On Saturday October 15 we had our first high grass pollen day for the 2016 season. Does 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 2015, 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, with extreme days those with 100 or more grass pollen grains. Also, that our counting season starts on October 1.
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 line. While that line isn't a perfect explanation of the data it's not a bad approximation either (for the technically minded, the R2 for the regression is 0.36).
So the earlier the first high day occurs the worse the season and vice versa.
The red dot shows October 15, 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. That's slightly above the average of 20 high and extreme days per season.
Or put another way, that's roughly a third of the days left before New Year's Eve. Not our worst year but bad enough.