Mesoscale Discussion 1903 NWS Storm Prediction Center Norman OK 0451 PM CDT Tue Oct 26 2021 Areas affected...portions of southwest Nebraska into central Kansas and northwest Oklahoma Concerning...Severe potential...Watch likely Valid 262151Z - 262315Z Probability of Watch Issuance...95 percent SUMMARY...The potential for severe thunderstorms is increasing within the warm sector, ahead of the cold front/dryline. Damaging gusts appear to be the main threats though a couple tornadoes and instances of large hail are also possible. A WW issuance is expected by 23Z. DISCUSSION...Latest METAR observations depict the gradual eastward movement of the dryline and cold front across the central Plains given the approach of a deepening surface low and couple mid-level trough. Convective inhibition continues to erode as the boundary layer mixes and surface temperatures exceed 80F and dewpoints approach the mid 60s F. 8-8.5 C/km mid-level lapse rates are overspreading the warm/moist low level airmass, contributing to 1500-2000 J/kg MLCAPE. Simultaneously, intensifying southerly low-level flow with the approaching upper trough will contribute to intensifying deep-layer and low-level shear, with up to 50 kts of effective bulk shear and 400 m2/s2 effective SRH expected to develop ahead of the dryline in the next few hours, when convective initiation will occur. Meridional/unidirectional tropospheric wind profiles and strong forcing for ascent ahead of a merging dryline/cold front suggests that transient supercell structures will develop and rapidly merge into line segments/squalls. The well-mixed boundary layer and up to 50 kt 850 mb flow suggests that strong to severe gusts should easily reach the surface within and in advance of any well-developed storm cores/line segments. Occasional bouts of large hail are also expected given the 8+ C/km mid-level lapse rates. Though modest, some low-level directional shear is evident in RAP forecast soundings, suggesting that the more persistent supercells or dominant storms embedded within the squall may acquire occasional, strong low-level rotation, with at least a couple tornadoes possible. However, the degree of tornado potential will be largely dependent on the number of discrete/dominant storms that can form and how long they persist, which remains uncertain. Nonetheless, organized severe storms are expected in the next few hours, and a WW will be issued to address this threat. ..Squitieri/Hart.. 10/26/2021 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ICT...OUN...GID...LBF...DDC...GLD...AMA... LAT...LON 35769974 36430009 37160018 38090035 39100060 40290093 40840079 41110059 41200025 40849966 40159898 39439854 38429798 37499781 36879785 36309814 35839841 35559897 35589944 35769974
Storm Prediction Center Mesoscale Discussion 1903
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