Processing METAR weather reports

In pmetar: Processing METAR Weather Reports

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  tidy = FALSE
)

Package pmetar

Pmetar is an R package that allows to download and parse current or historical METAR (Meteorological Terminal Aviation Routine Weather Report) reports, mainly for airports.

It has to be underlined that the package pmetar is not intended for flight planning or navigation.

Downloading a current METAR weather report

For downloading a METAR report we need to know an airport four letters ICAO code, International Civil Aviation Organization, or three letters IATA code, International Air Transport Association.\ Let's download a current METAR weather report for Warsaw Okecie Airport. Its ICAO, International Civil Aviation Organization, code is EPWA. A report can be got from Aviation Weather Center https://aviationweather.gov/data/metar/

library(dplyr)
library(pmetar)
metar_get("EPWA")

Now let's take a look at Newark Liberty International Airport, EWR IATA code. This type of code you find on your airplane tickets.

metar_get("EWR")

The above message is intended for professionals like pilots or air traffic controllers. The first purpose of preparing the pmetar package was the need of extracting wind speed and air pressure values from METAR reports for some airports in Poland. Later the package functionality was extended. We will go through the main functions with a historical METAR report from John F. Kennedy International Airport.

Downloading historical METAR weather report

The function metar_get_historical() allows to download METAR weather reports for a defined period of time. The default online source of METAR reports, from = "iastate" is the Iowa Environmental Mesonet web page of Iowa State University ASOS-AWOS-METAR http://mesonet.agron.iastate.edu/AWOS/.

dm <- metar_get_historical("JFK", start_date = "2020-06-27", end_date = "2020-06-29", from = "iastate")

dm <- c("202006270000 METAR KJFK 270000Z AUTO 19007KT 10SM CLR 23/18 A2990 RMK T02300180 MADISHF",
        "202006270005 METAR KJFK 270005Z AUTO 19008KT 10SM CLR 24/18 A2990 RMK T02400180 MADISHF",
        "202006270010 METAR KJFK 270010Z AUTO 20008KT 10SM CLR 24/18 A2990 RMK T02400180 MADISHF",
        "202006270015 METAR KJFK 270015Z AUTO 21005KT 10SM FEW110 24/18 A2990 RMK T02400180 MADISHF",
        "202006270020 METAR KJFK 270020Z AUTO 21005KT 10SM SCT110 24/18 A2990 RMK T02400180 MADISHF",
        "202006270025 METAR KJFK 270025Z AUTO 23008KT 10SM SCT110 24/17 A2990 RMK T02400170 MADISHF")

head(dm)

The second backup source, from = "ogimet" is Weather Information Service provided by Ogimet http://www.ogimet.com/. Please take into consideration that Ogimet usually blocks too frequent requests for data due to the server overload, the requested period is limited to 31 days and for the most of airports METAR reports are available from the beginning of the year 2005.

metar_get_historical("JFK", start_date = "2020-06-27", end_date = "2020-06-29", from = "ogimet")

In the package version from 0.4.0 it is possible to check the syntax of downloaded METAR reports with the function metar_is_correct(). Also in several functions the additional parameter check was implemented. The default value is TRUE. If it is set to FALSE decoding of METAR reports should work as in the previous package versions.

metar_is_correct(dm[1:5])

Let's one report with incorrect one and check how it works.

dc <- c(dm[1:5],
        "202006261625 SPEC KJFK 261625Z AUTO 28009KT 10SM CLR 30/12 A2995 RMK T03000120")
metar_is_correct(dc)

It is possible to select incorrect reports from input.

dc[!metar_is_correct(dc)]

The function has the parameter verbose which helps to identify incorrect reports. The index and the incorrect METAR are displayed

metar_is_correct(dc, verbose = TRUE)

The check of syntax was implemented in the following functions, however it must be enabled by setting check = TRUE. Only in the function metar_decode() it is set to TRUE by default.

• metar_decode()
• metar_dew_point()
• metar_dir()
• metar_gust()
• metar_pressure()
• metar_speed()
• metar_temp()

We will parse the last report from the above dm. In historical reports dates and hours are placed at the beginning of texts. Normally it's extracted and parsed, but for now let's remove it

(dm[length(dm)])
my_report <- substr(dm[length(dm)], 14, nchar(dm[length(dm)]))
my_report

It has to be noted that the report part after the RMK, remarks, is not analyzed, except the temperature information, which is provide more precisely in remarks.

Decoding main informatin from a single METAR weather report

The first element METAR indicates the text consist of a METAR weather report. If a report was issued under special circumstances, a text SPECI replaces METAR.

Airport

The second four letters element, KJFK identifies an airport from which a METAR issued. We can extract it

metar_airport(my_report)

and find the KJFK geographical coordinates, elevation, airport IATA code, airport name and source of information.

metar_location(metar_airport(my_report))

Day and time

The third element 282355Z includes a day of a month, a time and a time zone.

metar_day(my_report)
metar_hour(my_report)
metar_time_zone(my_report)

The fourth element, in our case AUTO informs that a report was generated automatically. If a report was manually corrected it is COR. This element is not taken into consideration by the package pmetar.

Wind speed and wind direction

Next, there is the text 07007KT where three first digits informs about a wind direction in degrees. Two next digits are a wind speed and the letters the end define units, here KT, hence a wind speed is in knots.

metar_dir(my_report)
metar_speed(my_report, metric = TRUE)
metar_speed(my_report, metric = FALSE)

The function metar_speed() reports a wind speed in m/s with the default value of the parameter metric = TRUE, or in knots when metric = FALSE.\ When a wind direction varies, a METAR report has additional component, like 140V200, which informs that a wind direction fluctuates from 140 to 200 degrees.

variable_direction_METAR <- "EPWA 281830Z 18009KT 140V200 9999 SCT037 03/M01 Q1008 NOSIG"
metar_dir(variable_direction_METAR)

In this case an output is character what can be useless for statistical calculations. If only main direction in the numeric format is needed, it is possible to set the parameter numeric_only = TRUE.

metar_dir(variable_direction_METAR, numeric_only = TRUE)

Visibility

The part 10SM is the visibility. In this case it's 10 statue miles. With the default value of the parameter metric= TRUE and numeric_only = FALSE we get output in meters. For metric = FALSE in statute miles.

metar_visibility(my_report, metric = TRUE)
metar_visibility(my_report, metric = FALSE)

When the visibility is described as CAVOK we have two options to decode it

metar_visibility("201711271930 METAR LEMD 271930Z 02002KT CAVOK 04/M03 Q1025 NOSIG= NOSIG=")
metar_visibility("201711271930 METAR LEMD 271930Z 02002KT CAVOK 04/M03 Q1025 NOSIG= NOSIG=", numeric_only = TRUE)

When the visibility is described as for example P6SM we can decode in two ways

metar_visibility("200005120845 METAR METAR MMGL 120845Z 27005KT P6SM FEW230 18/04 A3012 RMK 00190 062 903", metric = FALSE)
metar_visibility("200005120845 METAR METAR MMGL 120845Z 27005KT P6SM FEW230 18/04 A3012 RMK 00190 062 903", metric = FALSE, numeric_only = TRUE)

Weather conditions

The function metar_wx_codes() extracts and parses the below weather conditions codes.\ In the package versions starting from 0.4.0 the parameter sep with the default value ";" was introduce. It allows to avoid problems with saving output in .csv files. Two values are allowed, comma and semicolon. If you need to get the function output separated by commas just set sep = ",".

metarWXcodes

In our METAR examples part -RA informs about weather conditions.

metar_wx_codes(my_report)

This part of a METAR can be quite complex, like in the below example:

metar_wx_codes("202002022205 METAR KEWR 022205Z AUTO 24008KT 6SM -RA -SN BR SCT006 BKN014 OVC024 02/01 A2954 RMK T00200010 MADISHF")

Cloud coverage

Next part, SCT028 SCT035 BKN079, informs about a cloud coverage

metar_cloud_coverage(my_report)

Temperature and dew point

The temperature and the dew point can be extracted from two elements of a METAR report, before the RMK remarks marker 23/20 which can be found in the most reports. Or from the part after the RMK remarks marker T02300200, more precise but not always available.\ The temperature is coded in Celsius degrees, here 23/20, or more detailed in T02300200.

metar_temp(my_report)

If there is a letter M in the front of two digits, M23/00, or there is a digit one after T, T1230, the temperature is below zero Celsius degrees.\ The dew point can be decoded from the last two digits 23/20, or more detailed from T02300200. Dew points below zero Celsius degrees are decoded in the same method as above. For example 04/M03 or T00391033 mean that the dew point temperature is -3 Celsius degrees or more precisely -3.3 Celsius degrees.

metar_dew_point(my_report)

Here there is a report with the more precise temperature information in the RMK remarks part.

metar_temp("202001010851 METAR KEWR 010851Z 27010KT 10SM FEW030 BKN070 BKN100 BKN210 04/M03 A2969 RMK SLP054 T00391033 52012")
metar_dew_point("202001010851 METAR KEWR 010851Z 27010KT 10SM FEW030 BKN070 BKN100 BKN210 04/M03 A2969 RMK SLP054 T00391033 52012")

Pressure

In our example a pressure value is coded in the A2972 as inHg (inch of mercury). With the default parameter altimeter = FALSE, the function metar_pressure() returns a pressure in hPa.

metar_pressure(my_report)

The pressure value can be also presented in a METAR report as Q1008, already in hPa.

metar_pressure("EPWA 281830Z 18009KT 140V200 9999 SCT037 03/M01 Q1008 NOSIG")

If a pressure is needed in inHg (inch of mercury), the parameter altimeter has to be set to TRUE.

metar_pressure("EPWA 281830Z 18009KT 140V200 9999 SCT037 03/M01 Q1008 NOSIG", altimeter = TRUE)

Wind shear

Information about wind shear can be extracted with the use of the function metar_windshear().

metar_windshear("CYWG 172000Z 30015G25KT 3/4SM R36/4000FT/D -SN BLSN BKN008 OVC040 M05/M08 A2992 REFZRA WS RWY36 RMK SF5NS3 SLP134")

Runway visibility

Information about runways visibility can be extracted with the use of the function metar_rwy_visibility(), in meters.\ In the package versions starting from 0.4.0 the parameter sep with the default value ";" was introduce. It allows to avoid problems with saving output in .csv files. Two values are allowed, comma and semicolon. If you need to get the function output separated by commas just set sep = ",".

metar_rwy_visibility("CYWG 172000Z 30015G25KT 3/4SM R36/4000FT/D -SN BLSN BKN008 OVC040 M05/M08 A2992 REFZRA WS RWY36 RMK SF5NS3 SLP134")

or in feet

metar_rwy_visibility("CYWG 172000Z 30015G25KT 3/4SM R36/4000FT/D -SN BLSN BKN008 OVC040 M05/M08 A2992 REFZRA WS RWY36 RMK SF5NS3 SLP134",
                     metric = FALSE)

Putting all together

Decoding METAR reports

Let's come back to our dm list with historical METAR reports downloaded at the top of this document. Please notice that in all rows there are dates and hours in the front of METAR reports. It will be parsed and placed in the column METAR_Date below.

head(dm)

Now we can decode all elements and place them in the tibble. It is possible to choose between Metric (the default metric = TRUE) or Imperial (metric = FALSE) systems. Pressure values can be decoded in hPa (the default altimeter = FALSE) or in mmHg (altimeter = TRUE).\ In the package versions starting from 0.4.0 the parameter sep with the default value ";" was introduce. It allows to avoid problems with saving output in .csv files. Two values are allowed, comma and semicolon. If you need to get the function output separated by commas just set sep = ",". Also the parameter check with the default values TRUE was added. It allows to handle errors when the function is not able to decode METAR reports.

decoded_metars <- metar_decode(dm)

The following columns were created:

names(decoded_metars)

First rows of the tibble with decoded METAR reports:

print.data.frame(head(decoded_metars))

Let's take a look how the function handles the input data with one erroneous report.

metar_decode(dc)

The parameter check can set to FALSE and some values from incorrect reports can decoded. However the function can fail.

Decoding one METAR report with the function metar_print()

The function metar_print() it is possible to decode one report and display main parameters

metar_print(dm[1])

pmetar documentation built on Oct. 26, 2023, 1:08 a.m.