Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
115 ACUS01 KWNS 280603 SWODY1 SPC AC 280602 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0102 AM CDT Fri Jun 28 2024 Valid 281200Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF THE CENTRAL PLAINS AND MID MISSOURI VALLEY... ...SUMMARY... Severe thunderstorms may develop from parts of the central Plains into parts of the Middle and Upper Mississippi Valley today and tonight. Large hail, damaging wind, and a few tornadoes will be possible. ...Synopsis... An upper trough over the northern Rockies is forecast to intensify as it moves south and east over the northern Plains and Upper Midwest. Accompanying the trough, a zone of enhanced mid-level flow will overspread the northern and central High Plains, reaching the Great Lakes region by 12z Saturday. At the surface, a mature cyclone over the Dakotas will slowly fill through the day as it moves east along the international border. A cold front will trail the cyclone to the southwest, intersecting a secondary low over central KS. Rich low-level moisture and QG ascent from the advancing upper-level wave will support scattered severe thunderstorms over several areas of central CONUS near the front this afternoon and evening. ...Mid MO Valley and Midwest... Early in the period, widespread convection is expected to be ongoing across parts of the upper Midwest and western Great Lakes associated with overnight mid-level warm advection. This should result in a broad area of remnant cloud cover and delayed diurnal heating across parts of northern IA, IL, MN and WI. However, rich low-level moisture ahead of the approaching cold front may support at least modest destabilization through the day in the wake of the earlier storms. While it is uncertain if sufficient destabilization can support organized storms, 35-45 kt of deep-layer shear would allow for clusters or transient supercells capable of damaging gusts, if more robust convection evolves. To the southwest, substantial heating is likely over the southern and central Plains near the secondary surface low in KS. A warm front will lift north into eastern KS and western MO, with rich boundary-layer moisture (70s surface dewpoints) supporting MLCAPE of 2500-3500 J/kg by late this afternoon. Though forcing for ascent will not be overly strong, robust heating and surface convergence near the low will support isolated to scattered thunderstorm development across north-central KS, and along the cold front in eastern NE by mid to late afternoon. Veering wind profiles with height near the low will support semi-discrete supercells across the mid MO Valley. Backed surface winds, rich low-level moisture and plentiful low-level vorticity/CAPE near the triple point may create a favored mesoscale corridor for a few tornadoes from northeast KS, into northwest MO, and southern IA/NE. While some hail is also possible, given the potential for rotating storms, thermodynamic profiles are not overly favorable, with only modest mid-level lapse rates and large water loading. The initial semi-discrete convection should gradually grow upscale into clusters or a small MCS, moving east/southeast across parts of the Mid MO Valley this evening. Damaging winds and a QLCS tornado will be possible. Storms should begin to weaken overnight as they encounter progressively more stable conditions across central/eastern MO and western IL. ...Central Rockies/High Plains... As the upper trough and surface low advance eastward across the northern Plains, the trailing cold front will weaken as it moves south through the central Rockies and adjacent High Plains. Behind the front, weak upslope flow will develop with east/northeast surface winds through the early afternoon. Subtle ascent from the departing trough, along with diurnal heating of the moist post-frontal air mass, will support scattered thunderstorm development over northern/eastern CO, western SD and southeast WY. Moderate mid-level flow behind the trough will favor straight, but elongated hodographs favorable for organized clusters and supercells. Steepening low and mid-level lapse rates, and forecast MLCAPE of 1000-1500 J/kg will allow for isolated to widely scattered severe storms to evolve with a risk for damaging winds and hail across portions of the central High Plains. Significant hail of 2-2.5 inches and damaging gusts greater than 70 mph may also occur with the more organized storms. ..Lyons/Squitieri.. 06/28/2024 $$