website: www.microspacesystems.com/weather

I have developed this web page to help forcast the weather conditions for the Chelan area. I have been Hang Gliding since 1980 and have some good XC experience. I am by no means a weather guru, but I have tried to gather links that seem to work best for me for this area. Chelan is a small town, so weather sources are usually gathered from surrounding larger cities and geographic areas. Often times, the best judge of the weather seems to be a look out the window. If at 9:30 am it is generally clear and small CU's are starting, it is a good sign for a great XC day. CRCWnet is promising web cams from the Butte in several directions. They had one up there facing NW, then moved it to the lake looking W, and now it is pretty useless facing S into a tree. Keep checking to see if they give us something nice.

Typically I will start with the Wenatchee Underground link. Although this gives the forecast for Wenatchee, it seems to be the closest to what we will experience here in Chelan. Chelan will typically be a few degrees warmer, with more sun, and less wind. Keep the expected high in mind. The current conditions shown are for Ephrata, which will have more similar conditions to what we would experience to the East of Chelan.

I'll next visit the Instability section. NOAA has a new Thermal Index report from Ephrata, which is fairly accurate for our needs. Paraphrasing from the SAA Soaring Flight Manual:

Thermals are a product of instability. Their height depends on the depth of the unstable layer and their strength depends on the degree of instability. To arrive at an estimate of thermal height and strength, a thermal index (TI) is computed using a pseudo-adiabatic chart. A thermal index may be computed for any level but, ordinarily, indices are computed for the 850 millibar and 700 millibar levels, or about 5,000 and 10,000 feet respectively. These levels are selected because they are in the altitude domain of routine soaring and because temperatures are routinely available for these two levels. Strength of thermals is proportional to the magnitude of the negative value of the TI. A TI of -8 or -10 predicts very good lift and a long soaring day. Thermals with a high negative value will be strong enough to hold together, even on a windy day. A TI of -3 indicates a very good chance of reaching the altitude of this temperature difference. A TI of -2 to 0 leaves much doubt; and a positive TI offers even less hope of thermals reaching the altitude. The TI is a forecast value. A miss in the forecast maximum or a change in temperature aloft can alter the picture considerably. Basically, the more negative the value shown the better.

The ROAB report will give you the Thermal Index (TI) for various altitudes allowing you to see graphically the TI with altitude. I select the Complete Report for Spokane WA up to an altitude limit of 15000 MSL. I then take the forecast high from the Wenatchee Underground link and use that for the temperature. Since the sounding is taken at Spokane, 100 miles to the East, it's accuracy can vary wildly and we usually do not experience the degree of TI as calculated; instead of a TI of -3, typically the lift will be good up to about -5. I will usually look at the Complete Upper Air Data to see where the freezing level is (T = 0.0) as this will usually be close for Chelan as well. The upper winds can help to analyze the wind gradient. Chelan will often have more of a Westerly component than Spokane, but you may end up flying out to Spokane. Be aware that these soundings are taken extremely early in the morning. Sometimes it is useful to repeat the process using a temperature of 5 degrees less to give an idea how sensitive the conditions are to temperature changes and to get a feel for the TI during the earlier and later parts of the day.

I'll usually check the winds next. Jim Gallant's page is very indicative of current surface winds. This can help predict what direction you may want to take on a XC flight.

Hope your flights are high, far, and full of fun. Please stop by for a visit to share your experiences.

Lionel Space