VIRGA AND DRY MICROBURSTS - INVISIBLE MICROBURSTS
I have never been assaulted by a wet microburst, but when I was a flying doctor with the Indian Health Service, I flew on the edge of a clear air dry microburst, and it was a very rough ride. It was the most turbulence I have ever experienced in a light aircraft.
The problem with clear air microbursts is that they are difficult to detect.
There is no dumping of rain to tip you off to their presence. There is simply a focused massive downdraft that can crash your aircraft as you fly into and through it if you are at low altitude.
Imagine flying through a 70 mph downdraft when approaching the airport at 1000 feet altitude.
The only warning we had about the clear air microburst was that the down draft happened over a plowed field and stirred up an inverted mushroom of dust that tipped us off to its presence.
If we had not been flying over a plowed field, we would not have noticed it until we flew into it.
When I am sailing offshore, I am much more scared of clear air microbursts than wet microbursts. The wet microbursts have lots of clues warning of their presence.
A clear air microburst gives few clues until you are instantly hit by 70 mph winds.
If you are far enough away from a clear air microburst, you may notice a drop in air temperature from descending cold air before a massive air blast hits your boat.
In addition, you may experience an unexplained shift in wind speed and direction.
If you are sailing in the tradewinds, and you suddenly feel a cool wind blowing from a different direction, you should prepare for a possible onslaught of wind from a dry microburst. Be prepared to drop your mainsail and quickly reef your headsail.
A sudden cool wind blowing from a different direction is a call to arms, and it's time for all hands on deck in case they are needed.
Dry microbursts can happen in a clear blue sky.
At other times, you have an early warning system in the form of virga.
Normally, virga is simply a streak of rain falling from a cloud with the moisture evaporating before reaching the ground. When you look at a rain cloud you often see ragged cloud streaks hanging down beneath the rain cloud. Those rain streaks are called virga, and they are common.
Virga is also associated with microbursts.
The downward directed virga indicates the presence of strong downdrafts and alerts you to the possibility of a dry microburst.
The accompanying picture shows virga in the top of the photograph, and dust being kicked up in a field by a dry microburst in the middle of the photo. When you have virga with an inverted mushroom of dust on the ground, you definitely are experiencing a clear air dry microburst.
When you are sailing offshore, there is no inverted mushroom of dust to alert you to the dry microburst.
Your only clue is the presence of virga with the sudden appearance of cool air and a shift in wind speed and direction.
Once again we come back to the necessity for eternal vigilance when sailing offshore.
When you see significant virga and detect the wind shift and cool wind, you will know what is happening and take appropriate actions to protect your boat and crew.
Dry microbursts are sneaky, and that's why you need someone always on watch even when sailing in clear weather.
Awesome music video that captures the essence of what it's like to sail offshore in a catamaran around the world when conditions are less than perfect. David Abbott from Too Many Drummers sings the vocals, and he also edited the footage from our Red Sea adventures. This is the theme song from the Red Sea Chronicles.
Sailing up the Red Sea is not for the faint of heart. From the Bab al Mandeb to the Suez Canal, adventures and adversity are in abundance. If you take things too seriously, you just might get the Red Sea Blues.
If you like drum beats, and you like adventure, then have a listen to the Red Sea Chronicles Trailer.
Flying fish assault Exit Only in the middle of the night as we sail through the Arabian Gulf from the Maldives to Oman. And so begins our Red Sea adventures.
Sailing through Pirate Alley between Yemen and Somalia involves calculated risk. It may not be Russian Roulette, but it is a bit of a worry. Follow Team Maxing Out as they navigate through Pirate Alley.
Stopping in Yemen was just what the doctor ordered. We refueled, repaired our alternator, and we made friends with our gracious Yemeni hosts. We also went to Baskins Robbins as a reward for surviving Pirate Alley.
After you survive Pirate Alley, you must sail through the Gate of Sorrows (Bab Al Mandab) at the southern entrance to the Red Sea. The Gate of Sorrows lived up to its name with fifty knots of wind and a sandstorm that pummeled Exit Only for two days. Life is good.
Although I like the feel of a paper book in my hand, I love trees even more. When people purchase an eBook, they actually save trees and save money as well. Ebooks are less expensive and have no negative impact on the environment. All of Dr. Dave's books are available at Save A Tree Bookstore. Visit the bookstore today and start putting good things into your mind. It's easy to fill your mind with positive things using eBooks. No matter where you are or what you are doing, you can pull out your smart phone or tablet and start reading. You can even use electronic highlighters and make annotations in your eBooks just like paper books.
