Tropical moisture triggers flooding and freezing temperatures

IDAHO FALLS, Idaho (KIFI)- Eastern Idaho faces widespread rain, unseasonably cool temperatures and a Flood Watch through Monday afternoon as tropical moisture streams into the region. Rain will continue overnight into Monday, with temperatures dropping into the mid-30s tonight and high temperatures reaching only the low 50s on Columbus Day.

The persistent rainfall is fueled by deep moisture from the remnants of Tropical Cyclone Rachel interacting with cooler air moving down from the north. The National Weather Service issued the Flood Watch for areas along and east of the Interstate 15 corridor, where rainfall totals of one to three inches are possible, particularly across higher terrain and around Island Park.

Rain is expected mainly before 1 a.m. Sunday night, with a 100% chance of precipitation and overnight low temperatures near 36 degrees. Forecast models indicate a brief break in rainfall Sunday evening before a secondary surge of moisture pushes in from Nevada and Utah overnight into Monday morning.

Cold overnight conditions have prompted multiple frost and freeze warnings across the area. A Freeze Warning covers the Magic Valley, the Lava Beds and the Arco Desert, where temperatures are most likely to drop below freezing briefly. A Frost Advisory is in effect for the Snake Plain, where widespread low temperatures between 32 and 36 degrees are expected overnight.

On Monday, rain is expected mainly before 3 p.m., with an 80% chance of precipitation and daytime highs reaching near 52 degrees. Winds will shift out of the southwest at five to eight mph. Rain chances drop to 30% Monday night, mainly before 4 a.m., with cloudy skies and a low near 36 degrees.

Precipitation chances will diminish further on Tuesday to 20%, with high temperatures near 53 degrees. Rainfall late Monday into Tuesday will focus primarily on the far southeastern corner of eastern Idaho as the upper-level low tracks from Nevada into Utah.

Conditions are forecast to clear by mid-week as the low-pressure system moves east of the region. High pressure is expected to bring clearing skies and high temperatures returning to seasonal norms near 60 degrees on Thursday and mid-60s on Friday and Saturday.