How to read a precipitation map like an expert

A precipitation map is one of the types of weather maps, which in turn is one of the two most popular forms of weather forecast representation, along with a standard table. In this article, you will learn more about what a precipitation map is and how to read it like an expert.

What is a precipitation map?

A precipitation map is one of the three most common types of weather maps that shows what precipitation is in a particular time and place (two other maps / weather elements are air temperature and wind). In turn, precipitation on the map means most often and primarily rain, but it can also be a slush, a mixture of snow and rain, snow, and other types of precipitation, although a separate forecast is also made for the latter.

A modern precipitation map is a digital interactive (live) map you can get on some website or rather in a weather application for your smartphone and tablet.

With the development of digital technology, it is also has become possible to separate the precipitation map from the other weather elements, as well as to create separate maps for many of them. Previously, on paper maps, the elements were combined on one general weather map that included wind, precipitation, temperature, cloud cover, and more.

The data you see on a typical precipitation map is a forecast for today and, most often, the next 3–10 days from one of the several weather models, which, in turn, could be of one of the two main types: global with a forecast for the whole world and regional or local with a forecast for only some part of the world. For example, it could be a precipitation map for North America, the Mediterranean Sea coast, Southeastern Asia, and the like.

Accordingly, a precipitation map is needed to get the appropriate forecast in a visual form that the usual forecast table, graph, and other forms of presentation do not provide. It is also a way to get a bigger weather picture.

A precipitation map in the Windy.app for iOS

How to read a precipitation map like an expert?

To read any type of weather map correctly, you need to know that there is no single weather map, there are many, and they look different with different information and visualization depending on the source.

However, the weather map generally consists of the following basic elements, so keep your attention on them, while reading the map:

colors,
special symbols,
numbers,
letters or phrases,
lines,
different interactive elements.

So, let’s figure out how to read a precipitation map using the Windy.app as an example in 10 steps:

1. A Precipitation Map in the Windy.app is an interactive map with a worldwide forecast. The predominantly blue areas you see on the map are precipitation. You can call them “clouds,” but they are areas, not individual clouds. Within areas, there can be many different types of clouds that cause precipitation, such as cumulonimbus and nimbostratus, which brings severe weather with downpours or heavy rains.

2. Precipitation forecast is given for the next 10 days in 3-hour forecast step according to the American global weather model GFS.

3. You can also move the timeline at the bottom of the screen to see what the predicted precipitation has been over the past 10 days to catch patterns and better understand the forecast.

4. Enlarge the map to the area you want — for example, the southern coast of Spain near Barcelona, where there are many marinas for yachting if you are going on a boat trip.

A precipitation map in the Windy.app for iOS

5. Note the colors of the “clouds” on the map — from blue and green to orange and purple. There is color scale at the very top of the map. It describe the amount of precipitation for the area on the map and the time selected on the scale below.

In brief, light blue is light precipitation (light rain), blue — moderate rain, dark blue and green — heavy (rain and heavy rain), orange and purple — extreme (rainfall).

The unit of measure is mm per hour. If you are in the U.S., you can change them to inches in the app's Settings, which can be accessed from the Spot page or the app's Home screen.

Learn more about how precipitation is measured in dedicated article in the Windy.app blog.

6. Click on a particular point on the map to see the exact amount of precipitation for that point and time.

A precipitation map in the Windy.app for iOS

7. Click again on the window to go to the page of this point (spot) and get an even more detailed forecast in 1-hour step for this day and for the next (and past) 10 days.

A precipitation forecast in the Windy.app for iOS

8. Go back to the Precipitation Map and select the Accumulated Precipitation layer in the same way you did the first time. Now you see the total amount of moisture that will fall in a particular area over the next (or past) 12 and 24 hours, as well as over the next three, five, and ten days. So in this case, there will predictably be more orange and purple areas on the map, indicating more precipitation, because the time intervals have become much longer.

A precipitation map in the Windy.app for iOS

9. To understand the weather even better, turn on the Weather Fronts layer in the Weather Map Setting. Of all the lines, pay attention first to the red lines, which are warm weather fronts. They form when warm air moves into cold air territory. Warm fronts pass with overcast, rains, sometimes with thunderstorms. But other lines can also tell you about precipitation. Learn more about how to read a map of weather fronts.

A precipitation map in the Windy.app for iOS

10. In the same Weather Map Settings adjust the map’s transparency to get a better look at the details of the map.

Where to get a precipitation map?

From the Home screen or from the Spot screen in the Windy.app, go to the Weather Map and select the Precipitation or Accumulated Precipitation layers.

Text: Ivan Kuznetsov

Cover photo: Coen van de Broek Unsplash