SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Sat Oct 04 2025 Valid 042000Z - 051200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL HIGH PLAINS... ...SUMMARY... Isolated severe wind gusts/hail may accompany the stronger thunderstorms that develop from the central Rockies/High Plains into the northern Plains late this afternoon into tonight. ...20Z Update... The forecast remains on track, and only minor adjustments were made with this update. The MRGL risk in MN was expanded slightly southward based on the latest positioning of the surface front (per 19Z surface analysis). Marginally severe hail accompanying elevated overnight thunderstorms will be the primary concern here. Elsewhere, a northeastward extension of the SLGT risk into southern SD was considered, where middle/upper 50s dewpoints will contribute to slightly larger buoyancy along the surface boundary. While a localized uptick in thunderstorm intensity is possible here tonight (as depicted by some high-resolution guidance), confidence in this scenario is too low for the upgrade -- especially considering the late timing/nocturnally cooling boundary layer. See the previous discussion below for more details. ..Weinman.. 10/04/2025 .PREV DISCUSSION... /ISSUED 1110 AM CDT Sat Oct 04 2025/ ...Central Rockies/High Plains into the Northern Plains... An upper trough/low with attendant strong south-southwesterly mid-level jet will advance eastward today from the Great Basin across the central Rockies/High Plains, eventually reaching the northern Plains late tonight. At the surface, a cold front extends from the Dakotas southwestward to eastern WY/north-central CO. This front should serve as a focus for strong to isolated severe thunderstorms this afternoon through tonight. Recent observations and 12Z observed soundings along/ahead of the front show limited low-level moisture, with surface dewpoints generally in the mid 40s to 50s. Even with filtered diurnal heating through this afternoon, instability is forecast to remain rather weak as low-level lapse rates gradually steepen with deep boundary layer mixing. Stronger mid-level flow associated with the upper trough is expected to overspread the central High Plains by mid to late afternoon, where up to 500 J/kg of MLCAPE appears plausible. Current expectations are for high-based thunderstorms to spread northeastward from the central Rockies into the adjacent High Plains this afternoon and evening in a weakly unstable but strongly sheared environment. This may support an organized cluster or two, capable of producing mainly isolated strong to severe gusts. The greatest severe wind potential still appears focused across parts of southeast WY/northeast CO into the NE Panhandle, where the Slight Risk has been maintained with no changes. Other thunderstorms may eventually form this evening/overnight across parts of the northern Plains and northwest MN as low-level warm advection gradually strengthens in tandem with an increasing southerly low-level jet. This activity should tend to remain elevated along/north of the cold front. But, given sufficient MUCAPE and strong deep-layer shear forecast, the more robust cores may be capable of producing isolated severe hail/wind.
