Thursday, 4 December 2014

Anatomy of a fair sized storm.

In my review of our weather for November I explored the use of rain rate in saying something about the nature of a couple of storms in that month.  In those examples all I had to go on was what I extracted from the weather station output.  There are three reasons for that:

  1. For the first storm we were away from home and didn't have access to some elements of my blogging apparatus;
  2. The second storm was at 2300 and I was trying (unsuccessfully) to sleep through it; and, perhaps most importantly 
  3. I hadn't thought of doing so!

However on 3 December the weather forecast prophesied a thunderstorm in the afternoon and when I checked the 128km radar about 1418 (AEST) this looked like a good tip.
I then noticed some warning were evident for NSW.  One of these was for severe thunderstorms in the Canberra area.
Our place is just about at the end of the red arrow.

About 6 minutes later the 64km radar showed this (our house is at the edge of the white hem SW of the big storm).  It was just starting to rain.
By 1431 the Doppler Radar (128km range) was showing some serious wind coming from the North.
Indeed it came and blew several pot plants around and over when they got wet.

Here is the 64km radar image at 1448 with the body of the storm sitting right over us.  (Interestingly it wasn't supposed to get to Queanbeyan until about 20 minutes later.  But I still reckon  this was pretty spiffy forecasting.)
 By 1524 the storm cell had passed us by and we were just getting steady, and VERY welcome rain.
 I'm now waiting for the rain to pass to see what my weather station has to say about the whole business.  All four of my usual areas of interest - rain, temperature, humidity and wind seemed to have some interesting movements during the period.


In the following chart I have again multiplied the mm of rainfall x 10 to make them stand out better.
It is interesting that this time the storm started with a downpour and then settled down whereas on 16 November it gradually built up and then quickly stopped.  The peak rainfall rate was 151mm/hour, which is the second highest I have recorded (the highest was 167mm/hour with an accumulation of 14.2mm on 21 November 2013).


Essentially it plummeted. As cloud built up the temperature dropped from a high of 31oC to 25oC and then went down a further 8oC as the storm hit.  It has stayed at or near 17oC since then, as a result of cloud cover.


Not unexpectedly it rose quickly as the storm approached.  It stayed at 93-95% for the rest of the day.


The weather station showed an increase in wind as the storm came in but because it is (about 8m) lower mounted than standard and at least partly sheltered it doesn't show the fierceness of the key gusts.  So I haven't included a graph.

No comments: