Soaring Forecast
by Frank Pennauer
As of October 7th, the Soaring Forecast ends for 2007!
Look for our new website in early May 2008
(We will link to it when it's ready: www.thermalforecast.com)
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Current Forecast
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Long Range
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New Experimental forecast
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Thermal Forecast Table and Legend
For more information about gliding:
http://www.yorksoaring.com
Soaring Forecast Background and Explanation
Updated 14 May 2007A Soaring Forecast (current/next day) and a Long Range Soaring Forecast (when data is available) for the following two days will be published on this website.
Between May and October this forecast will be produced regularly for Arthur, Ontario and its surrounding area. During the other months forecast produced for various European areas might be made and shown on an experimental and requirement basis only.
The Current Day Forecast
This is produced with Micromet, a program originally developed by the University of Cologne. The data is obtained from RAOBS soundings taken at 0000Z from stations upwind of the forecast area considering temperature/humidity and wind throughout the full vertical extend of the airmass where the sounding was taken. Based on these soundings it calculates reverse trajectories of the movement of the air masses from the forecast area. When insufficient RAOB soundings are available sounding data is obtained from area specific computer model soundings. Additional data used are the actual early morning temperatures, dew point and the forecasted maximum temperature for the area.
The program uses the annual and diurnal radiation for the forecast area and any cloud cover (which it calculates based on airmass humidity data) that influences it. The convection simulation assumes a 1.2 degree Kelvin temperature difference compared to the surrounding air. It then considers dynamic entrainment, horizontal advection and turbulent entrainment of the raising air bubble. It also calculates condensation, raindrops and ice particle content.
Trajectories Map
Reverse Trajectories are shown in 1000m interval(0 to 7000m) toward the forecast area (point). The outer end points of these lines show its origin and the flow of the air parcel from there to the final point in the forecast area at the forecast time.
The program calculates between the time intervals with a constant airflow to the final point calculated from the surrounding stations through a distance weighted calculation. Hence following the Trajectories it can be seen which advective flow consideration have influenced the forecast area.
The coloring of the Trajectories lines are darkest at the 0 (ground) level and lightest at the 7000m level.
The trajectories give us a good idea where the airmass originates from and what characteristic it has. E.g. If the airflow is from the South it will be a relative warm air and most likely laden with moisture and picking up more moisture while moving across the lakes. But if the trajectories indicate an airflow from the North, it will be relative cold and dry continental air and because of this will not pick up any significant amount of moisture while moving over the lakes to the west and north of our flying area. As the characteristic of the airmass determines the quality of thermal activity, it's an additional help to make this prediction. Of course the airflow on the different levels will also give us an indication if it will be a good or bad soaring day, e.g If the low level flow is from the south and therefore warm but the higher level flow is northerly it might enhance the thermal activity. In reverse, it might be a rather weak thermal day, etc. etc.
Thermal Forecast Table
| Time | Local for area |
| Temp C | Temperature in Celsius measured 2m agl (above ground level) |
| Dew pt | Dew point in Celsius measured 2m agl |
| Cloudb. | Cloud base - Cumulus base or Blue base in meter agl |
| Conv.ht | Convection Height - If Cumulus this is Cu tops in meter agl |
| Cld.Cov. | Cloud cover - Cumulus cloud cover in eights (1/8, 2/8 etc) |
| Thermal | Blue - if convection height is 700m or higher |
| Cu - cumulus if base is 750m or higher | |
| Cb - cumulus if tops above 4000m | |
| Climb m/s | Average meteorological lift rate in m/s (2kt = 1m/s) |
| Cld. Spr. | Cloud spreading - Tendency for spread out of cumulus |
| Cld. Ins. | Cloud Insulation - Cover in eights of mid or high level clouds which might reduce radiation reaching the surface |
The Long Range Forecast
A long range forecast will be produced from Computer Model Soundings up to two days ahead when such soundings are available.
The forecast will be based on Dry Bulb and Dew Point Temperatures and showing forecasted Top of Lift, Blue or Cloud based and also Initial and Maximum Cloud Base and Cloud Tops and expected maximum meteorological lift in knots.
"Height Minus Three" refers to the height (msl) where the Thermal Index is Minus 3 degrees Centigrade. The thermal index is the difference between the environmental (observed) temperature at this height and the temperature of an ascending parcel of air, adiabatically cooling when it reaches this height. This is considered to be the maximum height gain achievable by a glider.
All heights on the Long range Forecast Table are shown are in meters above mean sea level (msl). Climb rate (average meteorological lift rate) in Knots.
Temperature in Celsius
Comments page
Surface winds, visibility, manually obtained adjustments to computer forecast etc.
Frank Pennauer --frpenn@gmail.com
© 2001 - 2007 Frank Pennauer/ Web host: GP Computer Systems / Ellen Papenburg