On the web dashboard and mobile app radar, you'll see a system on the map with a variety of colors and shapes. The different colors indicate the radar has determined there are raindrops in the sky.
Green is the lowest strength, which equates to light rain, which would be mostly a nuisance on the ground. In the winter months, light-moderate snow will usually show up as green as well.
Yellow is the next strength up. This will equate to more moderate rain on the ground. The kind of rain that'll make you rush to get back to the car, or start to slow traffic a bit on a freeway. Once a storm becomes strong enough to be represented by yellow, the chance that the storm becomes electrically charged and triggers a lightning delay goes up to around 30%. In winter months, moderate-heavy snow would show up as yellow as well. On the ground, this would look like a near blizzard or whiteout conditions.
Red is the next strength you'll commonly see. This will equate to a strong shower/thunderstorm. Expect lightning activity from any storm that contains any amount of red. Gusty winds would also be common under such a strong storm.
Purple is where things get interesting. Once purple shows up, hail enters the picture. There's no guarantee that at this point the hail would not melt before hitting the ground, but it is in the cloud. Possible hail sizes in this range would be pea size, or up to quarter size hail. Pea will not cause significant damage, but quarter-sized hail is when minor vehicle damage could occur.
Deep Purple is a step up from light purple. If light purple means hail, deep purple means large hail. Once dark purple appears on the map, you can assume hail is hitting the ground. The size of the hail on the ground depends on many factors beyond the scope of this article. Still, if you're concerned about the safety of your vehicle, or other outdoor equipment, deep purple would be the color to take action to protect things on the ground.
Because of the intensity deep purple represents, this is also when the National Weather Service will likely issue a Severe Thunderstorm Warning.
For winter weather, the color scale is a bit different.
Pink represents mixed precipitation. This usually occurs behind cold fronts and marks the transition between rain and snow. Within this transition, freezing rain can occur, so forecasts must be monitored closely since freezing rain can be very damaging to infrastructure. Freezing rain can also make driving extremely dangerous, even for areas accustomed to driving in winter.
Gray and Blue represent snow. Gray means light flurries, and blue represents more consistent snow. Deeper blues start to transition into blizzard conditions, which means visibility on the ground will be limited, and precautions should be taken.
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