Precipitation. Pattern and types of precipitation

The amount of precipitation is of constant interest to those who monitor the weather. It would seem that the forecast is 10-15 mm, and there is knee-deep snow or huge puddles on the streets. To make it easier for you to navigate the forecasts, we have prepared information on measuring precipitation.

Meteorologists distinguish between two concepts: the depth of snow cover and the amount of precipitation. What we see on the street after a snowfall is the height of the snow cover, which sometimes reaches 50 cm, although the amount of precipitation may be no more than 20 mm. One millimeter of fallen snow is equivalent to 1-1.5 cm of snow depth, depending on the structure of the snow.

According to meteorological instructions, a millimeter of precipitation is one liter of water per square meter. At all weather stations there are precipitation measuring buckets, from which, at 9 and 21 o'clock GMT, precipitation is poured into a special vessel, by which its quantity is measured. Solid precipitation- snow, hail - are melted, and then specialists measure the resulting water.

Everything in St. Petersburg is anomalous warm winter(oh, I wish I could jinx it!), and I, quite tired from the two previous winter reconstructions of the events of the film “The Day After Tomorrow,” am incredibly happy about this. Moreover, a year ago, around this time, there was already a frost outside the window of -20°. Snowboarders and skiers will have artificial snow on the slopes, so they won’t be offended, but I can live well without it.

But while the weather is hovering around zero, every morning turns into a dilemma for me: what to wear so as not to freeze and not sweat. And this is where two excellent sites with very accurate weather forecasts come to my aid. At one time, my friend helped me find them, but he doesn’t write on LiveJournal, so I’ll bring the light to the people. Those who know about them, do not rush to throw eggs at the button accordion, because many still go to the stupid and lying Gismeteo and Yandex to find out the weather.

Below is a short overview of two excellent sites: RP5 And YR.no, as well as answers to several questions that may arise after getting to know them. If it seems like there are too many letters, just take into account my recommendations and believe that these two resources have never failed or deceived.

This site, a guest from Norway, unlike RP5, in addition to very accurate forecasts, has very beautiful design. There is no Russian language, however. But there is English (switches in the upper right corner).
Feature of the site - a bunch different ways providing information, ranging from simple forecast tables familiar from Yandex for 9 days in advance (it is worth noting that the decoding is still very detailed), and ending with graphs and weather maps that change over time.
Personally, for me, the optimal and most understandable graph seems to be a moderately “loaded” graph, which can also acquire a line for pressure and a cloud diagram if you click on the Detailed button on the left, but this information seems unnecessary to me. The blue bars on the time axis are again the precipitation level in millimeters.

Now I will answer a couple of questions that may arise after reading these sites:

Q: Where do the British and Norwegians get their information about our weather? Our hydrometeorological center certainly knows better!
A: Not at all. Both the Hydrometeorological Center and everyone else know exactly the same thing about the actual weather. All information is collected by ground-based weather stations and made publicly available in a free system. international exchange weather data. Now anyone who has a supercomputer with a thousand or two processors can take this data, process it and try to predict what the weather will be like in a particular place in the near future. It's just a matter of who can do it more accurately.

Q: It is not clear to me when precipitation is designated as 2 mm/6 hours. What to really expect?
A: Very easy to understand. Here's how RP5 explains it:
"The ratio is direct: 1 mm corresponds to 1 liter per 1 square meter. That is, 12 mm is a large 12-liter bucket; 10 mm is a 10-liter bucket; 0.5 mm is a half-liter bottle; 0.2 mm is a glass of water per 1 square meter meter. Perhaps this explanation is not very solid, but it is understandable."
This opens up new horizons compared to those weather forecasts where rain, regardless of the predicted intensity, is indicated by a droplet or an umbrella. You can understand whether this umbrella is needed at all by these millimeters: 0.2-1 mm is very little, and most likely means heavy rain in places (that is, all 10 millimeters will fall on 10% of the city, and the sun will shine over the remaining 90%) . And 4-10 mm is already an impressive amount, spread over a huge area, and most likely the rain will continue to fall for a long time and everywhere.

Q: What rain, it’s winter here, frost -30! How to measure snow in millimeters?
A: Simply multiply by 10. 1 millimeter of precipitation equals 1 centimeter snowdrift.

Q: It would be great if forecasts from 10 different sources could be averaged.
Yeah, someone has already done this

The amount of precipitation is one of the most important characteristics of the weather, along with air temperature, and, of course, knowing it for a certain area, you can predict the weather for the future, you can even track climate changes, if any. But how to measure precipitation?

With snow, everything is more or less simple: we take a ruler, immerse it in the snow to the ground - and get the amount of precipitation in millimeters. But this trick doesn’t work with rain! After all, water is immediately absorbed into the soil, and that which is not absorbed (say, gets on the asphalt) evaporates relatively quickly, so we won’t get accurate results this way, even if it comes to flooding... how to measure the amount of rain?

There are special devices for this.

One of them is a rain gauge. In fact, it is something like a bucket, only very large - 5 square meters in area. Rainwater enters such a vessel through a cone-shaped funnel - so that the wind does not distort the measurement results by blowing into the vessel extra water, or vice versa – blowing it out of there. This design is installed on a weather site at a height of 2 meters. Once a day, the collected rainwater from the rain gauge is poured into a graduated vessel and measured in millimeters. Every millimeter is a liter of precipitation per square meter.

There are also soil rain gauges, which are buried in the ground level with it, and also field rain gauges, which are graduated glass vessels that are placed in agricultural fields.

But it is not always and not everywhere possible to check the results once a day! In the taiga, tundra, mountains and other hard-to-reach places, you have to check the results once a week, or even ten days - during this time the water can evaporate and the result will be distorted. To work in such extreme conditions There are total precipitation gauges. In design, it differs little from a conventional rain gauge, but when it is installed, Vaseline oil is poured into it. As a result, when water is added to the vessel, petroleum jelly floats to the surface, covering its surface with a thin layer that prevents the water from evaporating, preserving it for measurement.

However, you can determine the amount of precipitation without approaching the device directly, if it is a radio precipitation gauge. Its sediment collection tank is installed in such a way that when filled, it turns over, the water is drained from it, and this activates a mechanism that turns on the radio transmitter. Its radio signal is recorded at the nearest weather station, or it is sent to a meteorological satellite.

Another instrument used by meteorologists to measure the amount of rain is a pluviograph. Rainwater is collected in a vessel with an area of ​​5 square meters. The bottom of the vessel is cone-shaped, and there are holes in it into which water drains and enters the chamber through a pipe. The chamber contains a hollow float connected to a metal rod. At the top of the rod there is a arrow on which the pen is mounted, and next to the camera there is a drum with paper tape. The water accumulating in the chamber raises the float, it sets the rod with the arrow in motion, and the pen draws a curve on the tape, which is used to determine the level of precipitation.

Average annual quantity Precipitation forms an important part of climate data - those recorded using various methods.

Precipitation (most often includes snow, hail, sleet, and other types of water falling to the ground) is measured in units over a period of time.

In the United States, precipitation is usually reported in inches per 24-hour period. This means that if one inch of rain falls in a 24-hour period, and the water does not soak into the ground and flow down after a storm, there would be a layer of one inch of water covering the ground.

Low-tech precipitation methods use a container with a flat bottom and straight sides (eg a coffee cylinder). While a cylinder can help you determine whether a precipitation event is one or two inches of rain, they have difficulty measuring small amounts of precipitation.

Weather observers use more sophisticated instruments known as rain gauges and tip buckets to more accurately measure precipitation. Rain sensors have wide openings at the top for precipitation. The rain is directed into a narrow tube, one-tenth the diameter of the top of the neck. Because the pipe is thinner than the top of the funnel, the units of measurement are further apart than they would be on a ruler and accurate measurements of one hundredth (1/100 or 0.01) of an inch are possible. When the amount is less than 0.01 inches of rain, that amount is called a “trace” of rain.

A bucket equipped with a sensor records precipitation readings on a rotating drum or electronically. It has a funnel like a simple rain gauge, but the funnels lead to two tiny "buckets". The two buckets are balanced and each has 0.01 inch of water capacity. When a bucket is full, its bottom is emptied while the other bucket is filled with rainwater. Each tip of the bucket triggers a device to record an increase of 0.01 inches of rain.

Snowfall is measured in two ways. The first is a simple measurement of the layer of snow on the ground with a stick marked with units of measurement. The second measurement determines the equivalent amount of water per unit of snow. To obtain this ratio, snow must be collected and melted into water. Typically, 10 inches of snow produces one inch of water. However, this may refer to loose, fluffy snow, although just 2-4 inches of wet, compacted snow can produce an inch of water.

Wind, buildings, trees, terrain and other factors can change the amount of precipitation that falls, and such snowfall is typically measured against obstructions. Thirty-year average annual precipitation is used to determine the average annual precipitation for a particular location.