The National Weather Service in Fairbanks has issued a Red Flag Warning for lightning, which is in effect from 4 PM Friday to midnight AKDT Friday night. * AFFECTED AREA...White Mountains and High Terrain South of the Yukon River and Chatanika River Valley. * TIMING...From 4 PM Friday to midnight AKDT Friday night. * THUNDERSTORM COVERAGE INDEX...4. * WINDS...Southwest 3 to 7 mph. * HUMIDITY...As low as 32 percent. * TEMPERATURES...Lows in the mid 50s. Highs in the mid 80s. * IMPACTS...Rapid ignition, growth and spread of fires will be possible. Frequent lightning can promote new fire starts. Hot and dry conditions may lead to rapid spread of fires.