You can try something like this
<?php
$url = "https://api.weather.com/v2/pws/observations/current?stationId=IMATER7&format=json&numericPrecision=decimal&units=m&apiKey=YOURAPIKEY";
$outFileName = "current.txt";
$debug = "1";
$json = file_get_contents($url);
$data = json_decode($json);
file_put_contents($outFileName, $data->observations[0]->obsTimeLocal."\n"); // first line without APPEND flag
file_put_contents($outFileName, $data->observations[0]->metric->temp."\n", FILE_APPEND); // subsequent lines with APPEND flag
file_put_contents($outFileName, $data->observations[0]->humidity."\n", FILE_APPEND);
// extend as required
/* available fields:
$data->observations[0]->obsTimeUtc
$data->observations[0]->obsTimeLocal
$data->observations[0]->solarRadiation
$data->observations[0]->uv
$data->observations[0]->windDir
$data->observations[0]->humidity
$data->observations[0]->metric->temp
$data->observations[0]->metric->heatIndex
$data->observations[0]->metric->dewpt
$data->observations[0]->metric->windChill
$data->observations[0]->metric->windSpeed
$data->observations[0]->metric->windGust
$data->observations[0]->metric->pressure
$data->observations[0]->metric->precipRate
$data->observations[0]->metric->precipTotal
*/
if ($debug)
{
// only for testing ( prints to video )
print_r($data); echo "<br>";
echo $data->observations[0]->obsTimeLocal."<br>";
echo $data->observations[0]->metric->temp."<br>";
echo $data->observations[0]->humidity."<br>";
}
?>