This is a great topic because it can be pretty darn confusing trying to figure out how to set up your metars at first. I thought it might be useful to add to it, so here is a mini tutorial on the way I use it with expanded information on setting up your icons and current conditions when using the AJAX template.
In WD and on the "METAR Download" tab you can add several different metars to the metar list. The metar list is in the large white space area directly under where it says "Remove selected metar". To add a new metar to the list you type in the metar call letters next to where it says "Use this Metar Station ID". Then click on the greater than symbol (">") directly to the right of where you typed in the metar call letters to add it to the list... The metar call letters MUST be all CAPS (ie KAUN.TXT). When you click on any of the metars in your list, this will be the metar used for your sky conditions. Not to be confused with using the metar for a "metar icon" which then requires it to be 1st in the list. Personally I do not use it for icons, I only use it for night time sky conditions.
Again, it does not have to be first in the list for sky conditions. When you click on a metar in your list, the metar's call letters will display directly to the right of where it says: "Use this metar for local sky/icon conditions [and wunderground sky conditions] > KAUN.TXT <"
You must have a check mark in front of the above phrase in order to use the metar for sky conditions.
Below is some related information from great tutorial from a couple years back by Ken True that can really help you in getting everything set up properly and in the way you want it.
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By Ken True:
There are two different icons, a 'current condition icon' and a 'forecast icon'. The former (current condition icon) is controlled by several setup screens, since it's source may be selected to be from a nearby METAR, your weather station (rain/no rain), and/or a solar sensor (for cloud conditions based on insolation).
The summary image is what you see if you click on the WD main display where the picture is (just above the area showing the time, data received and data quality). It will pop open three windows, one is the Summary Image, one is the Metar (if metar enabled), and one is the forecast (if NOAA forecast downloads are enabled).
The Carterlake/AJAX templates don't use the 'summary image' nor the 'forecast icon' directly -- they use the icon number for the current condition to display a small icon which should represent the current weather condition.
To set up the icon with a solar sensor, I recommend you use the Control Panel, Solar Sensor Setup, Thresholds/Icon/Solar Description TAB
Tick all 5 check boxes in the 'Icon from solar/solar sensor',
If your solar sensor is obscured by surrounding trees or hills, then enable the fine-tune times to reflect when to ignore the solar sensor with minutes after local sunrise and minutes before local sunset.
Then select the Max Solar Time of Day/Time Zone/Lat/Long TAB and tick 'Update the solar value from this max reading...;, and set the Latitude/Longitude, timezone values and turn the main switch to ON and hit OK to save the settings.
Then in Control Panel, Summary Images & Icons, Main Screen icon/Forecast icon Setup/Text Scroll TAB,
Tick 'Use Downloaded Metar to update the Icon', 'Include extra weather conditions from downloaded Metar', Show the Metar image on the web page', and 'Your stations rain/wind/fog overrides the metar'. and hit OK to save the setting.
This assumes you've got a nearby METAR setup to pull (using the Control Panel, FTP &Connections Metar..., Metar Download TAB, then have ticked the 'Use the metar to update WD's main weather condition report' in addition to having a metar specified for download.
With all that, what should happen is the Solar sensor will rule during the day for cloud conditions based on percentage of solar v.s. expected max for time/lat/longitude. It will be replaced with 'rain/light rain/stopped raining' based on your rain gauge. Then at night, the icon will be set based on what the nearby metar has to say about cloud conditions, with your station's rain status overriding.
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