"Old woman said it could go either way": Understanding the sources of errors in short-term weather forecasts.

It's Impossible to Accurately Assess the Current State of the Atmosphere

To describe and evaluate the current mood of the atmosphere, scientists need to gather and process an enormous amount of data. Weather information is sourced from specialized meteorological devices and installations, each with its own advantages and disadvantages.

The period for ultra-short-term forecasts is up to 12 hours, while short-term forecasts range from 12 to 72 hours.

• Meteorological stations are locations where meteorologists record key weather parameters in real-time: temperature, humidity, pressure, and more. The problem is that these stations can only collect data in their immediate vicinity and are spaced quite far apart. As a result, a "blind spot" often forms between nearby meteorological stations where weather measurements are lacking.

5 Meteorological station on Ai-Petrijalita.com

• Meteorological radars are specialized radar systems used to locate precipitation areas and determine their type, direction, and intensity. Approximately every 10 minutes, a radar takes a three-dimensional snapshot of the atmosphere within a radius of up to 250 kilometers and reports the situation to meteorologists with precision down to the neighborhood! The downside is the insufficient number of devices. For instance, most Russian radars are located only in the European part of the country, leaving other areas without data coverage. The radar’s visibility is also imperfect—tall buildings can obstruct snapshots, and very light precipitation may escape detection due to the curvature of the Earth.

6 Meteorological radar, Mount Gorelaya, Murmanskrangefinder.ru/ huszar

• Meteorological sondes are autonomous balloons. A container with a thermometer, humidity sensors, and atmospheric pressure sensors is attached to a helium balloon that lifts the device to heights of up to 40 kilometers. Data collected is transmitted to scientists via antennas. After completing its task at a certain altitude, the balloon pops, and the container falls to the ground and is no longer used. By the way, this dedicated little meteorological sonde weighs only about 300 grams. The downside is that the device requires manual launch, making data collection difficult in open seas. Sondes are launched into the sky only twice a day and do not provide information about hard-to-reach areas of the Earth.

7 Meteorological sondeAmir Cohen / Reuters

• Meteorological satellites are true giants of data collection! They are in orbit and report on weather conditions on a planetary scale—tracking volcanic ash and smoke from wildfires, dust storms, areas of heavy precipitation, and even the boundaries of ocean currents. Satellites are currently the primary means of gathering information about weather and climate. However, not everything is perfect here either: they monitor "large" atmospheric processes, making it challenging to detect microclimatic changes in smaller areas.

8 Meteorological satellite "Electro-L". Archive photoNGO named after Lavochkin

The imperfections of all these tools prevent meteorologists from assessing the state of the atmosphere with absolute precision. Therefore, errors can creep into forecasts right from the measurement and data collection stages.

In global meteorology, nowcasting (from the English "now") is practiced—detailed weather prediction for periods ranging from a few minutes to two hours. This type of forecast, like ultra-short-term forecasts, is crucial for the operations of airports, spaceports, seaports, and navigation, as well as for major sporting events. 9 iStock

Short-Term Forecasting Requires Powerful Computers

More specifically, it requires supercomputers. Weather prediction for any timeframe involves a significant amount of calculations; however, short-range forecasts demand not only substantial computational power but also the highest performance from the computer. Supercomputers handle the processing of massive data volumes. For instance, British meteorologists utilize the powerful Cray XC40 with a performance of 7 petaflops (which is approximately seven thousand trillion operations per second!). In comparison, the main assistant of Russian meteorologists lags behind its UK counterpart, boasting a power of 1.2 petaflops.

0 Supercomputer Cray XC40metoffice.gov.uk

Medium-term forecasts can be generated up to four times a day, while nowcasting is a complex continuous process requiring quick computer responses. Sometimes, time becomes a critical factor in ultra-short-term forecasting. If calculations take longer than 20 minutes, they become unusable—data quickly lose their relevance.

Not All Weather Parameters Are Considered in Short-Term Forecasts

As mentioned earlier, time is the main enemy of nowcasting. For this reason, not all weather parameters are often included in forecasts, but only a select few.

The primary parameters of current weather conditions include air temperature, atmospheric pressure, humidity, wind speed and direction, precipitation type, and amount.

In short-term and ultra-short-term forecasts, one or two parameters may be considered. For example, wind gusts and precipitation, or atmospheric pressure and air temperature.

1 Forbes.com

Despite the fact that the average accuracy of short-term forecasts is over 95%, even in predicting such a near future, errors can occur. There is a more reliable way to forecast the weather: if your pet is sleeping curled up, expect frost. So before leaving your home, don’t forget to consult your furry meteorological assistant!