Understanding Storm Relative Velocity (SRV) in IW Pro

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Storm Relative Velocity (SRV) is one of the newest radar products available in IW Pro, giving weather enthusiasts another powerful tool for analyzing severe thunderstorms.

While standard Velocity remains the preferred product for most situations, Storm Relative Velocity can make areas of rotation easier to identify when storms are moving quickly.

What is Storm Relative Velocity?

Storm Relative Velocity is based on Doppler Velocity data but with one important difference: it removes the overall forward motion of the storm.

When thunderstorms are moving rapidly, that forward motion can sometimes make it more difficult to identify localized areas of rotation. By subtracting the storm's movement, SRV allows you to focus on the winds relative to the storm itself.

This makes Storm Relative Velocity particularly useful when investigating fast-moving severe thunderstorms, supercells, and squall lines that may contain embedded rotation.

Before You Begin

Storm Relative Velocity requires Storm Tracks to be enabled in Settings.

SRV uses the Storm Tracks system to estimate the storm's motion. Without Storm Tracks enabled, Storm Relative Velocity cannot calculate the storm-relative wind field.

If you do not see SRV working as expected, first confirm that Storm Tracks is turned on.

When Should I Use Storm Relative Velocity?

Storm Relative Velocity is most useful when storms are moving at moderate to fast speeds.

Examples include:

  • Fast-moving severe thunderstorms

  • Supercells

  • Squall lines with embedded rotation

  • Investigating possible areas of storm rotation

Because the storm's forward motion has been removed, localized areas of rotation may become easier to recognize than they are on the standard Velocity product.

When Should I Use Standard Velocity?

Standard Velocity remains the best choice for most situations.

For slow-moving storms, Storm Relative Velocity often provides little additional benefit and may actually be more difficult to interpret.

Think of SRV as another tool in your weather toolbox rather than a replacement for Velocity. Comparing both products together often provides the best understanding of what is happening within a storm.

Triple Panel Mode Makes Comparison Easy

One of the easiest ways to use Storm Relative Velocity is in IW Pro's Triple Panel Mode.

Configure the panels as:

  • Left: Reflectivity (REFL)

  • Centre: Velocity (VEL)

  • Right: Storm Relative Velocity (SRV)

This allows you to compare storm structure, wind motion, and storm-relative wind motion all at the same time.

Figure 1. Triple Panel Mode showing Reflectivity, Velocity, and Storm Relative Velocity. The storm in this example is moving northeast at approximately 62 km/h. Because of the storm's relatively fast movement, Storm Relative Velocity helps make localized areas of rotation easier to identify.

Notice that the differences between Velocity and Storm Relative Velocity may sometimes be subtle. SRV is designed to highlight rotation by removing the storm's forward motion. It is not intended to completely change the appearance of the radar image.

Looking at the Example

In the Reflectivity panel (left), we can see the overall structure and intensity of the thunderstorm.

The Velocity panel (centre) shows the winds moving toward and away from the radar. Because the storm itself is moving quickly, that overall motion influences the velocity display.

The Storm Relative Velocity panel (right) removes much of that forward motion, making localized wind patterns easier to examine. This can make subtle areas of rotation stand out more clearly than they do on the standard Velocity product.

Notice that this does not necessarily indicate a tornado. Rotation within thunderstorms is relatively common and can vary significantly in strength. Storm Relative Velocity is simply another tool that can help you better understand what is happening inside a storm.

Using SRV Alongside Other IW Pro Features

Storm Relative Velocity works best when combined with IW Pro's other advanced tools.

As you analyze a storm, compare:

  • Reflectivity to see the storm's structure.

  • Velocity to view the actual winds detected by the radar.

  • Storm Relative Velocity to better identify localized areas of rotation in fast-moving storms.

  • Storm Tracks to understand where the storm is moving.

  • StormRisk™ to view computer generated severe weather probabilities.

No single radar product tells the entire story. Using several products together provides the most complete picture of a storm's behaviour.

A Powerful New Tool for Canadian Weather Enthusiasts

Storm Relative Velocity has long been used by meteorologists as an additional tool for analyzing severe thunderstorms. IW Pro now brings this capability to Canadian weather enthusiasts, providing another way to explore and better understand fast-moving storms.

We encourage you to experiment with Storm Relative Velocity during the next severe weather event and compare it with standard Velocity. With a little practice, you'll quickly learn when SRV can provide additional insight into storm rotation and when standard Velocity is the better choice.

Introduction to Instant Weather Pro

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Welcome to Instant Weather Pro, our most powerful radar platform yet. It is built for those who want more control, more detail, and more precision when tracking the weather across Canada and the U.S.

Following our official partnership with the Northern Tornadoes Project at Western University, their team asked us to build a state-of-the-art radar suite to help track and validate tornadoes and hail across Canada. The result is a professional-grade radar system that is now available through IW Pro.

IW Pro is a next-generation radar platform offering the same high-resolution data trusted by meteorologists. Whether you're a storm spotter, first responder, outdoor event planner, farmer, or weather enthusiast, it delivers the tools you need in an intuitive, mobile-friendly interface. It also works seamlessly on desktop and laptop, allowing you to open multiple windows for side-by-side analysis or to track different storms simultaneously.

We are also planning to launch IW Pro as a subscription tier inside our popular Instant Weather app. All current subscribers will receive access to the app version as well as the website version at no additional cost.

Instant Weather Pro on iPad

🔍 What Makes IW Pro Different

Most weather apps use a "mosaic radar" view, which is a blended image from multiple radar stations. While that is great for getting a broad picture, it smooths out important details.

With Instant Weather Pro, you can:

- View individual radar stations directly and not just the combined mosaic.

- Choose from multiple radar products to get different types of data.

- Control the elevation angle (tilt) to see different slices of the atmosphere.

- Compare radar products using Dual Mode or Split Mode.

- Enjoy ad-free browsing with a faster and cleaner experience.

- Track weather using desktop, tablet, or mobile all through your browser.

🛰️ Compare Radar Products: Dual and Split Modes

Instant Weather Pro offers two powerful ways to compare radar products, helping it stand out from many other tools on the market.

🔄 Dual Mode (Side-by-Side)

Use Dual Mode to view two radar products at the same time, side by side.

- Great for tracking how features like wind rotation (Velocity) line up with precipitation patterns (Reflectivity).

- You can zoom and pan both views together to follow the storm from multiple perspectives.

Dual Mode on a laptop, showing Reflectivity (left) and Velocity (right) from the Didsbury, AB tornado (EF4) on July 1, 2023.

🧭 Split Mode (Swipe Slider)

Split Mode lets you compare two radar products in the same view using a draggable slider.

- Move the slider left or right to reveal one product on one side and the other on the opposite side.

- Unlike side-by-side views, everything stays perfectly aligned, making it easy to see exactly where features overlap.

- Ideal for quickly checking if a hook echo on Reflectivity lines up with rotation on Velocity.

Whether you prefer a side-by-side layout or a swipe-to-compare approach, IW Pro gives you the flexibility to analyze radar data your way.

Below is the Didsbury, AB tornado displayed in Split Mode. This iPhone-recorded video demonstrates how you can swipe between Reflectivity and Velocity radar products to observe how storm features align.

🛰️ Radar Products Available

IW Pro lets you switch between several advanced radar products, including:

- Reflectivity – See the intensity of precipitation.

- Velocity – Measure wind moving toward or away from the radar (great for spotting rotation).

- Correlation Coefficient, Differential Reflectivity, and Specific Differential Phase – Advanced tools used by weather experts to detect hail, debris, and rainfall structure.

Not sure which product to use? We'll explain each of these in upcoming posts to help you get the most out of them.

🕒 Access Past Radar with Historical Data

Missed a storm? No problem.

Instant Weather Pro gives you access to historical radar data, so you can revisit and review previous weather events which makes it ideal for storm analysis, research, or just satisfying your curiosity.

- Scroll through archived radar loops for past days.

- Analyze storms in detail using different radar products.

- Perfect for training, educational use, or verifying what happened.

This feature also helps us create clear blog visuals, even when the weather is quiet. Many of the radar examples in this blog were captured from past events.

💡 Customization at Your Fingertips

You can fine-tune your radar view by:

- Changing radar products with one click.

- Adjusting the elevation angle (tilt) for surface or higher-level scans.

- Choosing radar loop speed or stepping frame by frame.

- Switching color schemes (like green/red velocity view).

💰 Subscription and Access
IW Pro is currently available for $99.99/year through our website.

Please note: This is our current rate and is subject to change in the future.

What’s coming soon:

  • Monthly and app-based subscription options

  • Additional tiers to match your usage needs.

We recommend signing up on our website for the best value. App store purchases include additional platform fees.

🚀 Ready to Get Started?

Ready to explore advanced radar features? Subscribe to Instant Weather Pro today and take your virtual storm chasing to the next level.

And be sure to check back here on the blog as we’re building a growing library of helpful tips to make the most of your IW Pro experience!

Have questions or feature suggestions? Let us know as we're building IW Pro with your feedback in mind.