How the time change affects the forecast

ALLISTER AALDERS @allistercanada Allister Aalders is a weather specialist with SaltWire Network. Reach him at allister.



SaltWire Network


Whether you like it or not, the time has changed. While the time change doesn’t impact the weather that’s occurring, there are some subtle changes when it comes to weather forecasting. There may be some minimal effects on when the daily high temperature is achieved, but the time change affects what’s known as the climate day, which Environment Canada uses for data collection and record keeping. The climate day ends at 3 a.m. ADT/3:30 a.m. NDT during daylight saving time but ends at 2 a.m. AST/2:30 a.m. NST during standard time. There is also another benefit to those who forecast the weather. Many aspects of meteorology are based on what’s known as Z time or Zulu time – more commonly referred to as Co-ordinated Universal Time – or UTC. Most weather models run at least four times a day, and unless there is an error with the output, the model data is released around the same time each day, with the exact time varying between each individual model. Zulu time does not observe daylight saving time, which means that when clocks fall back one hour to standard time, the model data arrives one hour earlier. One hour might not seem like much, but in the world of news and deadlines, the extra hour is extremely beneficial to analyzing and preparing the forecast, especially during storms.