Area Forecast Discussion

KEY MESSAGES

- Active pattern this week with numerous rounds of showers and storms with heavy rain.

- There is a Marginal Risk, Level 1 out of 5, for severe storms this evening into tonight for the western portions of the outlook area. Primary hazards will be heavy rain and isolated damaging winds.

- An elevated flash flood risk may develop mid-week with repeating rounds of storms. There is a moderate chance (50-70%) for parts of the area to see over 2 inches of rainfall with localized areas of 4+ inches possible (5-15%), leading to rises on area creeks and streams.

SHORT TERM /THROUGH TUESDAY/

Issued at 145 AM CDT Mon Sep 14 2026

Today appears to be a rinse and repeat of yesterday with scattered showers (30-60% coverage) moving in late morning from the west along a WAA band north of an approaching warm front. There will be a small amount of instability in the form of 250-750 J/kg of MUCAPE which should support a few rumbles of thunder, but the overall severe potential is low (less than 5%). These showers and isolated storms are expected to exit the area to the northeast by the late afternoon as the low-level WAA weakens.

By tonight, the closed heights center over south-central Canada and its accompanying mid-latitude cyclone occludes and pushes a cold front southward into northern Iowa. Widespread storms (80-100% coverage) are forecast to develop along the boundary and propagate southeastward into our CWA. A 50-knot mid-level jet over the area will enhance the effective bulk shear, but the lack of steep mid-level lapse rates will keep the instability tame at 250-750 J/kg of MLCAPE. Therefore, the overall severe threat is once again low with these overnight storms. Still, there remains a Marginal Risk, Level 1 out of 5, for severe storms along and west of the I-380 corridor with isolated damaging winds as the primary threat.

The remaining storms are expected to decrease in coverage and intensity heading into Tuesday as the cold front inches its way southward towards the Iowa-Missouri border. As the severe threat with these storms diminishes, attention starts to turn towards the flooding potential, especially across east-central Iowa, as storms could train over the same area resulting in flash flooding. Latest CAM guidance is suggesting 1-2 inches tonight through Tuesday evening across northwestern Illinois and areas along and north of I-80 in Iowa with swaths of 3+ inches possible (10-20% chance). The WPC does have a Slight Risk, Level 2 out of 4, for excessive rainfall across the entire outlook area during the same time period.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

Issued at 145 AM CDT Mon Sep 14 2026

By Tuesday night, the cold front will stall out across northern Missouri and central Illinois and act as the focal point for rounds of showers and storm to redevelop late week. A nearly stationary longwave trough over the western CONUS and ridging over the Southeast will keep our upper-level flow out of the southwest through Thursday as weak shortwaves are pulled northeastward into the Midwest. This will keep PoPs around Tuesday night into Thursday as scattered showers and storms fire along and north of the stationary front. With PWATS over 1.75 inches likely (70-90%) area-wide through Thursday, the flooding threat will remain elevated, especially after the heavy rainfall tonight and Tuesday. There is a moderate chance (50-70%) of storm totals in the 2-3-inch range across eastern Iowa through Thursday with localized areas of 4+ inches possible (5-15%). Rises on area creeks and streams are likely.

Heading into Friday, a Front Range low in Colorado is forecast to form due to forcing from a lobe of mid-level vorticity pulled northward from the subtropics. This will introduce a more southerly component to the low-level flow as the stationary front finally converts to a warm front and moves northward into Iowa. The upper-level flow is expected to become zonal and force the Front Range low eastward Friday night into Saturday. The increased surface convergence will support another round of storms before the same boundary is left behind for Sunday, keeping PoPs around.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 102 PM CDT Mon Sep 14 2026

VFR conditions are expected through most, if not all, of the evening hours tonight before chances of showers and storms increase overnight (70-90%). Early this afternoon, some light showers continue to traverse over northeastern Iowa, with little in the way of visibility reductions. Upstream over central Iowa where rainfall has ceased, we're seeing southeast winds gusting around 20 to 25 knots as boundary layer mixing increases, which is expected to make their way over eastern Iowa this afternoon, so expect winds to pick up for a time through sunset.

A period of non-convective low-level wind shear should develop this evening across the area, with shear magnitudes around 40 to 50 knots. This LLWS could be short-lived around CID and DBQ as chances of thunderstorms develop there. One-hour thunderstorm probabilities from the latest HREF indicates values of 50-70% for these two terminals, so have decided to use TEMPO groups to highlight thunderstorm timing, with MVFR to IFR visibility reductions likely, with largely VFR ceilings. Where storms are a bit more delayed (MLI and BRL), the LLWS should persist for longer.

DVN WATCHES / WARNINGS / ADVISORIES

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