# Long range forecast

(Calgary, AB)

Canada - 30 day temperature forecast Example

OK - I've looked at the long range 2-4 month forecast maps and probabilities but I still don't understand if Western Canada is going to have normal precipitation and warm temps or another drought? Interpretation please!

Barry's Response - I usually start with https://weather.gc.ca/saisons/image_e.html?img=mfe1t_s -- This shows the forecast temperature anomaly over the next 30 days (it's updated every Thursday). It's only possible to tell if they mean above, below or near normal, then the second plot shows the accuracy of these forecasts.

Next, I look at the 90-day plots: https://weather.gc.ca/saisons/prob_e.html and then the 90-day forecast for the precipitation https://weather.gc.ca/saisons/image_e.html?img=s123pfe1p_cal&bc=prob

Included are the current and next two months. The temperature plots in the example show it was unusually warm in BC and Alberta (except Medicine Hat), Northern Saskatchewan, and Manitoba. For the same time period, all of BC, Alberta (except Medicine Hat), Saskatchewan and Manitoba are predicted to be unusually dry.

Medicine Hat should be near normal - which means warm and dry (compared to the rest of this region.)

Later, after comparing it with the actual weather, Medicine Hat had record precipitation and flooding in June that year. It takes a big flood to shut down a brick factory.

Long-range forecasts can be useful, but they should be interpreted with caution. Staying up to date with the latest forecast information is always a good idea.

You may have also notice some links entitled "probabilistic" and "deterministic" forecast. These are a bit more advanced...

## Understanding and reading Environment Canada's probabilistic and deterministic long-range forecasts requires close attention to detail and an understanding of the information provided.

Here's how to navigate these forecasts:

- Learn the terminology: Long-range forecasts often use specific terms to describe the likelihood of certain weather conditions. "Probability," "chance," "likely," and "possible" indicate the level of confidence. Understanding these terms and their probabilities is important.

- Long-range forecasts usually highlight key weather parameters, like temperature, precipitation, and general weather patterns. Observe forecasted ranges or values for these elements, as well as any significant trends or patterns.

- Examine a probabilistic forecast: Probabilistic forecasts give you a range of possible outcomes and their probabilities. Check out the probability values for different scenarios. You'll know what's likely to happen if you do that.

- The deterministic forecast provides a single outcome or prediction. It's usually based on a model or set of data. Pay attention to the level of confidence expressed in the forecast and any other information provided.

- Understand the limitations: Long-range forecasts have inherent limitations due to the complexity of weather systems and the uncertainties associated with predicting weather so far out. Remember that these forecasts are subject to change as new data becomes available, and they might not be as accurate as short-term forecasts.

- Understand long-range forecasts in the context of historical weather patterns, climate trends, and local knowledge. For a more comprehensive understanding of forecasted conditions, consult historical climate data or get expert advice.

That is what I do on a full-time basis.  Find out if it is necessary for your project.