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SPC Jun 17, 2024 1630 UTC Day 1 Convective Outlook

1 year 2 months ago

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Mon Jun 17 2024 Valid 171630Z - 181200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN/CENTRAL PLAINS INTO THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Scattered strong to severe storms should occur today across parts of the Upper Mississippi Valley, and over the central High Plains and northern Plains late this afternoon through tonight. Both severe/damaging winds and large hail appear possible. ...Upper Mississippi Valley/Upper Great Lakes... A loosely organized thunderstorm cluster is ongoing late this morning across northern WI into the U.P. of MI. With steep mid-level lapse rates present per the 12Z sounding from GRB, along with sufficient deep-layer shear to support organized updrafts, at least an isolated severe hail/wind risk should continue through the afternoon across this region along and east of a front. In the wake of this activity, large-scale ascent appears nebulous/weak across much of the upper MS Valley. Still, modest forcing associated with low-level warm advection through the day may be enough for additional convection to develop this afternoon along the southward extent of the front across this region. The best chance for this to occur appears to be across parts of northern IA/southern MN and perhaps western WI along and near the surface front, which may try to lift slowly northward through this afternoon/evening. If surface-based thunderstorms can develop across this area, they would pose some threat for severe hail and damaging winds given moderate forecast instability and sufficient deep-layer shear to support updraft organization. However, this scenario remains low confidence, as earlier convection has shunted the surface front well into IA this morning. This boundary is forecast to lift northward as a warm front tonight ahead of an mid/upper-level wave approaching from the northern/central Plains, and mainly a hail threat could persist across parts of MN and vicinity through early Tuesday morning with elevated supercells that may develop in a strengthening low-level warm advection regime. ...Northern/Central Plains... A pronounced upper trough/low over the Northwest will move eastward through the period over the northern/central Rockies and adjacent High Plains. Related surface lee cyclogenesis is expected to further occur through this evening over the central High Plains, focused on the northeast CO, southeast WY, and NE Panhandle vicinity. Multiple rounds and zones of severe thunderstorm potential still appear possible across much of the northern/central Plains this afternoon through tonight. Intense thunderstorm development may occur near the surface triple point in southwest NE and vicinity this afternoon, although the later timing of large-scale ascent associated with the upper trough casts some doubt on surface-based thunderstorm initiation. The presence of steep mid-level lapse rates and rich low-level moisture should aid in the development of moderate to strong instability as daytime heating occurs and as the warm front attempts to lift slowly northward across the central Plains. Deep-layer shear will be strong enough for supercells with associated large hail threat. Isolated very large hail may also occur. Some upscale growth/clustering along and near the front appears possible with time this evening, and a greater threat for severe/damaging winds may eventually be realized. Effective SRH is also forecast to quickly increase late this afternoon into the evening as a southerly low-level jet rapidly strengthens over the northern/central Plains. If any supercell can persist in this time frame, it would pose a threat for a tornado. A somewhat separate area of supercell potential is also evident across northeast WY/southeast MT, where modest low-level moisture return and upslope flow to the Bighorns may promote convective initiation later today as the upper trough continues eastward. Isolated to scattered large hail appears to be the main threat with this convection, if it develops and assuming sufficient instability can materialize. Otherwise, mainly elevated thunderstorms will likely develop and persist late this evening and overnight across a broader portion of the northern Plains. Large hail should be the main threat, although severe/damaging winds may occur with any convection that can remain near/south of the northward-lifting warm front. ...Southern High Plains... Isolated to widely scattered thunderstorms may occur with southward extent along the length of the dryline/lee trough this afternoon across the southern High Plains. Deep-layer shear should remain fairly modest (generally 20-30 kt). Still, any convection that can develop late this afternoon may pose an isolated threat for severe wind gusts and hail through early evening given a moderately to strongly unstable airmass. ...Lower Great Lakes/Upper Ohio River Valley... A remnant convective cluster/MCV over southern Ontario should broadly influence additional thunderstorm development to its east this afternoon across the lower Great Lakes and upper OH Valley regions. Instability is forecast to gradually increase with continued daytime heating and low-level moisture streaming northward. Deep-layer shear should remain generally weak (25 kt or less). Still, steepening low-level lapse rates and a moist/moderately unstable airmass could allow for some stronger pulse-type/occasionally clustering thunderstorms capable of producing localized wind damage this afternoon and early evening. ..Gleason/Lyons.. 06/17/2024 Read more