SPC Day 1 Convective Outlook — 06Z Forecast Discussion on 27 April 2024

164 ACUS01 KWNS 270605 SWODY1 SPC AC 270604 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0104 AM CDT Sat Apr 27 2024 Valid 271200Z - 281200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NORTH TEXAS...OKLAHOMA...SOUTHEAST KANSAS AND FAR SOUTHWEST MISSOURI... ...SUMMARY... Numerous severe thunderstorms are likely today and tonight across the southern and central Plains into the lower to mid Missouri Valley. The greatest potential for severe storms will be from north Texas into Oklahoma and southeast Kansas, where strong tornadoes, very large hail over 2 inches in diameter and widespread damaging winds (some over 70 mph), are expected to occur. A broader area of severe threat will extend from south-central Texas north-northeastward to the Great Lakes. ...Tornado Outbreak Expected Today From North Texas into Oklahoma...Southeast Kansas and Far Southwest Missouri... ...Southern Plains... An upper-level trough will move through the Desert Southwest today as an 80 to 90 knot mid-level jet translates quickly eastward through the base of the system. Ahead of the trough, a moist and unstable airmass will be in place across much of the southern and central Plains. At the surface, a low will move eastward across southwest Kansas with a dryline extending southward through far western Oklahoma and west Texas. Surface dewpoints to the east of the dryline will be in the mid to upper 60s F. In response to warm advection this morning, a cluster of thunderstorms is expected to develop to the east of the dryline across northwest Texas. This cluster is forecast to spread north-northeastward into western Oklahoma by late morning. Large hail and wind damage will be likely with the stronger cells within this cluster. An outflow boundary with this convection should setup across west-central Oklahoma by early afternoon, with a moist and unstable airmass extending eastward from the boundary across much of central and eastern Oklahoma northward into southeast Kansas. This undisturbed airmass is expected to be favored for the greatest severe threat this afternoon and evening. The mid-level jet is forecast to eject quickly northeastward across the southern Plains this afternoon. This will result in strong deep-layer shear across most of the southern Plains, and will create a large-scale mass response that will be very favorable for severe storms, including supercells and bowing line segments. As the core of the mid-level jet moves into the southern Plains during the mid to late afternoon, a 50 to 60 knot low-level jet will rapidly strengthen. RAP forecast sounding along and near the low-level jet during the late afternoon look very favorable for tornadoes, with backed surface flow, and long looping hodographs. As the low-level jet strengthens, 0-3 km storm-relative helicity is forecast to increase to around 400 m2/s2 across much of central and eastern Oklahoma into southeast Missouri. The more dominant and supercells that interact with the western and northern edge of the low-level jet are expected to become tornadic. Several strong tornadoes will be likely, and a few long-track EF3+ tornadoes will be possible. In addition to the tornado threat, forecast soundings have 700-500 mb lapse rates near 8 C/km across much of the warm sector this afternoon from north Texas to southeast Kansas. This will be favorable for very large hail, with hailstones over 2 inches in diameter likely with the more intense storms. Later in the evening, a line of severe storms is expected to form, moving eastward across eastern Oklahoma and north Texas. Wind gusts over 70 mph will be possible with the more intense parts of the line. QLCS tornadoes will also be possible with rotating cells embedded in the line late this evening into the overnight period. ...Central Plains/Lower to Mid Missouri Valley... An upper-level low will move through the southern Rockies today, as the exit region of a mid-level jet overspreads the central Plains. At the surface, a warm front will be located from near a surface low in southwest Kansas east-northeastward into the mid Missouri Valley. This front will be a focus for convective development this afternoon. A band of severe storms is expected to form near the front and move northward across northern Kansas into southern Nebraska during the early to mid afternoon. RAP forecast soundings in northeast Kansas near the front from 18Z to 21Z have MLCAPE near 3000 J/kg, 0-6 km shear around 60 knots, and steep low to mid-level lapse rates. This environment will be very favorable for supercells with large hail. Hailstones greater than 2 inches in diameter will be possible with the more intense storms. In addition, forecast soundings have 0-3 km storm-relative helicity in the 250 to 300 m2/s2 range, suggesting that tornadoes will be likely with the more discrete supercells. A few strong tornadoes will be possible. Further west into northwest Kansas and eastern Colorado, cold temperatures aloft, strong large-scale ascent associated with an upper-level low, and strong deep-layer shear will likely support lower-topped supercells with large hail and strong wind gusts this afternoon. ...Mid to Upper Mississippi Valley/Great Lakes... An upper-level trough will move northeastward across the Great Lakes region today. From near the trough, and southwestward into the mid to upper Mississippi Valley, a wide corridor of moderate instability will be in place by afternoon. A warm front will be in located along the northern edge of the instability, from Iowa northeastward into south-central Wisconsin and north-central lower Michigan. As surface heating takes place and low-level convergence increases along the front, thunderstorms will likely form in the vicinity of the boundary. Forecast soundings near the front at 21Z have MLCAPE around 3000 J/kg, along with 40 knots of deep-layer shear. This should support supercells with potential for large hail and wind damage. The severe threat should be greatest during the late afternoon and early evening. ..Broyles/Thornton.. 04/27/2024 $$