FIRST WARN SEVERE WEATHER STATEMENT
Issued: Tuesday, April 1, 2025 | Prepared by: Dr. Nick Palisch
Coverage Area: St. Louis Metro | Central Missouri | Southeast Missouri | Southern Illinois

MULTI-DAY SEVERE WEATHER AND CATASTROPHIC FLOODING EVENT UNFOLDING

The region is entering a dangerous and prolonged period of severe weather and flooding. Multiple rounds of severe thunderstorms and excessive rainfall will impact Missouri and Illinois from tonight (Tuesday) through Saturday, culminating in what could be a catastrophic, life-threatening flooding disaster in parts of southeast Missouri and southern Illinois.

This forecast is driven by a rare combination of synoptic and mesoscale features, including:

• A potent upper-level trough diving into the central U.S.

• A strong mid-level jet streak (>100 knots) providing large-scale lift

• A stalled frontal boundary acting as a focus for repeated storm development

• Deep Gulf moisture transport creating near-record levels of atmospheric water content (PWATs >1.5")

• Sheared, saturated environments highly conducive for severe convection and efficient rainfall production

TUESDAY NIGHT – LOW-END SEVERE RISK

Forecast reasoning:
Warm air advection and isentropic ascent above a shallow surface warm front will help develop elevated thunderstorms after midnight, primarily across northeast Missouri and west-central Illinois.

• Elevated CAPE (~500–800 J/kg) and steep mid-level lapse rates will support small to marginally severe hail (~1")

• Low-level wind shear will be modest, so organized severe convection is not expected

• Storms will remain elevated, limiting tornado and damaging wind potential

Expect a lull in activity by daybreak, allowing partial destabilization for Wednesday.

WEDNESDAY – SEVERE WEATHER OUTBREAK LIKELY

Forecast reasoning:
By Wednesday afternoon, the region becomes fully warm-sectored, with surface dew points reaching the mid-to-upper 60s, and possibly even 70°F in southeast Missouri. Meanwhile, deep-layer shear (50–70 kt) and 0–1 km shear (20–25 kt) will overlap moderate surface-based instability (CAPE of 750–1250 J/kg).

• A cold front approaching from the west will act as the main trigger

• Forecast hodographs show long, straight-line wind profiles, supporting splitting supercells

• Right-moving supercells will pose the highest threat for very large hail (2+"), damaging winds, and isolated tornadoes

• If any residual boundaries remain from morning convection, low-level helicity (SRH) could locally increase, enhancing tornado potential

Storm Mode and Risk:

• Initial discrete supercells between 1 PM–4 PM

• Transition to line segments or clusters by evening

• Potential for brief spin-up tornadoes within the line, especially in southern Illinois

• Wind-driven event possible if bowing segments dominate storm mode

THURSDAY & FRIDAY – SEVERE STORMS AND CATASTROPHIC FLOODING IN SOUTHEAST MO AND SOUTHERN IL

Forecast reasoning:
A quasi-stationary frontal boundary will remain parked over southeast Missouri and southern Illinois. As successive mid-level shortwaves eject northeast over the front, strong low-level moisture convergence and deep lift will repeatedly trigger thunderstorms.

By Thursday night into Friday:

• The environment becomes increasingly saturated

• Warm cloud depths and tall, narrow CAPE profiles point toward very efficient rainfall rates

• Storms may train repeatedly over the same areas, with precipitable water values in the 99th percentile

Severe Risk:

• While not as widespread as Wednesday, isolated severe storms are likely, especially Thursday evening into Friday

• Damaging winds and brief tornadoes are possible, particularly if embedded convection becomes surface-based

• Localized rotating updrafts may occur along the stalled boundary

CATASTROPHIC AND LIFE-THREATENING FLOODING – THURSDAY THROUGH SATURDAY

Forecast reasoning:
The combination of a stalled surface boundary, strong southwesterly low-level jet (30–40 knots), and enhanced upper-level divergence will result in repeated mesoscale convective systems (MCSs) across the same corridor — particularly targeting southeast Missouri and southern Illinois.

• Integrated water vapor transport (IVT) >95th percentile

• PWATs exceeding 1.5 inches

• Soil saturation from earlier rain will lead to rapid runoff

Forecast rainfall totals:

• Widespread: 6–10 inches

• Localized: 12–15 inches possible, especially if training continues overnight

• Heaviest rain axis expected along/east of the Ozark foothills into the Big Muddy and Kaskaskia River basins

Impact Expectations:

• Rapid-onset flash flooding

• River flooding reaching moderate to major stage, potentially record levels

• Washed-out roads, inaccessible communities, basement and structural flooding

• Overnight flooding risk heightened, especially Friday night into Saturday morning

GRADIENT WINDS – WEDNESDAY

Forecast reasoning:
A tight surface pressure gradient between a deep low in the Midwest and high pressure to the southeast will result in strong southerly surface winds.

• Sustained: 25–35 mph

• Gusts: 40–50 mph, especially across central and eastern Missouri into Illinois

• Potential for tree damage, spotty power outages, and difficult driving conditions for high-profile vehicles

KEY TAKEAWAYS

• Tonight (Tuesday): Isolated storms, low-end hail/wind risk

• Wednesday: Significant severe weather outbreak with large hail, damaging winds, tornadoes

• Thursday–Friday: Repeated rounds of severe storms and extremely heavy rain

• Thursday–Saturday: Catastrophic flooding likely in southeast Missouri and southern Illinois

• Prepare now for prolonged hazards: severe storms, power outages, flooding, and dangerous travel conditions

FINAL WORD FROM DR. NICK

This is not just a typical spring storm system. This is a multi-day, multi-hazard, high-impact event that will evolve with time.
Severe storms will be disruptive. The flooding that follows could be devastating.

From a meteorological standpoint, this is the kind of setup that raises every red flag — extreme moisture, stalled boundaries, strong upper-level support, and back-to-back convective events. This will strain infrastructure and emergency response systems.

Lives will be at risk.
Communities could be cut off.
Do not underestimate this threat.

We will continue issuing updates and live coverage through First WARN as conditions unfold.

— Dr. Nick Palisch
First WARN Meteorologist
Serving St. Louis | Central Missouri | Southeast Missouri | Southern Illinois