SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1256 AM CDT Sun Oct 24 2021 Valid 241200Z - 251200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE MID MISSISSIPPI VALLEY REGION... ...SUMMARY... Scattered severe thunderstorms associated with damaging wind gusts, isolated large hail and some tornadoes will be likely from parts of the Ozarks into the mid Mississippi Valley. A more isolated severe threat is expected in parts of the Arklatex, western Tennessee Valley, and lower Ohio Valley as well as along the Pacific Northwest Coast. ...Synopsis... Shortwave trough currently moving into the Four Corners region is expected to continue eastward throughout the day while amplifying. Current expectation is for this shortwave to be centered over the Lower MO Valley by 00Z Monday and over IL by 12Z Monday. Strong mid-level flow will accompany this system, spreading into the central Plains early this morning and then eastward/northeastward across the Lower MO Valley/Mid MS Valley by the early afternoon. At the surface, a low currently over south-central KS is forecast to progress northeastward ahead of the shortwave trough, reaching northeast KS by this afternoon before moving across northern MO this evening. A cold front attendant to this low will sweep eastward/southeastward in its wake. Expectation is for this front to stretch from northeast MO southwestward into south-central OK 00Z Monday and from central IN southwestward into north-central TX by 12Z Monday. A moist and moderately unstable air mass will precede this front, and thunderstorms, some of which could be severe, are expected from Lower MO Valley eastward into the mid OH Valley and southward through the Ozark Plateau into the Lower MS Valley. Farther west, a deep upper low just off the Pacific Northwest coast will help push a series of shortwave troughs and accompanying fronts into the region. The first shortwave is forecast to arrive early Sunday morning, followed by another on Sunday night/early Monday morning. Isolated thunderstorms are possible along the immediate Pacific Northwest coast. ...Mid/Lower MO Valley to Mid MS Valley/Mid-South... Early morning showers and thunderstorms will likely be ongoing north of the warm front from central/southern IA into central IL, supported by persistent warm-air advection. These showers and thunderstorms will likely continue throughout the day as the moist low-level flow persists ahead of the approaching shortwave trough. This same moist low-level flow should help advect low to mid 60s dewpoints into the warm sector, which will support moderate instability and the potential for strong to severe thunderstorms. Convective initiation is possible both along the front and along any confluence within the warm sector. Vertical shear is strong enough to support supercells and the potential for all severe hazards, including tornadoes. Main uncertainty delineating the primary severe hazards in this region will be storm mode, with a discrete mode favoring a greater tornado threat. Given the warm mid-levels and weakness within the hodograph above 850 mb, the current expectation is for a quick transition to a linear mode with strong wind gusts and embedded QLCS tornadoes as the main severe hazards. In addition to the threat over the warm sector, the area along the warm front also appears to have a relatively higher risk for severe. In this area, very strong kinematics and augmented lift could support a more organized line of storms capable of strong wind gusts and/or embedded tornadoes. ...Pacific Northwest Coast... More cellular convection in the wake of the front could result in isolated thunderstorms throughout the day. Strong vertical shear and modest buoyancy may support transient low-level rotation capable of brief tornadoes and/or strong convectively augmented wind gusts. The already modest buoyancy is expected to weaken further during the evening as the low-level cool and dry slightly. However, at this same time, low-level flow will back in response to the progression of the surface low, contributing to a lengthening of the low-level hodograph. As such, the threat for a brief tornado may extend into the evening. ..Mosier/Squitieri.. 10/24/2021 Read more LIVE: spc.noaa.gov
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