The National Weather Service says there is a potential for heavy snow in the northern part of Arkansas starting tonight. Cold air is moving in from the northwest while moist air is moving in from the south. The weather service says rain will fall over most of the state by evening, and there is a chance of thunderstorms in the state`s southeast. In the north of the state, rain later today is expected to change to snow. The weather service says snow is expected tomorrow in the state`s north and west, with rain changing to snow -- moving southwest to northeast. Southeast Arkansas could get some snow tomorrow. The storm system is forecast to move out of Arkansas tomorrow night. A winter storm watch is in effect for the state`s northern counties.