3. Manual (HELP)
Soaring forecast background information
0. Preview
This will give a short note on the expected weather/thermal conditions for the following day. Also presented is a prognostic computer model sounding for the following afternoon for Arthur East showing the expected convection base and cloud development based on the maximum forecast temperature
1. Current Day
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 extent 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 Celsius 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.
This forecast is displayed in two parts:
a. Trajectories Map
Reverse Trajectories are shown in 1000m intervals (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 colouring of the trajectories lines are darkest at the 0 (ground) level and lightest at the 7000m level.
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 flows have influenced the forecast area. The trajectories give us a good idea where the airmass originates from and what characteristics it has.
For example, if the airflow is from the south it will be relatively warm air and most likely laden with moisture and pick up more moisture while moving across the Great Lakes. This type of airmass would reduce thermal activity due to warm air advection aloft.
But if the trajectories indicate an airflow from the North, it will be relatively cold and dry continental air and because of this will not pick up any significant amount of moisture while moving over the Great Lakes to the west and north of our flying area. Such air would enhance thermal activity as it will bring in colder air aloft.
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.
Thermal Forecast Table
an explanation of terminology
| Time | Local for the forecast area |
| Temp C | Temperature in degrees Celsius measured 2m agl (above ground level) |
| Dew pt | Dew point in degrees Celsius measured 2m agl |
| Cloudb. | Cloud base - Cumulus base or Blue base in meters agl |
| Conv.ht | Convection Height - If Cumulus this is Cu tops in meters 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) Deduct the sink rate of glider to get average climb rate |
| 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 |
a. Cloud graph and Thermal Speed Graph
Cloud graph
Vertical column of numbers height above ground in thousands metres (eg. 1 = 1000m etc)
Horizontal bottom numbers is local time with temperature in deg C above
Numbers in the graph above time/temp. is a meteorological lift rate in m/sec
Lift rate only shown indicates Blue thermals
Cumulus clouds symbols, size indicates small/large or towering
Straight lines indicates stratiform clouds
The dots `````````` indicate start of condensation height indicating lowering visibility.
Numbers along top of graph shows any high level clouds in eights of sky covered
Thermal Speed graph
Vertical column of numbers (left side height above sea level in thousands metres (1 = 1000m etc)
Horizontal bottom column time interval 0 - 60 min indicating approximated duration of individual thermal.
Colour scale is met lift rate in m/sec (eg. dark blue = 1.8 - 2.9 m/s )
Notes:
The Thermal Forecast table and the Cloud Graph/Thermal Speed Graph are often similar but also can differ significantly. this is due to the computer calculation being based on two different convection models. It is suggested to interpolate the values between table and graph values and your personal experience within your flying area.
To obtain indicated average climb rate for your glider you have to deduct the sink rate of the glider in a 45deg turn. ( I use 1 m/sec glider sink rate for a 45 deg turn and manoeuvering the glider within the thermal)
1 m/sec = 200 ft/min = 2 kt
2. Comments for "Current day"
This section contains relevant information concerning , surface winds, visibility, and manually obtained adjustments to the computer forecast which the programs used is unable to assess the general weather situation, etc.
PLEASE NOTE
Current day is based on RAOBS taken at Midnight GMT (2000 EDT) and made available for download at 2200EDT. It considers up to 30 soundings taken upwind of the flying area, projecting the airmass overhead of the flying area for the time of the forecast period by applying reverse trajectories based on the strength of the airflow within the airmass. This forecast is more area specific hence a forecast for Arthur and Embro is made. .
NOTE : program were made specifically for predicting thermal activities and not to provide general weather forecasts). , Hence on days of active frontal passages 1. Current day Tables and Graphs might not be posted.
BUT 2. Comments on such days will still show a short note as to the general weather situation
4.Tutorial by Frank Pennauer
Presented as Met Notes will discuss different subjects relating to Meteorology for glider pilots New Notes will be added from time to time.
Additional Information for use of this forecast
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Frank Pennauer --frpenn@gmail.com
© 2001 - 2009 Frank Pennauer /
Web site: Sagitta Enterprise / Ellen Papenburg
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