SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Thu May 01 2025 Valid 011300Z - 021200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE LOWER MS VALLEY THROUGH THE TN AND OH VALLEYS INTO THE LOWER GREAT LAKES...AND FROM THE TX/OK PANHANDLES EASTWARD ACROSS OK AND NORTH TX.... ...SUMMARY... Lines and/or clusters of strong to severe thunderstorms are likely to impact parts of the Ohio Valley into lower Great Lakes, parts of the lower Mississippi Valley, and the southern Great Plains this afternoon through tonight. ...Synopsis... Early morning satellite imagery shows several shortwave troughs across the CONUS, including one entering the Lower MO Valley/Ozarks vicinity, another moving into NE, and another off the southern CA coast. The lead wave is forecast to progress quickly northeastward through the OH Valley and Great Lakes while losing amplitude under the increasingly confluent flow aloft. At the same time, another shortwave trough will drop southeastward through the northern High Plains into the northern/central Plains, leading to some amplification of the upper troughing across the north-central CONUS. Recent surface analysis revealed several lows within a broad area of low pressure across the central CONUS, one over west-central IL, another near the SD/ND/MN border intersection, and a third over north-central OK. A warm front extends eastward from the low over west-central IL, while modest troughing extends between the Upper Midwest low and the one over north-central OK. The west-central IL low is expected to deepen throughout the day as it moves northeastward ahead of its parent shortwave, with the attendant warm front advancing northward as well. The northernmost surface low is expected to progress slowly eastward as well, with its associated surface troughing also drifting eastward. A more stationary pattern is anticipated in the vicinity of the OK low throughout much of the period. ...TN/OH Valleys into the Lower Great Lakes... Low 60s dewpoints are already in place across the Lower OH and TN Valley this morning. Continued northward/northeastward advection of this low-level moisture is anticipated today as the surface low progresses northeastward. This increased moisture coupled with modest heating will help support moderate buoyancy across much of the region by early afternoon. Broad large-scale ascent and surface troughing are expected over the region amid this destabilization, which is forecast to result in widespread thunderstorms during the afternoon and evening. The convective mode will likely be dominated by linear structures, with one or more convective lines possible. Primary severe risk will be damaging gusts, supported by moderate southwesterly flow in the lower troposphere. Some hail is also possible, particularly during cell mergers. The tornado risk will be low but non-zero, as veered low-level flow limits the low-level shear. ...Lower MS Valley... The airmass across the region is expected to quickly destabilize as low-level moisture advects back into the region in the wake of the convection currently moving through. Upper 60s dewpoints coupled with modest heating will result in moderate to strong buoyancy and no convective inhibition by the early afternoon. Even modest low-level convergence should be enough to initiate deep convection, but any remnant outflow could also act as a focus for convective initiation. Robust updrafts are expected with initial development, with a quick trend towards outflow-dominant structures. Large hail and damaging gusts are the primary risks. ...TX/OK Panhandles into much of OK and north TX... Low-level moisture is expected to advect back northwestward into the TX Panhandle throughout the day. Cold mid-level temperatures are already in place (-16 deg C at 500 on the 12Z AMA sounding), so this added low-level moisture coupled with glancing ascent will likely result in late evening thunderstorm development. Most of the convection-allowing guidance is suggesting these storms will grow upscale quickly into an MCS, with some of guidance suggesting it could be quite and capable of producing significant wind gusts as it moves eastward across the TX Panhandle and into OK. Additionally, gradual increase in the low-level moisture beneath cold mid-level temperatures and associated steep mid-level lapse rates will result in strong buoyancy across southern OK. Modest warm-air advection could result in convective initiation across this region amid an environment that supports very large hail. Complex interaction is possible between the potential MCS and the more cellular development ahead of it, but some severe threat appears possible through early tomorrow morning. ..Mosier/Jewell.. 05/01/2025