SYNOP

Key takeaways

SYNOP belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SYNOP to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SYNOP from memory before moving on to harder problems.

Reference excerpt

SYNOP (surface synoptic observations) is a numerical code (called FM-12 by WMO) used for reporting weather observations made by staffed and automated weather stations. SYNOP reports are typically sent every six hours by Deutscher Wetterdienst on shortwave and low frequency using RTTY. A report consists of groups of numbers (and slashes where data is not available) describing general weather information, such as the temperature, barometric pressure and visibility at a weather station. It can be decoded by open-source software such as seaTTY, metaf2xml or Fldigi. SYNOP information is collected by more than 7600 staffed and unstaffed meteorological stations and more than 2500 mobile stations around the world and is used for weather forecasting and climatic statistics. The format of the original messages is abbreviated, and some items are coded.

Message format Following is the general structure of a SYNOP message. The message consists of a sequence of numeric groups, which may also contain slashes (indicating missing data) in addition to numeric digits. Leading numbers are fixed group indicators that indicate the type of observation following, and letters are replaced with numbers giving the weather data. Messages from shipboard weather stations, and in different regions of the world, use variations on this scheme.

YYGGiw IIiii iRiXhVV Nddff (00fff) 1snTTT 2snTdTdTd 3PoPoPoPo 4PPPP 5appp 6RRRtR 7wwW1W2 8NhCLCMCH (9GGgg)

YYGGiw: the date and time of the observation; YY for the day of the month, GG for the hour of the observation in UTC; iw for the manner of wind observation (a code number: 0 for estimated wind speed in meters per second, 1 for measured wind speed in meters per second, 3 and 4 likewise but in knots, or slash for no wind speed observations). IIiii: weather station identification code; II for a block number allocated (by the WMO) to a country or a region of the world, for example 02 for Scandinavia or 72 and 74 for the continental US; iii is the code of an individual station within a block. (For example, 02993 is the code of the weather station on Märket, 74794 of Cape Canaveral). iRiXhVV: iR indicates whether precipitation data is included or omitted. This is a code number from 0 to 4, with 0, 1 and 2 meaning data is included, and 3 and 4 indicating no precipitation data. iX is a code number indicating the manner of station operation, and the format used in group 7wwWW; codes 1, 2 and 3 indicate a staffed station, while codes 4 to 7 indicate an automatic station. h indicates the height above the surface for the base of the lowest cloud seen: 0 means from 0 to 100 feet or 0 to 50 meters, 9 means the base of clouds is 2500 meters or higher or that there are no clouds. VV indicates horizontal surface visibility: For codes 00 to 50, this indicates visibility in tenths of a kilometer (hectometers), for example "15" means 1.5 km. For codes 56 to 80, 50 is subtracted, and the resulting number indicates visibility in kilometers, for example "66" means 16 km. Codes 81 to 88 indicate visibility in a multiple of 5 km; "81" for 35 km, "88" for 70 km. Code 89 indicates visibility greater than 70 km; Codes 90 to 99 are used for shipboard observations, from "90" for less than 1⁄16 mile visibility, "95" for 1 mile, "99" for greater than 30 miles. Nddff and 00fff: N: total cloud cover in eighths of the sky (oktas); "0" for no clouds, "4" for half (4⁄8) of the sky obscured, "8" for total cloud cover, "9" for an obscured sky or a situation where cloud cover can't be estimated, "/" for no measurement in the case of automatic stations. dd for true wind direction in tens of degrees, with "00" meaning "no wind", "18" for wind from the south (175° to 184°), "36" for wind from the north (355° to 004°). ff for wind speed, in the units specified in the YYGGiw group. If wind speed is 99 units or more, this group will have the code "99" and will immediately be followed by the group 00fff, with the wind speed indicated there instead. 1snTTT: air temperature. Code sn indicates the sign, 0 for positive, 1 for negative degrees; TTT has the temperature in tenths of a degree Celsius. 2snTdTdTd: dew point temperature. Like the preceding 1snTTT group, sn stands for the sign, and TdTdTd has the temperature in tenths of a degree Celsius. If sn is 9, the last three digits are instead relative humidity in percent, from "000" to "100". 3PoPoPoPo: air pressure at station level, in tenths of a hectopascal. If the pressure is more than 999.9 hPa, the leading thousands digit is dropped; for example 30240 means a pressure of 1024.0 hPa. 4PPPP: air pressure at sea level, in tenths of a hectopascal, derived from station pressure. 5appp: three-hour pressure tendency. The digit a encodes the manner of pressure change, for example "3" means "decreasing or steady, then increasing; or increasing, then increasing more rapidly". Codes 1 to 3 indicate higher pressure than 3 hours ago, codes 6 to 8 indicate lower pressure, while codes 0, 4 and 5 indicate approximately the same pressure. Digits ppp indicate the actual pressure change, in tenths of a hectopascal. 6RRRtR: amount of precipitation, in millimeters. Digit tR indicates the length of time covered by this group, such as a measurement over the past 6, 12, 18 or 24 hours. 7wwW1W2: present (ww) and past (W1W2) weather. Staffed and automatic stations use different formats and tables for this group. These are looked up from a table, with various different codes, such as "35" for "severe duststorm or sandstorm, has begun or has increased during the preceding hour". 8NhCLCMCH: cloud types. Nh indicates amount of low-altitude clouds (in oktas, like in the Nddff group), or if none, the amount of medium-altitude clouds. CL, CM and CH indicate the types of low, medium, and high-altitude clouds present, with codes looked up from tables. 9GGgg: actual time of observation, in hours and minutes UTC, used when the actual time differs more than 10 minutes from the time reported in the YYGGiw group. After this first section, stations may include additional sections, prefixed by 222// (section 2, for staffed coastal stations, reporting sea surface temperature and wave data), 333 (section 3, used only in some areas of the world, for the "state of the sky in the tropics"), or 555 (various national code groups).

Example message This observation was from April 1, 2022, from LaGuardia Airport in New York City.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with SYNOP

Start with the simplest possible case. Write down what SYNOP claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to SYNOP before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about SYNOP ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of SYNOP

In research: SYNOP appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses SYNOP in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: SYNOP is common in secondary-school and first-year university syllabi. It links to neighbouring topics Earth sciences data formats, Meteorological data and networks, so understanding it makes those chapters shorter.
In everyday life: Look for SYNOP outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study SYNOP in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SYNOP means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain SYNOP out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SYNOP in simple terms?

SYNOP (surface synoptic observations) is a numerical code (called FM-12 by WMO) used for reporting weather observations made by staffed and automated weather stations. SYNOP reports are typically sent every six hours by Deutscher Wetterdienst on shortwave and low frequency using RTTY.

Why does SYNOP matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study SYNOP?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on SYNOP.