SPC Sep 14, 2024 1300 UTC Day 1 Convective Outlook
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0742 AM CDT Sat Sep 14 2024 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE NORTH-CENTRAL PLAINS... ...SUMMARY... Thunderstorms capable of isolated severe gusts and hail will be possible over parts of the north-central Plains. ...Synopsis... Blockiness in the eastern CONUS will continue to dominate the large-scale, mid/upper-level pattern through the period. An anticyclone will drift eastward to southeastward over the Great Lakes, poleward of a broad belt of low heights and several embedded vorticity maxima extending from the lower Mississippi Valley to offshore from the Carolinas. One of those perturbations will be the decaying remnants of a merger of a midlatitude mid/upper low with the remnants of Francine. This feature is forecast to drift erratically eastward to southeastward over the Mid-South, contributing to convective potential over a broad area of the Southeast, but with wind fields and lift too weak to support organized severe potential. Farther west, synoptic-scale height rises are forecast across most of the central/northern Plains, as a strong trough digs south- southeastward near the BC Coast and forms a 500-mb low near UIL at the end of the period. By then, associated cyclonic flow should cover a large part of the CONUS west of the Rockies, as well as for several hundred miles off the West Coast. The 11Z surface analysis showed a low over northern MS (associated with the remnants of Francine) with an occluded front arching across AL to a triple point near MGM, a warm front across southern GA, and a cold front across the western FL Panhandle. These boundaries should become more diffuse with time today as the deep-layer cyclone above the low continues its gradual degradation. Meanwhile, a quasistationary front from east-central ND across central SD to southwestern NE should weaken through the day, but with a remnant trough/convergence zone lingering near the present position. A weak surface low should form farther west today, in northeastern WY east of GCC, then migrate eastward into western SD toward RAP tonight. ...North-central Plains... Isolated to scattered thunderstorms are expected to develop this afternoon, in a narrow corridor of relatively maximized low-level convergence (corresponding to the weak front/trough) and favorably strong surface heating east through southeast of the low. Isolated severe gusts and hail will be possible as convection proceeds across SD and perhaps into southern ND this evening, before encountering progressively more-stable low-level conditions with a decreasing severe threat. A weak perturbation apparent in moisture-channel imagery over east-central WY should move northeastward across the western NE Panhandle to southwestern/south-central SD by mid/late afternoon, and may contribute subtle large-scale ascent to the environment. Still, with broader, ambient height rises superimposed on that, considerable mesoscale timing/location uncertainty remains on the most probable initiation zone within the southern part of the outlook area. The later initiation occurs, the farther north the unconditional severe-threat area will be. Activity should move north-northeastward into a corridor of favorable moisture and buoyancy, with peak MLCAPE in the 500-1500 J/kg range, atop a well-mixed subcloud layer. Greater lift and more backing of low level flow will be present over the SD part of the outlook, spreading northward into southern ND with time this evening, and supporting conditional potential for upscale growth of activity initiating in a hotter boundary layer near the Badlands. Stronger capping and weaker convergence over western NE cast some doubt as to formation and convective coverage in the Sandhills, though the environment will be favorable for marginal severe there as well. Modest low/middle-level winds nonetheless will veer strongly with height, leading to 25-35-kt effective-shear magnitudes in support of some organization. ..Edwards/Mosier.. 09/14/2024 Read more
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0742 AM CDT Sat Sep 14 2024 Valid 141300Z - 151200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE NORTH-CENTRAL PLAINS... ...SUMMARY... Thunderstorms capable of isolated severe gusts and hail will be possible over parts of the north-central Plains. ...Synopsis... Blockiness in the eastern CONUS will continue to dominate the large-scale, mid/upper-level pattern through the period. An anticyclone will drift eastward to southeastward over the Great Lakes, poleward of a broad belt of low heights and several embedded vorticity maxima extending from the lower Mississippi Valley to offshore from the Carolinas. One of those perturbations will be the decaying remnants of a merger of a midlatitude mid/upper low with the remnants of Francine. This feature is forecast to drift erratically eastward to southeastward over the Mid-South, contributing to convective potential over a broad area of the Southeast, but with wind fields and lift too weak to support organized severe potential. Farther west, synoptic-scale height rises are forecast across most of the central/northern Plains, as a strong trough digs south- southeastward near the BC Coast and forms a 500-mb low near UIL at the end of the period. By then, associated cyclonic flow should cover a large part of the CONUS west of the Rockies, as well as for several hundred miles off the West Coast. The 11Z surface analysis showed a low over northern MS (associated with the remnants of Francine) with an occluded front arching across AL to a triple point near MGM, a warm front across southern GA, and a cold front across the western FL Panhandle. These boundaries should become more diffuse with time today as the deep-layer cyclone above the low continues its gradual degradation. Meanwhile, a quasistationary front from east-central ND across central SD to southwestern NE should weaken through the day, but with a remnant trough/convergence zone lingering near the present position. A weak surface low should form farther west today, in northeastern WY east of GCC, then migrate eastward into western SD toward RAP tonight. ...North-central Plains... Isolated to scattered thunderstorms are expected to develop this afternoon, in a narrow corridor of relatively maximized low-level convergence (corresponding to the weak front/trough) and favorably strong surface heating east through southeast of the low. Isolated severe gusts and hail will be possible as convection proceeds across SD and perhaps into southern ND this evening, before encountering progressively more-stable low-level conditions with a decreasing severe threat. A weak perturbation apparent in moisture-channel imagery over east-central WY should move northeastward across the western NE Panhandle to southwestern/south-central SD by mid/late afternoon, and may contribute subtle large-scale ascent to the environment. Still, with broader, ambient height rises superimposed on that, considerable mesoscale timing/location uncertainty remains on the most probable initiation zone within the southern part of the outlook area. The later initiation occurs, the farther north the unconditional severe-threat area will be. Activity should move north-northeastward into a corridor of favorable moisture and buoyancy, with peak MLCAPE in the 500-1500 J/kg range, atop a well-mixed subcloud layer. Greater lift and more backing of low level flow will be present over the SD part of the outlook, spreading northward into southern ND with time this evening, and supporting conditional potential for upscale growth of activity initiating in a hotter boundary layer near the Badlands. Stronger capping and weaker convergence over western NE cast some doubt as to formation and convective coverage in the Sandhills, though the environment will be favorable for marginal severe there as well. Modest low/middle-level winds nonetheless will veer strongly with height, leading to 25-35-kt effective-shear magnitudes in support of some organization. ..Edwards/Mosier.. 09/14/2024 Read more
