FXUS63 KLOT 261740

AFDLOT



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

1240 PM CDT Thu Jun 26 2025



.KEY MESSAGES...



- Isolated to widely scattered showers and storms are possible

  again this afternoon and evening. The strongest storms will 

  be capable of strong to locally damaging wind gusts.



- Hot and humid conditions will continue through the weekend,

  especially this afternoon and again on Sunday when heat

  indices could exceed 100 degrees.



- Periodic shower and storm chances exist through early next

  week with many dry hours in between rounds.



- A bit of relief is anticipated early to middle of next week 

  with dry conditions and seasonal temperatures.



&&



.DISCUSSION...

Issued at 325 AM CDT Thu Jun 26 2025



Through Friday:



Today will be similar to yesterday when it comes to shower and 

storm potential. With the better mid-level forcing remaining 

northwest of the area, any storm development will likely be due 

to free convection within a hot and humid environment, 

potentially focused along any subtle convergence 

axes/boundaries. Hi-res guidance has not been all that great in 

resolving storms the past couple of days so am a bit leery of 

some of the drier solutions and expect at least isolated to 

widely scattered pulse storms by mid afternoon into early 

evening. Ample instability, high PWATs, and weak mid-level lapse

rates will once again be supportive of precip loaded downburst 

winds that could be strong to locally damaging - consistent with

SPC's Level 1 of 5 severe threat for the entire area. Given the

hit and miss nature of the storms many areas will stay dry 

through the daytime hours. If outdoors be sure to head indoors 

if you hear thunder.



Elected not to issue a Heat Advisory for the local area today

with this update. The reasoning for this is due to concerns 

that there will be just enough mixing to hold peak afternoon 

heat indices in the 98-102 degree range, which is solidly below 

our 105 degree criteria. Admittedly this makes us stand out a 

bit on the map of regional headlines. If it appears that dew 

points are struggling to mix out by late morning, a short-fused 

heat advisory issuance may be warranted for portions of the 

area. With all of this said, it is still going to be hot and 

humid out there today so be sure to take proper precautions to 

avoid heat related illnesses, especially those sensitive to 

heat. A late afternoon lake breeze may help cool things off 

slightly along the immediate Illinois shore before the rest of 

the area begins to cool toward sunset.



Heading into this evening and overnight, upstream convection 

across IA/MN/WI is expected to move into northwest IL this 

evening. As it approaches the general expectation is for it to 

be in a gradually weakening phase with the loss of daylight. 

However, it may hold together enough to produce strong to 

locally damaging outflow winds near the Rockford area. Expect 

further weakening as it enters the Chicago metro, though a gusty

northwest wind shift and frequent lightning may persist into 

the early overnight hours before eventually dissipating.



The shower and thunderstorm trends on Friday are less certain 

and may be tied to a few different features, the first of which 

being a remnant outflow boundary from the overnight storms that 

stalls out somewhere near/south of I-80 and could serve as a 

source of lift for isolated storm development. Additionally, 

some of the hi-res guidance is attempting to resolve a remnant 

MCV out of convection originating out of the KS/NE/MO border 

that tracks across the southeast CWA during the afternoon 

(generally southeast of I-55/80). If this were to occur, 

couldn't rule out a sneaky severe storm threat (though not 

currently outlooked by SPC at this time). Lastly, the trailing 

cold front will begin moving across the area by late afternoon 

which could serve as a focus for additional storm development 

into the evening (more on this in the long term discussion 

below).



Temperatures on Friday will be cooler than today, with highs in

the lower to upper 80s, warmest southeast of I-55 where 

afternoon heat indices will still peak in the low to mid 90s.



Petr





Friday Night through Wednesday:



Late Friday, we should find a cold front pushing south across 

our CWA while the associated surface low moves across the Great 

Lakes. Showers and likely embedded thunderstorms are expected to

push along and south of the front during the evening and 

overnight and are expected to clear out from northwest to

southeast behind the boundary. The front will become more 

zonally oriented and weaken substantially as it gets stretched 

across northern IL and gains distance from the departing parent 

low Friday night into Saturday. The deep moisture initially tied

to the front will also get sheared off to the east away from 

the surface for Saturday. The diffuse front will be parked in 

our south CWA during the day. Ample low level moisture will 

remain pooled near and south of the front to maybe stir up some 

showers and storms south of I-80, but chances look slim farther 

north on Saturday. The front doesn't even look to result in any 

obvious temperature gradient on Saturday with highs expected to 

be in the middle and upper 80s around the area, cooler around 

the lake with onshore winds.



Low level flow will turn southerly late Saturday ahead of 

another approaching wave. This should pull the whole area back 

into the lower 90s for Sunday and low level moisture will fill 

back in over the area. Heat indices during the afternoon are 

expected to be in the upper 90s to lower 100s. Scattered storm 

chances will increase into the afternoon and evening as the 

airmass becomes highly unstable. A real lack of shear should 

hinder an organized severe storm threat, but we'll have to keep

an eye on a potential for deep moist convection, which should 

wane into the night as instability does. Another cold front will

then move across the CWA Sunday night into early Monday. Lesser

instability and still a lack of shear should keep severe probs 

low near the front itself, but deep layer moisture ahead of the 

front could present a heavy rain threat. 



A slow-moving upper ridge and relatively high pressure will 

overspread the central CONUS keeping conditions quieter for a 

couple of days during the middle of next week. Mid-summer heat 

will continue through next week, generally near to a few degrees

above normal with highs forecast in the middle and upper 80s.



Doom



&&



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

Issued at 1240 PM CDT Thu Jun 26 2025



Key Aviation Messages for the current TAF period:



- Widely scattered showers and storms this afternoon/early

  evening



- Another period of storms tonight that may produce gusty

  northwest winds and reduced visibilities



Widely scattered showers and storms have blossomed around the 

airspace prompting VCTS to be added to Chicago terminals. Thunder

near Rockford cannot be ruled out completely this afternoon,

but chances were to low currently to mention in the TAF. Dry

periods will still exist due to the widely scattered nature of

the storms, but as storms pass an individual terminal heavier 

downpours and lightning will be possible. Cigs are projected to 

remain above 3000 feet, but vis may drop to MVFR levels during a

downpour. Winds will gradually become more southwesterly 

through the afternoon with gusts around 20 knots.



There is another chance for storms tonight that could last past

midnight. These storms could also feature a sharp gusty wind 

shift to the northwest as well as reduced visibilities due to 

heavier rain. Other than when storms are over terminals, winds 

will diminish overnight to around 10 knots. However, they will 

pick up again after daybreak and turn to the west with gusts 

around 20 knots.



DK



&&



.LOT WATCHES/WARNINGS/ADVISORIES...

IL...None.

IN...None.

LM...None.



&&



$$



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