Definition of temperature in weather reporting

[Stephen Tashi]

TL;DR Summary

What definition of temperature is used in reporting weather conditions. To measure air temperature must thermometers be put in a dark place?

In my town, newspaper stories say we've had several days of record high temperatures. The stories report temperatures in the range of 107 F. However, on the same days, online weather reports show temperatures as high as 116 F.

I think online weather reports use reports from amateur weather stations. ( On several days, I've seen the temperature measured by an (analog) outdoor thermometer in the shade of a covered patio get up to 115 F.) I speculate that "official" weather stations take more precautions than amateurs to shield their thermometers from radiant heat. Is that correct? Are there additional considerations to explain the differences in reported highs? - pehaps something about data rates? Does the definition of "temperature" in weather reporting require that the temperature stay at a certain value for a minimum length of time?

 

[Lnewqban]

Please, see:
https://en.m.wikipedia.org/wiki/Stevenson_screen

I am almost certain that in my area, the values registered at the weather station located in the international airport are taken as reference, as many oficial reports refer to that station.

 

[jim mcnamara]

Heat island effects. Urbanization changes ambient temperatures. Downtown is hotter than out in the exurbs.
https://www.epa.gov/heatislands

Microclimate is something that Biologists have great interest in. Example: many desert species cannot endure full sun exposure for long periods, so they burrow down one to two inches in the soil or hide in the shade of a rock. This can mean temperature changes on the order ten degrees C cooler. Seed germination is especially tied to soil surface microclimate in terms of moisture, insolation, etc.
https://en.wikipedia.org/wiki/Microclimate

Answer to your question is, thank you @Lnewqban, - the Stevenson Screen is the NOAA standard weather station. Microclimate accounts for different thermometer readings around the house, the heat island is a good explanation for big differences across a city and suburbs

 

[russ_watters]

In my town, newspaper stories say we've had several days of record high temperatures. The stories report temperatures in the range of 107 F. However, on the same days, online weather reports show temperatures as high as 116 F.

I think online weather reports use reports from amateur weather stations. ( On several days, I've seen the temperature measured by an (analog) outdoor thermometer in the shade of a covered patio get up to 115 F.)

Do you have sources you can share? It should be made pretty clear what the source is, in the report. I use NOAA/NWS as my primary weather source.

My home weather station is in a good spot though and agrees pretty well.

 

[Stephen Tashi]

Do you have sources you can share?

I use wunderground.com for the current temperature report.
However, I don't know how to get past temperature data for all the weather stations that site can show. I only see past temperature data for stations whose names suggest they are professional - such as Las Cruces International Airport Station.

 

[rsk]

I worked for the UK MetOffice as a forecaster for a few years.

Official temperatures are always measured out of direct sunlight, in those white slatted boxes known as Stevenson Screens - hence weathermen often qualify their temperatures with 'in the shade'.

However, those boxes can't remove the effect of urbanization, so temperaures in built up areas are recorded as higher than in the surroundings. (Interestingly the max temp in such areas often occurs a couple of hours later than elsewhere, as the heat built up during the strongest sunshine is released in the late afternoon/early evening).

As for max temperature - no, there's no rule to say how long the temperature should be sustained. The thermometer has a little gadget in it to record the highest position of the mercury (or similarly the lowest) from which max and min temps are taken.