The National Weather Service issued a red flag warning Tuesday, giving a signal that the high-danger fire weather is on its way as gusty winds and disturbingly low humidity levels extend across the eastern Sierra Nevada mountain range to western Colorado. (Photo : Getty Images) Red Flag Warning According to NWS meteorologists based in Reno, the red flag warning will stay in effect until 11 p.m. Tuesday evening and will begin on Wednesday. Red flag warnings are the highest alert of the agency and are used to indicate the possibility of extreme fire behavior. The critical fire weather is anticipated to sweep across five states. In California, meteorologists forecast southern Mono County and Alpine County to be the location that will be affected the most by wind gusts up to 45 mph and humidity levels less than 15%.