Day 1 Convective Outlook
This product has been superseded. View the updated product →
Issued: · Valid: –
Summary
Scattered severe thunderstorms are expected today and tonight across parts of the Mid-Atlantic, Southeast, and Central Plains into the Upper Mississippi Valley. Potential hazards include damaging wind gusts and tornadoes in the Mid-Atlantic and Southeast, and large hail and strong winds from Nebraska through Wisconsin.
Product Text
000 ACUS01 KWNS 201248 SWODY1 SPC AC 201246 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 AM CDT Thu Aug 20 2026 Valid 201300Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE MID-ATLANTIC...AND FROM THE CENTRAL PLAINS INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Scattered severe storms are possible today and tonight across parts of the Mid Atlantic, posing a risk for damaging wind gusts. Large hail and isolated wind damage will be possible with severe storms from Nebraska into northwest Wisconsin. ...Central Appalachians into the Mid-Atlantic... Broad upper troughing currently extends from the northern Plains through New England, with an embedded shortwave trough progressing across the Mid MS Valley into the Lower OH Valley. Showers and thunderstorms are ongoing ahead of this shortwave, and the expectation is that these showers and thunderstorms will continue weakening this morning. A moist airmass is in place downstream of this wave (i.e. from the central Appalachians and upper OH Valley into the Mid-Atlantic), and reintensification and/or new development is expected ahead of this wave as it continues northeastward into this diurnally destabilized region. Surface low associated with this wave is currently over the IN/OH/KY border vicinity. This low is forecast to deepen slightly as it moves northeastward just ahead of the parent shortwave trough. Modest low-level moisture advection will precede this low, and a warm front is forecast to lift northward across southern PA, northern MD, and most of NJ. Despite poor lapse rates, ample low-level moisture south of the front will support moderate buoyancy. Reintensification and/or new thunderstorm development is expected first near the Blue Ridge and across the higher terrain of southern PA and northern MD before increasing in coverage and intensity with eastward extent. A belt of slightly stronger mid-level flow will precede the shortwave, resulting 40 to 50 kt of effective bulk shear. This is more than sufficient to support a mix of supercells and organized line segments. Damaging wind gusts will be the primary risk, but southerly winds will enlarge low-level hodographs from the Delmarva into central NJ, supporting the potential for a couple of tornadoes. ...Carolinas into the Southeast... Ample low-level moisture and strong heating will result in an unstable airmass from the Carolinas into much of the Southeast. Low-level convergence along a cold front that will extend from the western Carolinas into AR this afternoon will result in scattered thunderstorm coverage. Vertical shear will be weak, and an outflow-dominant storm structure is anticipated. Even so, moderate to strong buoyancy and ample moisture (PW around 2") will support occasionally strong water-loaded downbursts, particularly from western TN into AL and MS where high temperatures in the upper 90s are anticipated. ...Central Plains into the Upper MS Valley... A reservoir of greater low-level moisture (i.e. dewpoints in the upper 60s) currently extends from AR/eastern OK northwestward across much of KS and into NE. Modest low-level moisture advection is anticipated throughout this corridor today, as a tightening surface pressure gradient results in stronger southerly surface winds. Mid 60s dewpoints could reach as far north as southwest MN. Moderate to strong buoyancy will develop within this corridor, with the greatest buoyancy likely from the CO/KS/NE border vicinity northeastward into southeast SD. At the same time, a cold front will progress southeastward across western MN, central SD and western NE, interacting with this buoyancy to support thunderstorm development. Thunderstorm initiation is anticipated first across the Upper MS Valley before expanding southwestward. Moderate northwesterly flow aloft will support supercell wind profiles, with elongated/straight hodographs, and the threat for all severe hazards. Large to very large hail (i.e. greater than 2 inch diameter) will be the primary severe hazard, particularly during the early evening as the storms move into greater instability. Isolated strong to severe gusts (i.e. 55 to 75 mph) are possible as well. Given the supercellular storm mode and low-level southerly flow, a low-probability tornado risk also exists. Some risk for isolated damaging gusts may persist into the early overnight across southern NE and northern KS if clustering can occur. ...AZ... Another round of scattered thunderstorms this afternoon and evening amid seasonably rich monsoon moisture (dewpoints in the upper 50s to 60s F) and moderate buoyancy. The lower elevations will be characterized by greater convective inhibition than yesterday, with the overall buoyancy slightly lower as well. Consequently, despite a similar upper pattern, the overall potential for strong gusts is expected to be lower than yesterday. Even so, isolated gusts are still possible as storms move off the high terrain into the deeply mixed airmass over the lower elevations. ..Mosier/Bunting.. 08/20/2026 $$