Lapse Rate

Some folks anxiously await the posting of the latest stock charts to determine whether they should be buying or selling. For me, it's the MM5 lapse rate forecast chart that has me riveted to my computer at 9:00 am each day, indicating whether I should be loading the glider on the truck. These red and blue lines and little barbs along the side tell me what kind of day to expect in a variety of different places.

In a nutshell, the vertical increments indicate altitude and the horizontal numbers are air temperature. The thin green diagonal lines are the dry adiabatic lapse rate, or the normal rate at which air becomes cooler with altitude. The red line is a computer projection of how a parcel of air cools as it rises in relation to the surrounding air. The blue line is the dewpoint at various altitudes.

The data used to plot the red and blue lines is gathered from balloon soundings conducted by the weather service. Of course, with any forecast, the farther out the projection, the less accurate it is likely to be, so I like to use the latest forecast to determine if I should be gearing up for a great soaring day.

This particular chart is for Lakeview, Oregon at 5:00 pm Sunday, the first day of the US Nationals. Having that red line parallel to the green one for a long way is a GOOD thing! That means that the lift goes VERY high, up above 14,000 ft., before it begins to taper off (veer toward the green temp. line). Of course, this forecast is still a couple days out, so it could change substantially, but it sure looks good so far.

Another great thing about this chart is the look of those wind barbs to the right of the graph. They indicate 10 knot winds from the SW, which is just right for Sugar Hill, the place where we will most likely be launching from. Sugar is notorious for its strong conditions, and if it's blowing hard up there, the lift can be difficult to stay in. I've seen people get blown back behind the ridge and into the rotor while chasing lift, and it doesn't look like a fun place to fly. Lighter winds mean the lift will be rising more vertically.

I sure hope this forecast holds. If it does, we'll be getting high and going far for sure...