Urban sprawl is a big contributor to the false readings.
They build an airport in the wide open space outside a city and a weather station is invariably placed at the airport.
They get normal readings for a few years until the new suburb grows up and brings the average temperature up. This has happened in just about every city.
You take a reading at a airport where jets are heating the surroundings with hot exhaust and paved runways are soaking up rays and you are bound to get erroneous readings. Airports are the worst locations for gathering scientific temperature data.
Or they locate the measurement equipment housing on the grass in the corner of where two large black asphalt tarmac ramp areas come together, so when the wind is from the west through the south the reading is not compromised, but when it is from any other direction (and especially from the NE through the SE), the wind passes over hundreds of yards of tarmac before it hits the gages.
This was the case at the Columbia, Missouri Regional Airport (COU) until just a few years ago when the station was moved a few hundred yards to the south. So, for about 20 years we had really bad readings or not so bad readings from this station depending on the wind.
A concerted effort must now be made to peer-review the location history of each station and to only use data from stations that are determined to be accurate. All other data must be disregarded.
I don't know how many times these past winters that Logan would be reporting 40 degrees and rain while the rest of Boston would be 31 degrees and snowing. In one ludicrous example I can remember a few years back, Boston proper got socked with a foot of snow and yet Logan Airport reported something like 4.3 inches of slush.
But if anybody knows the geography of Logan Airport, they would know that nobody lives out there but the seagulls. It is basically landfill, covered with concrete and surrounded by water on three sides so the temperatures are unduly influenced by the surrounding salt water and all the concrete. About the stupidest place you could put a weather station in the Boston area.