


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
475 FXUS63 KARX 080846 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 346 AM CDT Tue Jul 8 2025 .KEY MESSAGES... - Seasonable this week with highs in the upper 70s to middle 80s. - Chance (20-40%) for showers & storms this afternoon and evening. - More widespread showers and storms likely (55-75% chance) for Friday. Storms on Friday may be strong and capable of locally heavy rainfall. && .DISCUSSION... Issued at 346 AM CDT Tue Jul 8 2025 Today: Isolated to Scattered Showers and Storms Possible GOES-19 water vapor imagery and 08.06z RAP 500mb heights show a fairly pronounced mid-level trough situated over the region early this morning as weakly forced showers slowly dissipated overnight. As this trough pushes eastward, northwesterly mid-level flow will aid in some cooling aloft which will allow MLCAPE values to rise to around 1000-2000 J/kg concurrent with peak heating as shown in the 08.06z RAP. The key question that remains is if there will be enough convective forcing. The recent long-range RAP tries to suggest a theta-e gradient over the region which coupled with any remnant differential heating boundaries may be enough to support convection. The CAMs have mixed schools of thought on exact coverage for convection this afternoon and evening, however have maintained some low-end precipitation chances (20-40%) for the area to address this potential. Regardless, would expect convective coverage to decrease towards sunset as the nocturnal inversion builds in. Wednesday - Thursday: Dry, Seasonable As we head into Wednesday, upper-level ridging moves into the region which should allow for mostly sunny conditions on Wednesday. Minimal ensemble spread observed in the grand ensemble (GEFS/EC/Canadian ensemble) for high temperatures on both Wednesday and Thursday in the upper 70s to middle 80s as little modification to the ambient airmass is observed. Certainly looks like the best period of the week to get outdoors! Friday - This Weekend: Storms For Friday, Strong Storms Possible Conditions turn more active for Friday as a paired shortwave impulse and broader mid-level trough eject out of southwestern Canada and into the Northern Plains later on Thursday. As this occurs, increasing low-level moisture advection and a warm sector will attempt to push into the region. However, many questions still remain on any severe potential with this system. Overall question will be the location of the warm sector, dependent on exact position of the synoptic upper-level trough as well as if any convective contamination pushes eastward. If the warm sector is kept south into IA/IL and near I-80 (as shown in the 08.00z GFS), instability will be weak which would preclude any severe threat for the local area as opposed to a further north solution. The second piece of this puzzle is the aforementioned shortwave impulse pivoting around parent upper- level trough. Deterministic guidance in the GFS/EC/Canadian would suggest a narrow corridor of more favorable shear dynamics in the exit region of this impulse. The trouble with this is there still remains uncertainty on the exact trajectory of this impulse and potential collocation with the aforementioned warm sector. Where and if the more favorable shear overlaps the greater, uncapped instability in the warm sector, an organized severe threat seems plausible. Regardless of severe potential, certainly looks like a more favored airmass for heavier rainfall as increasing 850mb moisture transport and mean precipitable waters in the grand ensemble (GEFS/EC/Canadian ensemble) approach 1.75" to 2". Overall probabilities in the grand ensemble for 0.5" of rain or greater are fairly modest (30-60%) throughout the day on Friday. The main question will be the northerly extent of the warm sects and higher instability causes more vigorous rainfall rates locally. Either way, the recent Extreme Forecast Index does highlight portions of the region with a 50 to 60 percent chance to exceed model climatology for QPF with a shift of tails of 0 indicating a few EC members showing a the percentile QPF event. By the weekend, cannot rule out (15-25% chance) some lingering showers and storms in the northwesterly flow behind the broader upper-level trough. However, building subsidence behind the trough may keep these precipitation chances to a minimum. In any case, will likely cool down from the week long steady-state temperatures slightly for Saturday with the northwesterly flow in place. As a result, median high temperatures in the NBM range in the middle 70s to lower 80s for Saturday. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1234 AM CDT Tue Jul 8 2025 A line of storms has mostly dissipated and weakened across the forecast area progressing east through southeast Minnesota and northeast Iowa into western Wisconsin. Subsequent impacts will be low chance (<20%) for scattered storms through today concurrent with peak daytime heating. Have not included in either TAF (KRST & KLSE) given the very low confidence but will need to be accounted for in coming TAFs. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Naylor AVIATION...JAR