SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Mon May 19 2025 Valid 191300Z - 201200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FAR NORTH TEXAS...MUCH OF CENTRAL AND EASTERN OKLAHOMA...SOUTHEAST KANSAS...AND THE OZARKS... ...SUMMARY... Significant severe weather is likely from the central/southern Plains into the the Ozarks today into tonight. All severe weather hazards are expected, to include tornadoes (some potentially strong to intense), very large hail, and severe winds. ... Synopsis ... A large, amplified trough over the Rockies will shift slowly eastward into the Plains today. Embedded within this longwave trough, a complex evolution is expected. Downstream of the trough, a negatively tilted shortwave trough will deepen and close off across the northern Plains. Meanwhile, upstream, a closed low currently over Idaho will dig southeastward, open up, and eject into the central Plains. As this evolution occurs, strong midlevel flow (in excess of 50 knots) will remain across much of the central and southern Plains through the forecast period. By late in the afternoon, midlevel flow will strengthen to perhaps 70 knots in response to the ejecting low into the central Plains. At the surface, the main synoptic low will be somewhat diffuse/elongated over northwest Kansas into southwest Nebraska this morning. Extending southward from this low, a dryline will stretch through western Kansas into the Oklahoma and Texas Panhandles, continuing into west Texas. A warm front will extend eastward near the Kansas-Nebraska border before curving southeastward into Missouri into the southern Appalachians. The surface low is expected to gradually fill today as it slowly moves east/northeast into south-central Nebraska, Despite this, rich Gulf moisture will be maintained across the central and southern Plains. Dewpoint temperatures at or above 70F will advect northward from Texas through Oklahoma perhaps to as far north as northeast Kansas. During the afternoon, strong diurnal heating along the dryline may result in a sub-synoptic low developing across northwest Oklahoma. This low will slowly progress east along the Oklahoma-Kansas border during the afternoon, weakening with time. ... Southern and Central Plains into the Ozarks ... A strongly sheared atmosphere will already be in place at the start of the forecast period. As diurnal heating commences and 70F dewpoints advect northward, the atmosphere across much of the central and southern Plains will become strongly to extremely unstable as well, with surface-based CAPE values between 3000-5000 J/kg across the region. Multiple rounds of storms are expected across the region today. One such initiating mechanism looks to be a subtle shortwave trough embedded in the larger scale flow currently across eastern New Mexico. This wave should initiate thunderstorms across eastern Oklahoma northward into eastern Kansas by midday. It is unclear if these storms will initially be elevated, but as they move east and the atmosphere destabilizes further ahead of the line, a transition to more surface-based convection should occur. At the same time, the low-level jet is forecast to strengthen/reorganize across eastern Oklahoma/western Arkansas into western Missouri. This will yield ample low-level curvature to the hodograph. Thus, given the strongly sheared environment in place, supercells capable of producing all severe hazards, including strong tornadoes, will be possible with this first round of storms. By mid-to-late afternoon, 30-60 meter mid-level height falls should overspread the dryline as it mixes east into central Kansas southward into western north Texas. Rapid thunderstorm development is expected along the dryline given the forecast extreme instability. These thunderstorms should develop west of the better low-level jet/flow, where the low-level flow is expected to be a little more veered than across eastern Kansas/Oklahoma. This veered low-level flow still will result in a strongly sheered environment, but with more straight hodographs and less low-level curvature. The result should be another round of supercells, albeit with a tendency to split. These supercells will be capable of producing very large hail and tornadoes. The number of supercells across the dryline combined with a propensity to split, may result in destructive interference and result in a more episodic hail and tornado threat. In addition to the hail and tornado threat, the number of expected thunderstorms in the presence of a very moist and unstable atmosphere with steep lapse rates may result in strong downdraft winds. The most likely region for this will be across portions of northeast Oklahoma, northwest Arkansas, southeast Kansas, and southwest Missouri. A 45% wind area was included in this outlook. ... Southern Illinois into Southern Appalachians ... Along the northern periphery of shortwave ridging over the Southeast, a midlevel jet streak will cross the southern Appalachians during the afternoon. Here, an influx of steep midlevel lapse rates atop rich boundary-layer moisture will yield strong surface-based instability along/south of a warm front draped across the region. Scattered thunderstorms will spread east-southeastward along/south of the front from TN into the southern Appalachians, where the favorable buoyancy and around 40-50 kt of effective shear will promote organization into clusters and a couple splitting supercell structures. Damaging winds and large hail will be possible with the strongest storms. Overnight, additional thunderstorms may develop across southern Illinois and western Kentucky in association with warm-air advection ahead of the main area of thunderstorms to the west. These thunderstorms will also pose the potential for small hail and isolated wind damage. ..Marsh/Smith.. 05/19/2025