Update: York County is under a severe thunderstorm watch until 10 p.m. Thursday, the National Weather Service announced.
The watch extends to the rest of central Pennsylvania as well.
A warm front will lift northeast of the Susquehanna Valley this afternoon, followed by a cold front that will reach the lower Great Lakes in the evening, the NWS said. Lines of fast-moving thunderstorms could move into the region, and super-cell thunderstorms could form across central Pennsylvania.
The main threat from the storms will be damaging wind and large hail, but there is a possibility of a tornado, the NWS said.
A heat advisory also remains in effect until 8 p.m.
Previous story: York could see both dangerous heat and severe thunderstorms on Thursday.
York and the rest of central Pennsylvania will see very high temperatures during the day, with a high of 99 and a heat index of 100 to 104 in the afternoon, according to the National Weather Service. The area is under a heat advisory, with residents urged to confine strenuous outdoor activities to the early morning and evening.
There is also a moderate risk of severe thunderstorms, mainly between 8 p.m. and 2 a.m., the NWS said, as a warm front from the south meets a cold front moving across the Great Lakes. Storms Thursday afternoon and evening could produce damaging winds and hail, and a few isolated tornadoes are possible, the service said.
Friday will be mostly sunny with a 40 percent chance of showers and thunderstorms, the forecast said. The high will be 91 and the low 69.
Saturday will also be sunny with a chance of showers and thunderstorms, the forecast said. The high will be 88 and the low 67.
Sunday and Monday will both be partly sunny, with highs in the upper 80s and lows in the mid-60s.