SIDNEY — The National Weather Service is urging residents to stay alert Friday night as a potent mix of heavy rain and severe thunderstorms threatens much of western Nebraska, northeast Colorado and southeast Wyoming.

The weather service issued a Flood Watch and a Severe Thunderstorm Watch for the region, with forecasters warning of flash flooding, large hail, damaging wind gusts and isolated tornadoes.

The Flood Watch is in effect through late Friday night for northeast Colorado, including Logan, Morgan, Phillips, Sedgwick, Washington and Northeast Weld counties. Forecasters say the threat stems from a line of thunderstorms expected to develop behind a cold front moving across the region. Dew points are expected to rise into the 60s across the northeast corner of the state, providing the fuel for torrential downpours.

“Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying areas,” the Weather Service said in its advisory. “Widespread street flooding is also possible.”

Meanwhile, a Severe Thunderstorm Watch is in effect until 11 p.m. for portions of Nebraska, Colorado, and Wyoming. The Nebraska counties under the watch include Banner, Chase, Cheyenne, Deuel, Garden, Keith, Kimball, Morrill and Perkins. In Colorado, Logan, Morgan, Phillips, Sedgwick, Weld and Yuma counties are included, along with Laramie County in Wyoming.

Forecasters say there is a slight risk (Level 2 of 5) for both severe weather and excessive rainfall Friday evening. The greatest threat includes wind gusts over 60 miles per hour, hailstones over 1.5 inches in diameter, and heavy rain leading to flash flooding. An isolated tornado cannot be ruled out.

Weather officials say additional storm chances return Tuesday and Wednesday with the arrival of another front. Warmer temperatures are expected to return by the end of next week, but so are increased fire weather concerns.

Residents are urged to remain weather aware, have multiple ways to receive alerts and be prepared to act quickly if warnings are issued.