Arnold, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

356
FXUS63 KLSX 261030
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
530 AM CDT Tue May 26 2026

.KEY MESSAGES...

- Temperatures remain fairly steady with mild to seasonably warm
  conditions through the next several days.

- The highest confidence in rain chances (60-70%) largely center
  on this afternoon/evening across Southeast Missouri and
  southwest Illinois. Trends are beginning to lean drier for mid-
  to-late week.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 255 AM CDT Tue May 26 2026

CONUS views of IR satellite/pressure overlays show an expansive
ridge extending westward from the Atlantic Ocean into the
southeastern U.S. Moisture stream at the western edge of the ridge
is apparent via convective behavior over the Gulf with an extension
of cloud cover up through the mid-Missisppi, Ohio, and Tennessee
Valleys. Surface observations show a relatively moist BL with
dewpoints in the 50s/60s across the region.

Meanwhile, the narrow surface ridge that kept us dry yesterday, is
being pinched off with the amplification of the western upper level
ridge and height rises reorienting over the northern Plains as we
progress through the day. The elongated ridge becomes more so muted
through today as an open upper level low slowly pivots northward out
of eastern Texas. As the system lifts northward this afternoon, a
conditionally unstable environment overcomes weak, early day
capping, giving rise to developing showers and a few thunderstorms.
Both RAP/NAM soundings show an initially strong elevated dry layer
that gradually saturates over southeast Missouri and southern
Illinois by early to mid afternoon. Model sounding show a rapid
deepening of the dry layer from north to south with weak, but
persistent easterly low/mid-level flow. Despite surface based
instability approaching 2000 J/kg during diurnal peak, what develops
looks to be elevated in the warm/moist advection regime. Also,
considering the very weak shear (0-6km <15kts), concerns for
anything strong to severe are nearly nil with parameters showing
little overlap to produce better organized convection.

The bigger picture calls for wet conditions mainly across southeast
Missouri and southwest Illinois with a progressive, and possibly
sharp, cutoff to measurable rainfall with the depth of dry air to
the north of I-70. Where rain does fall, PWATs range from 1.5-1.8"
and could provide efficient rain production under thunderstorms.
This potential is more localized within the expanse of higher PoPs
(60-70%). LPMM shows the signal for locally heavy rain with a few
isolated amounts exceeding 1-2". HREF then does a nice job with the
broader characteristics in the cutoff to the north as probabilities
for measurable rainfall (0.01") of 60% or greater lining up from
Effingham, IL through St. Louis, to Jeff City with values rapidly
increasing to the south. The opposite is true to the north of I-70,
where probabilities quickly drop below 20% from Springfield, IL to
Troy and Columbia, MO. Where rainfall occurs, temperatures will be
several degrees cooler (low/mid-70s) than those who remain dry
(upper 70s/low-80s).

Activity wanes late this with remnant showers fading overnight. The
upper level ridge continues to strengthen from the mid-Mississippi
Valley through the northern Plains as a strong surface high drops
south from the Hudson Bay. This bring a backdoor cold front into the
area, shifting surface flow out of the north and northeast. Though
this does not entirely rule out additional showers Wednesday, the
trends lean drier, especially north and west of St. Louis. The
extent of cloud cover decreases through the afternoon with gradually
more sunshine to close out the day. Highs will largely be in the 80s.


Maples

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 255 AM CDT Tue May 26 2026

The long range pattern shows increasingly greater favor for dry
conditions. The surface high near the Hudson Bay (ref. short term)
builds south through the end of the week. Early, blended forecasts
left less room for confidence in dry vs. wet conditions by location.
This is due, in large part, to weak flow and lack of any strong
forcing signals. However, we are now seeing greater influence from
the building ridge and dry, east-northeasterly surface to mid-level
flow. The potential for rainfall looks to be decreasing and shifting
farther to the west/southwest. Extend LREF QPF probabilities for
>0.50" are telling... showing around 30% probability for total QPF
to reach this benchmark by Wednesday night, increasing to 70% by
Sunday. These probabilities remain almost stagnant along and north
of I-70 with somewhat a U-pattern decreasing chances (<30%) to the
north. If these trends continue, confidence will continue to
increase in a largely dry and slightly cooler outlook through the
end of this week, potentially into next weekend. NBM IQR and ECM/GFS
ensembles give some credence to this idea with a steady, almost flat
pattern to the lower quartile (25th percentile) and small, stair
step increases in the upper quartile. Temperature trends in the NBM
IQR are also nearly flat with a narrowing between low/upper IQR
stats, keeping near normal warmth through the end of the period.

In the grand scheme of things, while there are rain chances, the
trends are beginning to lean dry and should the trends continue, it
would lead to a nicer, drier pattern heading into next weekend.


Maples

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 521 AM CDT Tue May 26 2026

The potential for impacts is fairly small today with VFR
conditions and light surface flow through much of the period. A
weak system is expected to glance the central MO and metro
terminals later tonight into tonight. However, latest trends
continue to show less precipitation coverage with scattered
showers more prevalent over southeast MO and southwest IL. The
depth of dry air deepens from south to north, which staves off
precipitation the terminals through a majority of the period.
KUIN is securely in the drier sector and expected to remain VFR.

A thunderstorm or two is possible during peak heating today, which
will be the primary threat, aside from minor visibility reductions
in heavier rain. Due to the limited chances (15-25%) and noted
trends, prevailing precip groups were held from the TAF at this
time with PROB30 covering slightly better chances (25-35%) at
KCPS.

Maples

&&

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

$$

WFO LSX