I think the issue is because you don't have the DualImage.php capability installed.
Some of the forecasts are for 6hr periods and have different PoP for each time which would be displayed on the icon if DualImage.php were installed. If not available, then the first period forecast PoP is used for the static icon display.
For example, in your current JSON forecast ./forecast-ILZ070-0-json.txt it shows
{
"number": 2,
"name": "Tonight",
"startTime": "2020-05-22T18:00:00-05:00",
"endTime": "2020-05-23T06:00:00-05:00",
"isDaytime": false,
"temperature": 64,
"temperatureUnit": "F",
"temperatureTrend": null,
"windSpeed": "7 mph",
"windDirection": "SE",
"icon": "https://api.weather.gov/icons/land/night/tsra,20/tsra,60?size=medium",
"shortForecast": "Chance Showers And Thunderstorms",
"detailedForecast": "A chance of showers and thunderstorms before 3am, then showers and thunderstorms likely. Mostly cloudy, with a low around 64. Southeast wind around 7 mph. Chance of precipitation is 60%."
},
but on your page, it shows as a 20% chance icon (reflecting the tsra,20 in the icon spec.
If you install DualImage.php (and the forecast/icon-templates/*, then the script will display the full range of NWS dual-image icons.