Aviation weather charts are very useful for getting a big picture of  the current conditions. They can show you useful information such as: fronts, pressure systems, freezing levels, and current weather.

Surface Analysis Chart - Issued 8 times daily (0000Z – 0300Z – 0600Z – 0900Z- 1200Z- 1500Z – 1800Z – 2100Z)

The surface analysis chart shows current surface weather across the United States. It has been scaled down to fit onto the page, but the real chart is much larger and easier to read. Not only current weather is depicted, but also pressure systems and fronts. At first glance, a surface analysis chart can be daunting due to the amount of information presented. When you break it down, it becomes much easier to read. In the above chart, we can interpret a very large amount of information. There is a series of low pressure systems that have formed over the southern Midwest.  These low pressure systems have formed a large amount of fronts that are sweeping their way around the Midwest. There are two troughs that extend northward out of the 2 most northern low pressure systems. We can also look at the isobars which show a very large pressure gradient around the pressure system over Colorado, with this we can expect high winds.

Station models are also depicted on the surface analysis chart. These show you the current weather conditions at that reporting station. Things such as weather, wind velocity, wind direction, sea level pressure, temperature, dew point, and cloud cover are all depicted. An example can be seen below:
This station model has been enlarged from the chart above (it is located over central Mexico). The station points into the wind, which in this case depicts the wind out of the southwest.  Depicted is also the wind velocity. In this case we can see two ‘barbs’ sticking off the wind pole so we can interpret that the wind is blowing at 20 knots. Each barb is 10 knots. A ‘half-barb’ is 5 knots, and a flag is 50 knots. If no wind pole is shown, then wind is calm. The red number is the temperature in Fahrenheit, in this case 70°. The green number is the dew point in Fahrenheit, shown here as 48°. The circle of the station model represents the sky conditions. If the circle is clear then the sky is clear, it gets shaded in in 1/4ths. If it is 1/4th filled, the sky condition is few clouds. If it is half filled, then it is scattered. If it is fully filled in, then it is overcast. The amber three digit number is the current sea level pressure with the first 2 numbers of the sea level pressure dropped off. So for this station model, which has the sea level pressure depicted as 077, would be 1007.7 millibars. If the first number of the sea level pressure begins with an 8 or a 9, then you add a 9 to it. Otherwise, you add a 10 to the front of the 3 digits. Below is some examples:

410 <-> 1041.0mb
103 <-> 1010.3mb
987 <-> 998.7mb
872 <-> 987.2mb

Constant Pressure Charts – Issued twice daily (0000Z – 1200Z)

The constant pressure chart shows isobars (lines of equal pressure) for a given pressure. These can be very tricky to read, even when looking at the full sized version. Pictured above is the 850mb (millibar) chart, which is a pressure altitude of roughly 5,000 feet. Things depicted on the chart besides isobars and isotherms (lines of equal temperature). Also depicted on the constant pressure charts are station models of weather balloons sent up.

Isobars are shown with solid lines and have three numbers representing their height. The three numbers are the height of the isobar in decameters. Isotherms are shown with dashed lines and two numbers, which represent the temperature in Celcius. Using this information, we can look for things like troughs (extended dips in the isobars to the south) and ridges (extended increase in isobars to the north), as well as looking at winds aloft over an extended area.

Weather Depiction Chart – Issued 8 times daily (0100Z – 0400Z – 0700Z – 1000Z- 1300Z – 1600Z – 1900Z- 2200Z)

The weather depiction chart’s purpose is exactly what is implied in it’s title. It show you the current weather occurring around the United States. This chart is perfect for pilots because it will depict what kind of flight rules are in place for a given location. Areas that are shaded in are under instrument flight rules (less than 1000 feet ceiling and/or less than 3 miles visibility), areas that have encompassed in a solid line are under moderate visual flight rules (greater than IFR but less than VFR) and areas that aren’t encompassed in any lines are under visual flight rules (greater than 5 miles visibility and 3,000 foot ceiling). Weather stations are depicted on the chart (but do not include wind or temperature) which show the cloud base, cloud cover, visibility, and current weather. The cloud cover uses the same model as the station model and the number below the circle represents the cloud base. If visibility is restricted, the current visibility is depicted and it’s reason for being restricted.

Radar Summary – Hourly

The radar summary chart is issued hourly and depicts precipitation across the United States. It shows precipitation type, intensity, coverage, movement, echoes, and the tops of echoes. Contoured areas depict areas of precipitation, the more contoured the area is the more intense the precipitation. The tops of echoes (areas of precipitation) is displayed with three numbers (in hundreds of feet) and a line showing where the maximum height was recorded. Precipitation type does NOT use the same weather codes as METAR’s. Instead radar summary chart’s use their own simplified version which can be found below:

Severe thunderstorms and tornado warnings are also displayed on the radar summary. These warnings will be boxed in and have the warning number attached to it. A box with a warning number starting with ‘WS’ is a severe thunderstorm warning whereas a warning starting with ‘WT’ is a tornado warning.

On the chart, areas with no echo returns will display ‘NE’, standing for ‘No Echoes’. An ‘NA’ symbol stands for ‘Not Available’ and a ‘OM’ symbol stands for ‘Out for Maintenance’.

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Resources: For more detailed information, check out the FAA published book: Aviation Weather Services. This book contains all the information about every weather service available for pilots. This book is a valuable resource when it comes to studying for checkrides or trying to decipher the more uncommon weather products. Click on the book below to find out more.