38
votes
Accepted
What is the difference between mist and fog?
Quoting from the METAR decoder:
BR Mist (Foggy conditions with visibilities greater than 5/8 statute mile)
FG Fog (visibility 5/8 statute mile or less)
You may ...
- 16.7k
34
votes
Accepted
What does a dollar sign mean in a METAR?
A maintenance indicator sign, $, is included when an ASOS/AWSS (Automated Surface Observing System / Automated Weather Sensor System) detects that maintenance is needed on the system.
Reference: http:...
- 6,329
30
votes
Accepted
How is wind direction reported (blowing from or blowing to)?
As far as METARs are considered, the wind direction gives the direction from which the wind is coming. From METAR definitions:
Wind Direction.
The direction, in tens of degrees, from which the wind ...
- 99.9k
27
votes
What is the difference between mist and fog?
The main difference between the fog and mist is their density and as a consequence, the visibility. From UK Met office:
... they are two distinct terms for a similar phenomenon. Visibility less ...
- 99.9k
24
votes
Accepted
Why is mist abbreviated BR on METARs and TAFs?
According to a CFI's lesson plan on the internet, it comes from the French word for mist, brume.
- 23.2k
19
votes
How is wind direction reported (blowing from or blowing to)?
Wind numbers say where the wind is coming from. Wind 270 means that the wind is coming from the west, and blowing towards the east. If you point west (270), you will have the wind in your face as a ...
- 4,077
17
votes
Accepted
What does W13/S3 mean in this METAR report?
From metar-taf.com:
Information about the sea
Weather stations located at sea can report the temperature of the sea water and the height of the waves.
W12/S8 means ...
- 13.2k
15
votes
Why do NOTAMs consist of code instead of plain language?
The NOTAM format is from the time when people still would call the value of individual bits over a phone line.
Ok, that may not have happened, but my point is that data transfer was incredibly slow ...
- 82k
14
votes
How is wind direction reported (blowing from or blowing to)?
I always use the old saying;
The North wind doth blow, and we shall have snow...
Since this saying originated in England and in England it is colder to the North, we can conclude that a North wind ...
- 461
14
votes
Accepted
What constitutes a wind gust in a METAR report?
The definition of "Wind Gust" for METAR reports can be found in the Federal Meteorological Handbook No. 1, chapter 5:
5.4.4 Wind Gust. The wind speed data for the most recent 10 minutes shall be ...
- 9,132
14
votes
Accepted
What geographical area does a METAR cover?
Geographically METARS are for a single specific location (the station identified in the report).
An automated METAR with no human supervision covers the conditions within approximately 6 inches of ...
- 68.2k
14
votes
Accepted
What do multiple slashes in METAR mean?
Complete, unless you want to know the height of base of those TCU's!
The bulk of the information you're after can be found in AIS-GEN 3.5 Section 10.17 - AUTO METAR coding
In describing the coding ...
- 31.1k
13
votes
What are the criteria for "variable" in METAR reports?
There are two official sources to take into account:
ICAO Annex 3 to the Chicago Convention is the reference for meteorological information. Annex 3 applies to all ICAO members (countries), unless ...
- 69.9k
13
votes
Accepted
Why does GR mean hail in a METAR?
The French word for hail is grêle which is abbreviated GR. METAR is an international standard so you will see some non-English words included in the METAR.
- 5,759
13
votes
What does W13/S3 mean in this METAR report?
These values are related to sea state, and originate from a helideck. W13/S3 means:
Sea surface temperature = 13± 0.5°C
Waves are slight, that is between 0.5m and 1.25m
METAR from helidecks, like ...
- 69.9k
13
votes
Accepted
Are airport codes with digits valid or pseudo ICAO codes?
No, those are not ICAO codes. ICAO airport identifiers consist of four letters, full stop. But that does not mean that any code which is other-than-four-letters is "invalid" or "...
- 13.2k
12
votes
Why don't we get more user-friendly weather reports than METARs?
One use case where the compact METAR format is tough to beat is rapidly scanning meteorological trends. For that purpose, METARs are user friendly in the sense that they are expert friendly.
For ...
- 5,676
12
votes
What are ISA +10, ISA -15 and ISA -30?
First of all:
I have found out that an ISA atmosphere is:
15 degC temperature 05 degC dewpoint 1013.25 pressure
Not entirely correct. The temperature and pressure are ISA values at mean sea ...
- 2,164
12
votes
Accepted
What does I1001 mean in a METAR remarks?
It indicates ice accretion (buildup). This seems to be very obscure, I finally found it in some NOAA release notes for ASOS software v3.07:
(S01126) ADD ICE ACCRETION REMARK TO METAR/SPECI ...
- 71.5k
11
votes
Accepted
What does this METAR remark mean? 'RMK RWY 7 ATIS G LL'
I have a suspicion that you're looking at KLZU's METAR. Basically, they're inputting their manually written METAR into the system, and when they send it out they're adding the Runway in Use(RWY 7) and ...
- 6,329
11
votes
Accepted
What are ISA +10, ISA -15 and ISA -30?
ISA+X is the ISA atmosphere with X°C of variation.
It´s used to determine how diferent (in terms of Temperature) of the Standard the actual condictions are and adjust the calculations.
ISA as you ...
- 151
11
votes
What is the difference between RVR and visibility?
The definitions are somewhat different:
Visibility for aeronautical purposes is the greater of:
the greatest safe distance at which a black object of suitable dimensions, situated near the ground, ...
- 53.7k
11
votes
Accepted
How can I check before my flight that the cloud separation requirements in VFR flight rules are met?
Make it simple:
OVC: It's a ceiling. The only thing you're concerned about is the altitude of the base.
BKN: It's also considered a ceiling. The only thing you're concerned about is the altitude of ...
- 125k
10
votes
Accepted
What does N mean after a runway visual range (in a METAR)?
RVR often has a letter at the end to indicate the visibility trend, so you can tell if it's going to improve (and maybe you should circle overhead for a while) or worsen (and you should consider going ...
- 12.6k
9
votes
Accepted
Is it normal for visibility to be missing from the METAR?
My questions are:
Is it really normal to see reports without viz?
Yes! Well, maybe not "normal", but it does happen. Automated weather stations are like another piece of equipment and ...
- 58.5k
9
votes
Accepted
Can the "G" and "VRB" wind conditions be combined in METARs?
Yes, it is possible for a METAR to contain both VRB and G. VRB10G25KT is valid.
The reason it rarely happens is because, as wind speed increases, major variations in wind directions tend to disappear....
- 35.7k
8
votes
Accepted
Does the "Maintenance Indicator" sign on a METAR imply we can't trust it?
Not necessarily.
Automated stations have a number of sensors for detecting,
Wind speed and direction
Visibility
Obscurations to vision
Cloud coverage and ceiling
Temperature and dew point
Barometric ...
- 99.9k
8
votes
Accepted
How to programmatically access AIP data, METAR, TAF, NOTAMs?
ICAO is offering a very nice API for retrieval of, for example, aerodrome names/ICAO codes and NOTAM's. It is currently in public beta, which means that it is free to use. Once they finish testing it, ...
- 35.7k
8
votes
Accepted
What is 0650// in the metar?
This is most likely the minimum visibility (in metres), with the compass direction given as "//" (not possible to determine). A single slash is more common, i.e. ...
- 171
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