MD 1265 CONCERNING SEVERE THUNDERSTORM WATCH 451... FOR CENTRAL AND NORTHEAST SOUTH DAKOTA...FAR SOUTHERN NORTH DAKOTA Mesoscale Discussion 1265 NWS Storm Prediction Center Norman OK 0215 AM CDT Thu Jun 27 2019 Areas affected...central and northeast South Dakota...far southern North Dakota Concerning...Severe Thunderstorm Watch 451... Valid 270715Z - 270915Z The severe weather threat for Severe Thunderstorm Watch 451 continues. SUMMARY...A line of storms will continue to evolve as it travels northeast across WW 451, with a few damaging wind gusts and marginal hail expected. DISCUSSION...An initial line of storms over northwest SD has dissipated from the south, and merged with a band of storms associated with 850 mb warm/moist advection over central SD. Despite the loss of convection with the western line, severe outflow winds have spread well south of the area and through Rapid City. Over the last hour, the warm-advection storms (now extending from Corson county through Pierre and toward Chamberlain) have shown signs of marginal hail and wind. The air mass ahead of this line remains strongly unstable, and new outflow produced should aid a continued northeastward propagation. Further, strong outflow from the western SD activity is now merging with northern portions of the leading line over north central SD. It is possible that lift will then increase as the deeper outflow undercuts existing storms. Trends will continue to be monitored for any line enhancement, and possible downstream watch into the eastern Dakotas. ..Jewell.. 06/27/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...FSD...ABR...BIS... LAT...LON 43679899 43989957 44419998 44960029 45400071 45710117 45920181 46370161 46800090 46830058 46619926 46339861 45889812 45239792 44609783 44259786 43949807 43679899 Read more View the full article

MD 1264 CONCERNING SEVERE THUNDERSTORM WATCH 450... FOR PARTS OF WESTERN NEBRASKA AND SOUTH DAKOTA Mesoscale Discussion 1264 NWS Storm Prediction Center Norman OK 0958 PM CDT Wed Jun 26 2019 Areas affected...Parts of western Nebraska and South Dakota Concerning...Severe Thunderstorm Watch 450... Valid 270258Z - 270400Z The severe weather threat for Severe Thunderstorm Watch 450 continues. SUMMARY...Thunderstorms spreading across and northeast of the Badlands may continue to intensify late this evening, while another evolving cluster of storms poses an increasing risk for strong surface gusts and hail across into northwestern South Dakota by 10 PM-Midnight MDT. Trends are being monitored for a watch extension and/or new severe weather watch north and east of severe thunderstorm watch 450. DISCUSSION...Large-scale forcing for ascent associated with the mid-level short wave trough has been weak enough that thunderstorm increase and intensification has been slowed by mid-level inhibition associated with the very warm elevated mixed-layer air. Still, isolated stronger storms have been accompanied by severe hail, and severe gusts (52 kt) at Chadron, as well as near severe gusts (48 kt) at Alliance. A conglomerate surface cold pool generated by this convection appears to have developed, with 2-4 mb 2-hourly surface pressure rises noted at Chadron and Alliance in 27/02Z surface data. At least attempts at vigorous new convective development continue on the northern portion of the cold pool, now spreading into the Badlands of South Dakota. As this progresses northeastward, into a more weakly capped (as inferred from the 700 mb thermal gradient) boundary layer still characterized by large CAPE, there still appears potential for rapid intensification near/north of the Interstate 90 corridor. Additionally, strong to severe convection is in the process of growing upscale to the east of the Bighorns. This activity may continue to evolve into an increasingly organized mesoscale convective system, in the presence of at least moderately large CAPE and westerly deep-layer shear, while developing eastward along the lower/mid tropospheric baroclinic zone into northwestern South Dakota through 04-06z. As it does, thermodynamic profiles appear supportive of increasing potential for strong surface gusts, in addition to a continuing risk for severe hail. ..Kerr.. 06/27/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ABR...LBF...UNR...BYZ... LAT...LON 45360467 45760385 45810217 45080110 44619978 43970036 43170145 42930195 43540230 43810304 44330286 44610492 45360467 Read more View the full article

No Mesoscale Discussions are in effect as of Thu Jun 27 02:01:02 UTC 2019. View the full article

MD 1263 CONCERNING SEVERE THUNDERSTORM WATCH 449... FOR MUCH OF MONTANA AND FAR NORTH-CENTRAL WYOMING Mesoscale Discussion 1263 NWS Storm Prediction Center Norman OK 0703 PM CDT Wed Jun 26 2019 Areas affected...much of Montana and far north-central Wyoming Concerning...Severe Thunderstorm Watch 449... Valid 270003Z - 270100Z The severe weather threat for Severe Thunderstorm Watch 449 continues. SUMMARY...The severe threat continues across WW 449. DISCUSSION...Within the past hour, satellite/lightning imagery has indicated an overall increase in convective coverage across WW 449. The environment continues to support damaging wind gusts and large hail given weak to moderate instability (700-2500 J/kg MUCAPE) and strong deep shear (50 kts 0-6km shear). The boundary layer across this region is well mixed, with weak low-level wind fields (outside of thunderstorm cores) and cloud bases rooted around 3km. Thus, the expectation is that storms will be outflow dominant and perhaps grow upscale into linear segments - especially across southeastern Montana - which should continue to foster a wind/hail threat through the next few hours. Additional convection just south of the WW (across far northeastern Idaho and northern Wyoming) will also enter the WW area and pose a wind/hail threat. ..Cook.. 06/27/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...UNR...BYZ...GGW...RIW...TFX...MSO... LAT...LON 47931317 48221254 48271130 48070940 47300648 46430510 45650486 44850503 44480623 44570750 44820872 44871053 44751141 45401209 46171282 46971335 47551343 47931317 Read more View the full article

MD 1262 CONCERNING SEVERE THUNDERSTORM WATCH 450... FOR EASTERN WYOMING...WESTERN SOUTH DAKOTA...AND WESTERN NEBRASKA Mesoscale Discussion 1262 NWS Storm Prediction Center Norman OK 0701 PM CDT Wed Jun 26 2019 Areas affected...Eastern Wyoming...western South Dakota... and western Nebraska Concerning...Severe Thunderstorm Watch 450... Valid 270001Z - 270200Z The severe weather threat for Severe Thunderstorm Watch 450 continues. SUMMARY...Rapid thunderstorm intensification and upscale growth appears possible through 7-9 PM MDT. Strongest storms pose a risk for large to very large hail, and perhaps some risk for a tornado, before the risk for damaging wind gusts becomes more prominent. DISCUSSION...Convective development which initiated near/northeast of the Laramie Mountains is now east of the Interstate 25 corridor, and continues to spread northeastward and eastward into the adjacent High Plains. This appears to be occurring just ahead of a weak mid-level trough axis, within 15-20 kt west-southwesterly deep layer mean ambient flow. Due to pronounced veering of wind fields with height, deep-layer shear is sufficiently strong for organized severe convection, including supercells, however. And, objective analysis indicates that the environment across the Sand Hills of Nebraska into the Badlands of South Dakota has become characterized by strong instability. This includes CAPE in excess of 4000 J/kg, in the presence of steep lapse rates. As storms spread into this environment through 01-03Z, rapid thunderstorm intensification appears possible, with considerable further upscale convective growth in the presence of strengthening southerly 850 mb flow to 30 kt. This may be most pronounced near the Nebraska/South Dakota border area, near/northwest of Chadron, through the Badlands, where inhibition associated with very warm elevated mixed-layer air appears weakest. ..Kerr.. 06/27/2019 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LBF...UNR...CYS... LAT...LON 43440451 43820429 44360207 41950207 41410259 41500351 42440380 42920450 43440451 Read more View the full article