Radar — KLSX
Surface Analysis — Central U.S. (South)
Satellite
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Nearest monitored road: West McCarty Street (Primary)
- a late season heat wave continues through at least saturday with peak heat index values of 100-105f+ along/south of i-70. Areas just north of i-70 have been added to the heat advisory, and the rest of the advisory has been extended to saturday.
- isolated to scattered thunderstorms are expected this afternoon. These storms are not expected to strong enough to produce severe weather, though small hail, gusty winds, and brief heavy downpours are possible.
Issued at 340 AM CDT wed sep 16 2026
A robust upper level ridge remains in place over much of the southeastern conus, with mid-and upper level heights approaching climatological maximums across that portion of the country. There is a baroclinic zone on the northwestern flank of the ridge, currently drifting north out of the mid-mississippi valley. This feature will remain outside of our area and will be the primary focus for continued precipitation and cloud coverage over the next several days as the ridge amplifies and drifts westward.
Today, lingering cloud coverage associated with the above front are limiting temperatures in northern missouri and central il, but the much of rest of the forecast area is expected to bake under mostly sunny skies. Moisture will also be anomalously high, which should push heat index readings above 100 degrees for areas along and south of i-70. While deep-layer moisture will be highest along the front, there appears to be a secondary band of extreme precipitable water currently arcing from the arklatex, through SW mo, and into the ohio river valley. This feature is also expected to drift north today, and most model guidance has shown all morning that this will lead to isolated to scattered thunderstorms along the i-44 corridor during peak heating this afternoon. Indeed this convection was underway around 1PM, and should continue through around sundown. Given rising heights and weak deep-layer SHEAR, this convection is not expected to be very strong, but it may at least bring a brief break to the heat for some areas.
Tomorrow looks like it will be similar to today, with just a few differences. First of all, the ridge will be centered over the lower mississippi valley, a bit further west than today. Additionally, the front will be stalled further north, likely over iowa. This should result in hot temperatures across the vast majority of the forecast area. Humidity is expected to remain high, pushing the heat index toward or above 100 for most locations. There are also some indications that the secondary band of high pws may kick off another round of weak, isolated convection, roughly along the i-44 corridor.
Issued at 340 AM CDT wed sep 16 2026
The ridge will remain in place through a least saturday, though it is expected to start weakening on friday. Despite the gradually falling heights, persistent deep southwesterly flow will continue to advect warmer temperatures into the region, with mean 850mb temperatures well above 20c on both days. That southwesterly flow will also keep the baroclinic zone to our north, limiting precip chances and cloud coverage. The only saving grace for friday and saturday is that our humidity will be a bit lower, particularly on saturday. Nevertheless, our heat index reading will top out right around 100 on both days, especially for areas along and south of i-70. With that, we've decided to extend the heat advisory through saturday for those locations. We've also added a tier of counties north of i-70 to the advisory as it looks like they will now reach criteria, though that portion of the advisory will end on friday.
From sunday into early next week, a broad, slow moving upper trough will push through the northern plains and upper midwest, finally breaking the grip of the ridge (at least temporarily). An associated cold front will slide into the region, likely late sunday or on monday, bringing some relief to the heat. While there is little doubt the start of next week will be cooler than this week, just how cool it will get remains an open question. Ensemble mean high temperatures are right around seasonal normals, but there is notable spread in the guidance, with reasonable outcomes ranging from highs in the upper 80 to low 70S. Along with cooler temperatures, that front is likely bring at least a little rain to the region, though at this time there is little signal for impactful precipitation.
Issued at 1211 PM CDT wed sep 16 2026
Primary aviation concerns now surround thunderstorm chances this afternoon. Model guidance is in good agreement in a line of isolated to scattered showers and storms developing this afternoon in the vicinity of i-44 before ending around sundown. While confidence is high in these storms developing, their limited areal coverage leads to low confidence in them actually impacting a terminal. For now, i've kept a prob30 in for the metro terminals, and added one to kjef.
Otherwise, there is a limited concern that lower cigs may build back into uin overnight and tomorrow morning, but at this time, it appears most likely that those clouds should stay to the north.
Issued at 231 PM CDT mon sep 14 2026
Daily record high temperatures may be threatened for both st. Louis (kstl) and columbia (kcou) this week. Note: records at quincy (kuin) are not shown below due to cooler temperatures forecast:
9/15 9/16 9/17 9/18 9/19 kstl 101/1939 98/1954 97/1931 97/1925 96/1955 kcou 101/1893 99/1954 98/1895 98/1893 98/2022