Storm Spotter User Guide

Storm Spotter is no longer available.

Storm Spotter is a premier weather radar app available on the iPhone, iPad & iPod touch. It was designed to provide power features for meteorologists or severe weather enthusiasts while still maintaing a simple interface that a normal user would have no difficulty using. On this page I will show you how to make your way around the app and how to use the different radar products that are provided.

Home Screen

This is where you will spend the majority of your time in the app. It contains all the relevant information about the radar image that is currently displayed as well as the controls to navigate around the rest of the app.

On the top left of the map is the station name of whatever radar you are currently connected to. If there is room on the screen to display it, the city that the radar is located in will be displayed as well. If the radar you are connected to is down for any reason, the color of the text will be orange and the label will indicate that the radar is down.

On the top right of the map is all the info about the radar image that is currently displayed on the map. First is the product type. I will give more info about the different product types later in the guide. Below the product type is the time-step of the image. The time-step will display both the actual time of the image and how long ago it was. You can configure the time to either display in your devices’s local time or UTC time in the settings of the app. If there is no image display or if the image displayed is over ten minutes old, the time-step label will turn red to alert the user.

Just below the map is the color bar. This bar is used as a scale to give meaning to the colors of the radar image on the map. To get values and units for any of these colors, simply slide you finger across the bar.

Below the color bar is the set of controls. From left to right, these buttons are the data button, the location button, the radar products button, the animation button, and the settings button.


The map is the main part of the app. It is where all of the weather data is actually shown. The map has four map types that can selected in the settings: standard, satellite, hybrid, and terrain. All four maps have their own advantages. If you are in an area with a slow network connection, I recommend using standard as it uses the least amount of bandwidth.

Tapping and holding on the map will get rid of all the toolbars around it and make the map full screen. This behavior can be disabled in the settings.

Radar Sites

The first thing that you will notice is the group of dots that are covering the map. These dots represent radars sites. The red dot is the radar that you are currently connected to, orange dots represent radars that are down or not currently working, and all the remaining radars are black dots.

As you pan and zoom around the map, Storm Spotter will automatically connect you to the radar site closest to the center of the screen (this behavior can be disabled in the settings). Note that you will not be automatically connected to a radar site that is down. If you want to manually connect to one, simply tap on the radar dot and press the radar button of the left side of the popover that comes up.

Tapping on any radar site will bring up a popover that displays the station name as well as the city and state the radar is located in. On the right side of the popover will be a chevron that brings up a page with some more info about the radar. Also if you have auto-radar selection disabled, a button will be on the left to connect to this radar.

Radar Image

The radar image is also shown on the map. An image can only be shown for one radar site at a time.


The last thing that shows up on the map is warnings. The three types of warnings that Storm Spotter supports are Tornado, Severe Thunderstorm, and Flash Flood. Tornado warnings are red, Severe Thunderstorm warnings are yellow, and Flash Flood warnings are green.

The warnings are displayed as a polygon on the map. Any area that is enclosed by the polygon is considered to be in the warning. To make the warnings stand out above the radar, they are displayed with a subtle black outline.

You will notice that on each warning outlines there is a small dot that is the same color as the warning. If you tap on this dot, it will bring up a popup (similar to the one you get for tapping on the radar). This popup will tell you how long until the warning expires and it will provide a button that will bring up the actual text of the warning.

Data Button

This button looks and behaves a little different depending on what device you are using. If you are using an iPhone or an iPod touch, it will bring up the data list over the map. If you are using an iPad, the button will look like a chevron and will either slide in the data list next to map or slide it off. Also on the iPhone, if there are any active warnings in the United States, the data button will turn red on the iPhone. I did not enable this feature on the iPad because the data list can easily be displayed alongside the map.

The data list itself has four main areas. On the bottom left of the screen is a refresh button. Tapping this button will refresh all the data in the app. The app does this automatically every two minutes, but I provided this option for people who are impatient (as I sometime am) and want faster checks. To the right of the refresh button is a clock that displays the current time in UTC.

In the actual table view are two list of data sources. Tapping the top cell will bring up the radar list and tapping the second one will bring up the warning list.

Radar List

The radar list provides a list of every radar in the app sorted by state. Tapping a radar will dismiss the list and connect you to that radar on the map. Tapping the chevron will bring you to the same radar detail page that you can access from the map.

On the bottom of the screen is a segmented control that allows you to either display the full list of radars or just the radars you marked as favorite. To add radars to your favorite list, you can do it from the radar detail page, or you can tap the edit button that appears when looking at the favorites list.

Warning List

The warning list provides a a list of every active severe weather warning in the U.S. Tapping on a warning will dismiss the list and zoom you into that warning on the map and also connect you to the closest radar to that warning. Tapping on the chevron will let you view the text for that warning.

Like the radar list, the warning list can be viewed three ways. They can be organized by time until expiration, distance from whatever radar you are connected to, and distance from you. Note that if you have location services disabled, the third option will not be available.

Location Button

Pressing the button will show your location on the map (represented by a blue orb). It will zoom you into your location and connect you to the closest radar. To dismiss location, simply tap the button again. If your location is currently on the screen, the location button will be blue.

Radar Products Button

The radar products button brings up a grid of different radar products. I put the products into a grid instead of a standard list because it makes it much more convenient to switch between products without having to scroll through a long list.

The available products are Base Reflectivity (Tilts 1-4), Base Velocity (Tilts 1-4), Storm Total Rainfall, Vertically Integrated Liquid (VIL), and Echo Tops.

The tilts represent the level of the radar beam. So viewing a higher tilt will show a higher elevation section of the storm.

The Nation Weather Service published a good F.A.Q. that covers a lot about how radars work.

Base Reflectivity

The units of Base Reflectivity are dBZ. It is a logarithmic measurement of the amount of power returned to the radar from the radar beam. Higher amounts of reflectivity represent higher rates of rainfall and really high values are typically hail.

The NWS does a good job going into a bit more detail about how this product works.

Base Velocity

The units of Base Velocity is m/s. Base velocity used to identify rotation in a storm. It measures the component of the wind speed either toward or away from the radar. Green indicates motion toward the radar while red indicated motion away from the radar. Rotation can be inferred in areas where motion toward and away from the radar are located right next to each other.

More info can be found here. You can also read about Storm Relative Velocity, which is a similar product.

Storm Total Rainfall

Storm total rainfall is simply an estimate of amount of rain (in inches) that has been continuously updated since the last one-hour break in precipitation.

Vertically Integrated Liquid

Vertically Integrated Liquid, or VIL, is a measurement of the amount of liquid water in a column of air. It is measured in kg/m^2. VIL can be used to help identify hail.

Echo Tops

Echo tops are the highest elevation that the radar records precipitation for a given storm. It is measured in kft. It can be used to quantify the intensity of the storm. Higher echo tops usually indicate stronger updrafts in storms.

Animation Button

Pressing this button will animate the radar image. It will automatically download the last six images and play them sequentially. Tapping again will bring you back to the newest image and stop the animation.

Settings Button

The setting page has five categories:


This is just general info about the app and includes all the different ways to contact or connect with me.


  • Auto-Lock: If this switch is off, then Storm Spotter will not allow the device to auto-lock after a set time. It will stay on until you manually turn it off.
  • Full Screen: Determines if you can make the map go into full screen mode by tapping and holding on the map.
  • Shake to Update (iPhone and iPod touch only): Determines if you can update the data by shaking the device. I disabled this on the iPad so I could not be held accountable for a bunch of people looking silly by shaking their iPad in public 🙂
  • Time zone: simply picks the time zone that the radar image time step is displayed in.

Map Settings

  • Determines the map type of the map. Either Standard, Satellite, Hybrid, or Terrain.

Radar Settings

  • Auto Radar Selection: Determines if the app automatically handles switching radar sites as you move around the map.
  • Reduce Clutter: Clutter reduction is for the reflectivity product. If enabled, it filters out everything below 22.5 dBZ (which is generally ground clutter and not precip). Note that this setting should be disabled for winter weather precip, as dBZ is lower for winter products that for rain and hail.
  • Opacity: This is the level of transparency of the radar image. 0% is completely transparent, while 100% is completely opaque.

Warning Settings

  • Allows you to determine which warnings are displayed on the map. Note that this does not effect if they are downloaded. All three warning types are always downloaded.