FXUS63 KLOT 271958

AFDLOT



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

258 PM 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 much of the period.



&&



.DISCUSSION...

Issued at 258 PM CDT Mon Oct 27 2025



A large expansive quasi-stationary area of high pressure 

centered over western Quebec Canada will continue to foster dry 

easterly lower-level flow across our region through Tuesday. 

Meanwhile, an upper trough currently traversing the northern 

Rockies will become considerably elongated across the Plains 

tonight into Tuesday as it becomes sandwiched between an upper 

ridge over the Upper Great Lakes, and a building ridge in the 

west. Ultimately, this will force the southeastward ejection of,

and the deepening of, a closed mid-level low into the Ozarks 

Tuesday night, before shifting into the Ohio Valley and carving 

out a larger scale upper trough across much of the eastern 

states for the second half of the week.



The weather across the area tonight will remain quiet with 

seasonable lows in the low to mid 40s (warmest in the city). 

Otherwise, as we head into Tuesday higher-level cloud cover will

begin to increase from the west as the system takes shape over 

the Plains. Rain chances during the day will ramp-up west of the

area over IA through the day within a region of increasing low 

to mid- level deformation along the northern periphery of the 

developing low. While this area of rain will try to work 

eastward into northwestern parts of IL later in the afternoon, 

it still appears that our easterly feed of dry lower level air 

will largely eat away at the eastern extent of this area of rain

for much of the area, particularly areas east of I-39. 

Accordingly, we do not anticipate much more then a few light 

showers impacting western sections of the area during the mid to

late afternoon hours on Tuesday. Areas farther east, including 

the Chicago metro area look to remain dry through the day. High 

temperatures should once again top out around 60 in most areas, 

albeit with more afternoon cloud cover. 



Surface low pressure is expected to consolidate and mature 

ahead of the main mid-level low late Tuesday night and Wednesday

over the TN Valley. As this occurs, increasingly lower level 

east- northeasterly winds across our area will continue a steady

feed of drier air from the east. It thus appears unlikely that 

much of northeastern IL and northwestern IN will see much if any

rain from this system. Instead, we expect the main rain chances

Tuesday night into Wednesday to quickly become shunted south 

across central and southern parts of IL and IN. With this in 

mind, we continued to trim down rain chances across northeastern

IL and northwestern IN, largely keeping any low chances south 

of I-80 into Wednesday.



For the later half of the week into the weekend our area will 

reside along the western periphery of a larger scale mid and 

upper trough setting up across the eastern states. This should 

thus place our region in close proximity to a region of enhanced

northwesterly flow, which look to steer at least a couple of 

reinforcing impulses southeastward into our region. Each of 

these impulses may result in some on and off periods of 

scattered showers, along with some flare up in lake effect 

showers, particularly this weekend into early next week.



KJB



&&



.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...

Issued at 1225 PM CDT Mon Oct 27 2025



No significant aviation weather concerns for the 18Z TAFs.



Forecast area sits between surface high pressure over eastern

Canada, and low pressure over the Plains. This will continue to

provide relatively dry, easterly low-level flow to the region 

through Tuesday. Surface winds near 15 kts with a few higher 

gusts this afternoon will diminish to around 10 kts with sunset 

this evening. Winds will increase again late morning to midday 

Tuesday, with some higher gusts around/a little above 20 kts 

possible in the afternoon. 



Otherwise, VFR conditions are expected through the period, with

increasing high cloud cover Tuesday. Spotty light rain is 

possible over eastern IA and eventually central IL by late 

Tuesday, though this is expected to remain south of the 

terminals. 



Ratzer



&&



.LOT WATCHES/WARNINGS/ADVISORIES...

IL...None.

IN...None.

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

     nearshore waters.



     Small Craft Advisory from 7 PM Tuesday to 4 AM CDT Saturday 

     for the IN nearshore waters.



&&



$$



Visit us at weather.gov/chicago