The day looked so promising. No storms, light winds, and an amazing lift forecast. So why did we sit on launch for 3 hours waiting for it to calm down (or pick up)? It is a common occurrence, especially in the spring and can be a maddening experience for newer mountain pilots. The most likely reason? Air pressure!

I am not going to go into any real depth in how air pressure is derived nor all the nuances it creates. I just want to focus on how the air pressure number can actually apply to your flying experience. In a very simplified nutshell, air pressure is the weight of the air mass sitting on top of you. In a high pressure you generally have a lot of air (or heavy/cold air) sitting on top of you. A low pressure you have much less air on top of you (even less if it is cold air).

When air along the surface of the earth heats up, it becomes energized and tries to escape upwards into the sky, creating a thermal. A high pressure pushes down on this warming air, not letting it release. As the sun bakes the ground, the air gets hotter and hotter and eventually has so much energy it breaks through and rockets into the sky. These high pressure rocket thermals are often very small and violent, making flying in them pretty scary and often dangerous. A low pressure (or dropping pressure) is the opposite. As the earth heats there is nothing to contain the warming air so low energy thermals release like a herd of schizophrenic cats. The air feels hollow and has no organization to it. It often creates windy conditions on launch because the air is always escaping. When flying through such air it is constantly turbulent and feels like flying through “sky diarrhea.”

Air pressure is the key ingredient to how the air is going to “feel” when you are flying. When the air is thermic, you don’t want to fly under high pressures, nor under low pressures. The key is finding the sweet spot. Enough high pressure to keep the thermals organized, but low pressure enough for the thermals to release in a less violent manner. 
When I first started flying I was told the optimal air pressure was between 29.90 and 30.10. I noticed this was true….sometimes, but more often than not it wasn’t a consistent experience. So, I decided to start collecting my own data. It consisted of air pressure, air temperature, and what the air “felt” like to fly through it. Over the years I continued collecting the data every time I flew (all year long). The data was collected across all seasons, over many years, and I soon began to see a clear pattern emerge. Being the nerdy dork that I am, I began plotting the data and very quickly developed what I call the “AMBROSE PRESSURE ZONE” index. It is a number (0-7) based on air temperature and air pressure** and describes what the air feels like (at least to me).

**Air Pressure: ALWAYS use the Altimeter Pressure (never station pressure) when determining air pressure. Get your data from an airport station!**

---

Zone Descriptions:

ZONE 0 – DANGEROUS!: This is very disorganized air due to such a relative low pressure. Wing collapses are frequent and is not recommended to fly in this air.

ZONE 1 – ATTENTION: Air pressure is lower than you want. It is still flyable but will require vigilance as frequent wing collapses are expected. Definitely less fun to fly, but possible.

ZONE 2 – GOOD: Conditions are good, but the pressure is on the lower side. Thermals may not be fully organized and the air a bit gusty. Pay attention to possible wing collapses, but those should not be too frequent.

ZONE 3 – SWEET: Great conditions, but pressure is just slightly on the lower side. Thermals will be good, but you may find them a bit disorganized at times.

ZONE 4 – SWEET: Perfect conditions, but the pressure is just slightly on the higher side. Thermals will be good, organized, and climb rates will be quick and stable.

ZONE 5 – GOOD: Conditions are good, but the pressure is on the higher side. Thermals will be more organized, but may be on the stronger side. Just pay attention to thermal strength and possible sharp edges.

ZONE 6 – ATTENTION: Air pressure higher than you want. It is still flyable but if thermic air is expected it will require very active piloting as any thermals will be strong and sharp. If a collapse happens, it will be dynamic so be ready to catch it. Definitely less fun to fly, but possible. If no thermals are present, air is fun to fly in.

ZONE 7 – DANGER POTENTIAL: The pressure is too high to be flying if thermic air is expected. Thermals will be very small, sharp, and like rockets. If wing collapses it is likely to be very violent and dynamic. Probably think about not flying today if thermals are present.

Zones will change throughout the day (especially in spring) as the air warms and thus the pressure changes. To use the graph, just plot current air pressure against current air temperature. You will then have a pretty good idea what that thermic air is going to feel like. My personal favorite is to fly in a Zone 4. I am not a fan of flying in lower pressure air. It just feels hollow and less fun to fly in.

---

As you are making your decisions to fly each day, I hope this PRESSURE ZONE graph can be of help to you. I have been using it for many years and it has helped me focus on conditions that are actually safer and more fun to fly in. 
Happy flying and I hope to see you somewhere high above the Wasatch.

---