


Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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199 FXUS63 KLOT 060815 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 315 AM CDT Fri Jun 6 2025 .KEY MESSAGES... - Lingering Canadian wildfire smoke will make for poor air quality through this evening. - Shower and thunderstorm chances will return over the weekend, particularly late Saturday-Saturday night and then on Sunday afternoon. && .DISCUSSION... Issued at 315 AM CDT Fri Jun 6 2025 Through Saturday: A broad upper trough continues to reside over the central CONUS with a couple of shortwaves (one moving across IA and the Upper Midwest and the other moving across the southern Plains) traversing through the pattern. While both of these shortwaves will continue to eject east today, their trajectories will cause them to largely miss our area resulting in generally rain-free conditions through tonight. However, as the cluster of storms associated with the southern wave moves across the Mississippi Valley there is a non-zero chance (15-20%) that an isolated shower may brush our far southern CWA (areas along and south of US-24) this afternoon. Otherwise, the main forecast concern for today will be some lingering wildfire smoke which will lead to poor air quality across portions of northern IL and northwest IN through this evening. As a result, an Air Quality Alert remains in effect until midnight for the Chicago metro area and northwest IN. That said, surface smoke concentrations are expected to gradually diminish through the afternoon so not expecting reduced visibilities to be much of an issue today. Outside of the smoke, expect partly to mostly cloudy skies with high temperatures in the mid-70s inland and lower to mid- 60s near the lake due to light onshore winds. Heading into Saturday, any lingering wildfire smoke is expected to advect east which should allow air quality to improve. While most of our Saturday should be dry, another shortwave trough will be ejecting out of the northern Rockies and moving into the southern Great Lakes by Saturday evening. Thus chances for showers (and perhaps an isolated storm) will increase Saturday afternoon especially for locations south of I-80. Regardless, temperatures will be similar to today with highs in the mid to upper 70s inland and 60s near the lake. Yack Saturday Night through Thursday: The larger scale weather pattern is expected to turn more unsettled with a few periods of showers and storms across the Midwest through the Great Lakes later this weekend through early next week. Within this evolving pattern, there are two distinct weather systems of interest, both of which will play major roles in driving our chances and timing of showers and storms through this period. The first, is noted in the water vapor imagery as a positively tilted impulse (southwest to northeast orientation) over southern ID early this morning, while the second is currently moving from the Gulf of Alaska onshore across far northwestern British Columbia Canada. The southern ID impulse is expected to transverse the central Rockies later today before sliding eastward across the Corn Belt on Saturday. As it does, ensemble guidance continues to come into better agreement in the development of a surface wave of low pressure along the remnant west-to-east oriented frontal boundary draped across MO into southern IL late Saturday into Saturday night as the mid-level system moves across the Mid- Mississippi Valley. If this occurs paired with PWATs rising to or just upwards of 1.5" (~up to 150% of normal for early June), a corridor of enhanced low-to-mid level deformation induced frontogenesis may foster some rather efficient rainfall rates (with perhaps isolated embedded t-storms) just north of the surface low track Saturday night. This potential continues to be corroborated by an upward trend in the ensemble probabilities of 24-hour rainfall amounts (QPF) of 0.5" or higher. The past few runs of the ECMWF ensemble (EPS) and the GFS ensemble (GEFS) for example, now peak these probabilities around 50-60% south of I-80 and 30-50% up to the I-88 corridor. Following Saturday night`s shower and storm chances, our attention turns to the digging mid-level trough/low across the northern Plains and Upper Midwest by early Sunday. This feature is expected to send a surface cold front southeast across our area Sunday afternoon and evening. Temperatures in advance of this approaching front should reach the 75-80F range with dew points from the upper 50s to lower 60s. Seasonably strong mid and upper-level flow will translate to otherwise supportive effective deep layer bulk shear for organized late day convection. However, some key limiting factors at this time include: the presence of rather lackluster mid-level lapse rates; only modest large scale forcing until evening; and veering winds in the cold frontal trough reducing low-level convergence. Nevertheless, we`ll need to continue to monitor this for a low-end/conditional severe threat (primarily damaging winds), particularly across northwestern parts of IL. Convection would likely be on a weakening trend through the evening as it moves southeastward towards the I-55 corridor. The upper-level low will settle over the Great Lakes region by Monday. As it does, a series of embedded compact waves rotating around it`s southern periphery could drive additional diurnally- enhanced showers (and maybe a few isolated thunderstorms), particularly Monday afternoon, and possibly again Tuesday afternoon. Thereafter, a deamplifying mid-level ridge is expected to cross the region for the second half of next week. Accordingly, this will support a period of drier and warmer weather. Thus, after a cooler start to the week, with highs in the low to mid 70s, temperatures are expected to rebound back into the 80s mid to late week. KJB && .AVIATION /06Z TAFS THROUGH 12Z SATURDAY/... Issued at 1158 PM CDT Thu Jun 5 2025 There are no significant aviation weather concerns anticipated through the period. The only item of note in the near term will be the continued hazy conditions overnight, with some associated minor VSBY restrictions. While some VSBYs may drop as low as 3 or 5 miles overnight (possibly lower at KGYY), most terminals are expected to remain VFR. Winds will remain light (around 5 kt or less) from the north-northwest through the night. The hazy conditions look to end this morning, so we are currently not anticipating any VSBY restrictions from mid- morning onward. Winds will turn northeasterly at most terminals by mid-morning, with speeds likely to average in the 7 to 11 kt range through the day. KJB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Air Quality Alert until midnight CDT tonight for ILZ005-ILZ006- ILZ012-ILZ013-ILZ020-ILZ021-ILZ103-ILZ104-ILZ105-ILZ106- ILZ107-ILZ108. IN...Air Quality Alert until midnight CDT tonight for INZ001-INZ002- INZ010-INZ011. LM...None. && $$ Visit us at weather.gov/chicago