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Learning hub · Meteorology · Lesson 6

Weather charts and the briefing

A chart shows the big picture and a METAR shows the detail. Together with a briefing, they let you decide whether to fly before you reach the aeroplane, and that decision is the most important weather skill.

About 12 minutes, plus the quiz. Part of Meteorology. It builds on Reading a METAR and a TAF.

1. The surface pressure chart

The surface chart (a synoptic chart) shows the situation at sea level at a given time. Its main features are these.

  • Isobars: lines of equal pressure in hPa, often drawn at regular steps such as 4 hPa (check the chart). Close together means strong wind. The wind blows almost along them, anticlockwise around a low and clockwise around a high in the northern hemisphere.
  • Highs (H) are usually settled, with sinking air and clear or layered cloud. Lows (L) are usually unsettled, with rising air, cloud and rain.
  • Fronts: a line with symbols. A cold front is usually blue with triangles, a warm front red with half-circles, an occlusion purple with both. The symbols point in the direction the front is moving. See Clouds, stability and fronts for the weather each brings.

Find the lows and fronts nearest your route, ask which way they are moving and how fast, and compare the chart at different times to see the trend. A forecast chart is a model of what will happen, and its details, such as the exact front position, are uncertain.

2. Significant weather charts

A significant weather chart (SIGWX) is a forecast of the weather that matters to aircraft. In general it shows areas of thunderstorms and cumulonimbus, areas of turbulence and icing, the freezing level, fronts and low-visibility areas. Low-level charts cover the levels used by light aircraft, and high-level charts the levels used by airliners. Symbols and colours vary between providers, so read the key on each chart and note the chart’s validity time and the heights it covers.

For a student pilot, the useful questions are: are there cumulonimbus or thunderstorms near my route, is there an area of icing or turbulence at my altitude, and where is the freezing level?

3. Where to get official weather

In Europe, aviation weather is provided by the national meteorological service of each country or by an organisation it appoints, and it is available through the aerodrome’s briefing system or the national AIS. The AIP of each country lists its meteorological services in its general part, GEN 3.5. In Romania, the national meteorological service is the National Meteorological Administration (ANM). Which organisation provides the aeronautical reports and forecasts for a given aerodrome is listed in the AIP Romania, so check the AIP and your flight school to learn which website or briefing office to use, since the names and addresses can change.

Apps, including VectorEFB, display weather data to help you plan, but the official source is the one to rely on for a decision.

4. The briefing and the go/no-go decision

A weather briefing for a VFR flight normally includes:

  • the general situation: the pressure chart, fronts and where they are moving;
  • METARs and TAFs for departure, destination, alternate and the aerodromes along the route;
  • significant weather, including thunderstorms, icing and turbulence, and warnings such as SIGMETs;
  • winds and temperatures at the heights you will fly;
  • the freezing level, cloud bases and tops, and how the weather is expected to change.

Then comes the decision. Compare the weather with the legal minima for VFR in the airspace (see SERA and the AIP), and then with your personal minima: limits you set in advance, in calm conditions, that are stricter than the legal ones. A student pilot’s minima could be a higher cloud base, a better visibility, a lower crosswind and no forecast thunderstorms. Write them down, and agree them with your instructor.

Check the trend, not only the snapshot. If the weather is getting worse, if the forecast is uncertain, or if you have only a small margin, the answer is no-go, or go with a plan: an early departure, a safe route, a diversion option and the fuel to do it. A cancelled flight costs little. Turning back is always an option.

Training only. For a real flight, use official current charts, forecasts and the AIP, and follow your instructor’s and school’s rules.

5. Try it yourself

Work each one out on paper first, then open the answer to compare. The numbers are invented.

  1. A surface chart shows isobars 4 hPa apart. Between your departure aerodrome and the destination the lines are twice as close as elsewhere on the chart. What does that suggest, and what else do you check?
    Show the answer

    Closer isobars mean a steeper pressure gradient and a stronger wind. You would expect strong wind and gusts along that stretch of the route, and check the wind forecast at your flight altitude and the drift and groundspeed it gives (see the wind triangle).

    Also check turbulence in the lower layers, the crosswind at departure and destination, and whether a front is the cause of the tight gradient.

  2. Write personal minima for a student pilot on a local flight, using your own limits, then test this forecast against them: cloud base 1,800 ft, visibility 6 km, wind 20 kt gusting 30 kt at 60° to the runway, no thunderstorms. Say go or no-go.
    Show the answer

    The minima are your own, so the answer depends on them. A cautious student might write: cloud base at least 2,500 ft, visibility at least 8 km, wind below 15 kt with a crosswind below 8 kt, no thunderstorms forecast. (These numbers are only an example and must be agreed with an instructor.)

    Test: cloud 1,800 ft is below 2,500, visibility 6 km is below 8, gusts to 30 kt at 60° to the runway give a large crosswind. Three limits are broken, so the answer is no-go. One broken limit is already enough.

  3. The morning briefing for a flight at noon shows a cold front 100 nautical miles west of the route, moving east at 25 kt. Roughly when does it reach the route, and what might you do?
    Show the answer

    Distance divided by speed: 100 ÷ 25 = 4 hours. If the briefing is at 0800, the front arrives around 1200, right when you plan to fly. The forecast speed and position are uncertain.

    Options: fly early, before the front, with a safe margin and a plan to land; delay until after it passes and the weather clears; or cancel. Do not plan to cross the front. A cold front can bring a narrow band of heavy showers, gusts and sometimes thunderstorms.

6. Watch

How to read a surface pressure chart, from the UK national weather service: isobars, highs, lows and fronts.

Open on YouTube if the player does not load. Not made by VectorEFB; check what you learn against your flying school’s material and your instructor.

More to watch

A talk on the go/no-go decision. This video is American, so wording and some rules differ from European (ICAO/EASA) practice.

Open on YouTube if the player does not load. Not made by VectorEFB.

7. Check yourself

Five original practice questions. Answer them, press Check answers and read each explanation.

1. What do closely spaced isobars on a surface chart indicate?

The isobars are close where the pressure gradient is steep, which gives a strong wind.

2. In the northern hemisphere, around which type of pressure system does wind circulate clockwise?

Wind circulates anticlockwise around a low and clockwise around a high in the northern hemisphere.

3. What are personal minima?

Personal minima are a decision made in advance, when calm, so that the decision to cancel is easier in the moment.

4. Which is most reliable for a real flight decision?

Real decisions rely on official current data. Other sources can help your picture, but they are not official.

5. A significant weather chart shows an area of CB along your route at your planned altitude. What is the sensible action?

CB means thunderstorm hazards: severe turbulence, hail, icing and wind shear. The plan must avoid it.

Back to the learning hub.

For training and situational awareness only. Not certified for navigation. Always use official charts, the AIP, NOTAMs and a proper weather briefing for real flights.