Significant Weather and Wind Charts — Page 505, Lesson 482

I want to walk you through the symbols and conventions used on significant weather and wind charts. These charts are a core part of your flight documentation, and understanding every mark on them is essential for safe flight planning. Let’s start with the symbols for significant weather, the tropopause, and the freezing level. I’ll take these one by one as they appear in the symbology. First, there is a symbol that refers to a “squall line”. This symbol is used in flight documentation for flights operating up to FL100 — that is, up to flight level one hundred, or roughly 10,000 feet. A squall line is a line of severe thunderstorms, so when you see that symbol on a low-level chart, you know to expect a line of intense convective activity. Next, there is a symbol for radioactive materials. When you see this symbol on the chart, the following information must be included at the side of the chart: the radioactive materials symbol itself; the latitude and longitude of the accident site; the date and time of the accident; and a note to check NOTAM for further information. So this marks a known or reported radioactive contamination area. Then we have the volcanic eruption symbol. For this symbol, the following information must be included at the side of the chart: the volcanic eruption symbol; the name and international number of the volcano, if known; the latitude and longitude; and the date and time of the first eruption. You are also instructed to check SIGMETs and NOTAM or ASHTAM for volcanic ash. SIGMETs are warnings of significant meteorological conditions, NOTAMs are notices to airmen, and ASHTAMs are special NOTAMs for volcanic ash. So this symbol alerts you to an active volcanic eruption that could produce ash clouds hazardous to flight. There is also a symbol that does not refer to icing due to precipitation coming into contact with an aircraft which is at a very low temperature. That is an important distinction — this particular symbol is not for that type of icing. So if you see it, do not interpret it as that specific icing phenomenon. Finally, there is a visible ash cloud symbol. This symbol applies only to model VAG, not to SIGWX charts. SIGWX charts are the significant weather charts we are discussing. So on a standard significant weather chart, you will not see this visible ash cloud symbol — it is reserved for a different chart model. There is also an important general note: height indications between which phenomena are expected — top above base per chart legend. This means that when a phenomenon is shown on the chart, the top and base heights of that phenomenon are given according to the chart’s legend. You always read the top height above the base height, as specified in the legend. Now let’s move to fronts, convergence zones, and other symbols. These are shown in Figure 27.3. And then we come to winds. Corresponding to the charts listed above — the significant weather charts — there are charts of similar coverage, each chart showing wind and temperature for a particular flight level. The flight levels are listed in column 3 of page 3-5-10 of the GEN section of the Air Pilot, which is Appendix A to Chapter 18. On these wind charts, winds are given every 5° of latitude and longitude using the symbology shown in Figure 27.2 and Figure 27.3. An example of a wind chart is Figure 27.4. So to summarise: you have significant weather charts that use specific symbols for squall lines, radioactive material, volcanic eruptions, and certain icing and ash phenomena. Alongside those, you have wind and temperature charts for specific flight levels, with wind data plotted at every five degrees of latitude and longitude. Understanding these symbols and their placement is fundamental to reading your flight documentation correctly.