460 ACUS02 KWNS 130606 SWODY2 SPC AC 130604 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 0104 AM CDT Mon Apr 13 2026 Valid 141200Z - 151200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF IOWA INTO NORTHERN ILLINOIS AND SOUTHERN WISCONSIN... ...SUMMARY... Isolated to scattered severe thunderstorms are expected on Tuesday and Tuesday night from the Southern Plains to the Great Lakes. Large to very large hail, a few tornadoes, and damaging wind gusts will be possible, particularly across parts of eastern Iowa, northern Illinois, and southern Wisconsin. Additional strong storms, mainly producing strong wind gusts, will be possible across parts of the Northeast. ...Synopsis... A broad swath of enhanced deep-layer southwesterly flow will overspread the southern High Plains to the Great Lakes on Tuesday. An upper shortwave trough over the Great Basin will slowly pivot east through the period, emerging over the central/southern High Plains by Wednesday morning. A weak shortwave impulse is also forecast to move across the northern Plains and Upper Midwest. At the surface, low pressure will be centered over the Mid-MO Valley for much of the period, with a warm front extending east/northeast from north-central IA into southern WI and central Lower MI. Meanwhile, a dryline will extend southwest across eastern KS into western TX. Ahead of these boundaries, a seasonally moist airmass will be in place, with mid-60s dewpoints common. The aforementioned surface boundaries will become a focus severe thunderstorm development Tuesday afternoon into the nighttime hours. ...Mid-MS Valley and Great Lakes vicinity... A severe risk is expected to develop by late afternoon within the warm frontal zone from Iowa into northern IL/southern WI in a persistent warm advection regime. While height tendencies are forecast to remain mostly neutral, low-level convergence along the boundary and a glancing influence from a weak shortwave impulse migrating across the northern Plains into northern MN/Upper MI should provide focused ascent. A southwesterly 850-700 mb jet is also forecast to increase across the region by late afternoon into evening. Cool temperatures aloft (around -16 C at 500 mb) and steep midlevel lapse rates atop a moist boundary layer will support MLCAPE around 2000-3000 J/kg amid elongated/straight hodographs. As a result, large to very large hail will be possible with initial supercell thunderstorms. Storm motion and southwesterly deep-layer flow may result in convection moving to the cool side of the warm front. Even so, elevated storms will pose a risk for significant hail. With time, and as the low-level jet increases during the evening, convection may consolidate/grow upscale into one or most bowing segments and progress eastward into Lower MI/IN/OH, posing a continued risk for hail and an increasing risk for damaging wind gusts. Any supercells that develop and can be sustained within the warm sector will also pose a risk for a few tornadoes (some strong), very large hail and damaging gusts. ...Southern Plains into eastern KS/western MO... Moderate destabilization is forecast along the surface dryline by afternoon. Strong heating along/just west of the dryline will promote mixing, while low-level confluence and subtle height falls (by 21-00z) provide sufficient forcing for ascent for isolated thunderstorm development. Supercell wind profiles will be present amid steep midlevel lapse rates and elongated hodographs. Large to very large hail, locally strong wind gusts and a couple of tornadoes will be possible. Storms should develop northward during the evening into eastern KS and western MO as the low-level jet increases. ...Northeast... Rounds of thunderstorms are expected during the afternoon and evening within a warm advection regime. MLCAPE should increase to around 1000 J/kg within a moistening low-level airmass. Strong deep-layer westerly flow and steepening low-level lapse rates will support isolated strong wind gusts across the region. ..Leitman.. 04/13/2026 $$