Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1211 AM CDT Sat Apr 22 2017 Valid 221200Z - 231200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MID-SOUTH... ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE LOWER MISSISSIPPI VALLEY TO THE MIDDLE ATLANTIC COAST.... ...SUMMARY... Scattered thunderstorms will be noted along a corridor from portions of the Lower Mississippi Valley to the Middle Atlantic Saturday. Gusty winds and hail may accompany some of this activity, especially over Mississippi into southern Tennessee. ...Discussion... Short-range model guidance continues to suggest 500mb speed max will sag southeast across the Arklatex region late in the period which should encourage upper trough to dig across the Mid-South by the end of the period. Large-scale forcing for ascent should focus along the cool side of a slow-moving front from AR to the central Appalachians and convection should be most concentrated along this corridor. Latest thinking is remnant MCS from late Friday convection will extend from near the AR/LA border...northeast into the TN Valley at daybreak Saturday. Early-day storms should force the surface front into LA early in the period and the effective wind shift will likely be shunted to near the MS border by 18z. Boundary-layer heating is expected to aid destabilization across the warm sector and renewed frontal convection should develop as readings warm into the upper 70s to near 80. Forecast soundings do not exhibit particularly steep lapse rates but deep-layer shear is expected to support organized clusters/line segments capable of producing gusty winds/hail with the strongest activity. Downstream across the Middle Atlantic...weak short-wave ridging is expected to develop by early afternoon in the wake of ejecting speed max. This mid-level feature should allow surface front to sag toward the VA/NC border during the afternoon where it will likely serve as the focus for convective initiation. Forecast soundings suggest strong heating will be observed east of the higher terrain, south of the front, and convective temperatures should be breached within an otherwise weakly forced environment. Even so, shear profiles will likely support organized updrafts and a few supercells could evolve near the frontal zone. Isolated hail/wind are the primary risks. ..Darrow/Leitman.. 04/22/2017Read more
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