What does "Chance of Thunder Showers" really mean?

miketucker · #1 (**permalink**) 08-09-2011

I sail in Lake Ontario on a Hunter 36, based in the Outer Harbour Marina in Toronto. This is my first full season of sailing. This past weekend my wife and I made the 25 NM trip south across the lake to Niagara-on-the-Lake for an overnight stay. We had beautiful weather both ways (although a little more wind would have been nice).

We almost didn't make the trip because the forecast was calling for "Chance of thunder showers" for most of the time we would be sailing. I checked the Environment Canada radar before each crossing and everything looked clear, and as it turned out everything was fine. But those forecasts made me very nervous and had me constantly scanning the skies for approaching thunderheads (which never materialized).

How dangerous is it to be caught out on Lake Ontario if a thunder storm does develop? I'm fairly confident in my ability to handle the boat in the rain/wind/waves that might be encountered (assuming I have enough advance notice to get the sails properly reefed or even dropped completely). How worried should I be about lightning?

How seriously should I take warnings of 'chance of' thunder showers/thunder storms? Did I just get lucky over the weekend? What sources of weather forecasts are reliable in my area? I check the Marine Forecasts for Lake Ontario, and use the Environment Canada weather radar. Most of the 'possible thunder shower' warnings were coming from The Weather Network, it occurred to me that maybe they are very 'conservative' with their predictions, preferring to predict possible rain and have the weather turn out to be nice than the other way around? That seems generally sensible, but it almost cost me a very nice weekend of sailing.

Mike

Barquito · #2 (**permalink**) 08-09-2011

I would imagine that if you like playing the odds, it would go something like this: Say there was a 30% chance of thunderstorms. In ten trips across the lake you would get nailed in three times. Of those three, maybe one would be no big deal, and one would be hair raising. Having the skills and a boat that can handle most any wx (short of a long November gail, or the Chi-Mac storm) would make me comfortable.

tommays · #3 (**permalink**) 08-09-2011

Well

Last night it went from a sunny 5 knots

To god help anybody in the way 40 knots and downpour

To 5 knots and sunny in 45 minutes

And pretty much the same thing today nice day right now BUT towards evening another system will be passing through

Without being able to look at weather radar its tough to make a call on what your in for

DRFerron · #4 (**permalink**) 08-09-2011

Sometimes it means they're just guessing.

On the Chesapeake (and at my house in PA), I've noticed that if the forecast is 50% chance or below, we probably won't get rain, but I keep an eye out. Anything above that and I take it as a definite and plan accordingly.

I've never sailed on any of the Great Lakes but my understanding is that storms can be extreme. I would suggest that you start paying attention to the weather (at home and at the boat) as a normal part of your day, not just when you want to go sailing. Learn the prevailing winds, how the environment changes leading up to a storm. Think about it until weather becomes second nature to you.

Three days before a planned trip, even a day sail, I start looking at the weather. In the northern hemisphere most systems move west to east. So if I see a storm tracking across the upper midwest, it may be strong enough to keep moving towards the mid-atlantic without breaking up. I keep an eye on things until I leave the dock and then every so often I'll listen to the marine forecast while I'm on the water. The Chesapeake is notorious for summer squalls.

A good barometer is also a handy thing to have on board. It's not just falling barometric pressure that you have to watch out for, but how fast it falls. Quickly and something's up.

Sudden change in wind direction or temperature sometimes means a front is nearby.

Get a good weather book or take a class to learn how to read the weather. It could save your life someday no matter how much you think you can handle your boat in a storm.

Heavy Weather Sailing by Adlard Coles is popular and there are others. I think the Pardys wrote a book on sailing in heavy weather. I have their video on the subject.

In the end, if my gut says don't go, I don't go. I try to be educated enough to know what to do should I get caught in a storm, but many times I've made the decision not to go and sat at the dock listening to maydays on the radio. The few times I did go, I had a miserable sail. Others will disagree and love the challenge and excitement, but I prefer to have my boat and myself and family around to sail another day.

RobGallagher · #5 (**permalink**) 08-09-2011

Quote:

Originally Posted by miketucker

I sail in Lake Ontario on a Hunter 36, based in the Outer Harbour Marina in Toronto. This is my first full season of sailing. This past weekend my wife and I made the 25 NM trip south across the lake to Niagara-on-the-Lake for an overnight stay. We had beautiful weather both ways (although a little more wind would have been nice).

We almost didn't make the trip because the forecast was calling for "Chance of thunder showers" for most of the time we would be sailing. I checked the Environment Canada radar before each crossing and everything looked clear, and as it turned out everything was fine. But those forecasts made me very nervous and had me constantly scanning the skies for approaching thunderheads (which never materialized).

How dangerous is it to be caught out on Lake Ontario if a thunder storm does develop? I'm fairly confident in my ability to handle the boat in the rain/wind/waves that might be encountered (assuming I have enough advance notice to get the sails properly reefed or even dropped completely). How worried should I be about lightning?

How seriously should I take warnings of 'chance of' thunder showers/thunder storms? Did I just get lucky over the weekend? What sources of weather forecasts are reliable in my area? I check the Marine Forecasts for Lake Ontario, and use the Environment Canada weather radar. Most of the 'possible thunder shower' warnings were coming from The Weather Network, it occurred to me that maybe they are very 'conservative' with their predictions, preferring to predict possible rain and have the weather turn out to be nice than the other way around? That seems generally sensible, but it almost cost me a very nice weekend of sailing.

Mike

As I understand it; A 30% chance of thunder showers means that there is a 30% chance that any one place in the forecast area will be hit by a thunderstorm. In other words, the thunder showers will most probably be out there, but, there is only 1/3 of a chance they will come over you.

I also look for the marine forecast that says high wind, dangerous lightning, hail, or waves that will be X% higher than predicted. That stuff often comes with small craft advisories.

A smart phone is a big help. I use Wunderground.com

As for getting struck by lightening, I'm in Fisher's Island Sound, CT. so I don't know if being in fresh water is a factor. I have a keel stepped mast and getting anywhere near it in lightening makes me nervous, to say the least.

Then again, sailors drown, get run down by power boats, get hit in the skull by a boom, and do untold damage to their livers every year. I have yet to read about one getting hit by lightening. Sailboats yes, sailors?.... so, of course, I get the bright idea to google it...

Laser sailor gets struck by lightning | The Daily Sail

sailortjk1 · #6 (**permalink**) 08-09-2011

Quote:

How dangerous is it to be caught out on Lake Ontario if a thunder storm does develop?

The Great Lakes are not to be taken lightly. Have seen or heard of the recent tragedy in the Chi/Mac Race?
We routinely sail longer distances on the Great Lakes. If we have a trip planned and there are scattared showers amd thunderstorms, we generlly take our chances, but than again, we have many years of experince under our belts. If we are on our marina and simply want to go out for a day sail and there are thunderstorms in the area, we probably stay secured to the dock.
Tommays gave you a fine example 5 knots to 40 knots in a matter of minites.
You also received excellant advise from DRF. Make sure you and the boat are preparred everytime you go out. You never know what might happen.

SailKing1 · #7 (**permalink**) 08-09-2011

Living in VA Beach between the ocean and the bay we have a chance of showers everyday during the summer. So I have taken "chance of showers" to mean because the heat from the pavement is going to cause a sea breeze and the subsequent drawing of moister into the air, there's a strong possibility that we will have showers at the end of the day. And we typically do. The question becomes where, for how long, and how severe. Hence the common reference to bay squalls that last for 10 to 15 minutes.

I would think living on Lake Ontario you get the same. We typically do not pay much attention to it unless there is a storm front that is moving our way from elsewhere.

welshwind · #8 (**permalink**) 08-09-2011

I have a theory about Chance of Rain. I've noticed that our weatherpeople seem to use Chance of Rain/Thunderstorms much more often than in the past. I've concluded that if there is even the slightest chance, they now will say 'Chance of ...' whereas before they would say "Partly Sunny" or something like that. I believe that is because when they said "Partly Sunny" but it rained, people were upset with them. If they say "Chance of Rain" AND IT DOESN"T RAIN, people are happy. And they come out looking more like winners :-) even though they are still wrong.

rockDAWG · #9 (**permalink**) 08-09-2011

As the weatherman says: Tomorrow, the weather will be either sunny, raining, stormy or blizzard, it all depends on the weather. Just be prepared and have Plans B and C ready.

If for day sail, I seldom pay much attention until the hour I set sail. Just get a mental picture what is weather pattern looks like. i go out regardless. A proper sail area is the key, be prepared to duck into a safe harbour or sail to an open area.

My son and I used to love to sail our 14.2 ft Catalina in 20 to 30 kn storm with horizontal driven rain. We almost turtled her every time. It is good that it was not like a Hurricane, we knew that the storm will only last half hour, we just have to hang on to the boat.

. Learning how to prepare and practice the prudent task improve our survival skills in the big pond.

Boasun · #10 (**permalink**) 08-09-2011

It means: You are going to get wet with the possibility of lighting strikes and some wind.