633 FXUS63 KARX 131045 AFDARXArea Forecast Discussion National Weather Service La Crosse WI 545 AM CDT Sat Sep 13 2025
.KEY MESSAGES...
- A taste of summer warmth this weekend and into early next week, featuring highs in the 80s and muggy dewpoints. Cooler weather returns towards the end of next week.
- Periodic bouts of showers Sunday and through the start of the new week (20% chance), with the better shot of widespread showers and storms coming mid-week (30-50% chance).
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.DISCUSSION... Issued at 335 AM CDT Sat Sep 13 2025
Return of Summertime Warmth!
The main story for the weekend and into early next week will be the return of summertime heat. Mid-tropospheric warm air (+18-20 C) arrived yesterday with the surface warm front lifting to around the MN/IA border early this morning. The recent global and convective allowing guidance have backed off on the northward progression of the warm front compared to yesterday at this time, resulting in slightly cooler forecast temperatures. However, we are still capable of mixing down the warmer air aloft and no matter how you slice the forecast it will be an unseasonably warm and muggy day with highs in the mid to upper 80s from western WI on west.
It isn`t until the upper tropospheric ridge axis passes to the east on Sunday and into Monday that we see enough of a southerly push to eject the warm front northward (possibly resulting in our warmest temperatures of this stretch by Tuesday). Despite the downstream ridge forming an Omega Block, there will be enough erosion of the ridge`s western flank by a series of waves to break it down by midweek. Before this breakdown, high temperatures will be fairly consistent in the mid to upper 80s. Following the ridge breakdown, this warmer air shunts to the south and a more seasonal airmass takes its place. The exact timing of this transition will depend on trends with upstream convection Tuesday and Wednesday.
Mostly Dry through Early Next Week
A band of elevated showers and storms that brought a focused corridor of 1-2+ inches of rain along the I-94 corridor continues to wane early this morning and should depart by sunrise. It is worth noting that we could see some light sprinkles this morning based on some of the latest HRRR/RAP soundings, but impacts will be very minor and transient given the high cloud bases and deep layer of dry sub-cloud air to overcome.
A negatively-tilted shortwave carving out the ridge over the mid to upper Missouri River valley Sunday night into Monday morning may be enough to force some light showers through the region--mainly west of the Mississippi River. The better risk for widespread showers comes midweek as the longwave ridge begins to break down, with one or more thunderstorm clusters working through during this period. The global models are still resolving the characteristics of this wave and it is tough to nail down specifics at this range in the forecast.
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.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 545 AM CDT Sat Sep 13 2025
Aside from a band of IFR/LIFR fog and low stratus in the wake our overnight rain from EAU to DLL that should dissipate by mid-morning, VFR conditions are forecast for the rest of the day into the evening. Will need to continue to monitor the potential for fog overnight, especially along and east of the Mississippi River. Winds will be from the south to southeast at around 5-10 kts for the TAF period.
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.ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None.
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DISCUSSION...Skow AVIATION...Skow
NWS ARX Office Area Forecast Discussion