textproduct: La Crosse

KEY MESSAGES

- Frost development is possible late tonight into Thursday morning with dry and mild conditions through the day Thursday.

- Shower and storm potential increases Thursday evening into the overnight (30-60%) with periodic shower and storm chances through mid next week. Sunday and Monday bring the potential for strong to severe storms.

- Temperatures warm into the 80s through the weekend into early next week.

DISCUSSION

Issued at 137 PM CDT Wed May 13 2026

Tonight - Thursday: Dry and Mild

Mid to upper-level troughing continues shifting eastward this afternoon as ridging and high pressure build into the Upper Midwest. Rather benign conditions are expected over the next 24 hours as this ridging moves through, outside of some breezy winds and directional changes to them. There is the potential for patchy frost for those in central Wisconsin (along/north of I-94) late tonight into Thursday morning as conditions favor efficient radiational cooling as the ridge passes overhead. Opted to issue a Frost Advisory for this period to account for the potential and favorable conditions for efficient radiational cooling.

Ridging will be short lived, shifting east of the region Thursday afternoon and setting up southerly flow. Winds strengthen west of the Mississippi River (especially closer to I-35) during the afternoon hours as 925-850hPa winds increase to 25-30kts. Daytime heating should allow these winds to transfer to the surface, leading to gusts of 25-30mph with highs reaching into the mid 70s.

Thursday evening - Mid Next Week: Shower/Storm Potential and Warmer

As the aforementioned ridging shifts east, a 500hPa shortwave trough pivots through the region Thursday evening atop warm air and moisture advection nudging northward. CAMs depict showers developing during the evening hours as the wave moves through. The highest confidence in rainfall is along and north of I-90 where deeper moisture is depicted in 13.12z RAP/HRRR soundings (30-60%). There is some dry air noted in the subcloud layer though, generally 8kft deep, which will hinder how much rain makes it to the surface, but a few hundreths of rainfall seems reasonable. Also can't rule out some rumbles of thunder given a few hundred J/kg of MUCAPE.

Longwave troughing deepens and shifts eastward Sunday into Monday. A shortwave trough ejects into the Great Plains off the main longwave Sunday, deepening a surface low that then shifts northward. The warm front of this system shifts into the region Sunday afternoon, providing the first bout of strong/severe potential. There is a question of how far north the warm front is able to make it and dependent on this would determine where the severe potential manifests. Currently this potential looks to be highest up to around I-90 based on AI convective guidance, where confidence is highest the warm front will move north of. Assuming surface based convection, instability grows to 1000+ J/kg per the 13.12z GFS with 40-50kts of 0-6km shear, although most of this appears to be located in the 0-3km layer, such that updrafts may struggle to sustain themselves.

The main longwave trough moves east across the United States Monday, taking on a negative tilt as it does and sending a cold front through the region. The low level jet increases in magnitude ahead of this feature allowing for an increase in low level helicity. A 500hPa jet streak of 50-70kts should also act to enhance deep layer shear. With 1250-1750 J/kg of MUCAPE depicted during this time as well, strong to severe convection seems favorable. CSU-MLP is fairly excited about severe weather potential in across the Upper Midwest Monday, suggesting 30-45% probabilities for severe weather. The main question is how quickly the cold front moves through the region and subsequently where the greatest potential for severe weather will exist.

Additional concern comes in the form of heavy rain as PWATs climb to 1.25-1.5 inches Monday per the 13.00z NAEFS, above 95th percentile of climatology along with warm cloud depths around 10kft. The 13.13z NBM also highlights 40-60% probabilities for greater than 0.5 inches of rain with some signal for above 2 inches in a 24 hour period. However, the 13.00z EFI suggests the axis of anomalous rainfall resides primarily to our northwest. All said, a period of all hazards severe weather is possible Sunday and Monday with heavy rain also a concern.

Apart from the shower/storm potential, the bouts of warm air advection under this more active pattern will lead to a warming trend through the weekend. Highs tend into the upper 70s to low 80s with Friday being the warmest day, possible reaching the mid 80s for some.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1220 PM CDT Wed May 13 2026

VFR conditions are expected for the TAF period with a 4-7 kft CU deck east of the Mississippi River gradually mixing out through the afternoon. Northwest winds of 10-15G20-25kts gradually relax through the afternoon and become light and variable this evening. Winds increase from the SSE to the west of the Mississippi River after 06Z to 10-15G20-25kts by midday Thursday, with these winds not starting to increase until after sunrise east of the river.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Frost Advisory from 1 AM to 7 AM CDT Thursday for WIZ017-029- 034-042>044. MN...None. IA...None.