textproduct: Chicago

KEY MESSAGES

- 20-30% chance for patchy fog late tonight through early Monday morning, mainly south of I-80 and west of the Fox Valley. - Generally dry conditions are expected through the upcoming work week with a slow warming trend back to above average temperatures again by mid to late week.

DISCUSSION

Issued at 1250 PM CST Sun Nov 15 2026

A broad area of high pressure continues to reside across the Great Lakes and most of the Midwest this afternoon which will continue to promote mostly clear skies through tonight. While temperatures will continue to warm into the lower 50s this afternoon, once the sun sets temperatures will quickly begin to cool back into the 30s before settling into the mid to upper 20s overnight. The combination of this stout radiational cooling and light winds will generate some marginally favorable conditions for patchy fog development tonight into early Monday morning (20-30% chance). The main limiting factor for the fog tonight will be how deep moisture depths get this evening before mid-level winds increase after midnight and start to mix down some drier air. For now have opted to maintain patchy fog in the official forecast for areas south of I-80 where low-level moisture is currently expected to be highest, but also opted to extend some fog mention into portions of northwest IL west of the Fox Valley where radiational cooling will be strongest. Regardless, fog coverage should be rather hit and miss and generally shallow which should cap visibilities generally in the 2-4 mile range at worst. However, if fog fails to materialize then expect another morning of widespread frost.

The surface high will begin to shift into the Ohio and Tennessee River Valleys on Monday as a modest shortwave pivots through the Great Lakes. Given the dry conditions beneath this shortwave, no precipitation is expected with the wave but some scattered mid-level clouds may be seen Monday afternoon. In the wake of this shortwave, mid-level ridging will build across the Midwest and Great Lakes which will keep the dry weather around through at least the middle of the week. Winds will also turn southwesterly and increase a bit which will begin to usher in some warmer air. The combination of this warm advection and the mostly sunny skies will allow daily temperatures to climb into the mid to upper 50s to near 60 by Thursday. Overnight lows however, will continue to dip into the 30s Monday and Tuesday nights as the dry conditions continue to promote good radiational cooling.

Heading into the later half of the week, the broad trough currently off of the Pacific Northwest will move onshore Tuesday night and then eject across the Mountain West towards the northern Plains and Upper Midwest by Wednesday night. At the same time, a secondary shortwave trough is forecast to move onshore near southern California and eject northeastward along the southern periphery of the mainstream trough. Depending on the degree of phasing between this secondary shortwave and the main trough, this secondary trough could pivot over northern IL and the central Great Lakes on Thursday. Initially it looked as if this shortwave would bring with it some chances for rain showers on Thursday, but recent guidance trends have started to back away from this scenario due to a lack of sufficient moisture return ahead of the wave. So while an isolated shower or two cannot be fully ruled out on Thursday just yet (especially in our west/northwest CWA), our current forecast will have some silent 10-14% POPs and advertise mostly dry conditions. Aside from the rain chances, this shortwave will also bring with it some breezy southwest winds as our area becomes sandwiched between a surface high over the Mid-Atlantic and a deepening surface low over southern Ontario. Thus, expect wind gusts on Wednesday and Thursday to be in the 20-30 mph range.

Our next notable chance for rain does not look to arrive until next weekend when another trough and associated low pressure system drag and cold front through the region. In the wake of this cold front, longer range ensemble guidance does show a return to more seasonable temperatures with highs more in the 40s and overnight lows in the 20s and 30s.

Yack

AVIATION /18Z TAFS THROUGH 00Z TUESDAY/

Issued at 1120 AM CST Sun Nov 15 2026

Forecast concerns for the terminals..

- Weak lake breeze will result in a period of easterly winds at ORD, MDW, and GYY late this afternoon and evening.

- 20-30% chance for some patchy fog to develop after midnight outside of the Chicago terminals.

High pressure will continue to reside across the Great Lakes through the TAF period. As a result light (around 3-5 kts) will prevail through this afternoon before directions become more southwesterly overnight. However, a weak lake breeze will move through ORD, MDW, and GYY after 21z this afternoon resulting a period of east-northeast winds. Wind speeds are then expected to increase into the 10-12 kt range by Monday afternoon where they will persist for the remainder of the period.

While mostly clear VFR skies are expected through the period, there is a 20-30% chance for some patchy fog outside of the Chicago metro tonight (mainly at DPA and RFD). Recent forecast soundings continue to show the moisture depths being rather shallow so confidence on fog coverage remains low. For now have opted to forego a formal mention of fog in the DPA and RFD TAFs but will continue to monitor trends closely. That said, if fog does materialize it seems visibilities should generally remain between 2-4 miles before conditions improve after sunrise Monday morning.

Yack

LOT WATCHES/WARNINGS/ADVISORIES

IL...None. IN...None. LM...None.