Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0319 AM CST Thu Jan 21 2021 Valid 241200Z - 291200Z ...DISCUSSION... Medium-range models are exhibiting reasonable agreement Day 4 (Sunday) and into Day 5 (Monday), after which divergence in solutions begins to increase markedly. On Day 4 (Sunday), the western U.S. trough is progged to begin ejecting -- and deamplifying as it does -- across the Desert Southwest and southern Rockies, and finally into the southern Plains, as it acquires negative tilt through latter stages of the period. As this occurs, height falls will overspread northern and central Texas and Oklahoma, atop southerly low-level flow providing theta-e advection into the region. While a capping inversion -- remnants of prior anticyclonic flow/subsidence aloft -- will likely hinder potential for surface-based convection through much of the day, isolated to scattered storms may evolve by early evening across parts of central and northern Texas, and possibly into southeastern Oklahoma. While questions persist with this scenario, including degree of surface-based instability which may be present, shear profiles will be quite supportive of organized/rotating storms. Therefore, though details remain sketchy, enough consistency exists within tonight's model runs, and those from prior days, to warrant inclusion of a conditional 15% risk area for severe storms. By Monday, differences begin to become apparent with evolution/progression of the weakening mid-level system as it shifts eastward toward/into the Midwest/Ohio Valley. Likewise, similar differences are manifest in the strength/advance of the associated surface low. This uncertainty, combined with likelihood for weaker instability with eastward extent, suggests lesser/decreasing severe potential, and diminishing confidence -- both therefore mitigating against risk area inclusion at this time. Beyond Day 5, model differences -- suggestive of an inherent lack of predictability -- preclude any assessment of convective potential through the remainder of the medium-range period.
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