![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
521 FXUS63 KARX 160352 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1052 PM CDT Thu Aug 15 2024 .KEY MESSAGES... - Showers and storms persist into the evening hours today with gusty winds being possible in any stronger storms that develop. Additional showers and storms are likely (50-80% chance) for Friday. - Fog potential tonight into tomorrow morning east of the Mississippi River. - Slightly below normal temperatures through next week with sporadic shower and storm chances. && .DISCUSSION... Issued at 309 PM CDT Thu Aug 15 2024 Rest of Today - Tonight: Showers and Storms This Evening, Fog Potential Overnight East of the Mississippi River The general synoptic setup this afternoon can be seen on GOES-16 water vapor imagery and 15.16z RAP 500mb heights with a surface low and corresponding upper-low situated on the ND/MN state line. As this low slowly works its way southeast, pieces of shortwave energy can be noted in the cyclonic flow, aiding convective initiation across the Great Plains and Midwest. Attention this afternoon turns to how much instability we have managed to build in order to aid convection as we approach peak heating. As of 1830z, noting some developing cumulus across portions of southeast MN leading to shower activity. Still some questions with how these showers will deepen over the coming hours though. While the 15.17z RAP continues to increase MLCAPE values to around 1000-2000 J/kg locally into the evening, currently satellite trends have kept a fairly persistent low-level cloud deck over much of the local area into the afternoon. As a result, ongoing convection could struggle to deepen with limited instability where cloud cover persisted. If storms are able to tap into more instability where clearing is present, DCAPE values of 600-900 J/kg in the 15.17z RAP would support an isolated threat for some stronger wind gusts as storms move east. With the aforementioned cloud cover lingering over portions of the area through peak heating this afternoon, particularly along and east of the Mississippi River, diurnal mixing processes likely will be minimized in these locations allowing low-level moisture to remain in place going into the overnight. Consequently, noting deterministic soundings developing a near surface inversion with this low-level moisture, particularly across southwestern Wisconsin. The main question will be if any cloud cover lingers into the overnight hours which could hinder any fog development. A key point of interest in the 15.12z HREF visibility probabilities overnight is there is minimal deviation between the 4 mile probabilities (40-70%) and the 1/4 mile probabilities (20-50%) in southwestern Wisconsin. As a result, areas that manage to develop fog would favor low visibilities that could lead to fog becoming locally dense before fog dissipates Friday morning. Friday: Seasonable With Additional Showers/Storms Likely Looking towards Friday, the previously stated low pressure system pushes southeast into north-central Wisconsin on Friday afternoon. Consequently, this will further instigate shower and storm development throughout much of the day on Friday. The overall setup generally shows a piece of vorticity associated with a subtle shortwave that progresses through the area during the late morning and early afternoon. As instability increases by afternoon, convection will develop along an associated surface boundary that will progressively push eastbound. With minimal 0-6km bulk shear in the 15.15z RAP to maintain any organized convection, storm mode will be very pulse-like in nature. The one caveat to the afternoon showers and storms tomorrow will be the possibility for any non-supercell funnels that can develop. With the vertically stacked low and a surface boundary pushing through the area, the non-supercell tornado parameter in the 15.15z RAP is highlighting portions of central and north-central Wisconsin with values greater than 1 during the afternoon. After this round of convection moves through during the early afternoon hours, limited instability in the 15.15z RAP would suggest limited able for deep convection to occur. However, given some of the CAMs holding onto showers later into the evening with marginal instability and weak pieces of energy pivoting around the low, held onto some precipitation chances through the evening (20-40% chance). Saturday - Wednesday: Continued Seasonable Temperatures With Spotty Shower and Storm Potential As we head into the weekend and next week, the aforementioned vertically stacked low will slowly continue to migrate eastward. As the associated trough axis becomes more neutrally tilted, a deepening ridge to our west will help posture our region in northwesterly flow pattern. Consequently, this will aid in keeping our temperatures near to slightly below average into next week. This is reflected in the 15.12z grand ensemble (GEFS/EC ensemble/Canadian ensemble) with median high temperatures trending in the middle 70s to lower 80s with inter- quartile spread of generally around 5 degrees through the first half of next week. Shower and storm chances will be possible with any shortwaves embedded in the flow but guidance currently having low confidence in how these may resolve at this time. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1053 PM CDT Thu Aug 15 2024 Partly to mostly cloudy skies for the overnight period. Some areas of patchy fog will be possible, especially for areas along and east of the Mississippi. If enough clearing does take place, IFR and LIFR fog could develop, especially in the river valleys. There is currently between a 20 and 30% chance of these lower flight categories occurring overnight. Scattered showers and storms will be possible across the area from Friday late morning through the rest of the day. MVFR conditions are likely to occur during the afternoon with lower flight categories expected for Friday night due to low stratus clouds. Southwest winds will transition to northwest winds Friday afternoon with some gusts between 15 and 25kts, especially in southeast Minnesota and northeast Iowa. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Naylor AVIATION...Cecava