![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
107 FXUS63 KARX 111934 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 234 PM CDT Sun Aug 11 2024 .KEY MESSAGES... - Low potential for valley fog tonight driven by the coverage and thickness of high clouds. - Seasonal temperatures on the docket for this week with highs generally in the mid-70s to low 80s. - Slight shower risk for a few locales on Monday, otherwise dry through midweek. Increasing risk for several days of showers for the latter part of the week, but confidence in specifics is low. && .DISCUSSION... Issued at 230 PM CDT Sun Aug 11 2024 Tonight: Fog Potential, Light Showers in Northeast Iowa The main forecast concern for tonight revolves around whether valley fog will develop after midnight. A 10 kft layer of winds < 10 kts in the RAP/HRRR profiles and lower visibility output from MOS-driven guidance certainly catches ones attention for fog development, but concerns linger over the thickness of overnight cirrostratus blowoff from convection over South Dakota and southwest Minnesota. While confidence is very high we will have some form of cirrus cloud deck move through, the main uncertainty is the thickness of the cloud shield. If the cloud shield is too thin, it may have minimal impacts on radiational cooling and allow for fog to form. It will be a delicate balancing game and we may see fog in some locales and not others depending on the degree of insulation from the clouds. For now, did add some mention of fog in the Mississippi River and tributaries north of La Crosse, but held off for points south where the cloud shield may be thicker. Cloud trends will certainly need to be monitored this evening. A compact shortwave noted upstream in water vapor imagery in southeastern Montana slides to the ESE over the next 24 hours and gradually weakens during this time. The main forcing for ascent and theta-e advection will be displaced south of the region, but there are a few ensemble members that bring some light precipitation to northeast Iowa late tonight into early Monday morning. Did maintain some slight chance PoPs in the forecast in these areas, but any impacts look to be quite low. Monday - Wednesday Morning: Mostly Dry, Seasonal Temperatures The filling shortwave axis migrates east of the region by mid to late morning on Monday and takes the main precipitation shield with it. Upper level ridging amplifies on Monday and Tuesday over the High Plains, keeping the region in northwesterly flow. Scattered diurnal showers are forecast to develop north of I-94 in the afternoon on Monday and possibly again Tuesday afternoon, though coverage and amounts look to be low. The overall airmass slowly warms in the wake of our anomalous cold snap at the end of last week, with highs returning back into the upper 70s to low 80s for Tuesday and Wednesday. Wednesday Afternoon - Saturday: Wetter Pattern Arrives The next appreciable chance for showers and storms arrives for late in the week as a deeper shortwave arrives in the wake of our early week ridge. The medium to longer range guidance differ on how the low will evolve, with some solutions cutting off and slowing the system while others are more progressive with the upper trough. There isn`t a really clear cut trend in the ensemble guidance at this range in the forecast as to which scenario has the better probability, so the going forecast has a smattering of 20-60 percent PoPs for Wednesday through Sunday. The highest confidence in impactful precipitation looks to be from Wednesday night into Thursday, with lesser confidence in there being rain during the day on Wednesday and for Friday into the weekend. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1225 PM CDT Sun Aug 11 2024 Predominantly VFR conditions are expected for the TAF period with a low (20%) risk for light showers south of a AEL to DBQ line early in the morning Monday. Confidence in valley fog formation tonight remains on the low side given that high clouds will be passing through during this time. Most other variables do point towards fog, so cloud coverage and thickness will need to be monitored this evening. Winds this afternoon will be 5-10 kts from the W/NW, becoming light and variable this evening into Monday morning. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Skow AVIATION...Skow