09/05/2026
FIRST WARN FORECAST
Saturday, September 5, 2026
First. Accurate. Trusted.
EXTREME HEAT CONTINUES TODAY, COOLER AIR ARRIVES SUNDAY AND MONDAY
The prolonged late-summer heatwave reaches its final dangerous peak today before a noticeable change in the weather pattern brings cooler and less humid conditions for Sunday and especially Labor Day. Saturday will remain dangerously hot, with afternoon temperatures climbing into the mid-90s to around 100 degrees and heat index values reaching approximately 105 to 110 degrees across portions of the region.
A few isolated showers and thunderstorms will be possible this afternoon and evening, particularly across southeastern Missouri and southwestern Illinois. However, coverage will remain limited, and most locations will stay dry. The more important weather story today is the heat, not the rain.
The pattern begins to change tonight as a backdoor cold front moves southwestward through the region. This will mark the beginning of a much-needed break from the extreme heat, although temperatures will remain above average through much of the Labor Day weekend.
SATURDAY: ANOTHER DANGEROUSLY HOT DAY
The upper-level ridge responsible for nearly a week of excessive heat is finally beginning to lose its grip on the Mid-Mississippi River Valley. However, that change will come too late to prevent another very hot day across the region.
Temperatures will again reach the mid-90s to around 100 degrees, with the highest readings possible across parts of Missouri and Illinois. Increasing moisture ahead of the approaching front will result in higher dewpoints, which means the heat will feel even more oppressive than the thermometer suggests.
Heat index values are expected to reach 105 to 110 degrees in many areas. These conditions can become dangerous quickly, particularly for anyone spending extended periods outdoors, working in the heat, exercising, or without reliable air conditioning.
This will be the final day of the current stretch of extreme heat, but it should be treated seriously.
ISOLATED STORMS THIS AFTERNOON
The approaching front and increasing atmospheric instability will provide a better opportunity for isolated showers and thunderstorms this afternoon and evening.
The greatest chance for development will be across southeastern Missouri and southwestern Illinois, with a few additional showers or storms possible elsewhere. Most locations will remain dry.
Atmospheric instability will be sufficient for a few storms to become briefly strong, and an isolated microburst or damaging wind gust cannot be ruled out. However, limited wind shear should prevent widespread severe weather, and most storms will be short-lived.
Any showers and thunderstorms that develop should diminish rapidly this evening as daytime heating fades.
SUNDAY: THE HEAT FINALLY BEGINS TO BREAK
The backdoor cold front will move completely through the region by Sunday, bringing a significant change in temperatures and humidity.
Sunday will still be warmer than average for early September, with temperatures generally ranging from the mid-80s to lower 90s. The warmest conditions are expected across central and southeastern Missouri, where higher humidity will linger behind the front.
There remains some potential for heat index values to reach 100 degrees in those areas, but confidence in widespread excessive heat has decreased. At this time, additional heat headlines do not appear necessary for most of the region.
A stray shower or thunderstorm could clip portions of northeastern or central Missouri Sunday afternoon or evening, but the overwhelming majority of the area should remain dry.
LABOR DAY: A MUCH-NEEDED BREAK
Monday will bring the most noticeable improvement in the weather.
High pressure will build into the region while significantly drier air filters southward. Afternoon temperatures should range from the mid-80s to around 90 degrees, with considerably lower humidity.
Dewpoints will fall into the 60s, with some locations along and east of the Mississippi River potentially seeing dewpoints in the 50s Monday afternoon. That will make a substantial difference compared with the oppressive humidity experienced this week.
While temperatures will still run somewhat above average for early September, Monday should feel dramatically more comfortable.
For the first time in several days, outdoor plans should be much more manageable.
THE HEAT RETURNS TUESDAY
Unfortunately, the cooler weather will be short-lived.
The upper-level ridge will begin shifting eastward again Tuesday, allowing warmer air to return from the southwest. Temperatures will once again climb into the mid-90s to around 100 degrees Tuesday and Wednesday.
There is one important difference compared with the current heatwave. The next warmup is expected to be much shorter.
Moisture will take longer to return Tuesday, meaning heat index values should remain relatively close to actual air temperatures. This could keep Tuesday from becoming as oppressive as Saturday.
By Wednesday, increasing moisture near an approaching cold front could push heat index values higher. However, clouds, showers, thunderstorms, and the timing of the front will make Wednesday's temperatures considerably more uncertain.
At this point, it is too early to determine whether additional heat headlines will be required.
A MORE ACTIVE WEATHER PATTERN DEVELOPS LATE NEXT WEEK
The weather pattern becomes increasingly unsettled from late Wednesday into the second half of next week.
A series of upper-level disturbances will gradually weaken and flatten the ridge that has dominated our weather pattern. The cold front moving through Wednesday may stall or progress southward only slowly, creating a boundary between warmer air to the south and more seasonable air to the north.
That boundary could become a focus for periodic showers and thunderstorms.
Rain chances from Wednesday onward remain uncertain, but ensemble guidance suggests precipitation probabilities generally ranging from 30 to 60 percent at various times. The exact location of the front will be critical to determining who sees rain and who remains dry.
Temperatures also become more difficult to forecast late next week. Current guidance generally favors readings in the 80s to around 90 degrees Thursday and Friday, although considerable variation remains possible depending on the position of the front.
HEAT SAFETY
Today is another day to take the heat seriously.
Drink plenty of water, limit strenuous outdoor activity during the hottest part of the afternoon, take frequent breaks in air conditioning or shade, and never leave children or pets unattended in a vehicle.
Remember that heat illness can develop quickly. If you experience dizziness, confusion, severe headache, nausea, weakness, or other signs of heat-related illness, move to a cooler location and seek medical attention when necessary.
THE BOTTOM LINE
Saturday will be the final and potentially most dangerous day of this extended heatwave, with temperatures in the mid-90s to around 100 degrees and heat index values reaching 105 to 110 degrees.
A few isolated thunderstorms are possible this afternoon and evening, but most locations will remain dry.
A backdoor cold front will bring a welcome change beginning Sunday. Temperatures will fall into the 80s and lower 90s Sunday, followed by an even more comfortable Labor Day with lower humidity and temperatures primarily in the mid-80s to around 90 degrees.
The break will be brief. Heat returns Tuesday and Wednesday, but the next warmup appears likely to be considerably shorter than the prolonged heatwave we are leaving behind.
By late next week, a more active pattern may develop as the ridge weakens and a frontal boundary settles across the region. That could finally provide a more sustained transition toward typical September weather.
Meteorological fall has arrived, but summer has certainly made it clear that it is not ready to leave quietly.
