Understanding Weather Fronts in IW Pro

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Have you noticed the coloured lines, triangles, semicircles and H and L symbols on the IW Pro radar?

The Weather Fronts feature adds information from traditional surface weather maps directly to the IW Pro radar. This can help you understand the larger weather pattern behind what you are seeing on radar, not just where rain or snow is occurring, but some of the atmospheric features helping to produce that weather.

Turning Weather Fronts On or Off

Weather Fronts can be enabled or disabled at any time.

Open Settings, expand the Weather Features section and use the Weather Fronts toggle to turn the layer on or off.

Once enabled the fronts and pressure systems will appear on the radar map.

Where Does the Weather Front Information Come From?

The fronts displayed in IW Pro are official fronts from the U.S. Weather Prediction Center (WPC).

The information is updated every three hours.

This is important to keep in mind when using the radar animation. The precipitation on the radar can move while the plotted weather fronts remain in the same position. The fronts are not currently animated continuously between WPC updates.

For example, if you play the radar loop, you might see an area of rain or thunderstorms moving eastward while a nearby cold front appears to remain stationary on the map. That doesn't necessarily mean the front itself isn't moving. It means that the position of the front shown on the map is based on the latest available WPC update.

We would eventually like to make this feature more dynamic by automatically moving the fronts between official updates using weather-station observations.

How to Read the Weather Fronts Map

The Weather Fronts layer uses the familiar symbols found on traditional surface weather maps. Understanding a few basic symbols can tell you quite a bit about the weather pattern.

🔵 Cold Front

A cold front is displayed as a blue line with blue triangles.

A cold front marks the leading edge of an advancing colder air mass. The triangles point in the direction the front is moving.

Cold fronts can be associated with showers and thunderstorms, particularly when warm and humid air is present ahead of the front. Temperatures and humidity often decrease following its passage.

🔴 Warm Front

A warm front is displayed as a red line with red semicircles.

It represents the leading edge of an advancing warmer air mass. The semicircles point in the direction the front is moving.

Warm fronts are often associated with increasing cloud cover and areas of precipitation ahead of the front, followed by warmer conditions after it passes.

🔴🔵 Stationary Front

A stationary front is shown using alternating red semicircles and blue triangles on opposite sides of the line.

This represents a boundary between two air masses that is moving very little or not at all.

Because a stationary front can remain over the same area for an extended period, it can sometimes contribute to prolonged cloud cover or precipitation.

🟣 Occluded Front

An occluded front is displayed as a purple line with alternating triangles and semicircles on the same side.

Occlusion occurs when a cold front catches up with a warm front. These systems are commonly associated with mature low-pressure systems and can produce widespread cloud and precipitation.

As with cold and warm fronts, the symbols point in the direction the front is moving.

High and Low Pressure Systems

Weather Fronts also lets you see the locations of high- and low-pressure systems.

🔵 H High Pressure

A blue H marks the centre of an area of relatively high atmospheric pressure.

High-pressure systems are often associated with quieter and clearer weather, although the actual conditions depend on the season and overall weather pattern.

🔴 L Low Pressure

A red L marks the centre of an area of relatively low atmospheric pressure.

Low-pressure systems are frequently associated with clouds, precipitation and more unsettled weather. Warm fronts, cold fronts and occluded fronts are commonly connected to low-pressure systems.

A pressure value may also be displayed near the H or L, indicating the atmospheric pressure near the centre of the system in millibars (mb).

What Are the Orange Lines?

You may also notice orange lines on the map.

These can represent troughs, which are elongated areas of relatively low atmospheric pressure.

Unlike a cold or warm front, a trough doesn't necessarily separate two distinct air masses. However, troughs can still be important areas for rising air, cloud development, precipitation and thunderstorms.

Putting It All Together

One of the advantages of displaying Weather Fronts on the IW Pro radar is being able to compare the larger weather pattern with what is actually happening on radar.

Weather Fronts in IW Pro

For example, you might be able to see:

  • a line of thunderstorms developing along or ahead of a cold front;

  • an area of steady precipitation associated with a warm front;

  • precipitation wrapping around a low-pressure system;

  • showers or thunderstorms developing near a trough; or

  • relatively quiet weather underneath an area of high pressure.

The radar shows you where precipitation is occurring, while the Weather Fronts layer provides additional information that can help explain why the weather pattern looks the way it does.

Combine Weather Fronts With Other IW Pro Layers

You can view Weather Fronts on a relatively uncluttered map by turning off other layers as above or combine them with other information available in IW Pro.

For example, you can display radar information, alerts and radar station information at the same time. Alternatively, turning some of those layers off can make it easier to focus specifically on the fronts and pressure systems.

Experiment with the different layers to find the combination that gives you the information you want without making the map too busy.

A Note About Timing

Because the fronts are updated every three hours rather than moving continuously, don't use their exact plotted position as a minute-by-minute indication of where a front is located.

The triangles and semicircles indicate the direction a front is moving, but the front itself will remain at its plotted position in IW Pro until updated information is received.

This is why you may occasionally notice that the precipitation has moved relative to a front while you are watching the radar.

Learn More About Weather Maps

For more information about fronts, pressure systems and the other symbols used on surface weather maps, NOAA's JetStream weather education site has a helpful guide.

https://www.noaa.gov/jetstream/wxmaps

Understanding these symbols can make the Weather Fronts layer in IW Pro much more useful and give you a better picture of what is happening in the atmosphere when you are watching weather develop on radar.