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SPC Aug 24, 2019 0600 UTC Day 1 Convective Outlook

5 years 10 months ago

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1250 AM CDT Sat Aug 24 2019 Valid 241200Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS THIS AFTERNOON THROUGH TONIGHT... ...SUMMARY... Severe storms capable of widespread damaging winds, very large hail and a couple of tornadoes are expected late this afternoon into tonight across parts of the central and southern Plains. Additional isolated severe storms capable of hail and strong gusts are possible across parts of western North Dakota this afternoon and evening. ...Central/Southern Plains... Decaying remnants of overnight convection will move across the central/southern Plains vicinity during the morning. Cloud cover is likely to inhibit convective redevelopment for much of the day, but south/southeasterly low level flow will maintain mid 60s to low 70s dewpoints across much of OK/KS westward toward a surface trough across far eastern CO into the OK/TX Panhandles. Cloud cover will remain across much of NE to the north of an effective warm front just north of the NE/KS border. However, partial clearing west of the I-35 corridor in OK/KS will aid in a corridor of strong destabilization by late afternoon. While the main mid/upper level trough will shift eastward across the northern Plains, guidance is in good agreement that a strong shortwave impulse will migrate through northwest flow aloft from eastern CO into western KS/OK. Forecast soundings depict unusually strong vertical shear for this time of year, with effective shear values from 35-50 kt. Furthermore, strong, vertically veering winds through around 3 km will result in large, curved low-level hodographs. Finally, during the evening, a southerly low-level jet is forecast to increase to around 40 kt across the southern Plains. Most guidance, CAMs and otherwise, are remarkably consistent in developing isolated cells by late afternoon/early evening in convergent low level flow near a strengthening surface low over eastern CO. Initial cells are expected in the vicinity of the CO/KS border into southwest NE and perhaps southward along the surface trough toward the OK/northern TX Panhandles. Any cells that remain discrete during this initial development will pose a threat for very large hail (possibly greater than 2 inches in diameter) given midlevel lapse rates greater than 8 C/km and supercell wind profiles. Additionally, aforementioned low level hodographs and deep boundary-layer moisture will support potential for a couple of tornadoes. As ascent increases with the approach of the midlevel shortwave in conjunction with the increasing low-level jet, storms are expected to grow upscale into one or more bowing segments tracking east/southeast across KS/OK and perhaps the northeast TX Panhandle. Given the overall thermodynamic environment and the expectation that a strong cold pool will be generated given the extent of forecast convection, widespread damaging winds appear possible across portions of western and central KS/OK into parts of the OK/TX Panhandles during the evening and nighttime hours. ...Western North Dakota... The main upper-level shortwave trough will pivot eastward from the northern Rockies to the northern Plains today. However, stronger deep-layer flow will remain displaced to the west of the northern Plains. Midlevel lapse rates also are forecast to be somewhat modest, from around 6.5-7.5 C/km, despite stronger height falls and cooling aloft after 00z. Nevertheless, southerly low-level flow will maintain low to mid 60s dewpoints and 1000-2000 J/kg MLCAPE will develop by late afternoon. Isolated cells are expected to develop as ascent increases toward 00z. Effective shear around 25-35 kt will be sufficient for a few organized storms capable of hail. Steep low-level lapse rates and weak 0-3 km winds will also support a few strong downbursts. ..Leitman/Wendt.. 08/24/2019 Read more