Note:  I originally wrote this article for the General Aviation Council of Hawaii Winter 2013 newsletter. The results weren’t quite what I expected, but still proved interesting. Instead of highlighting where turbulence occurs, the pilot reports instead highlighted areas where aircraft tend to fly (i.e., Oahu, mainly with reference to HNL or CKH). –JB

In the Winter 2012 newsletter, I talked about mechanical turbulence and mountain waves. Moderate turbulence is the most common reason for an AIRMET around the Main Hawaiian Islands. In the 12 year period from 2001 to 2012, an AIRMET for turbulence was in effect for at least a portion of the day for over half of the time. By contrast, an AIRMET for mountain obscuration/IFR conditions was in effect for less than a quarter of the time, and an AIRMET for icing was in effect for less than five percent of the time.

Even though turbulence is common, there is little specific information available as to where it occurs (other than “over and downwind of the mountains”). The National Weather Service in Honolulu will begin a project this summer to quantify where turbulence is most likely to be encountered. By taking pilot reports of turbulence and sorting them based on atmospheric stability and low-level wind fields, we will be able to map where turbulence occurs during different weather patterns.

You can help us!

We will use an archive of pilot reports to determine where turbulence normally occurs. You can help by making an extra effort to send pilot reports of turbulence from now through the summer.

Beyond this project, pilot reports are an important part of the normal forecast process. They provide meteorologists with a validation of ongoing conditions, and allow us to calibrate computer guidance to improve future forecasts. Remote sensing equipment like radars and satellites are good, but can’t tell what is actually happening. For that we need reports from people actually in the air.

In addition to reports of turbulence (light, moderate, severe, extreme), we also need reports of smooth air. These types of reports will help to outline the edges of the turbulence areas.

You can quantify turbulence using the U.S. Standard Turbulence Criteria Table as follows (from FAA Order JO 7110, “Flight Services”):

• Light: Loose objects in aircraft remain at rest.

• Moderate: Unsecured objects are dislodged. Occupants feel definite strains against seat belts and shoulder straps.

• Severe: Occupants thrown violently against seat belts. Momentary loss of aircraft control. Unsecured objects tossed about.

• Extreme: Aircraft is tossed violently about, impossible to control. May cause structural damage.

When the project is complete, the results will be available through the aviation page of the WFO Honolulu website.

John Bravender
Aviation Program Manager
National Weather Service Honolulu