How To Report Snowfall And Its Equivalent Rainfall in METAR and SYNOP

Meteorologists, forecasters, and weather enthusiasts have been using METAR and SYNOP codes for decades to report the weather conditions at airports worldwide. Now you can use these same codes to report snowfall and precipitation worldwide. This post will discuss how to report snowfall and rainfall in METAR and SYNOP.

Snow/Rain Reporting in METAR:

Snowfall is reported in METAR by writing SN along with +,++,-, to indicate the intensity of snowfall. Let’s take an example :

METAR LUDO 050000Z 00000KT 1000  +SN FEW015ST SCT035 OVC100 M01/M01 Q1025 RH 100%.

In the above example, the weather phenomenon is snow which is shown in METAR as +SN. ‘+’ indicates heavy snowfall(intensity of snowfall).

Similarly, rain is reported in METAR just like snow as discussed above. From the above example:

METAR LUDO 050000Z 00000KT 1000  +RA FEW015ST SCT035 OVC100 26/20 Q1025 RH 69%.

As shown in the example RA indicates rainfall and plus sign shows its intensity i.e heavy rainfall.

Phenomenon                        Symbol

Rainfall                                  RA

Drizzle                                  DZ

Thunderstorm + Rain           TSRA

If more than one phenomenon during reporting a METAR then more severe phenomena is reported first and then the other least significant weather phenomena. For example, if a thunderstorm and rain both are occurring at the same time then a thunderstorm is written first, and the rainfall i.e TSRA.

Snow/Rain Reporting in SYNOP:

Reporting of rainfall alone without snowfall is discussed in : How to Report Rain In a Weather Synoptic Observations (SYNOP)/ FM-12. In this post, we will discuss how to report snowfall and how to convert snow into equivalent rainfall. First, we discuss how to report snowfall in SYNOP:

SNOWFALL Reporting in Weather SYNOP:

There is a group 4ESSS in section 3 to report snowfall in SYNOP.

here 4 is the indicator of the snow group in section 3. E is code for the ground state. SSS is the amount of snowfall in the preceding three hours in cm.

Code for E is:

0  predominantly covered with ice

1 compact or wet snow covering less than half of ground

2 compact or wet snow covering more than half of the ground but not completely covered

3 even layer of compact or wet snow cover entire ground

4 uneven layers of compact or wet snow cover entire ground

5 loose dry snow covering less than half of ground

6 loose dry snow covering more than half of the ground but not completely covered

7 even layer of loose dry snow covering the entire ground

8  uneven layer of loose dry snow covering entire ground

9 snow covering ground completely with deep drifts .

for example, if there is 5.2 cm snowfall in three previous three hours and the state of the ground is completely covered by an uneven layer of snow we will report snowfall in SYNOP as 44052 i.e first digit 4 is an indicator of snow group,2nd digit 4 is for the state of the ground and last three digits are for amount of snowfall in cm which was 5.2 cm.

According to WMO standards, Snowfall is reported in cm in SYNOP.We can convert snowfall from cm to inches by value in cm divided by 2.54.

HOW to Report Rainfall Equivalent of Snowfall in SYNOP:

Snowfall is converted into its equivalent water content and then that water content is reported as rain in the rainfall group. As discussed above snowfall is reported in the 4ESSS group. Similarly, its equivalent rainfall is reported in all rainfall groups of SYNOP which are applicable according to the time of SYNOPTIC hour which is discussed in the rainfall reporting post in detail. To convert snowfall into equivalent water follow the following procedure:

  • Put some hot water in the rainfall measuring cylinder. Measure water and add this water to the rain gauge. The snow in the rain gauge will melt. Pour water from the rain gauge into the rain measurement cylinder. Measure the water. Subtract the amount of warm water added to it. For example, if we add 5mm of warm water and after melting snow, we get 10 mm then we have to subtract 5 from 10 and we get 5mm of rainfall as snow equivalent water.
  • Another method to find rainfall equivalent snow water is to heat up the container of rain gauge containing snow. Measure the water in the rainfall measurement cylinder.
Holds BS Degree in Electrical Engineering and MS Degree in Meteorology and currently working in the field of meteorology as an assistant weather forecaster. Love helping people know what the weather is doing. Researcher of the weather conditions and make forecasts for several different locations.

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