September 23, 2020

More rain coming (but not that much!)

  • Vancouver Island Inland Sections Forecast - No watches or warnings in effect.

    Forecast Issued 05:00 AM PDT Wednesday 23 September 2020 - Wednesday: Rain. Amount 15 to 25 mm. Becoming windy late this morning. High 19. UV index 1 or low. Wednesday night: Showers. Amount 10 to 15 mm. Windy early this evening. Low 12. Thursday: Showers. Amount 10 to 15 mm. High 16. UV index 1 or low. Thursday night: Showers. Low 11. Friday: Periods of rain. High 18. Friday night: Rain. Low 10. Saturday: Periods of rain. High 20. Saturday night: Rain. Low 11. Sunday: Rain. High 17. Sunday night: Cloudy with 60 percent chance of showers. Low 12. Monday: Cloudy with 60 percent chance of showers. High 18. Monday night: Cloudy periods. Low 11. Tuesday: A mix of sun and cloud. High 21.

So we had some rain Sunday

It wasn’t a lot for a whole days worth… but it was a lot for a few minutes!

Here’s the proof:

That might not look like much, but we got about 16 mm (2/3 of an inch) in the 20 minute period between 17:25 and 17:45 on Sunday. And the majority of that, about 13 mm in just 10 minutes.

Let’s break it down further (note you can get to the actual graphs I am using to see the data yourself by going to the Data View on the front page and tapping/clicking on the weekly link under the rain gauge. You zoom in with a pinch out or drag.)

Take the second bar in the graph. It shows just under 2 mm in five minutes and a peak rain rate of 30.23mm/hr.

Under normal circumstances that would be considered a heavy rain. Rain rates of 15-30mm/hr are pretty common during a winter storm. Environment Canada usually issues rainfall warnings if we expect to see 50 mm in 12 hours or 100 in 24.

Now look at the next bar! 6.1 mm measured in 5 minutes and a rate of 209 mm/hr!

But then it intensified and the biggest accumulation saw 7.37 mm in 5 minutes or 356 mm/hr!

That is 10x more than what we would normally consider a heavy rain. This was truly torrential.

I did a little searching and found this article from the NOAA about typical tropical storm rainfall.

Tropical storms and hurricanes or their remains are capable of producing extremely heavy rainfall and often produce serious flooding and flash flooding. A presentation by Rusty Pfost documented some of the more impressive rainfall associated with tropical cyclones. He notes that rainfall rates of up to 6 inches [152 mm, 15cm] per hour have been reported and that 43 inches [1000mm, 1 metre] of rain was reported in 24 hours at Alvin, Texas as a result of the remains of Tropical Storm Claudette. Flooding resulting from the rainfall associated with tropical systems accounted for 292 deaths during the 1970-1999 which was 59% of the total deaths from tropical systems (Rappaport et al. 1999).

https://www.wpc.ncep.noaa.gov/research/mcs_web_test_test_files/Page1637.htm

So by that source what we experienced was just a little taste of what can come from Tropical Storms or Hurricanes. Given how many reports there were of our streets and sidewalks turning into raging rivers in central Port Alberni, it is no wonder people were so impressed.

Alberniweather has certainly never seen anything like it since 2005.

The Island Weather station at Alberni Elementary saw a similar amount but seems to have missed or been left out of a bit of the downpour and measured it just a bit earlier.. It measured about 10mm in 10 minutes.

Suffice to say, we got plenty of rain. If you want to see some videos check out Sunday’s blog post and also check out the CTV link here where they gathered a bunch of video as well.

On to the forecast. Rain Tuesday

It might seem like nothing much but we are expected to get some reasonable rain amounts. 15-20mm in the next 24 hours. (Rather than 15 minutes!)

Below is the imagery going from Monday 2-5AM to Tuesday night. It begins across the Island in the 2-5AM period, intensifies in the early morning and then tapers off before noon. However, showers linger, particularly around central VI, into Tuesday night.

2-5AM Tuesday
5-8AM Tuesday
8-11AM
11AM-2PM
2-5PM
5-8PM
2-5AM Wednesday

The last image shows more showers Wednesday morning too, the gardens really do not need any water this week.

For the most part the action should be over by Thursday and we should see some nice sunny breaks. But it won’t warm up just yet. There are not any expected dry spells for at least the next week.

But at least there aren’t any more torrential thunderstorms forecast either!

2 thoughts on “More rain coming (but not that much!)

  1. It seemed very heavy here too Chris, but I only measured 9 mm for the storm event (I cehcked the gauge at 6 pm). We’re located less than a kilometre to the north east from Alberni Elementary, and at a higher elevation, so it could just be the storm was very localized and centred more in you direction. Fun to watch though!

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