SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1230 AM CDT Thu Jul 03 2025 Valid 031200Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHEAST AND NORTHERN PLAINS... ...SUMMARY... Scattered severe thunderstorms capable of producing severe/damaging winds and large hail are forecast across parts of the Northeast and northern Plains today. ...Northeast... An upper trough with an embedded 40-50 kt mid-level speed maximum will pivot across the Northeast today. A related surface cold front will likewise develop eastward across this region through the afternoon/evening. Filtered daytime heating of a seasonably moist low-level airmass will support the development of moderate instability along/ahead of the cold front by late morning/early afternoon. Aided by the enhanced mid-level flow, deep-layer shear will likely be strong enough to support updraft organization, including a mix of multicells and perhaps some supercells. Scattered severe/damaging winds should be the primary severe threat as low-level lapse rates gradually steepen. But, some large hail may occur given favorable shear, especially if any supercells can be sustained. The Slight Risk has been expanded northward to include more of New England, as recent guidance trends show potential for organized severe convection along/ahead much of the length of the front. ...Northern Plains... An upper ridge will persist over much of the Plains today. Even so, a weak mid-level disturbance is forecast to advance eastward from MT across the northern Plains this afternoon/evening on the northern periphery of the upper ridge. This feature should encourage isolated to scattered intense thunderstorm development along/near a warm front extending across parts of ND by late afternoon/early evening. Moderate to strong instability is expected along/near this boundary, aided by steep lapse rates aloft. Modest low-level southerly flow is forecast to gradually veer and strengthen with height through mid/upper levels. This will support sufficient deep-layer shear (30-40 kt) for organized convection, including some supercells initially across western/central ND. These supercells should pose a threat for scattered large hail, some of which may be 2+ inches in diameter given a rather favorable thermodynamic environment forecast. With time this evening, there may be some potential for upscale growth into a small bowing cluster with eastward extent into central/eastern ND. If this mode transition occurs, then the severe/damaging wind threat would likewise increase. Although low-level flow should remain fairly modest, a tornado or two also appears possible, particularly along/near the front where effective SRH should be locally enhanced. ...Upper Midwest... Compared to the northern Plains, there is generally less confidence in overall thunderstorm coverage and development across much of the Upper Midwest through the period. Weak forcing aloft and the persistence of the upper ridge should tend to limit convective development in an otherwise moderately to strongly unstable airmass. Still, any thunderstorms which can develop, perhaps aided by modest low-level warm advection this evening/tonight, could pose an isolated severe hail/wind threat. The Marginal Risk area has been adjusted northward/westward some based on latest guidance trends showing multiple potential zones of isolated strong/severe thunderstorms. ..Gleason/Lyons.. 07/03/2025