![National Oceanic and Atmospheric Administration](/build/images/header/noaa.d87e0251.png)
![National Weather Service](/build/images/header/nws.4e6585d8.png)
![United States Department of Commerce](/build/images/header/doc.b38ba91a.png)
Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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
37
38
39
40
41
42
43
955 FXUS63 KARX 201949 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 249 PM CDT Sat Jul 20 2024 .KEY MESSAGES... - Fog may occur late tonight into early Sunday morning, particularly in southeastern Minnesota and northeastern Iowa. - Seasonable temperatures and largely diurnal showers and storms are favored through Wednesday afternoon. && .DISCUSSION... Issued at 248 PM CDT Sat Jul 20 2024 Tonight: Potential Fog 19z WV satellite shows an upper low over north central IA with multiple perturbations rotating around this feature which, along with the pocket of cooler temperatures aloft, have led to scattered showers in the western portions of the CWA. Elsewhere, convection has struggled to develop due to capping and a lack of notable forcing for ascent. This afternoon, expect this general pattern to continue with spotty showers and perhaps a rumble of thunder possible in the western portions of the forecast area and in Clark/Taylor Counties where a weak, slow moving surface boundary may help a few parcels become freely buoyant. Moving ahead to tonight, deterministic guidance is insistent that fog will develop, particularly in SE MN/NE IA. Given that temperatures there may drop into the lower 60s due to light winds and dewpoints this afternoon are in the low to mid 60s in many locations, fog does appear plausible. That said, the potential for high clouds introduces uncertainty on this point. Additionally, while deterministic GLAMP suggests many area could reach 1/4 mile of visibility, related NBM probabilities for less than 1 mile of visibility are only 20-40 percent. Therefore, am not thinking dense fog will occur and have generally kept fog mentions to the patchy category. Sunday through Wednesday: Seasonable Temperatures, Diurnal Convection As northwesterly flow aloft and pooled 925/850mb moisture remain in place, each afternoon will likely feature a few showers and thunderstorms. Best chances for more coverage appear to reside Sunday and Tuesday afternoon and evening as guidance is in decent agreement that an upper wave will help cool temperatures aloft a bit as peak surface heating is reached. Additionally, Tuesday may feature a non-zero but still quite low chance for a strong storm as deep shear trends upward from near zero to 20 knots. As drier air slowly filters in following a frontal passage Wednesday, the chance for diurnal showers looks to decrease to around 10 percent or less for Thursday and, as heights aloft build, closer to zero for Friday afternoon. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1243 PM CDT Sat Jul 20 2024 Strong signal in both deterministic and probabilistic models for fog - perhaps LIFR - continues. That said, still a possiblity that high clouds help prevent fog from forming, so have elected to keep things MVFR tonight into early Sunday morning with this update. As for TS possibilities, this is looking increasingly unlikely during this TAF period, so have left out all mentions of precip. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Ferguson AVIATION...Ferguson