Thursday, July 20, 2023

Why So Much Smoke From Canada This Summer?

The air quality across the Great Lakes, Ohio Valley and much of New England recently has been very poor due to the smoke from Canadian fires in eastern Ontario and portions of Quebec.  

June 28 Air Quality Levels

June 28 Air Quality Over Great Lakes

Earlier in the week, smoke from the fires in western Canada were the culprit. 

Current Conditions in Canada

Area Burned vs All Years Since 1980

Fire Stars Since 1980

Why has smoke from the north impacted our air quality and sky condition this summer?  Has this happened before?  Is this low air quality unprecedented? 

The smoke movement has to do with the overall weather pattern across North America. In late May and June the pattern featured an abnormally strong and stagnant ridge of high pressure over central Canada and high pressure over Texas. The flow is clockwise so the winds steered the smoke from Quebec south into the Great Lakes. Now in July the ridge over Canada has weakened. A trough has replaced the ridge. The dominant flow has been northwesterly bring in fast moving cold fronts from the west and northwest recently. The flow steered smoke from the fires in western Canada into the upper mid-west and Great Lakes. 

Watch how the high pressure ridge (warmer colors) developed in May across Canada.  Also notice how the ridge faded and emerged further east then central Canada by early June. Also notice how there was little southern high pressure. Pockets of blue indicate low pressure.  No sign of the Bermuda high to establish a southwesterly wind across the central US keeping the smoke north.

Upper Level Pattern (3 day periods) - Early May thru June 24-26

This abnormally strong Canadian ridge created record setting temperatures in May and June across western Canada

Soil moisture dropped both in western and eastern Canada.  Dry conditions began to spread across the Great Lakes.

When we look at the air pollution data since 1980 for Cleveland and surrounding locations, the time of year where pollution becomes more of a problem is summer.  Warm and often times stagnant air creates conditions that keep pollution from dissipating.  What really stands out on this graphic is the frequency of low air quality in the 1980s and 1990s between May and August. Look at the summer of 1988. 36 days with highs in the 90s with a few 100 degree days and little wind. Compare this to early summer of 2023 (bottom of graphic - red arrow). Only a few days in late May, June 28 and July 17-18 air quality was considered poor.

This was the same pattern that kept the humidity in northern Ohio at decades low levels in May and most of June although the recently higher July humidity brought up the seasonal average.

Both summer time high pressure ridges are not linked. Often times they will merge briefly. That has not happened this summer.  Below is a long range forecast for July 31, 2023.  Notice both ridges are distant.

This is also the same pattern that has kept most of the extreme heat in the deep south and away from the Ohio Valley. 

If this were a typical late spring and summer with the Bermuda High establishing itself over the southeastern US, the dominant flow would be southwesterly keeping the smoke up north. Look for this pattern to continue from time to time in August and September. The developing El Nino is probably a contributor.