Millimetre Matters: Long dry summer of 2017

Millimetre Matters: Long dry summer of 2017

After a winter of record precipitation, June, July and August are far below normal

Barry Coulter

We may not be in drought country here in southeast BC — not yet.

But following what was a winter and spring of unusually high precipitation, the dryness that has marked our long, hot summer is almost unprecedented.

Cindy Yu, a meteorologist with Environment Canada, provided the Townsman with the statistics showing just how far below normal the precipitation has been since June.

“For the month of July we’ve had eight per cent of the normal precipitation,” Yu said. “Three millimetres instead of 38.3 mm. And so far in August we’ve received 2.4 mm of precipitation, the normal is around 28.

“So both months have been really dry.

“Even in the month of June — we had some precipitation earlier in June, but late June and onward have stayed really dry. Even June we received only 24.8 mm, the normal is around 62.2/ So 40 per cent of normal.”

While it certainly has been a dry year, Yu said that while there are many people looking at the global trend of weather patterns — it’s hard to say if “certain oscillations are affecting the weather,” or if these trends are the new normal.

“One reason is that we’ve actually had a pretty wet spring,” she said. “In March, April and May we had more than a normal amount of precipitation. So in a sense, it’s normal for us to go from a wet period to a dry period.

“But [this summer] is a prolonged period of lack of precipitation.”

What makes this dry period more remarkable is unusually wet winter that preceded it.

“From December through February, Cranbrook had 191 per cent of normal precipitation,” Yu said. “And most of that fell in February. February is supposed to be one of our driest months, where our normal amount of precipitation is around 18.9 mm. Most of that should fall as snow. But in that particular month, we reported 83.8 mm of precipitation, about four times the normal.”

“So stats-wise, we’ve seen some well above normal numbers, then we’re dipping down to some well below normal numbers”

But as summer heads into its last days, Yu said a more transitional period is pending.

“The sun angle is lowering and we’re getting into more of a cooler air mass as we head into September. For this week, even though we’re expecting that trough of low pressure, it doesn’t look like it will be bringing much precipitation. Then we’re expecting the ridge to hang around for most of next week. I think the drier than normal trend will continue into September.

“But the good news is the overall pattern is changing. Even though we’re getting a ridge next week it’s not as amplified as the ones we’ve gotten in the last month or so. So we are seeing cooler temperatures, and overall the weather pattern is trying to change. So that’s a good sign.”