Some smoke relief in sight, dry lightning risk for southeast
theweathernetwork.com
Thursday, August 10, 2017, 2:01 PM - Smoke from wildfires in British Columbia continues to choke the province, with a widespread air quality statement still in place Wednesday. However, forecasters say there is some relief in sight.
"Clearing is expected to begin Thursday and Friday in the Lower Mainland, as an upper level low brings in some much needed moisture to the region," says The Weather Network meteorologist Brett Soderholm.
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The clearing will also be due in large part to the southwest flow that will develop Thursday, which will help guide the smoke northeast and out of the Lower Mainland for the weekend.
2017 has been B.C's second-worst wildfire season in terms of land burned. More than 110 so-called "wildfires of note" (those which are highly visible or pose a threat to public safety) are currently active, as extreme heat and dry conditions continue across the province.
The Kootenays saw some thunderstorm risk Wednesday, with a similar risk of storms on Thursday prior to the low moving in.
Currently, there is very little available moisture over the region, meaning thunderstorms that do form are likely to be quite dry. This is concerning as dry lightning is a key source of ignition for new wildfires.
PATTERN REVERSAL
A ridge of high pressure has been responsible for the unusually-persistent warmth settled over much of southern B.C. Last week saw numerous high temperature records fall, including some that had stood for more than 100 years.
While the heat looks to stick around for the next several days, the ridge has started to shift eastward, with temperatures likely to drop below seasonal by the end of the week.
Rain is expected for the central B.C. coast Saturday, with some unsettled weather reaching the south coast and southern interior for Sunday and into early next week.
"It looks like the dominate trough position will be over western North America for late August, so a cooler and potentially wetter ending to the month," says The Weather Network senior meteorologist Doug Gillham.
Wildfire smoke, however, complicates the forecast.
CHALLENGING FORECAST
Because it diminishes the amount of sunlight reaching the surface, haze and smoke in the air are an important "wildcard" when it comes to the forecast.
On the one hand, with less heat input from the sun, temperatures can struggle to rise as high as they otherwise might, meaning it can be hard to reach forecast high temperatures. By the same token, however, nighttime lows are also impacted. As less heat manages to escape the surface during the night, overnight lows and morning temperatures can stay warmer than expected, making for a higher 'starting point'.
While it's fairly straightforward to track general areas of smoke in the atmosphere and the overall expected wind flow, specific concentrations are very difficult to determine without surface observations and visible satellite (which is, of course, only available during daylight).
All in all, it makes for a very tricky temperature forecast.
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