I wrote a Dailywave (TodayILearnt post) about using your Radar to avoid lightning storms was a real boon.
There have been so many questions about this that I decided a dedicated article on this topic alone was needed.
Firstly, to do this you need one of the more modern radar systems that have a weather mode and preferably doppler.
Personally I have a fairly new B&G HALO 20+ Radar. If you’re interested the spec can be found here, not sponsored or making any money out of it but will give you an idea of the Radar I am personally using. Having said that most modern Radar can do these things and have these features.
Now B&G talk about Pulse compression and 4G broadband Radar etc etc. but most of this is just technology. What you really want to know is what it can do for you.
Broadband radars can distinguish between different target signal response and also be “aimed” rather than just thrown out. For instance the HALO series have a “Bird” mode which looks for small hard signals on the surface (birds) and can be used to detect flocks of birds for fishing!!
But what we are interested in is its ability to do “Weather mode”, which both points the Radar skyward a little and also uses its broadband to detect differences in the density of clouds. This last part is the key and along with doppler allows you to work out how potent the cloud is and where it’s moving relative to you.
Many of you will be familiar with using Radar on your Chart Screen as an overlay. The problem here is that the screen overlay only uses (to my knowledge) the core radar data being sent back from the dome rather than the full Broadband signal. The difference can be seen below, you’ll note one is a solid red colour (adjustable to the colour your want) and the other shows a gradient.
Above you can see the bay we are sailing across, you can also see the solid “Block” shown on the chart overlay. it looks nasty and it is but not all of it. On the right you see the 4G “View” where the yellow and blue colours represent thinner cloud, which might result in some rain but not too much wind or lightning. The red, however, shows very dense water vapour in the cloud, which means a lot of energy and power stored up there. This is to be avoided if you can. NOTE: you can also see that the land comes back a solid red at its edge, remember the radar is trying to see “UP” so if there is no up it will return what it finds, but further inland you can see thunder clouds, not land.
These images are from a recent sail down the “foot” of Italy and are a real example of a lightning storm we dodged on the way.. using our Radar. So let’s walk through how we did that.
One thing that is nice about the B&G Radar is that they are actually two Radar heads in one unit so I can have one setup for “Weather” and the other setup for normal “Offshore” mode. The Chart Screen here has the normal Radar “A” selected for its overlay and that is setup as mode “Offshore”.
Once I have this setup I can use the Screen selection from B&G to select either the Chart which will show one Radar set on “offshore” mode for navigating and avoiding those fishing boats and the other Radar on the Radar screen set to “Weather” which I’ll use to work out what the weather is doing and what we should do.
Detecting and avoiding Lightning!!!
We knew, on this particular trip that Thunderstorms had been forecast with very high localised winds and ground reaching lightning strikes.
We kept an eye on the weather and in particular kept an eye on a lightning app, because we had 4G connectivity. If we didn’t we would just rely on our Radar.
The app we use is called ‘Lightning’ and shows (alerts us) to lightning strikes near by. Once the app had alerted us that we had a live one, so to speak, near by, we started monitoring it on the Radar screens.
We turned on our Weather radar and started to get an idea of how far the nasty concentrated part of the storm reached and where it was going and how it was behaving.
By tracking it visually and also using tools within the Radar (Like MARPA , although MARPA will struggle with something this big), we could work out where it was going and how fast and by keeping an eye on its density (red, blue or yellow) how fast it was growing or shrinking.
We watched for a while and once we understood what it was doing we made a plan, taking into consideration the lifespan of a thunderstorm.
Firstly understand the lifespan of a thunderstorm.
Thunder storms or Cumulonimbus clouds form when heat creates lifting currents and water vapour rises until it reaches higher altitudes and condenses. This is a very simplistic view of a Cumulonimbus formation but will do for our needs. I studied clouds and these in particular when I was flying.
Nimbus clouds have a lifespan which goes like this: they grow and fill with water vapour and power, they condense and create massive wind currents inside the cloud which causes massive static electricity build up and starts to “charge” the cloud with positive and negative zones.
They can grow quite quickly before your eyes and they reach very high altitudes and therefore, and this is important, steered by higher air streams NOT the wind they create on the surface.
As the air and water vapour goes up the cloud creates a wind that circles the cloud, Anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere, just like water going down your drain.
As such the winds will veer around the cloud and having sail up can be a disaster as the wind will vary very quickly in strength and direction – higher speeds closer in, lower further out, just like your drain water.
They do not generally have enough fetch to create really bad sea state but will create a really confused seastate.
Once they have reached the higher altitudes and the power that was pushing moist air upward (the sunshine on land mostly) starts to recede, both by getting toward the end of a day and by the cloud itself blocking out the sunshine, the cloud will start to release its hold on the water vapour and it will fall toward earth.
At this point it will create much more friction, much more electrical charge and you will start to get lightning.
Importantly, as this happens the energy in the thunderstorm will dissipate and the cloud itself will disappear over a period of time.
So it’s important to understand where your cloud is in its lifespan. Is it still growing or is it dispensing its power and soon to shrink?
Our Action plan
By monitoring it using the Radar screen with our Radar on Weather mode, we could see it was getting denser not lighter, because there was increasing red colour on our screen. It was moving out into the gulf in front of our path and we could also see and hear the lightning and thunder starting.
We were 8Nm away from it and it was moving out in front of us but also tracking slowly in the same direction.
There were others forming further out in the Gulf. We could see them on the radar and still more forming on land.
We decided to drop our sails, start our engines (both until they were both warm and then went back to one) and motored.
We dropped our speed down to 3-4kts and noted that this was enough to keep our distance away from the thunder system constant at around 5-6Nm. We changed our course by about 20 degrees to move us further out into the gulf and away from those forming on land still.
Slowly we watched as the really big system put on a display for us out front and on our Radar we could see the storm slowly build and then slowly recede into rain and less dense cloud.
As it weakened we kept adjusting our course and speed to keep us on course as much as possible until we were able to resume directly toward our destination.
We kept our sails down and kept a watchful eye as there were still thunderstorms forming on the land and creating a spectacular display for us, but we calculated that they would have expended their lifespan by the time we got there or if they didn’t or suddenly veered out to sea we also would veer away until they ran out of steam.
The Chart view still showed significant RED blotches, but by now we knew that they were just rain cloud, the Red in the Weather Radar had all gone and only blue and yellow remained, so we motored inside them and the boat got a wash.
Using Radar we managed to plan our way around some biggish thunder storm systems today. It’s easy, a bit like a computer game, where you monitor, decide where it’s going and when it will die and plot a course appropriately to miss the dangerous part of it.