River Flood Warning 36, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
615 PM CDT Sun Apr 19 2026

.KEY MESSAGES...

- Warmer and mostly dry weather is expected for the first half of this
  week.

- The potential for widespread showers and thunderstorms returns
  to the forecast late this week.

&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 138 PM CDT Sun Apr 19 2026

A weak cold front is pushing through the northern forecast area this
afternoon, allowing a cool airmass to graze northeast Missouri
through south-central Illinois tonight and resulting in similar
temperatures to last night. Seeing as little to no frost developed
this morning, confidence is low in widespread frost building
tonight. However, radiational cooling will be at play, so the
potential for patchy frost to develop on elevated surfaces is higher
than yesterday. The cool airmass will push east on Monday, opening
the region back up to low-level southwesterly flow by the afternoon.
Weak WAA will work in tandem with a second day of clear skies to
lift afternoon highs into the low 60s to low 70s - just a touch
warmer than today.

Jaja

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 138 PM CDT Sun Apr 19 2026

The pressure gradient in the low-levels will tighten over the Mid-
Mississippi Valley on Tuesday as low pressure to our north pushes
into high pressure to our southeast. The stronger flow will advect
much warmer air into the region with widespread mid to upper 70s
forecast for highs Tuesday afternoon. After a similarly warm
Wednesday, temperatures will rocket into the low-80s Thursday
afternoon ahead of our next notable system. Deterministic models
match each other well, all placing a southwest-northeast oriented
cold front in northwestern Missouri at 06z Friday. The set-up looks
similar to what we've been seeing these past couple of weeks: A cold
front in the eastern Plains initiates convection that's weakening by
the time it reaches the eastern half Missouri after sunset. How
quickly it does or doesn't weaken will determine our potential for
stronger thunderstorms. The cold front is forecast to clear the CWA
to the south late Friday before buckling back northward as a warm
front and ushering another chance of rain this weekend.

Jaja

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 614 PM CDT Sun Apr 19 2026

Dry and VFR flight conditions will persist this TAF period with
winds slackening around 00z this evening and veering to
northeasterly tonight as a weak cold front continues passing and a
surface high pressure center traverses the Great Lakes. Winds will
continue to veer to southeasterly and southerly on Monday.

Pfahler

&&

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

WFO LSX

Hazardous Weather Outlook
National Weather Service St Louis MO
119 PM CDT Sun Apr 19 2026

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-201830-
Greene IL-Macoupin IL-Montgomery IL-Bond IL-Fayette IL-Clinton IL-
Marion IL-Washington IL-Randolph IL-Adams IL-Brown IL-Pike IL-
Calhoun IL-Jersey IL-Madison IL-Saint Clair IL-Monroe IL-Knox MO-
Lewis MO-Shelby MO-Marion MO-Monroe MO-Ralls MO-Pike MO-Boone MO-
Audrain MO-Moniteau MO-Cole MO-Osage MO-Callaway MO-Montgomery MO-
Lincoln MO-Gasconade MO-Warren MO-Saint Charles MO-Franklin MO-
Saint Louis MO-Saint Louis City MO-Jefferson MO-Crawford MO-
Washington MO-Saint Francois MO-Sainte Genevieve MO-Iron MO-
Madison MO-Reynolds MO-
119 PM CDT Sun Apr 19 2026

This Hazardous Weather Outlook is for portions of eastern and
central Missouri as well as west central and southwest Illinois.

.DAY ONE...This afternoon and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

There is a chance of thunderstorms Thursday through Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Jaja