Chilliwack – Weather Data for May 2020 recorded by Roger Pannett, Volunteer Weather Observer for Environment Canada at Chilliwack.
| Variable | May 2020 | 30 Year Average |
| Mean Maximum | 20.61 C | 18.4 C |
| Mean Minimum | 10.18 C | 7.6 C |
| Mean Temperature | 15.39 C | 13.0 C |
| Rainfall | 105.4 mm | 98.3 mm |
| Snowfall | 0.0 cm | 0.0 cm |
| Total Precipitation | 105.4 mm | 98.3mm |
| Days of Rain | 16 days | 12 days |
| Days of Snow | – | – |
| Total Days of Precipitation | 16 days | 12 days |
| Frosts | – | – |
| Relative humidity average | 63.9 % | . |
The cool & unstable weather conditions of late April continued into the first week of May. The passage of a vigorous cold front on May 2nd, produced heavy showers, hail and thunder storm activity. The high passes also experienced snowfalls of up to 10 cm. On May 4th, beneath clear skies, temperatures fell to a cold 3.3 ⁰C. 2.7 ⁰C below normal.
On May 10th, with a transient ridge of high pressure, moving across the province, producing clear sunny skies and outflow winds, temperatures peaked for the month at a hot, record breaking 30.4 ⁰C with a dry 19% relative humidity. U.V levels rose to a very high 9, further rising to 10 in the sunshine on May 27th.
On three consecutive days, seven high temperature records occurred.
Date. New Record. Previous Record.
May 9th High max 29.5 °C (+11.1°C) 28.8 °C in 2019.
May 9th “ mean 21.05 °C (+8.45 °C) 20.7 °C in 2019.
May 10th “ max 30.4°C (+12.7°C) 29.5 ⁰C in 2019.
May 10th “ mean 21.85°C (+9.55°C) 21.05°C in 2019.
May 10th “ min 13.3°C (+ 6.4°C) 12.6°C in 2019.
May 11th “ mean 22.25°C (+9.95°C) 21.3°C in 2019.
May 11th “ min 15.5 ⁰ C (+8.8 ⁰C) 13.9 ⁰ C in 2013.
Prior to mid-month & onwards unsettled conditions retuned. On May 30th, an active low-pressure system entering B.C. from Washington state produced thunder storm activity and a record rainfall of 31.7 mm. (Previous rainfall record for the day was 24.9 mm in 1940.)
With mean temperatures for the month 2.39 ⁰C above normal (standard deviation + or – 1.4 ⁰C) it was the 9th consecutive May with temperatures above normal. A trend never previously observed since Chilliwack temperature records commenced in 1895.
With rainfall 7% above normal, it was the wettest May in 6 years.
On May 31st, the Fraser River at Mission had risen to 5.25 meters. Bank full is recorded as being at 5.49 meters.
The 2020 precipitation total to date is 761.9 mm on 92 days compared to the average of 859.1 mm on 80 days.
