FXUS63 KLOT 262329

AFDLOT



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

629 PM CDT Thu Jun 26 2025



.KEY MESSAGES...



- Chances of showers and t-storms will continue at times tonight

  into Friday.



- After a bit of a reprieve from heat and humidity Saturday

  (especially near the lake), another hot and humid day is

  expected Sunday.



&&



.DISCUSSION...

Issued at 249 PM CDT Thu Jun 26 2025



Another day of hot and humid conditions across the area this

afternoon. Some isolated showers and thunderstorms have brought

some temporary relief to a few places this afternoon, but the

majority of the area is experiencing another day with

temperatures in the 90s and heat index readings near or just

above 100 degrees. Atmosphere is hot, humid, and uncapped, which

has allowed for some "air mass" convection to pop this

afternoon. The threat of these isolated to widely scattered

storms could linger through sunset, but unless we get some

amalgamation of cold pools to force additional storms, coverage

should remain pretty isolated through sunset.



Water vapor imagery shows a well defined shortwave over the

northern Plains moving gradually east to the upper Mississippi

Valley. More organized convection has been developing in

association with this shortwave from southern MN south into

central IA. This convection is expected to continue to shift

gradually eastward toward the MS River the rest of the 

afternoon. Stronger shear associated with this shortwave is

north of our latitude, so despite the instability, anticipate

this convection should fall apart after sunset as it crosses the

MS River into northwest IL. Kept the highest pops later this

evening into the early overnight over our northwestern CWA, with

much lower chances for this activity surviving long enough to

bring any organized rain chances over our eastern CWA. 



Composite outflow/weak synoptic front is expected to move across

our CWA tomorrow. Strongest forcing associated with the

shortwave trough is expected to pass well north of the area, but

with air mass expected to become moderately to strongly unstable

and uncapped in advance of this boundary tomorrow. Certainly

plausible that scattered thunderstorms could develop ahead of

this front tomorrow afternoon, particularly across NW IN and our

east central IL counties. Slightly drier and more stable 

conditions in the wake of the front should result dry weather 

over our northwest CWA.



Transient surface high will move across the western Great Lakes

Saturday with lower dewpoints making the still seasonably warm

temperatures more tolerable. The position of the high should

also allow for a prominent lake breeze to move well inland

during the afternoon, providing for nature provided AC for areas

closer to the lake. 



That high will scoot off the east of the region Sunday with

southerly winds likely to drag the heat and humidity back north

into the area. Highs on Sunday should top out in the low-mid 90s

with heat indices again near to just over 100 degrees. Southern

flanks of another shortwave trough passing north of the area 

Sunday should lead to increasing chances of showers and storms 

later Sunday afternoon into Sunday evening. Stronger shear and 

better threat for organized convection should remain to our 

north, but the air should be very moist and moderately to 

strongly unstable again Sunday afternoon, so if convection makes

it into the area, wet microbursts and torrential downpours 

would be a threat.



Longwave trough is progged to dig into the Great Lakes Region

early next week with much more comfortable humidity, especially

by Tuesday and Wednesday. Temps will remain seasonably warm 

away from the lake, but not as hot as many of the days we've 

experienced recently. 



- Izzi



&&



.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...

Issued at 629 PM CDT Thu Jun 26 2025



Forecast concerns include...



Chance of thunderstorms early this evening.

Chance of thunderstorms northwest IL late this evening.

Possible mvfr cigs Friday morning.



Isolated thunderstorms continue to develop and lift northeast

across the area early this evening and this activity is expected

to continue through sunset. Brief heavy rain and locally gusty

winds will be possible with the strongest storms.



A line of thunderstorms across IA will move into northwest IL

late this evening and are expected to steadily weaken as they

move toward and then past RFD. Have maintain prob thunder for

RFD for this activity but most guidance suggests thunder chances

are decreasing for the Chicago terminals and have removed

thunder. Timing for any lingering showers and a possible

northwest wind shift looks to be later, in the early morning

hours and adjusted timing accordingly.



There is a chance of thunderstorms late Friday morning through

mid afternoon, mainly southeast of the terminals, possibly as

far north at MDW/GYY. Confidence is low for both coverage and

location and maintained a dry forecast for sites on Friday.



Most guidance brings an mvfr deck into at least northwest IL in

the predawn hours with it persisting through mid morning and

have included mvfr cigs at RFD. Further east, confidence is low

with the expectation that the precipitation will weaken and

possibly dissipate. Some mvfr level cloud cover is possible at

the Chicago terminals Friday morning and trends will need to be

monitored.



A lake breeze is slowly moving northeast, back toward the lake

currently. This wind shift is not expected to reach ORD/MDW with

south/southwest winds continuing through sunset. However,

prevailing winds may become southerly or briefly south/southeast

for a few hours later this evening, before turning back to the

southwest overnight. Winds will turn west/southwest Friday

morning with gusts into the lower 20kt range possible. Winds

will diminish with sunset Friday evening and turn to the

northwest. Winds may shift to the north or northeast late Friday

evening for the Chicago terminals. cms



&&



.LOT WATCHES/WARNINGS/ADVISORIES...

IL...None.

IN...None.

LM...None.



&&



$$



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