710
FXUS63 KLSX 042320
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
620 PM CDT Sat Apr 4 2026

.KEY MESSAGES...

- Cooler than normal temperatures will persist through Tuesday.
  Frost/freeze conditions are possible Tuesday morning (30-60%)
  over northeast Missouri and west-central Illinois.

- Temperatures warm above normal Wednesday onward with increasing
  chances for showers and thunderstorms late in the week.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 150 PM CDT Sat Apr 4 2026

A cold front continues to slide to the east-southeast this afternoon
with much cooler temperatures being accompanied by drying trends.
Conditions are improving, but the process is gradual. Skies break a
little too late in the day to have much of an impact, resulting in
steady temperatures in the 50s through early this evening. Dry,
northwesterly flow will aid in clearing from west to east tonight,
allowing temperatures to fall into the 30s. These temperatures might
initially bring concerns for frost with a couple of limiting factors
that should mitigate this potential. Locations along and southeast
of I-44/I-70 in Missouri/Illinois, respectively, remain in the upper
30s to near 40F. Cooler locations to the north will largely be in
the mid-30s with a few low-30s over the far northeast stretch
Missouri. Despite the cooler readings, sustained winds >5 knots
should keep frost from developing.

High pressure continues to work across the region with mostly clear
skies Sunday through Sunday night. The mid-level air mass that
briefly visits the area through the first half of the day falls in
the 20-25th percentile of climatological averages. This favors a
seasonably cool setup through Sunday with modest warming.
Considering recent rainfall has left behind moist surfaces, and
northwest flow persists, highs will capped at the mid-50s to low-
60s. Winds lighten Sunday night as the surface high centers over
northwest Arkansas with west-southwest surface flow. This subtle
shift will be just enough for a slightly warmer Monday morning.
Morning lows range from the upper 30s to low-40s.


Maples

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 150 PM CDT Sat Apr 4 2026

An anomalously strong, 1040mb surface high (99th percentile) is
expected to build southeast out of the south-central Canadian
Provinces into the north-central CONUS Monday, pushing a reinforcing
cold front through the region early Monday morning. Northwesterly
flow persists in the upper levels thanks to longwave troughing over
the New England Region and ridging over the Intermountain West. The
setup supports seasonably cool temperatures as cold air advection
stalls, bisecting Missouri and Illinois. The front doesn`t have much
and impact along and south of I-70, where highs will be similar to
Sunday`s temperatures. Along and north of Hwy 36/I-72, advection
will be strong enough to cool temperature enough so that highs only
make it into the low-50s.

The aforementioned boundary remains nearly stationary through the
region Monday night as mean SLP plots show the surface high crossing
southern Wisconsin. Guidance has shown a narrow band of forcing and
light QPF extending from northwest Missouri through central
Missouri. NAM sounding show saturation roughly between 850-500 mb
with surface dewpoint depressions of 5-10 degrees. LREF ensembles
indicate a 50% probability of measurable precipitation around Troy,
MO, increasing to around 80% between Chillicothe and Kirksville.
Probabilities drop significantly at or above 0.05". Considering the
cooler airmass, nocturnal timing, lift in the DGZ, and sounding at
or below freezing just off the surface, light rain/snow main
transition to snow as the primary precipitation type early Monday
morning. NBM guidance makes this look less impressive with few
northwestern counties (Monroe, Shelby, and Knox), but it may be
something to keep an eye on with better support for minor
accumulations just north/west of the CWA.

Guidance continues to trend cooler and in favor of near-freezing
temperatures by Tuesday morning. LREF probabilities for <32F climb
from 30% around Hwy 36/I-72 to around 60% near the MO/IA border.
While this is the case, sustained winds of 5-10 mph should couple
with cloud cover to prevent much in the way of frost. Should
temperature trends continue to cool, however, freeze products may be
the best approach here. We continue to monitor this potential for
agricultural interests. Tuesday will be the last cool day, and
probably the coolest, as the surface high slides across the southern
Great Lakes. Highs in the 40s and 50s will make for a chilly day
under partly to mostly cloud skies.

A big transition is in store Tuesday night into Wednesday with winds
veering out of the south/southwest. NBM IQR is unusually tight
(<10F) for this distance in time, providing higher confidence than
normal. Mean upper heights show the New England Region trough
quickly exiting east, while the western ridge begins to break down.
Zonal flow draws warmer air eastward from the Plains with mid-level
temperatures warming around 10C for Wednesday. This marks the start
of a milder period through the end of the week with NBM IQRs
remaining relatively flat with highs largely in the 70s.

Dry conditions that extend through Thursday will be impeded by
increasing rain chances late in the week. A broad ridge over the mid-
Atlantic begins to shift slightly eastward with southwesterly flow
drawing moisture northward as several disturbances eject from a
cutoff low over the southwest CONUS. This sets up at the back side
of the ridge with pattern that may become conducive for multiple
waves from showers and thunderstorms late Friday into next weekend.
Global guidance is currently in disagreement on QPF totals, but this
isn`t all that surprising with lower resolution unable to resolve
some of the mesoscale details.


Maples

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 600 PM CDT Sat Apr 4 2026

Mainly dry and VFR conditions are expected through the period.
West to northwesterly winds will decrease between 01-03Z and lose
their gusts, with winds mainly around 10 knots the rest of the
period.

Britt

&&

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

$$

WFO LSX