Hi, there is a way to get this string:
See WundergroundForecastDemo.ino
Serial.println("getForecastIcon: " + forecasts[i].forecastIcon);
However, typical ESP8266 project doesn't have much RAM memory left, so playing with "your" or live downloaded bitmaps is very limited. So far, the best results are with embedded to the program memory, simplified 4-colors bit array pictures or monochrome bitmaps (fonts).