The National Weather Service has issued a heat advisory today for the western two-thirds of Kentucky. Heat indices from 100 to 105 degrees are possible. Those working outdoors need to take precautions, the weather service said.Some areas of Kentucky could see a heat index of more than 105 this afternoon — particularly the northern half of the state. Extreme caution is needed.The high today will reach the upper 90s over much of the state, and heat index values may climb over 105, the weather service said. Humidity levels will increase for Thursday but that would lower the temperature slightly, NWS said. There could be scattered showers with a heat index of about 100.