The season so far

In an earlier blog I used satellite imagery to forecast that 2016 would be a heavier than normal grass pollen season.

As the latest BoM images are showing lots of green across the Victorian countryside, my prediction still stands.

Another way of assessing how the season is progressing is by looking at the cumulative total of grass pollen grains. That is, add each daily count to the sum of all the previous daily counts from October 1 – that’s the red line in today’s graph – and compare that line to the cumulative counts for other seasons. The blue line is our average grass season and the two dashed lines are 1993 – our worst season with an eye-watering total of 6,700 grass pollen grains – and 2015, our mildest season with just over 1,000 grass pollen grains.

To put 'worst' and 'mildest' into some perspective, there are 92 days between October 1 and December 31, which is the period we count. So in 1993 the average grass pollen count was over 70 grains per day. That’s well into the high range and on a high day it's likely all people sensitive to grass pollen will experience hay fever symptoms. By comparison, in 2015 the average daily count was only about 11, a number comfortably in our low range of grass pollen counts.  Most people will not experience hay fever symptoms on a low day.

Today was also our first extreme grass pollen day, that's when the daily average was over 100 grass pollen grains per cubic metre of air.  It's our first extreme day since November 28 2013 and users of our app have rated their symptoms today as moderate, that's just one step below our top rating of severe.

Happy halloween

Say what you like you’d scarcely believe
The devilry of pollen on All Hallows Eve.
Flying with witches and making you sneeze
They’re so full of tricks these ghosts on the breeze


Grass, tree and weed

We rated last Wednesday, October 26, as a moderate pollen day because we counted an average of 34 grass pollen grains per cubic metre of air and our high days start when there are at least 50 grass pollen grains per cubic metre.  But users of our free app said they still had some hayfever that day, with the average user experiencing mild symptoms and some level of discomfort.

As well as 34 grass pollen grains that cubic metre of air also had an average of 221 other types of pollen.

What was included in other pollen?

Pollen counters like to classify pollen into three broad types: Grass, tree and weed.

As can be seen in today's picture, on Wednesday all three types were present.

The main types of tree pollen were cypress and birch and the weed pollen we saw included daisy (capeweed, Arctotheca calendula, is flowering at the moment) and plantain (Plantago, in no way related to the banana-like fruit that's also called plantain).

Warm days and northerly winds mean we're forecasting high for the weekend ahead.  But following this advice can help you manage your hayfever and enjoy the lovely spring weather.

First high pollen day of 2016

first high day 2016a

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.

The plane trees are flowering