HOT, DRY, AND UNSTABLE CONDITIONS EXPECTED THROUGH SUNDAY. . ISOLATED TO SCATTERED THUNDERSTORMS SUNDAY AFTERNOON AND EVENING. A strong ridge of high pressure will amplify over the Pacific Northwest leading to very hot, dry, and unstable conditions. An upper weather system will also clip the region Sunday, producing isolated to widely scattered thunderstorms across central Oregon in the afternoon. The combination will result in conditions conducive to extreme fire behavior, particularly for any ongoing fires in the region. The National Weather Service in Pendleton has issued a Red Flag Warning for abundant lightning, which is in effect from noon to 10 PM PDT Sunday. * AFFECTED AREA. Fire Weather Zones 611 Deschutes National Forest -minus Sisters Ranger District and 640 Central Mountains of Oregon. * TIMING. Noon to 10 PM Sunday. * RELATIVE HUMIDITY. As low as 12 percent. * TEMPERATURES. Up to 97. * THUNDERSTORMS. Isolated to widely scattered. Lightning activity level of 2 to 3. * OUTFLOW WINDS. 35 to 45 mph. Thunderstorm outflow winds may result in erratic fire spread. * IMPACTS. Any lightning strikes combined with hot and dry conditions could cause new fire starts.