<p>I've noticed that Environment Canada's precipitation forecasts for the Great Lakes region (east of Toronto) are usually one of the following:</p>
<ul>
<li>30% rain</li>
<li>40% rain</li>
<li>60% rain</li>
<li>70% rain</li>
</ul>
<p>But not usually higher than 70%.</p>
<hr />
<p>Whereas, I've heard the forecast in the prairies (Winnipeg) often have a higher certainty, such as:</p>
<ul>
<li>80% rain</li>
<li>90% rain</li>
</ul>
<hr />
<p>That makes me wonder:</p>
<p>Is it easier to make high-certainty precipitation predictions in places like the prairies  vs. the Great Lakes region?</p>
<p>For example, would Lake Ontario and/or the Oak Ridges Moraine make it harder to predict precipitation in the Great Lakes region — since inbound storms might be affected by those features?</p>

CC BY-SA 4.0
2022-08-04T08:07:11.623Z
It's not a confidence in the forecast, it's the Probability of Precipitation (PoP). If it's 50 %, there is 1 in 2 chance that a significant amount of rain will fall over the considered area during the considered time interval. So if you see higher values in a region, it just means that this region gets more rain, not that the forecast there is more reliable.
Jean-Marie Prival
<weather-forecasting><precipitation>
Do geographic features like large lakes or a moraine make it more difficult to predict precipitation?
User1974
# Do geographic features like large lakes or a moraine make it more difficult to predict precipitation?

(Asked by: username_0 on 2022-08-03)

I've noticed that Environment Canada's precipitation forecasts for the Great Lakes region (east of Toronto) are usually one of the following:

* 30% rain
* 40% rain
* 60% rain
* 70% rain

But not usually higher than 70%.

---

Whereas, I've heard the forecast in the prairies (Winnipeg) often have a higher certainty, such as:

* 80% rain
* 90% rain

---

That makes me wonder:

Is it easier to make high-certainty precipitation predictions in places like the prairies vs. the Great Lakes region?

For example, would Lake Ontario and/or the Oak Ridges Moraine make it harder to predict precipitation in the Great Lakes region — since inbound storms might be affected by those features?

**Tags:** weather-forecasting, precipitation

> **Comments:**
> **username_1**: It's not a confidence in the forecast, it's the Probability of Precipitation (PoP). If it's 50 %, there is 1 in 2 chance that a significant amount of rain will fall over the considered area during the considered time interval. So if you see higher values in a region, it just means that this region gets more rain, not that the forecast there is more reliable.  

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## 0 answers

