A warm and breezy Friday will give Iowa one more mainly quiet day before the weather pattern becomes considerably more active. Most of the state will remain dry through the daylight hours, with temperatures climbing into the upper 70s and 80s and southwest winds increasing during the afternoon. The first opportunity for thunderstorms arrives tonight as a cold front begins moving southeast across the state, although storm coverage remains uncertain. Northwestern Iowa has the best chance of seeing storms before Saturday morning.
The bigger weather story develops this weekend and continues through at least the middle of next week. Several weather systems will cross the Midwest while repeated surges of warm, humid air move north into Iowa, creating multiple opportunities for thunderstorms and locally heavy rain. Some storms could become severe, particularly around Monday, while repeated rainfall may eventually create flooding concerns in parts of the state. Forecast confidence is relatively high that Iowa is entering a wetter pattern, but the exact placement and timing of the heaviest rain and strongest storms will depend on boundaries left behind by earlier thunderstorms.
Thunderstorm Chances Increase Tonight
The first thunderstorms may reach northwestern Iowa tonight as the cold front moves southeast from Minnesota and South Dakota. Storm development remains somewhat uncertain because moisture is limited and the strongest atmospheric lift will pass north of Iowa, so many locations could see little or no rain overnight. If thunderstorms do develop, northwestern Iowa has the greatest chance of seeing stronger storms before the activity weakens or moves farther southeast overnight. Large hail and damaging wind gusts would be the primary hazards with any stronger storm, while the tornado risk in Iowa appears considerably lower than farther north across Minnesota. Thunderstorms should become more isolated or scattered as they move into central Iowa because the atmosphere will become less favorable for maintaining organized severe weather. Residents in northwest Iowa should keep an eye on local weather radar this evening, but the forecast does not support widespread severe thunderstorms across the entire state tonight.
Saturday Storm Risk Focuses on Southern Iowa
Saturday will bring cooler conditions to northern Iowa while a lingering frontal boundary provides another opportunity for thunderstorms farther south. The boundary is expected to slow considerably after moving through the state, and differences in cloud cover and afternoon heating could help thunderstorms redevelop near or south of Interstate 80. Southwest Iowa currently has the better opportunity for a few stronger storms, with the severe weather risk extending into southeast Nebraska, northeast Kansas, and northern Missouri. Any storm that becomes well organized could produce large hail or strong wind gusts, but widespread severe weather is not expected based on the current forecast. One of the biggest uncertainties is exactly where the front stalls, because even a relatively small shift north or south could change which Iowa communities see storms during the afternoon and evening. Temperatures should generally range from the 70s in northern and western Iowa to near 80 or the lower 80s farther southeast, giving parts of the state a brief taste of more fall-like weather.
Rain Becomes More Widespread Sunday
Rain chances increase much more noticeably Sunday as moisture begins returning northward and another disturbance moves across the central Plains and Midwest. Showers and thunderstorms are expected to become more widespread across Iowa, with some areas potentially seeing more than one period of rain during the day and Sunday night. A strengthening southerly low-level jet, which is a ribbon of faster winds a few thousand feet above the ground, will transport increasingly humid air into the state. That moisture will interact with a stalled frontal zone and provide a favorable setup for thunderstorms capable of producing heavy rainfall. Current guidance favors central Iowa and surrounding portions of the Midwest for some of the heavier precipitation, with widespread amounts around 1 to 2 inches possible in the broader Sunday into early Monday period and locally higher totals where storms repeatedly move over the same locations. Confidence is increasing in a wet Sunday and Sunday night, although the precise corridor of heaviest rain will continue to shift as the location of the front becomes clearer.
Severe Weather Potential Increases Monday
Monday appears to have the greatest potential for organized severe weather during the upcoming active pattern, although important timing details remain unresolved. A stronger weather system will move across the northern Plains while a warm front lifts northward and a cold front approaches Iowa from the west. Warm, moist air returning ahead of the system should provide enough instability for thunderstorms, while stronger winds several thousand feet above the ground could allow storms to organize. Damaging wind and large hail would be concerns with stronger storms, and the overall severe weather setup will need to be watched closely as higher-resolution forecast guidance reaches the Monday time frame. The exact magnitude of the risk will depend heavily on how much rain and cloud cover linger from Sunday night because widespread morning storms could limit afternoon instability in some areas. Iowa residents should treat Monday as a day to monitor future weather updates rather than assuming severe storms are guaranteed at any specific location.
Heavy Rain and Flooding Could Become a Concern
Heavy rainfall may eventually become as important as the severe weather threat because several rounds of thunderstorms could cross Iowa between Sunday and Wednesday. The atmosphere is expected to contain unusually high amounts of moisture for September, allowing thunderstorms to produce efficient rainfall rates when they develop. Current longer-range guidance suggests portions of Iowa could receive more than 2 inches of rain during the multi-day period, while localized totals of 3 to 4 inches or more cannot be ruled out if storms repeatedly track across the same areas. Some forecast guidance shows a greater than 50 percent chance of exceeding 2 inches in parts of the region, while the probability of exceeding 4 inches is much lower but still significant enough to monitor. Flash flooding, ponding on roads, rises on smaller streams, and eventually river flooding could become concerns where the highest totals occur, especially if heavy rain falls over areas that receive repeated storms. The rain forecast will become more precise over the next several days, but confidence is high enough to begin paying attention to drainage areas and locations that are normally susceptible to flooding.
Cooler Weather Follows the Weekend Front
Temperatures will vary considerably across Iowa as fronts move back and forth through the state over the next several days. Friday remains warm with widespread 80s, while Saturday should turn noticeably cooler across northern and western Iowa behind the first cold front. Sunday will generally feature highs in the 70s, although clouds and rain could keep some areas cooler. A brief surge of warmer air may push temperatures back into the 80s in parts of Iowa Monday before another front moves through. Behind that system, highs may fall into the 60s and lower 70s across portions of the region Tuesday through Thursday, particularly where clouds and rain persist. The overall weather this week will begin to feel more like early fall, although periods of humidity will return whenever southerly winds pull moisture northward ahead of each storm system.
Looking Ahead
The main message heading into next week is that Iowa is entering an active weather pattern rather than facing one single storm system. Thunderstorms are possible at several points from Sunday through Wednesday as multiple disturbances interact with a frontal boundary that may linger near the state. Sunday and Sunday night bring increasing concern for heavy rain, while Monday currently appears to offer the best combination of ingredients for organized severe thunderstorms. Additional rain chances could continue Tuesday and Wednesday, and another disturbance may keep precipitation chances in the forecast even later in the week. The greatest forecast uncertainty involves the placement of the front and the tracks of individual thunderstorm complexes, which will determine who receives the heaviest rain and whether instability is able to recover between storms. Anyone making outdoor, agricultural, or travel plans should check the latest weather forecast frequently because day-to-day details are likely to change as each round of storms affects the environment for the next one.
Stay with IowaWeather.com throughout the weekend and into next week for the latest Iowa weather updates, local weather radar, severe weather information, and changes to the rain forecast as this active pattern develops.