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A Brief Introduction to Weatherweb Tephigram Forecasts The charts you are currently viewing are predicted tephigrams (essentially height against temperature charts). Tephigrams are useful in that they give an indication as to the level of cloud in the atmosphere, how deep it may be and also how stable the atmosphere is. In the sample below the first thing to read is the time the tephigram is valid for. "MODEL DATA GFS1 09 UT TUES 24 MAR 2009" means that the chart is valid for 0900 GMT on the date given. Data is based on 0001 GMT last night, so a time of T+36 is 36 hours from that time i.e. midday tomorrow. Next check the station code. This should be the code for the station you chose, for example EGJJ is Jersey. Also given is a latitude and longitude coordinate for the station. Below this is a very useful index, the predicted freezing level (in metres). The other indices can be interpreted by searching the internet for an explanation of tephigram indices. Next let's look at the graph itself. Heights are shown in brown in millibars down the left hand side with temperatures in brown along the bottom of the chart. These are fixed. There are two lines on the chart. The solid red line is the predicted actual temperature of the air at that level for the time shown, the solid blue line is the predicted dewpoint for the time shown at that level. Where these two meet the air is more moist, i.e. cloud. There are two other lines; red dotted and blue dotted. These are the predicted profiles for temperature and dewpoint should a parcel of air be lifted by some mechanism (heating, topographically or frontal). They show the path that the air parcel would take should this happen. They indicate how stable the air is, how likely showers are to form and what height the base and tops of the cloud are, as well as cloud depth. Along the right hand side of the chart are the wind barbs. These point in the direction to which the wind is coming from. A full feather is 10 knots, half a feather is 5 knots. So, two whole feathers and one half is a predicted wind for that level for the time selected of 25 knots. We spend much time at Weather School talking about tephigrams and how to use them. Why not come along and find out more? Copyright Simon Keeling 2009