It's likely some WD settings.
When the page first displays, the iconnumber from testtags.php is shown, and that is
$iconnumber = '0'; // icon number
which is for day_clear.gif (Sunny)
When the ajaxWDwx3.js script starts, then the condition icon from clientraw.txt
48 Current Condition Icon Icon 18 (Overcast)
is shown.
My guess is that you currently have WD set to display conditions from a nearby metar (which is showing clear), but also set to override with a solar sensor (which you don't seem to have, so is reporting 0 W/m2 and creating the overcast-and-gloomy).
See
https://saratoga-weather.org/wxtemplates/setup-WD.php and just turn off the settings that say for Solar to override, and you should be good to go.