SPC 0100Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 PM CDT Thu Jun 19 2025 Valid 200100Z - 201200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY... ...SUMMARY... Scattered severe thunderstorms with large to very large hail and damaging wind gusts are expected across the northern Plains and upper Mississippi Valley this evening into tonight. Isolated severe gusts will also be possible from central and eastern North Carolina north-northeastward to New England. ...Northern and Central Plains/Upper Mississippi Valley... Latest water vapor imagery at mid-levels shows a ridge over the High Plains, with west-northwesterly flow over much of the central and northern Plains. At the surface, a 1002 mb low is located over north-central South Dakota, with a trough extending south-southwestward into northwest Kansas. An axis of low-level moisture is analyzed from central Plains northward to near the surface low and northwestward into western North Dakota. Along this corridor, the RAP has MLCAPE mostly in the 2000 to 3000 J/kg range. A severe storm is currently ongoing near the instability max in southwest North Dakota, with additional isolated severe storms located in north-central Nebraska and northwest Kansas. Moderate deep-layer shear is present across much of the central and northern Plains, which will contribute to an environment supportive of supercells this evening. A severe threat with more longevity is expected in the northern Plains. The Bismarck 00Z sounding has a 0-6 km shear around 40 knots, with nearly dry adiabatic low to mid-level lapse rates. This will support supercells with large to very large hail, possibly greater than 2 inches in diameter. This, combined with surface dewpoints in the lower 60s F and substantial directional shear from the surface to 700 mb, will also support an isolated tornado threat. Concerning future convective development, the latest HRRR maintains a widely spaced coverage for much of the early to mid evening, but then begins to increases thunderstorm coverage over eastern parts of the northern Plains late this evening. As the nose of a low-level jet moves into the eastern Dakotas, a cluster of severe storms is expected to develop and move eastward into the upper Mississippi Valley tonight. Supercells with large hail will be possible with cells than remain discrete. However, linear mode should become favored, which will likely support an increase in the potential for severe gusts. ...Eastern States... A mid-level trough is currently evident on water vapor imagery over the southern and central Appalachians. Ahead of the trough, a moist airmass is present from the Carolinas north-northeastward into New England. The RAP suggests that instability is weak along and ahead of the surface trough. Short-term model forecasts suggest that scattered convective coverage will continue over the next few hours. 00Z soundings across the region show moderate deep-layer shear and have steep lapse rates around 850 mb. This should support an isolated severe threat over the next couple of hours as low-level flow gradually increases. Severe wind gusts will be the primary threat, associated with short bowing line segments. ..Broyles.. 06/20/2025