland reached 93 just after 4 p.m. for a new record. We know a lot about May 18, 1936.  That same day Boston, Hartford and Providence also had their records broken.  May 18, 1936 was hot. It was hot across much of New England including Portland and we have the data to prove it.  Portland, Boston, Hartford, Worcester and Providence all broke/tied records today.

The record high for the city of Portland today is 92, set back in 1936.

If Boston removed 1936 from their database, then the next-warmest May 18 is 1949. You may be told that 1949 set the record high for Portland. That afternoon, the jetport reached 82 degrees.  If you use only jetport data it looks as if the record for this date is being shattered more dramatically that it really is.

Portland has good weather records in a database which have been kept since 1871. We ought to be using them.

The record high at the Portland Jetport was set back in 1949. But the high for this date in Portland was set in 1936.


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