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After a crazy roller-coaster of spring weather, trees are finally puffing their pollen out into the air across much of Canada. How bad could this allergy season get?
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Pollen season is upon us. Who's getting it bad this year?

Scott Sutherland
Meteorologist/Science Writer

Monday, April 25, 2016, 7:31 PM - After a roller-coaster of spring weather, trees are now puffing their pollen out into the air across much of Canada. And after the "pollen vortex" and "pollen tsunami" of the past two years, how bad will this allergy season be for suffferers?

Many Canadians experienced a very different winter and transition into spring this year, especially compared to 2014 and 2015. Despite that, however, allergy sufferers across the country may not notice much of a difference.

What's going on this year?

In any average spring, there's a fairly typical pattern to how different tree species release the pollen that they produced during the previous year's summer and fall (winter has much less impact on pollen season). Some tree species - Alder, Cedars, Maples and Poplar - pollinate earlier in spring, while other species - Ash, Birch, Oak and Pines - pollinate later in the season. How the weather behaves in spring can have a significant impact on this schedule, though.

For some insight on what can happen during either an early warm-up or a late start to spring, we contacted Frances Coates, president and CEO of Aerobiology Research Laboratories, an Ottawa-based company that monitors and reports pollen and spore concentrations.

"If the warm-up continues we will get an early season, and most probably shorter one, if it stays really warm," Coates explained.

"If the pollen season has already started and we get a long cold freezing stretch, like we did in southern Ontario this year, the pollen season can go to very low counts, or it can just end," she said. Once the season ends due to a prolonged cold snap, it can start up again when temperatures rise, resulting in a later season for those early pollinators.

A late season, which is what many regions of the country saw in 2014 and 2015, comes with its own set of consequences.

"What can happen with a late season," Coates added, such as the one that is happening in the Ottawa region this year, "is that the early pollen can be late enough that the season for the late pollinators can start occurring while the early season is still upon us."

The swirling concentrations of pollen this situation caused in late springs of 2014 and 2015 made headlines as the "pollen vortex" and the "pollen tsunami," respectively. Some reports even referred to each of those years, in turn, as having "the worst allergy season on record," although Coates is quick to point out that the severity of a season is highly subjective, varying from allergy sufferer to allergy sufferer.

Another pollen "vortex" or "tsunami" in 2016?

Although buzz-words like "pollen vortex" and "pollen tsunami" may be a bit over the top at times, it's worth considering whether we may end up seeing pollen counts this year that are similar to the late seasons from the past two years.

Looking back at Winter and Spring 2015, it was generally warmer across the western half of Canada, with especially brutal cold and snowy weather across the eastern half of the country. That pattern of cold weather across Manitoba, Ontario and points eastward persisted well into April, and even into May for some areas. This resulted in an earlier pollen season in the west, and a generally late, and very concentrated, pollen season in the east.

In 2016, a near-record strength El Niño, which reached its peak in November 2015, helped produce a generally warm winter and a mild transition to spring, right across Canada - something of a repeat of winter 2015 for B.C. and Alberta, but a very different season for the rest of the country. What happens in spring is what really matters for pollinators, though, and by late March, the eastern half of the country experienced a roller-coaster of up and down temperatures - warm spells followed by cold blasts - that lasted well into April. With some significant snowstorms accompanying these cold blasts, it was more reminiscent of what was seen by those regions in Spring 2015.

Thus, the same pattern of pollen seasons has been developing this year as well - an earlier pollen season in the west, and a generally late, and potentially concentrated, pollen season in the east.

According to Aerobiology's records, the generally warm spring in British Columbia this year has produced a "bumper crop year" for pollen levels, and Vancouver and Victoria have been experiencing a very early season (especially with early pollinating Alders). Elsewhere, pollen counts had been very low or non-existent through March and the start of April, however, according to Coates, "the seasons have finally come around for the early pollen, in most locations."

Reports from Aerobiology for major centres across the country show mostly late pollinators active in B.C. and Alberta, and early pollinators dominant from Saskatchewan through to Atlantic Canada.

A sample of pollen forecasts from The Weather Network. Data courtesy: Aerobiology

As for what's likely to happen during the rest of the season, it will depend on the weather.

Based on the current forecasts, we've likely seen the last of the cold outbreaks for the year, so the late start for early pollinators in the eastern half of the country probably won't have any major overlap with the later pollinators. For those allergic to these early pollinators, that will likely mean a short period of "bad days" that would pass fairly quickly. The next concern after that would be for anyone was also allergic to one or more of the late pollinators, although the season for those trees should be fairly normal, overall.

If the weather does happen to throw another curve or two, and the eastern half of Canada has one or more of these quick blasts of cool weather, the early pollinator season may be drawn out to the point where it will overlap significantly with the late pollinators. In this case, anyone allergic to both early and late pollinators (and worse yet, more than one species) may be in for a very rough time through May and possibly into June.

Some things to keep in mind during allergy season

Regardless of similarities in weather and general trends in pollen counts, pollen seasons can still be very different from one another. The amount of pollen a tree species produces is dependent on the weather they experienced during the previous year's summer and fall. If the weather was favourable, they may have a large supply of pollen to release when they finally get their chance in spring, and if it was unfavourable, there will be less pollen to release, no matter how the spring plays out.

For those who put up with seasonal allergies each year, it's important to have an idea of what you may reacting to. Some species of tree, such as Alder, Birch and Oak, tend to cause allergic reactions more than species like Maples and Poplar. Also, while one species of tree may be putting out a very large amount of pollen, others may be releasing far less. Watching the pollen forecasts from day to day and comparing them to how you feel could help identify which species you react to most. A visit to your doctor, to be specifically tested for allergies, would make it far more clear.

Also, although trees are the main seasonal allergy in spring, there are other sources of seasonal allergies throughout the year. Grass pollen is typically what's responsible for allergic reactions during June and July, after the trees are usually done. Mould spores and fungal spores cause reactions as well, although they do not receive as much attention as pollen when considering seasonal allergies. Ragweed is a very common allergen in late summer, because it is highly allergenic and, as Coates explained, it has a high degree of cross allergenicity, meaning that if you are allergic to one species of ragweed, you will very likely be allergic to all of the roughly 50 species of it throughout North America.

Sources: Aerobiology | CBC | With files from The Weather Network

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