Arnold, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

030
FXUS63 KLSX 251859
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
159 PM CDT Sat Apr 25 2026

.KEY MESSAGES...

- There is the potential for severe thunderstorms Monday afternoon
  and evening. Large hail, damaging winds, and tornadoes are all
  possible.

- Warm weather continues through at least Monday before a shift
  toward cooler weather for the rest of the week.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 158 PM CDT Sat Apr 25 2026

Our recent cold front has brought us a dry, sunny day, but the front
has stalled to the south and moisture is already beginning to return
over the Plains. Looking aloft we see a large trough over the
Canadian Prairies and another over the North Atlantic. In between,
ridging has led to persistent warm temperatures even despite the
recent surface cold frontal passage. Westerly flow across the
Rockies has led to the establishment of a lee trough in the High
Plains, triggering the moisture return east of there. This leads to
another round of storms developing over the Plains of Oklahoma and
Kansas today, but this activity will remain to our west and south,
keeping us dry.

On Sunday, moisture pushes even further north in the Plains with the
next round of storms Sunday afternoon focusing on Kansas and
Nebraska. Surface based convection stays well west of our area
Sunday afternoon as we remain in the dry air for one more day. But
that moisture return finally gets redirected toward our area
beginning Sunday night into Monday morning as a shortwave trough
emerges out of the Rockies and drives a surface low northeast
through the Midwest. We may see some elevated convection early
Monday morning on that moisture return, particularly across
northeast Missouri closer to the surface low and upper trough. Any
threats with this activity should be limited to lightning and hail
as they would not be surface based. But they will be the herald of
the moisture arriving back into our region.

Kimble

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 158 PM CDT Sat Apr 25 2026

Monday is clearly the most impactful weather day of the week. Not
only does it bring the greatest severe weather threat but it also
initiates a shift in the weather pattern toward cooler conditions
for the rest of the week. The shortwave trough drives a surface low
northeast out of Kansas toward the Upper Mississippi River. Ahead of
the low, we`ll find our area solidly in the warm, moist sector ahead
of a cold front arriving from the northwest late in the day. The
moist sector will be characterized by moderate to very strong
instability (1000 to 3000 CAPE) along with strong wind shear (45 to
55KT 0 to 6 KM). Once storms form in this environment they will
quickly organize into supercells with a primary threat of large to
very large hail and tornadoes. As storm coverage grows,
consolidation into one or more clusters is expected with damaging
winds becoming a greater threat along with a continued tornado
threat. Storm coverage is likely to be greater to the north closer
to the surface low, while further south in the open warm sector
ahead of the front coverage may be more isolated especially
initially.

There remains some uncertainty on the track of the low, with some
guidance taking this as far north as Minneapolis or as far south a
Des Moines. A closer track would favor greater storm coverage and
potentially more backed low level winds and a greater tornado
threat. There`s also some uncertainty on how unstable the warm
sector becomes with clouds potentially being a limiting factor.
However, greater low level moisture and cooling aloft with the
arrival of the trough will help ensure access to instability
sufficient for supercell thunderstorms. So while we may be able to
further refine the timing and location of the greatest threat in the
coming days, for now we remain confident in a broad severe weather
threat across the warm sector Monday afternoon and evening
encompassing our entire forecast area.

All guidance indicates that Monday night`s cold front clears our
area by early morning Tuesday, shifting us back to a cooler, drier
air mass. However, the next shortwave trough moves east pretty
quickly behind the departed one on Tuesday, this time tracking
further south through the MidSouth. Most guidance keep the moist
sector well south of our area at this point, though some do have the
front wobbling back north briefly on Tuesday to the point where we
could see surface based convection in the southern CWA Tuesday
afternoon. The more likely scenario is that any convection will be
elevated in association with synoptic forcing with this trough. In
either case, the better chances for another round of rain will be in
the southern half of the forecast area on Tuesday afternoon and
evening.

Monday and Tuesday`s shortwave troughs help to expand the broader
Canadian trough to encompass much of the lower 48 states by Midweek.
This shifts the storm track to the south and puts us solidly in a
cooler and largely drier pattern to end the week with Gulf moisture
trapped well to the south. There may be a few embedded shortwaves in
the Thursday/Friday time period that bring some light rain chances,
but the threat for thunderstorms, particularly severe thunderstorms,
ends after the early week activity. As additional cool air spills
south later in the week we`ll see daily highs and lows some 10 or
more degrees below normal as we head into the first part of May.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1220 PM CDT Sat Apr 25 2026

Dry and VFR conditions continue with light easterly winds. There`s
some potential for river valley fog by morning, mainly at SUS, but
confidence is too low to include in any terminal forecast at this
stage.

Kimble

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX