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Area Forecast Discussion
Issued by NWS Chicago, IL
Issued by NWS Chicago, IL
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225 FXUS63 KLOT 300836 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 336 AM CDT Sun Jun 30 2024 .KEY MESSAGES... - Dangerous swimming conditions at area beaches today and tonight due to breezy onshore winds and high waves. - Return to more typical summer temperatures and humidity Tuesday onward with periods of showers and thunderstorms too. && .DISCUSSION... Issued at 336 AM CDT Sun Jun 30 2024 Through Monday: High pressure will begin to build into the area today in the wake of last night`s cold front which will establish a period of seasonably cool temperatures and comfortable humidity through Monday. Winds will continue to settle into a northerly direction (northeasterly for those along the IL lakeshore) this morning and increase in speed with gusts of 20 to 25 mph expected by this afternoon. As a result, temperatures today will be notably cooler with highs toping out in the low to mid-70s. Though, the aforementioned onshore winds will keep temperatures in the mid to upper 60s for areas near the lake. In addition to the cooler temperatures, the breeze onshore winds will also build waves at area beaches resulting in dangerous rip currents and swimming conditions. So if planning to head to the beach today take heed of the Beach Hazard Statement in effect and stay out of the water. The breezy winds will diminish this evening which will allow waves to gradually subside overnight. However, winds will remain onshore into Monday morning which will still support some hazardous swimming conditions especially for weaker swimmers. The diminishing winds in addition to the mostly clear skies and low humidity will also make for a rather chilly night with temperatures expected to dip into the upper 40s to lower 50s across the area with more moderate readings in the mid-50s near the lake. Temperatures will rebound Monday afternoon as winds turn southerly and climb into the mid to upper 70s inland and lower 70s near the lake. Monday Night through Saturday: The aforementioned surface high will begin to move eastward Monday night as an upper trough begins to eject into the northern Plains. Ahead of this trough a narrow plume of higher moisture and instability is expected to be streaming northward across the Mississippi Valley which should allow for the development of showers and thunderstorms across the northern Plains and upper Midwest. While this area of showers and storms is forecast to gradually spill over into northern IL (mainly north of I-88) late Monday night into Tuesday, the cooler and drier airmass over our area should weaken the showers/storms as they arrive, at least initially. However, increasing southerly flow across the area on Tuesday will replenish the moisture and aid in destabilizing the atmosphere as temperatures warm Tuesday afternoon. Therefore, shower and thunderstorm coverage does look to increase across our area Tuesday afternoon. Though the lack of more organized synoptic forcing over northern IL and northwest IN should keep the highest storm coverage north of I-80 and more so near the IL-WI line. The aforementioned trough will continue its eastward propagation across the northern Great Lakes and into Ontario on Wednesday which will force a cold front through northern IL and northwest IN. Given that the front is expected move through Tuesday evening and overnight, the unfavorable diurnal time may allow for the loss of more robust instability and in turn cause the showers and storms along the front to gradually weaken with southward extent. Regardless, the front should exit to our south sometime late in the day on Wednesday which should offer at least a few dry hours on Wednesday. Heading into the July 4th holiday on Thursday, the front is forecast to gradually lift back northward as a warm front Wednesday night into the day on Thursday. Depending on how far north the front gets will determine the extent of shower and storm coverage during the Thursday into Friday timeframe as another shortwave trough pivots into the Great Lakes. At this point, guidance is favoring an afternoon and evening show for our area on Thursday with the greatest coverage in our southern CWA. However, this general timing is still low confidence given that we are still several days out and existing storms on Wednesday will play a role in frontal placement. Therefore, those with outdoor plans for the 4th should keep an eye on this period. Regardless of how Thursday plays out, it does appear that another front should push through on Friday and finally bring the periods of showers and storms to a close heading into next weekend. Though the typical late June early July heat and humidity is forecast to remain through the period with highs in the mid to upper 80s and dew points in the 60s to around 70 each day. Yack && .AVIATION /06Z TAFS THROUGH 12Z MONDAY/... Issued at 1245 AM CDT Sun Jun 30 2024 Secondary cold front will move across the terminals early this morning with winds becoming more northerly behind the front with some sporadic gusts possible through sunrise. At the Chicago terminals (ORD and MDW) winds will tend to back to north- northeast after sunrise and likely remain somewhat gusty through the day. Winds should quickly subside and become calm or light northeast or easterly this evening. MVFR lake stratocumulus should move into GYY this morning and potentially affect ORD and MDW for a couple few hours later this morning. Confidence in a potential period of MVFR CIGS at ORD and MDW was too low to add into the TAFs, but the most likely timing for potential MVFR looks to be 13-17z time frame. This will be something to monitor for potential inclusion into later TAF updates. - Izzi && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Beach Hazards Statement through late tonight for ILZ006-ILZ103- ILZ104. IN...Beach Hazards Statement through late tonight for INZ001-INZ002. LM...Small Craft Advisory until 4 AM CDT Monday for the IL and IN nearshore waters. && $$ Visit us at weather.gov/chicago