Oct. 21, 2013
How bad is this year going to be?
Last Saturday (19 October) we had the first high grass pollen day for the 2013 season - Achooo! Can this date tell us anything about the season ahead?
The graph shows the date of the first high grass pollen day for each season from 1996 to 2012, plotted against the total number of high and extreme grass pollen days for that season.
Remember that our high days are when the grass pollen count is 50 or more grass pollen grains per cubic metre of air, and our extreme days when there is 100 or more grass pollen grains. Also, that our counting season starts on October 1 and finishes on December 31.
The graph shows that our earliest high grass pollen days are in early October and our latest in mid-November. The line shows a relationship called a linear regression that attempts to explain the data points using a simple equation. The line isn't a perfect explanation of the data but it's not a bad approximation either (for the technically minded, the R2 for the regression is 0.54).
So the earlier the first high day the worse the season and vice versa.
The red dot shows October 19, the first high day for this season. Based on this date we can expect about 25 high and extreme grass pollen days by December 31.
Put another way, that's about a third of the days left in the year. Not our worst year but bad enough.