Bonneville County and surrounding regions of southeast Idaho are bracing for a significant weather pattern shift this week, with a heat advisory in effect Monday followed by an influx of moisture and storm potential through midweek.
The National Weather Service has issued heat advisories for Monday covering the Magic Valley, Snake River Plain, and South Hills areas. High temperatures are expected to reach near 100 degrees in some low-elevation locations, particularly across the lower Snake River Plain where Bonneville County sits. Residents in Idaho Falls, Ammon, Iona, and Ucon should prepare for hot conditions before the arrival of cooler, wetter air later in the week.
Tonight and Monday Forecast
Tonight will feature mostly clear skies with a low around 59 degrees. Isolated dry thunderstorms are possible in high elevations, mainly across central mountains and southern hills. Humidity levels are expected to remain slightly elevated.
Monday will bring sunny and hot conditions with highs near 97 degrees across most of the region. The real shift begins Monday evening, when monsoonal moisture is forecast to move into the area, setting the stage for more active weather patterns through midweek. Monday night will see partly cloudy skies with lows around 63 degrees.
Wet Pattern Takes Hold Tuesday and Wednesday
Tuesday marks the beginning of the wet period, with a slight chance of rain developing between noon and 3 p.m., followed by a slight chance of showers and thunderstorms after 3 p.m. The precipitation chance is modest at 20 percent, but conditions will deteriorate as the day progresses. Highs are expected to reach around 93 degrees. Tuesday night will see a chance of showers and thunderstorms before 9 p.m., transitioning to a chance of rain between 9 p.m. and midnight. Skies will be mostly cloudy with lows around 61 degrees and a 30 percent precipitation chance.
Wednesday brings the highest probability of precipitation for the week. Showers are likely with a possible thunderstorm after noon, and a 60 percent chance of measurable rainfall. Highs will dip to near 88 degrees as cooler air settles in. Wednesday night will remain unsettled with showers likely and possibly a thunderstorm before midnight, followed by a slight chance of rain after midnight. The low will be around 58 degrees with a 60 percent precipitation chance.
While some areas may experience wetting rains on Tuesday and Wednesday, forecasters note that most locations are not expected to receive extensive rainfall amounts. The storms will be scattered, with coverage concentrated in certain zones across the county and surrounding regions.
Transition to Drying Pattern
After Wednesday, the storm potential will decrease significantly. Thursday through Sunday will see isolated storm coverage at best, with general clearing and warming expected. Temperatures are forecast to rise after the midweek weather system moves through, returning the region toward more typical summer conditions.
Residents planning outdoor activities should take the Monday heat advisory seriously, staying hydrated and limiting exertion during peak heating hours. Those with plans for Tuesday and Wednesday should monitor updated forecasts and be prepared for sudden thunderstorms, particularly in afternoon and evening hours.
What Comes Next: The monsoonal moisture arriving Monday evening represents a significant shift from the heat-dominated pattern of recent weeks. East Idaho has recently broken heat records with temperatures soaring past 103 degrees, so the arrival of cooler, wetter air should provide relief for the region. Residents should monitor National Weather Service updates throughout the week as storm probabilities can change with each forecast update. By late week, drier conditions are expected to return, though temperatures will likely remain warm rather than returning to the extreme heat of the past several days.