206
FXUS63 KLSX 181839
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
139 PM CDT Sat Jul 18 2026

.KEY MESSAGES...
- A cold front stalls near the Mississippi River on Sunday. To the
west, hot and humid conditions continue. To the east, a little
cooler conditions are expected with some smoke. Along the front,
afternoon showers are likely.

- Heat and humidity spread area wide on Monday, but a cold front
Tuesday will bring substantial heat relief for the rest of the week.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 135 PM CDT Sat Jul 18 2026

Regional satellite imagery shows surface high pressure over
Louisiana with a westerly flow to the north of it across
Missouri and Illinois. Although cumulus has formed, showers have
been hard to come by so far. One pocket of convection over
southwest Missouri will continue to push eastward this afternoon
and likely affect our southern forecast area. Otherwise only
isolated showers with occasional embedded lightning are
expected. To the north a cold front is pushing south through
Iowa and northern Illinois. Scattered storms are expected to
form in the vicinity of this boundary this evening. Considering
a hot and humid low levels, any stronger cores could produce
locally gusty or damaging winds. However, storms are expected to
decrease in coverage and intensity as the front pushes southward
into our area this evening.

This front is being driven by a trough moving through the Great
Lakes into New England. As this trough moves east, the front
loses its push southward, resulting in a stalling boundary in
our area tomorrow. The front is likely to stall just west of the
Mississippi River in a roughly northwest to southeast
orientation. To the east of the front, it will be a little
cooler with highs only in the 80s. With this air mass coming out
of the Great Lakes and southern Canada, there`s some potential
for smoke as well. See the latest Air Quality Alert for portions
of Illinois. Along and to the west of the front, temperatures
rise into the 90s again with humidity even a bit worse than it
is today as moisture pools near the front. So we`ll see another
day of 100 to 105 heat index values. However, the front will
also serve as a focus for afternoon thunderstorms which will
provide brief local heat relief in spots. With little wind shear
available, these storms will be primarily capable of gusty
winds and heavy local downpours. Latest guidance has been a
little more aggressive in pushing the front westward, so it`s
possible the St Louis area may get a better break from the heat
than initially expected.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Issued at 135 PM CDT Sat Jul 18 2026

The front lifts back northeast Sunday night into Monday putting
the entire area back into the hot and humid air mass again for
Monday. For many locations this will be the hottest day of the
week with highs in the low to mid 90s and heat index values
peaking near 105. But the next trough will be dipping down into
the Northern Plains bringing with it our next more substantial
cold front. This front pushes north to south across our area
during the day on Tuesday. For more southerly areas that remain
ahead of the front for a good portion of the day, it`ll be
another hot and humid day, potentially even hotter than Monday.
But to the north the heat relief begins. We`ll have to watch
this day for the potential for thunderstorms. Although current
NBM POP remains fairly low as guidance does favor areas further
east along the front, there`s still 40 to 60 percent of low
resolution ensemble guidance that produces rain in our area in
the 24 hours ending Tuesday night. With better wind flow aloft,
the potential for more organized thunderstorms with primarily a
wind threat will be higher here than with any of the other
convection expected in this 7-day forecast.

Although the core of the coolest air with this air mass will be
aimed more to the east across the Ohio Valley and Northeast,
we`ll still feel the cool down. For the middle of next week
we`re looking at highs in the low to mid 80s with a substantial
drop in humidity. Dewpoints fall into the 50s. It`s hard to get
much drier this time of year in the absence of a drought as
local evaporation and transpiration tend to modify dry air
masses quickly. Either way, it`ll be a noticeable break from the
humidity.

Although the front makes it all the way to the Gulf coast of
Florida, it does get hung up across the Southern Plains. Here
continued humidity along with shortwave troughs dropping through
the northwest flow will produce a few rounds of showers and
storms. Our area may be peripherally impacted by this as early
as Thursday night. Our air mass largely moderates in place over
the coming days with temperatures drifting closer to normal with
continued modest humidity. But by this weekend we start to see
the moisture creeping back toward our area with the upper ridge
expanding its influence into the center of the country leading
to another potential period of hot weather.

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1216 PM CDT Sat Jul 18 2026

VFR expected today with a light WSW wind. A few pop up showers
are possible, but should be few and far between. A front drops
in from the north tonight with thunderstorms possible along it.
These should be dissipating as they arrive. They`ll have the
best chance of affecting UIN, but confidence remains low that
they`ll even survive that far. The front gets stalled near or
just west of the Mississippi River on Sunday, with a very light
NNE wind east of the front. More widespread showers and storms
are likely in the vicinity of the front Sunday afternoon, most
likely affecting the St Louis metro area.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 7 PM CDT Tuesday for MOZ041-047>051-
     059>065-072>075-084-085-099.
IL...Air Quality Alert from 4 AM Sunday to midnight CDT Sunday
     night for ILZ058>060-065-095>097.
     Heat Advisory until 7 PM CDT Tuesday for ILZ069-074-079-
     100>102.

&&

$$

SHORT TERM...Kimble
LONG TERM...Kimble
AVIATION...Kimble