The National Weather Service has issued a tornado warning for Allegheny, Washington and Greene counties on Wednesday. More: Read the current weather alerts for your county Interactive radar: Track storms moving through your area A severe thunderstorm capable of producing a tornado was located over McDonald, or 8 miles northwest of Canonsburg, moving east at 40 mph. HAZARD...Tornado. SOURCE...Radar indicated rotation. IMPACT...Flying debris will be dangerous to those caught without shelter.