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
36
020 ACUS01 KWNS 210544 SWODY1 SPC AC 210543 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1243 AM CDT Fri Jun 21 2024 Valid 211200Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY AND OVER THE FOUR CORNERS REGION... ...SUMMARY... Scattered strong to severe storms are expected from parts of the northern High Plains into the upper Mississippi Valley on Friday. Scattered strong/severe thunderstorms are also possible in the Four Corners vicinity. A few strong storms may also be noted into parts of the lower Great Lakes to southern New England. ...Northern High Plains to the upper Mississippi Valley... Latest water-vapor imagery depicts a low-amplitude short-wave trough over eastern WA/OR. This feature is forecast to shift into the northern Rockies later today. Surface high pressure over MB/SK/Dakotas will ensure southeasterly low-level flow deep into MT ahead of the short wave. 40kt 500mb flow will develop across central MT as the ridge flattens and scattered robust convection should easily develop within a flow regime favorable for supercells. Forecast sounding for central MT exhibit favorable deep-layer shear with strong buoyancy and relatively low cloud bases. Scattered supercells should evolve by early afternoon then propagate southeast along the instability axis toward south-central MT by early evening. Very large hail, gusty winds, and even a few tornadoes can be expected. Downstream across the upper MS Valley, low-level warm advection will focus along a frontal zone that is expected to be draped across WI/southern MN into southeast SD. Latest model guidance suggests a weak short-wave trough will approach eastern SD/MN border by 22/00z. This feature should encourage some increase in the LLJ across IA into southern MN. Strong diurnal heating south of the boundary will ease CINH across the warm sector and scattered storms are expected to develop. Updrafts may initially develop along the cool side of the boundary but with time surface-based updrafts are expected. Hail, wind, and perhaps a few tornadoes can be expected with supercells near the front. ...Four Corners region... Remnants of TS Alberta are progressing west across Mexico as upper ridging builds west into the middle of the CONUS. This flow regime is creating favorable trajectories across the southwestern US for seasonally high PW plume to advance into the Four Corners region. Weak low-latitude short-wave trough over southern CA will eject across the Great Basin which will strengthen mid-level flow across southern UT into southwestern CO. Scattered supercells should develop along the southern fringe of this short wave where strong shear will support organized longer-lived updrafts. Large hail is the primary risk but some tornado risk does exist with this activity. ...Lower Great Lakes to southern New England... Strong boundary-layer heating will once again be noted across the lower Great Lakes region into portions of southern New England. It appears a zone of low-level confluence will extend across the upper OH Valley into southern New England which should help focus scattered convection by peak heating. Gusty winds will be the primary concern with the most robust updrafts. ..Darrow/Wendt.. 06/21/2024 $$