FXUS63 KARX 272344

AFDARX



Area Forecast Discussion

National Weather Service La Crosse WI

644 PM CDT Mon Oct 27 2025



.KEY MESSAGES...



- Rain showers move in late tonight through Tuesday, the big

  question being how far east they progress. Recent trends are

  now pointing to a westward shift in the rainfall and areas

  east of the Mississippi River may stay mostly dry.



- Cooling off through the week with highs falling to the upper

  40s to around 50 by Saturday.



- Drier after Tuesday with a token chance of showers Friday into

  the weekend.



&&



.DISCUSSION...

Issued at 130 PM CDT Mon Oct 27 2025



Tuesday - Tuesday Night: Rainfall Details



An amplifying upper tropospheric Great Lakes omega block 

gradually nudges eastward this afternoon and tonight, with an 

upstream longwave trough elongating and eventually splitting on 

Tuesday as it runs up against the downstream block. Much of the 

wave energy slides southeastward under the block across the Ohio

River Valley on Tuesday and gradually ejects into the 

northeastern CONUS to end the week. A surface front slides 

eastward with this advancing upper tropospheric trough and 

stalls as the wave energy bifurcates around the ridge. This 

surface front then pivots and washes out Tuesday night as the 

southern low takes over.



Despite being on our doorstep, there remains ample uncertainty 

in how far east the associated rain showers can advance before 

being undercut by drier air off the Great Lakes ridge. The exact

morphology of the upstream wave as it cuts off has been a point

of uncertainty in the forecast for days and plays directly in 

the eastward progression of the front and rain shield. An 

aggregate look at the GFS/EC upper level plots over the last few

days has shown a slight westward expansion of the Great Lakes 

ridge, resulting in the trough splitting and the surface front 

stalling sooner than earlier forecast.



The big question is...how much stock to put into these trends? 

Forecast soundings from the RAP/HRRR show ample saturation and 

isentropic lift above this low-level dry wedge, so the rainfall 

will be generated aloft, it is just a matter of how much 

precipitation loading it will take to overcome this dry air. 

Have trended the forecast in the drier direction, especially for

the morning hours east of the Mississippi River. With the 

boundary stalling sooner and farther west, the previously 

advertised heavy rain axis looks to be shifting west of the 

forecast area.



Along with the westward shift in the precipitation field, the 

medium range solutions are clearing the rainfall sooner Tuesday

night into early Wednesday morning. 



Outlook for the Rest of the Week



A progressive northwesterly flow pattern sets up for the end of

the week, with a col/ridging passing through late Wednesday 

into Thursday and an elongated trough rotating down for Friday. 

Cyclonic flow lingers into the weekend with weak perturbations 

rotating through that will bring periodic light rounds of 

rainfall. The overall impacts from this rain look to be minimal.

The northwesterly flow will steadily cool temperatures to near 

or slightly below seasonal norms with highs in the mid to upper 

40s to end the week.



&&



.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...

Issued at 629 PM CDT Mon Oct 27 2025



Guidance continues to trend toward a slower arrival for showers

and associated low ceilings west of the Mississippi River so 

have slowed them accordingly in the aviation forecast. 

Additionally, have kept reductions all west of the Mississippi 

as this rain looks to encompass less of the area overall once it

does arrive. Expect additional timing refinements over the 

coming cycles.



&&



.ARX WATCHES/WARNINGS/ADVISORIES...

WI...None.

MN...None.

IA...None.



&&



$$



DISCUSSION...Skow

AVIATION...Ferguson