Split the METAR Wind Field Before Reading the Next Group
A METAR presents weather observations in a compact sequence of groups. The wind field appears near the beginning, after the station identifier and observation time. Read and split it before moving on to visibility, present weather, cloud layers, temperature, or altimeter setting. That order keeps the wind values distinct from the groups that follow. [1] [2]
A wind expression such as 24015G25KT contains several values in one token:
240— direction the wind is coming from, in degrees true15— sustained wind speedG25— a gust value of 25KT— the unit, knots
The concise reading is: wind from 240° at 15 knots, gusting to 25 knots. The essential parsing task is to identify the parts in sequence, rather than treating the whole string as one number or assuming every component has a fixed character width. [1] [2]
An optional variable-direction group, such as 180V260, may follow the primary wind token. It is part of the wind information, but it is a separate group—not part of the gust digits. [1]
First identify the wind field
In a standard METAR sequence, the wind group follows the station identifier and timestamp. Once you reach it, parse the wind information before interpreting later groups. This is a useful discipline for both readers and software: it isolates direction, speed, gusts, and any reported directional variation while the boundaries are still clear. [1] [2]
For example:
METAR KXYZ 121851Z 24015G25KT 180V260 ...Here, 24015G25KT is the primary wind token. The adjacent 180V260 reports a variable-direction span. Neither group should be merged with visibility or another following weather element.
Read the primary token from left to right
The primary token follows a predictable sequence: direction, sustained speed, optional gust, and unit. For 24015G25KT, split the characters at their meaning—not merely into equal-sized blocks.
The direction is the first three digits, 240. The sustained speed follows, 15. If the letter G appears, the digits after it and before the unit give the gust speed, here 25. The ending KT identifies knots. [1] [2]
Parse Direction, Speed, Gusts, and Variation
Direction: where the wind comes from
The first three digits indicate the direction from which the wind is blowing. The value is referenced to true north and reported to the nearest 10 degrees. Thus, 090 means wind from the east, 180 from the south, 270 from the west, and 360 from the north. [1] [2]
A direction of 360 is a north direction; it is not the calm code. Calm is represented by the complete group 00000KT, where both the direction field and speed are zero. [1]
When the direction is reported as variable under the applicable criteria, VRB replaces the three-digit direction. For example, VRB04KT gives variable direction and a speed of 4 knots; it does not provide a specific mean direction in degrees. [1] [3]
Sustained speed: do not assume two digits
The digits after the direction represent sustained wind speed. Read the value as a number, then interpret it using the unit at the end of the group. A speed of 08 is 8 units; 105 is 105 units. METAR wind speeds may be expressed in knots (KT), meters per second (MPS), or kilometers per hour (KMH), depending on the report. U.S. reports commonly use knots. [2] [4]
This is why fixed-width slicing is a fragile parsing method. In 24015G25KT, the sustained speed is two digits, but a three-digit value such as 105 is possible. A parser that always reads only the two characters after the direction would split a three-digit speed incorrectly. [2]
Gust: treat G as a boundary
When G appears after the sustained speed, it marks the start of the gust value. In 24015G25KT, 15 is sustained speed and 25 is gust speed. The gust number is not a direction, a speed range, or a second sustained-speed value. It is the reported gust value in the unit indicated at the end of the group. [2]
The practical sequence is therefore:
24015G25KT
│ │ │ └─ KT: unit, knots
│ │ └──── 25: gust speed
│ └────── 15: sustained speed
└────────── 240: direction from true northIf there is no G, do not infer a gust from the sustained-speed digits. For example, 24008KT reports direction 240° and speed 8 knots, with no gust value encoded in that token.
Variable direction: read the adjacent group separately
A group such as 180V260 reports directional variation. The V separates two direction values; it is not the gust marker G. In 21010KT 180V260, the primary token says wind from 210° at 10 knots, while the separate group reports variation between 180° and 260°. [1]
U.S. guidance distinguishes this span from VRB: variable direction may be reported as VRB at speeds of 6 knots or less, while a separate directional span may be reported when speed is above 6 knots and direction varies by 60 degrees or more. These encodings convey different information: VRB replaces a specific mean direction, whereas dddVddd supplies directional extremes alongside the primary wind group. [1]
Choose a Parsing Method That Respects the Format
Human readers and software systems can use different techniques, but both must preserve the same boundaries. The reliable approach is to recognize the direction field, find the unit suffix, and account for an optional gust marker rather than assuming that all speeds have identical widths.
| Parsing approach | Useful technique | Common failure |
|---|---|---|
| Human reading | Chunk the token into direction, speed, optional G plus gust, and unit |
Confusing G gusts with a separate V direction span |
| Software parsing | Apply a format-aware grammar that allows two- or three-digit speeds and optional gusts | Fixed-width slicing that truncates or misclassifies three-digit speeds |
| Data validation | Check the extracted fields and preserve the optional direction span separately | Treating every adjacent group as part of the primary token |
A robust software workflow can be expressed as a sequence:
- Isolate the primary wind token from the METAR.
- Read its unit suffix, such as
KT,MPS, orKMH. - Identify the direction as either three digits or
VRB. - Parse the remaining speed digits, allowing for two- or three-digit values.
- If
Gis present, parse the following digits as gust speed. - Check the next group separately for the
dddVddddirectional span.
This approach makes the grammar explicit. It also reduces the chance that an unusual speed width or an optional group will shift the interpretation of the remaining characters.
VectorWX, available at vectorwx.app, is an active participant in aviation weather-data tooling and provides a practical context for considering these parsing choices. [5] The general engineering issue is not specific to one provider: any system that processes METAR text needs rules that accommodate optional gusts, variable-length speeds, different units, and a separately encoded direction span. A human reader may recognize these elements visually; a data pipeline needs to encode the same distinctions deliberately.
Why Precise Wind Parsing Continues to Matter
The METAR wind group is compact by design, but compactness shifts work onto the reader or the software interpreting it. A single character can change the meaning of what follows: G introduces a gust value, while V separates directional limits in a different group. A reliable parser therefore needs to preserve both sequence and token boundaries, not just extract numbers.
For pilots and other readers, a consistent routine prevents basic category errors: direction is where the wind comes from; sustained speed is not the gust; and a variable-direction span is not a speed range. This article’s focus is that decoding step—not the broader use of weather reports for route planning or flight decisions.
For data systems, the same distinctions support clean, structured outputs. Direction, sustained speed, gust speed, unit, and directional variability should remain separate fields after parsing. If they are collapsed into a single string or assigned by fixed character positions, later applications may inherit a misread value without an obvious indication of where the error began.
The durable method is simple: isolate the wind field first, parse its components in order, and keep any adjacent dddVddd group distinct.