What do the two horizontal lines under the cloud mean in iphone weather software?

This is a weather sign of a thunderstorm.

Thunderstorms are caused by thunderstorm cumulonimbus clouds, which move on a large scale, much more violently than showers, accompanied by discharge, and are common in summer. So the sign of thunderstorm weather is rain clouds plus lightning below.

Meteorological symbols are specially made by meteorological departments to facilitate people to better understand weather conditions and meteorological information. When observing a weather phenomenon, meteorological observers should input corresponding symbols in the "weather phenomenon" column of the observation record book of the day. Except for a few phenomena, the starting and ending time should be recorded at the same time.

Extended data:

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Weather forecast mainly uses a large number of collected data (temperature, humidity, wind direction and speed, air pressure, etc.). ), and then use the current understanding of atmospheric processes (meteorology) to determine future air changes. Because of the chaos of the atmospheric process and the fact that science has not fully understood the atmospheric process today, there will always be some errors in the weather forecast.

The satellite cloud image of China Central Meteorological Observatory was taken from Fengyun-1 and other meteorological satellites. Using satellite cloud images for analysis can improve the accuracy of weather forecast. Weather forecast is usually divided into three types: short-term weather forecast (2 ~ 3 days), medium-term weather forecast (4 ~ 9 days) and long-term weather forecast (10 ~ 15 days or more). CCTV mainly broadcasts short-term weather forecast every day.