Area Forecast Discussion

KEY MESSAGES

- Isolated to scattered showers and thunderstorms are forecast today through Monday, mainly during the afternoon and evening.

- The primary thunderstorm threat is locally heavy rainfall, especially on Sunday and Monday.

- Summer-like heat and humidity build into the region starting Tuesday next week, with a 30% chance of heat index values reaching and exceeding 100 degrees through the rest of the week.

SHORT TERM

(Through Sunday Night) Issued at 211 AM CDT Sat Jun 6 2026

Quasi-zonal flow extends across the Central Plains eastward through the Middle Mississippi Valley as a cutoff spins over the Southern Plains per water vapor imagery. A bifurcated low-level jet is fueling convection over the Middle Missouri Valley and Great Lakes. Of immediate concern, upwind propagation vectors favor the convection over the Middle Missouri Valley moving south- southeastward toward the CWA through this morning. However, with the western prong of the low-level jet weakening through the morning and the air mass south of the convection being increasingly dry and stable, confidence remains high that this convection will struggle to reach the CWA. A reasonable worst-case scenario is that outflow helps force isolated to scattered weak showers and thunderstorms across Knox, Lewis, Adams, and Brown counties around sunrise.

Our next round of convective potential comes this afternoon as the atmosphere ahead of the aforementioned cutoff drifting northeastward becomes increasingly unstable. The 00z HREF and REFS means have approximately 2,500-3,000 J/kg of SBCAPE across the CWA during peak heating today, with this instability and weak forcing from the cutoff inducing CI at roughly 3pm. Deep-layer shear of 10-20 kts favors disorganized single cells to multi-cells primarily west of the Mississippi River where lift will be greatest; though, there is at least a low threat (15-20% chance) for showers and thunderstorms area-wide. There is a low chance that residual outflow boundaries and/or a weak front just north of the CWA may provide a focus for CI in proximity to greater instability this afternoon and evening. The greater instability favors relatively stronger updrafts compared to elsewhere in the CWA, leading to a localized threat of hail up to 1" in diameter and damaging wind gusts. However, the weak shear suggests that updrafts will tend to be too short-lived to provide a severe threat; therefore, the SPC Day 1 Marginal Risk will not be publicly messaged.

Diminishing instability with the loss of day-time heating will lead to decreasing convective coverage this evening. The exception will be areas west of the Mississippi River where forcing from the approaching cutoff will keep a low chance (30%) for showers and thunderstorms going through the overnight hours. As this shortwave continues to pass overhead during the day Sunday and instability builds once again, convective coverage will increase. Thanks to more widespread lift via the shortwave, the entire CWA has a 80-90% chance of seeing scattered showers and thunderstorms at times Sunday into Sunday evening. Deep layer shear is expected to be weak once again, with the greater storm coverage and PWAT just under 2" supporting a threat of locally heavy rainfall.

Elmore

LONG TERM

(Monday through Friday) Issued at 211 AM CDT Sat Jun 6 2026

With the aforementioned cutoff only slowly lifting northeastward through the Midwest, guidance consensus is that rain chances will linger across the Middle Mississippi Valley on Monday. Uninhibited Gulf flow will keep dew points in the low 70s, yielding SBCAPE around 2,000 J/kg to as much as 3,000 J/kg per the 90th percentile of ensemble guidance. While deep-layer shear of around 20 kts leads to low confidence in organized severe convection, when coupled with PWAT around the 99th percentile of climatology, there is concern for localized heavy rainfall.

Confidence in the forecast decreases as we get into the middle of next week through the end of the week, with both deterministic guidance and ensemble clusters differing on the phasing of an upper- level trough over the northwestern CONUS and expansive ridging over the southern CONUS. A deeper trough and one that encroaches more upon the Midwest will keep the ridge further south relative to the CWA, favoring temperatures topping out around 90 degrees Tuesday through Thursday (50-80% chance per global ensembles). If the ridge is able to build further northward into the CONUS, then portions of the CWA could see high temperatures warm into the mid 90s (30% chance). The current forecast (NBM) favors the warmer solutions and represents a realistic "worst-case" scenario. If this scenario comes to fruition, then the first heat headlines of the season will be needed for portions of the CWA.

Elmore

AVIATION

(For the 18z TAFs through 18z Sunday Afternoon) Issued at 1217 PM CDT Sat Jun 6 2026

The TAF period will be characterized by at least low chances (20 percent) of showers and thunderstorms throughout. However, confidence is highest in development and impacts this afternoon into evening at all terminals, warranting PROB30 groups. Thunderstorms will be capable of IFR visibilities and gusty winds. The chance of showers and thunderstorms increases through the day on Sunday, but mainly near or beyond the TAF period. Otherwise, a period of MVFR ceilings is likely again Sunday morning, primarily at KCOU, KJEF, and KUIN.

Pfahler

LSX WATCHES / WARNINGS / ADVISORIES

MO...None. IL...None.