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Friday, July 16, 2021

SPC Jul 16, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Fri Jul 16 2021 Valid 162000Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF WESTERN SOUTH DAKOTA AND NEBRASKA... ...SUMMARY... A few severe storms are still possible across a portion of the northern/central Plains this afternoon and evening, with isolated large hail and severe wind gusts the main threats. Isolated strong to severe storms with gusty/damaging winds should continue through the early evening from parts of the Mid-South to the Ohio Valley and Northeast. ...20Z Update... Severe probabilities have been removed from ME as storms have generally moved offshore and weakened. Based on observational trends and short-term guidance, minor adjustments have been made to the remaining Marginal Risk area extending from parts of the Mid-South to OH Valley and Northeast. Isolated strong to damaging wind gusts with multiple small clusters will likely remain the primary severe threat across these regions through the early evening. See Mesoscale Discussion 1298 for additional information. The Marginal Risk across portions of the northern/central Plains has been expanded eastward a bit to account for ongoing convection across central ND/SD. This activity is occurring in a low-level warm advection regime on the eastern periphery of moderate boundary-layer instability across western ND/SD. Still, the presence of strong deep-layer shear suggests some threat for hail/wind with any storm that can persist through the rest of the afternoon. No changes have been made to the Slight Risk across parts of western SD/NE. Storms are expected to gradually increase in coverage and intensity this afternoon, beginning shortly across the Black Hills region and vicinity in western SD. Given the presence of 1500-2000 J/kg MLCAPE, steep mid-level lapse rates, and around 35-45 kt of effective bulk shear, both isolated large hail and severe wind gusts may occur with organized storms as they develop generally southeastward through the remainder of the afternoon and into the evening. ..Gleason.. 07/16/2021 .PREV DISCUSSION... /ISSUED 1134 AM CDT Fri Jul 16 2021/ ...Central High Plain region... Low amplitude upper ridge is in place across the Central Plains. However, weak perturbations continue to move through the northern periphery of this feature. At the surface mid 60s F dewpoints reside beneath steep mid-level lapse rates resulting in a corridor of moderate instability with up to 2000 j/kg MLCAPE. As the boundary layer continues to destabilize and cap weakens storms will likely develop over the higher terrain including the Black Hills as well as along a lee trough/dryline feature and spread southeast through the warm sector later this afternoon. Up to 35 kt effective bulk shear may be sufficient for some of the initial storms to develop updraft rotation. Storm coverage is somewhat uncertain, but some evolution into one or more clusters will be possible into the evening. Isolated damaging wind and large hail will be the main threats. ...Ohio Valley through northern Arkansas... A moist boundary layer resides south of a convectively reinforced boundary that extends from northern PA through the OH Valley and into northern AR. A couple of MCVs are evident within the precipitation band along and north of this boundary. The warm sector will continue to destabilize with moderate instability (1500-2000 J/kg MLCAPE) this afternoon. Storms are already in the process of intensifying from southern IN through southern IL where strong diabatic heating is occurring. While vertical shear will remain weak to modest (25-35 kt), storms may organize into line segments and become capable of producing isolated damaging wind through early evening. ...Maine... See swomcd 1297. Read more LIVE: spc.noaa.gov
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