Surface Observations Study Guide
and METAR Reference

This page can help you study for the standard National Weather Service (NWS) test that one must take in order to become a certified surface observer in the United States. It is also a handy reference for understanding American METAR reporting and coding practices.

I compiled this guide while studying for my own certification test, but that was at a point in my career where I was already accustomed to reading and using METAR observations. Thus I left a lot of information that I already knew out of the guide. I am working on revising the guide to be comprehensive, not glossing over the more commonly known information. If you are already a student of meteorology, you probably do not need what I left out, and you may not even need all of the material that I did include. Nonetheless, this page is best used as a companion to the source material (see below).

The official study guide for the test is the "blue book," the NWS Training Guide in Surface Weather Observations. That book does not actually contain all the answers to its own questions, which is silly. It references the NWS Observing Handbooks, numbers 7 and 8, for answers to some questions. In the time since the training guide was last updated in 1998, these handbooks have been superseded by FAA Order 7900.5B. My guide (this page) was derived from the blue book and the FAA document. (Please see the disclaimer.)

This guide offers three levels of "difficulty:"

The hover feature in Level 1 relies on support for CSS opacity, but that should not be a problem for modern browsers. If you switch to it and you see all the answers, try a newer browser.

General rules

What is the order of elements in a METAR report? 
How often must one do time (accuracy) checks on the official station clock? 
How long must the station retain carbon copies of forms? 
What if SPECI criteria are met at the time of a normal METAR? 
Where does the station ID go in the report? 
What determines the time used in the METAR report? 
What determines the time of a SPECI report? 
What is the maximum allowable time before the scheduled observation time that one can begin taking the ob? 
What time format is used in column 2 of the form? 

Wind

What numeric value is used to code north? 
How is speed coded on the manual form? 
How would this be coded: Wind direction indicator says 250°, and air movement is detected, but there is no reading on the speed indicator 
How would this be coded: Wind direction is varying from 200 to 300 deg, with a speed of 4 knots? 
What are the criteria to record direction as variable? 
What is the minimum fluctuation to declare a wind gust? 
How is direction encoded? 
What is the criterion for recording a Peak Wind? 
What is the format of an encoded Peak Wind (in remarks)? 
What type of north is used for wind direction? 
What are the criteria for dddVddd format variable wind? 
What is the main difference in squalls and gusts? 
What defines a squall? 
What defines a wind shift? 

Visibility

Define visibility. 
Define prevailing visibility. 
When observing visibility, from how many locations should one take an observation? 
What are the best objects to use for nighttime visibility markers? 
What are the reportable values for a manual observing station? 
When is it necessary to report sector vis? 
How are sector visibilities to be reported? 
What are the criteria for variable vis? (i.e., when should one not average) 
How is variable vis reported? 
When is the tower vis to be reported? 
How is tower vis reported? 
Define "runway visual range." (here abbreviated as RVR) 
Where does RVR go in report? 
When is RVR reported? 
What is the METAR format of RVR? 
What are the reportable RVR values? 
Can variable RVR be reported? 
What should the observer do if there are problems with the RVR sensor? 

Weather

Define "light rain." 
Define "moderate rain." 
Define "heavy rain." 
Define "light ice pellets." 
Define "moderate ice pellets." 
Define "heavy ice pellets." 
Determine -RA or -PL from accumulation rate 
Determine RA or PL from accumulation rate 
Determine +RA or +PL from accumulation rate 
Determine -SN or -DZ from visibility 
Determine SN or DZ from visibility 
Determine +SN or +DZ from visibility 
What defines the beginning of a thunderstorm? 
What defines the end of a thunderstorm? 
When obscuring phenomena or other precipitation is also present, how should the intensity of SN, DZ types be reported? 
What is the maximum allowable visibility for heavy snow? 
What is the maximum allowable visibility for moderate snow? 
Give the proper order of weather types in the report. 
List weather types that cannot be assigned intensity. 
When is lightning reported in present weather? 
How does one note the direction from the station where vicinity phenomena are observed? 
How would one code "vicinity patchy fog?" 
When is the presence of volcanic ash reported? 
What are the criteria to report BR, DU, FU, SA, HZ, PY? 
Define "shallow" or "partial" fog. 
Define "drifting" as it applies to snow, dust, etc. 
Define "blowing" as it applies to snow, dust, etc. 
Define "showers." 
What produces a thunderstorm? 
Define "freezing precipitation." 
What visibility criteria are associated with an obscuration? 
How would one code "thunderstorm with showers?" 
Give the criteria defining a sandstorm or duststorm. 
Give the criteria defining a heavy sandstorm or heavy duststorm. 
Snow and blowing snow are occurring. You can't tell if snow is actually falling. What do you report? 
How does one determine the intensity of snow occurring alone (without other weather)? 
When may FG be reported only with qualifiers? 
What are the temperature range and visibilities associated with fog? 
What are the temperature range and visibilities associated with freezing fog? 
What are the differences in reporting hail with GR versus GS? 

Sky

Define "ceiling". 
What fraction of sky cover is coded VV? 
What fraction of sky cover is coded SKC? 
What fraction of sky cover is coded FEW? 
What fraction of sky cover is coded SCT? 
What fraction of sky cover is coded BKN? 
What fraction of sky cover is coded OVC? 
When an obscuration layer is present, what remark is included in the ob? 
What should one do if ceiling height is variable? 
What should one do if sky coverage is variable? 
What is the maximum number of sky cover layers that can be reported? 
What is the transmissivity requirement of sky cover layers? 
Define "obscuration." 
What if a surface-based obscuration covers 8/8, but the sky can be seen through it? 
What if an obscuration aloft covers 8/8, but the sky can be seen through it? 
What if a surface-based obscuration covers 8/8, but the sky is hidden? 
What if an obscuration layer aloft covers 8/8, and hides 6/8 of the sky? 
What is the rule on coding the layer of a surface-based obscuration? 
In what order are sky cover layers reported? 
What is the resolution to which sky cover layer heights less than or equal to 5000 ft are reported? 
What is the resolution to which sky cover layer heights of at least 5000 ft, but less than or equal to 10000 ft are reported? 
What is the resolution to which sky cover layer heights of at least 10000 ft are reported? 
When a sky cover value falls halfway between two reportable amounts, what is reported? 
What is the coded height of a layer 50 feet or less above the surface? 
How would one use the observed height where a ceiling balloon disappears? 
When several layers are reported as broken, what is the ceiling? 
What are the criteria for variable ceiling? 
How does one code a sky cover layer at an elevation below that of the station? 

Temperature and dewpoint

Temperature follows which element in a METAR/SPECI? 
How is a missing temperature observation coded? 
Temperature and dewpoint are determined to what precision? 
When ventilating a psychrometer, when is the dry-bulb thermometer read? Are there exceptions to this rule? 
When is dewpoint reported with respect to ice? 
When is it not necessary to use the wet-bulb temperature in order to determine the dewpoint? 
How should 24-hour maximum and minimum temperatures be recorded in columns 57-58 of the MF1M form? 
Describe the rules for rounding and coding negative temperatures and dewpoints. 
When reading thermometers, which of the wet/dry bulbs are read first? 

Pressure

If two aneroid instruments are used to determine altimeter setting, how often should they be compared to each other? When should the comparison be entered in column 65 of the manual form? 
When two instruments are read to determine the altimeter setting, and the readings are different, which reading do you use as altimeter setting? Why? 
When using an aircraft-type altimeter to determine the altimeter setting, to what height should you set it to before reading it? How often should you reset the indicated height? 
When pressure values fall in between reportable values, how should one round to arrive at a reportable value? 
How is the 12-hour mean temperature derived for the purpose of pressure calibration? 
What are the criteria to include a pressure change remark? 
What units are used for sea-level pressure? 
The barograph correction value should be entered in the MF1M form to the nearest... 
Station pressure is determined by adjusting the corrected barometric pressure to compensate for the difference between the height of the barometer and what? 

Remarks

What is the order of remarks? 
What is the order of the additive data? 
What does NOSPECI mean when present in an encoded observation? 
How would one code obscuration clarifications? E.g., how would one indicate in remarks that snow obscures 5/8 sky? 
When is snow depth entered in column 61 of the MF1M form? 
When is a 24-hour precip total group included? 
When is a snow depth (4/) group included? 
What is the format of a pressure change remark? 
What is the format of a "snow increasing rapidly" remark? 
What are the three elements of a lightning remark? 
What are the abbreviations and definitions of lightning flash frequencies for a lightning remark? 
What is the format of a peak wind remark? 
When does the timestamp on a remark have hours and minutes? 

Remarks order

Remark mnemonic (syllables) 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 

Additive data order

Additive mnemonic 
1 
2 
3 
4 
5 
6 
7 

SPECI criteria

Wind shift 
Visibility 
Runway visual range 
Tornado, funnel cloud, waterspout 
Thunderstorm 
Hail 
Freezing precipitation 
Ice pellets (sleet) 
Squall (also give definition) 
Ceiling 
Sky condition 
Volcanic eruption 
Aircraft mishap (always, unless...) 
Any meteorological condition which the observer finds important 

last updated 2012.04.04 :: return home

Though all efforts have been made to present correct information, the information provided here is given without any warranty or guarantee of accuracy. The author of this website, Jake Wimberley, will not be held responsible for any errors in the content of this page, or for any failures by the user in passing any certification exam the user may take. Use at your own risk.