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
121 ACUS01 KWNS 200527 SWODY1 SPC AC 200526 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1226 AM CDT Fri Sep 20 2024 Valid 201200Z - 211200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTHWEST LOWER MICHIGAN INTO PARTS OF INDIANA...ILLINOIS...AND SOUTHEAST MISSOURI...AND OVER PARTS OF THE CENTRAL PLAINS... ...SUMMARY... Isolated strong to severe thunderstorms are possible during the late afternoon over parts of Illinois, Indiana, and southwest Lower Michigan. Isolated strong to severe storms are also possible across parts of the south-central Plains. ...Synopsis... A leading shortwave trough will weaken as it moves across the upper Great Lakes today, while a secondary and stronger system moves into MT and the northern Plains late. An upper high will hold over the southern Plains, which will aid a strengthening midlevel height gradient over the central and northern Plains as the wave approaches from the northwest. Meanwhile, a deep upper low will affect southern CA and move into AZ through Saturday morning. At the surface, a trough will develop over the northern High Plains late in the day, with high pressure over the eastern states. A weak/residual boundary will extend roughly from Lake MI into central IL, MO, and toward I-70 in KS, with a moist air mass to the south. Mid to upper 60s F dewpoints will return north late this evening and overnight as southerly winds around 850 mb increase to over 40 kt. Otherwise, a cold front associated with the MT disturbance will push across the Dakotas and into central NE overnight and through 12Z Saturday. ...Western Lower MI into IN and IL... Daytime heating of a moist low-level air mass will yield a moderately unstable and uncapped air mass near the weak surface boundary. Scattered thunderstorms are anticipated from western Lower MI southwestward into southern MO as a result. However, forecast soundings indicate poor midlevel lapse rates along with substantial midlevel dry air, which may diminish severity somewhat. That said, locally strong gusts will be possible, and perhaps small to marginal hail. ...Central Plains... Strong heating and southwest surface winds will lead to a plume of steep low-level lapse rates from the TX Panhandle toward the KS/OK border this afternoon. Meanwhile, higher dewpoints will remain near a stalled front over KS, which will support high-based storms initially over northeast NM across the Panhandles and into southwest KS. Given the very deep mixed layers, a few strong to severe gusts may occur. With time, outflow may yield downstream development with more robust cores and perhaps marginal hail across south-central KS. During the late evening, the returning boundary and associated theta-e advection may support a rash of storms from near the NE/KS border, with veering 850 mb winds over time redirecting said advection and lift eastward across the KC Metro. Strong wind gusts appear to be the main risk with such activity. ..Jewell/Thornton.. 09/20/2024 $$