SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0750 AM CDT Thu Jun 19 2025 Valid 191300Z - 201200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE MID-ATLANTIC... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN PLAINS/UPPER MIDWEST... ...SUMMARY... Severe thunderstorms are expected across much of the Mid-Atlantic region today, and to a lesser extent into the Carolinas and over portions of New England. Severe/damaging wind gusts are the primary concern. An isolated large hail threat should also develop across parts of the northern Plains/Upper Midwest, primarily during the evening/overnight hours. ...New England/Mid-Atlantic into North Carolina... An upper trough will move eastward today from the Great Lakes/OH Valley across the Mid-Atlantic and Northeast. Seasonably strong southwesterly mid-level flow around 40-50 kt will accompany this upper trough passage, and aid in sufficient deep-layer shear for organized severe thunderstorms across these regions. Recent visible satellite imagery and surface observations show mostly clear skies and a moist low-level airmass already in place from the Appalachians towards the Mid-Atlantic Coast. Ample diurnal heating through this afternoon should support moderate to locally strong instability across much of the Mid-Atlantic, with somewhat weaker instability with northward extent into interior New England. Current expectations are for multiple cells/clusters to initially form over the higher terrain of the Appalachians/Blue Ridge Mountains by early to mid afternoon, and subsequently spread east-northward to the coast through the afternoon and evening. Given steepened low-level lapse rates and enhanced low/mid-level flow associated with the upper trough, scattered to potentially numerous severe/damaging winds will likely be the primary threat with this convection. The greatest concentration of wind damage should be focused across parts of the Mid-Atlantic, where the Enhanced Risk has been maintained with only minor expansion. Otherwise, isolated hail may also occur with any of the more cellular convection, even though mid-level lapse rates are not forecast to be overly steep. A brief tornado or two also appears possible, although low-level winds will generally be veered to west-southwesterly, limiting 0-1 km SRH. ...Southeast... A band of thunderstorms is ongoing this morning across parts of the Mid-South/Southeast. This activity has generally remained sub-severe overnight, and on the southern periphery of an upper trough to the north. With strong daytime heating of a rather moist low-level airmass in place to its south and modest deep-layer shear for updraft organization, there is some opportunity for this convection to either restrengthen through the afternoon as it spreads southward, or for redevelopment to occur along its outflow. Have adjusted the Marginal Risk for damaging winds based on the current position of ongoing thunderstorms, and their potential to move southward across parts of the Southeast/central Gulf Coast states this afternoon/early evening before eventually weakening near the Gulf Coast. ...Northern Plains/Upper Midwest... Upper ridging will be maintained today over much of the Rockies and High Plains. This will tend to suppress convective development for much of the day. Still, a weak mid-level shortwave trough will move from western Canada across the Canadian Prairie provinces today, eventually reaching parts of the northern Plains and Upper Midwest tonight. This feature, along with increasing low-level warm/moist advection associated with a strengthening southwesterly low-level jet across the northern/central Plains this evening, may be sufficient to aid at least isolated robust thunderstorm development tonight generally along and north of a surface boundary. Strong MUCAPE, steep lapse rates aloft, and ample deep-layer shear would likely support supercells with associated threat for large hail in a favorable northwesterly mid/upper-level flow regime. There is still some uncertainty with the placement and overall coverage of these supercells tonight, but based on latest guidance trends the Slight Risk has been expanded eastward to include more of central/eastern MN and western/northern WI. Isolated damaging winds may also occur if an MCS is able to develop, although this remains highly uncertain. ...Central Plains... Moderate to strong instability is forecast to develop this afternoon across parts of the central Plains along/east of surface lee troughing. Even though deep-layer shear and forcing aloft will not be as pronounced as farther north, there appears to be some chance for high-based convection to develop and pose an isolated hail/wind threat. ..Gleason/Kerr.. 06/19/2025