FXUS63 KLOT 271132

AFDLOT



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

632 AM CDT Mon Oct 27 2025



.KEY MESSAGES...



- A passing storm system may provide periods of rain across the

  area during the middle of the week, favoring areas south of

  Interstate 80. 



- Expect seasonable temperatures through next weekend.



&&



.DISCUSSION...

Issued at 310 AM CDT Mon Oct 27 2025



An upper-level low centered near the Bootheel of Missouri early

this morning will move ESE to the Carolinas through tonight as 

a strong ridge over Ontario remains mostly stationary. A deep 

reservoir of dry air advecting from the east and northeast will 

suppress precip well south of the area, with only some cirrus 

attempting to lift northward through the day.



A longwave trough over western Canada and the northwest U.S. 

will become considerably elongated across the Great Plains over 

the next 24-48 hours between the ridge over Ontario and a 

rapidly building west coast ridge. A narrow north to south 

oriented band of rain is expected to develop west of the 

Mississippi River late tonight into Tuesday in association with 

a modest area of mid-level moisture below a broad entrance 

region of a northwest pointed upper-jet maximum. Extensive low 

to mid-level dry-air advection from a pseudo-Hudson Bay high to

the northeast will steadily erode the eastern edge of the 

precip band Tuesday into Tuesday night before the main vorticity

lobe of the tough detaches and pivots southwest of the area. 

Expectations are that much of the area will remain dry on 

Tuesday, with rain potential ranging from low-end chance PoPs 

(30%) near the Wisconsin line to likely PoPs (up to 70%) toward 

central Illinois Tuesday night into Wednesday morning. It is 

highly likely that there will be a sharp north to south gradient

in precipitation somewhere over the forecast area, with a 

distinct possibility that much of northern Illinois remains dry 

with this event.



The newly formed low to the southwest, the original low over 

the Carolinas, and even the remnants of Hurricane Melissa will 

congeal into a longwave trough over the Northeast late in the 

week, with signals of a couple reinforcing waves crossing the 

area from the northwest this weekend into early next week. 

Ensemble guidance continues to depict a loose omega block 

developing as the west coast ridge amplifies. Our area would be 

situated on the western edge of the main longwave trough to the 

east, yielding sporadic bouts of scattered rain showers and 

perhaps some lake effect rain showers during this time. Temps 

will remain seasonable as arctic air remains well north of the 

area.



Kluber



&&



.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...

Issued at 630 AM CDT Mon Oct 27 2025



VFR conditions are forecast through the period.



After daybreak winds are expected to increase up to around 

13-15kt out of the east with an occasional gust into the upper 

teens possible. Winds begin to ease after sunset though 

sporadic gusts may linger into the evening in Chicago.



Mostly clear skies are expected today with increasing high 

cloud coverage occurring overnight into Tuesday morning ahead of

an approaching weather system.



Petr



&&



.LOT WATCHES/WARNINGS/ADVISORIES...

IL...None.

IN...None.

LM...Small Craft Advisory until 7 AM CDT Wednesday for the IL 

     nearshore waters.



&&



$$



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