April Showers

We've had a few rainy days here to start things off in April. Environment Canada doesn't track historic data on May flowers (that I'm aware of, anyway), but today we're going to look at what it has to say about April showers.

Rainy Months

Here we have the typical distribution of rain for each month of the year, going back to 1995.

If you've been to Edmonton Weather Nerdery before this chart might look pretty familiar, but today is actually the first time that I've ever used it. In the past few months we've spent a lot of time looking at a similar chart for snow, and last summer we looked at total precipitation (rain + snow). But this is the first time that I've looked at rain by itself.

The average rainfall for each month is the white line in the middle of this chart. It's surrounded by a band for the 25th-75th percentiles, which is where we'll fall about half of the time. And then there are the 2nd highest & 2nd lowest amounts since 1995, and then finally the very highest & lowest.

The recent average rainfall for April is 15mm, and the rain we had this weekend has already pushed 2017 up above that to 21mm. The rainiest April since 1995 was in 2010 with 39cm, and that was still below the average rainfall that we get in May, which is 42mm. And May is well below June, which is well below July. So April in Edmonton is not a particularly rainy month.

2016 Rain & Precipitation

April is a shoulder-season month though, and it might get rain one day and then snow the next. So this chart shows how the amount of rain compares to the total precipitation (rain + snow), using 2016 as a reference.

June, July and August are the only months of the year which are fairly reliably snowfree, and so the centre section of this chart is pretty consistent, whether we're looking at rain or at precipitation. But all of the other months will typically see a combination of rain and snow, and so the chart for total precipitation shifts up a bit.

That shift isn't huge though, because we really don't get that much precipitation (rain or snow) during the winter. I've mentioned this before, but our average precipitation in July is 93mm, compared to a total of 87mm for all 5 winter months from November-through-March combined.

April Rain or April Snow?

Since April will usually get a mix of rain and snow, here we have the rain and snowfall amounts separated out, going back to 1995.

There is a lot of variation from year to year, but the 5-Year averages tend to be in the range of 15-20mm of rain and also 15-20cm of snow. In the last 5 years we've ranged from a very low 2016 with 5cm of snow and 4cm of rain; to 2012 with 24cm of snow and 36cm of rain.

Last week I was saying that we might see a bit more snow this spring, because right now we're only at 4cm while the average is about 20cm. But as is always the case, the average is skewed a bit by the really snowy years. In the 22 years that are shown here, there were 8 other Aprils which had 6cm of snow or less. So 2017 could stay as one of those low-snow Aprils, or we might get another storm? But then May also gets some snow about half of the time.

In terms of April showers though, with 21mm so far we've already had more rain in April 2017 than in 17 of the last 22 years. And there's more in the forecast for this week.