Heat index pushes 100°, fuels thunderstorm chances this weekend

 Oppressive heat and humidity will return this weekend, with afternoon high temperatures pushing the low 90s Sunday and Monday. Factoring in the heat index, it will feel much closer to 90 degrees Saturday afternoon, and into the low triple digits Sunday and Monday.

That humidity will not only feel uncomfortable, but it will also provide the necessary fuel for thunderstorms. Ingredients for severe storms include moisture, instability, lift, and wind shear. We will have abundant moisture and instability, characterized by the mid-70s dew points. But lift and wind shear will be the limiting factors. Without a trigger to initiate storms, the fuel will remain untapped.

Even subtle waves can fire off strong storms with such high levels of energy, though. These small waves are hard to predict placement and timing ahead of time. If storms develop in such an environment, they will turn strong to severe rather quickly. The first opportunity for some severe storms would be Sunday afternoon, but limited forcing may keep many spots dry. Strongest storms will be capable of damaging wind gusts and very heavy rain.

Clusters of storms may redevelop along remnant outflows left over from previous storm complexes, particularly Sunday night into Monday. Overnight storms would be capable of gusty to damaging winds, heavy rain, and potentially large hail. Additional storms will be possible Monday afternoon, with highest coverage East of I-39 and across Michigan.

Both Sunday and Monday are under a highlight from the Storm Prediction Center for severe weather, with a Level 2/5 Slight risk Sunday and an equivalent 15% outlook for Monday. Exact timing of storms will become clearer as the waves and associated small-scale details come into focus. At the moment, coverage and duration of storms will be small, with many dry hours each day. But if you have any outdoor plans, be sure to keep an eye on the radar and be ready for any warnings that are issued!

 

Heat, humidity, and storm chances slide back in over the weekend

Comfortable Friday:

This comfortable stretch of weather will carry us right through the end of the work week. While the day may begin will more clouds overhead, increasing sunshine will help temperatures climb a little higher the last few days, reaching around 80 degrees. 

Not only are we staying comfortable air temperature-wise, humidity levels will stay in check as well, with dew points temperatures holding in the upper 50s. In the end, this will be great weather for those attending the Woman's Baseball World Cup but also City Market this evening. As we head into the overnight hours, skies remain partly cloudy as a weak disturbance approaches from the northwest. Hi-res models suggest a very isolated sprinkle or shower may result late Friday night into early Saturday. Any shower activity that does manage to develop will be spotty and short-lived.

Weekend Outlook:

The combination of a strengthening high pressure system to our west and persistent southwest winds at the surface will lead to a noticeable increase in both the temperature and humidity departments. 

Afternoon highs are expected to climb into the mid 80s Saturday, then low 90s, while dew point temperatures surge into the upper 60s, possibly low 70s. This warmer, more humid air will provide the atmosphere with a tremendous amount of storm fuel. At the same time, disturbances riding along the northern edge of the ridge may track into the Great Lakes, providing that spark for storms to develop. Some of which may be strong to severe. 

Saturday's Risk:

Fortunately, for those heading to the Beloit Farmer's Market Saturday morning will only have to worry a out a passing sprinkle or shower. It seems the better severe thunderstorm ingredients will line up further to the north of the Illinois/Wisconsin border, in areas across central and northern Wisconsin. That is where a Marginal Risk is currently in place.   

Sunday's Risk:

As for Sunday, the Stateline remains under a risk for severe weather, a level 2 Slight Risk for some, and a level 1 Marginal Risk for others. However, there are still several uncertainties that need to be worked out over the next few days. 

The overall environment will be favorable for strong to severe thunderstorms, given the expected heat, humidity, and the large amount of atmospheric fuel in place. The questions marks however will be storm placement as capping will have a huge impact on Sunday's potential as well as the placement of any surface boundaries. Despite the uncertainty, remain weather aware. If the Stateline does see any clusters of complexes of storms move through, damaging winds will be the primary concern.       

Storm threat returns as heat builds back in for the weekend

It hasn't necessarily felt like late July the last couple of days as cooler air has settled into the region. Highs both Wednesday and Thursday warmed to the mid-70s, falling 10-15 degrees below the monthly average. While it may have felt nice it won't last as we feel a quick return to the late July heat and humidity by the weekend.

Skies will remain mostly cloudy Thursday evening as temperatures slowly fall back through the upper 50s/low 60s Friday morning. A few sprinkles may fall south of the viewing area during the morning but locally our skies are expected to remain dry. Temperatures during the afternoon will rise into the upper 70s, close to 80 degrees. High pressure will continue to slide further away from the area allowing a warmer and slightly more humid air mass to return to the Midwest and Great Lakes. This as a strong ridge of high pressure builds to our west where temperatures will reach well into the 90s, likely reaching the triple digit mark in many locations.

Locally, we remain on the eastern edge of the ridge. Close enough where temperatures are forecast to rise into the low 90s Sunday and Monday, but not directly under the ridge to heat us up any further. However, the location of the Stateline in proximity to the outer ridge could lead to a few storm complexes coming close to, or right overhead, the area Sunday and Monday.

As of Thursday evening, the Storm Prediction Center is already highlighting parts of the Midwest and Great Lakes as favorable areas for thunderstorms, some severe, both days. It's still too early to pinpoint exactly where storms will develop and who will see what, but the risk for thunderstorms will increase Sunday and Monday.  

Pleasant weather holds on before heat builds this weekend

Staying Comfortable:

If you enjoyed yesterday's refreshing weather, you will love what's in store for today. High pressure remains firmly in control across the area, leaving conditions quiet and comfortable. Expect a mix of clouds and sun with temperatures peaking once again below-average, in the upper 70s. Similar to yesterday, this will make for another pleasant summer afternoon for any outdoor activities. 

Clouds will increase somewhat overnight as a weak upper-level disturbance slides in. While this feature may be enough to squeeze out a stray sprinkle or very light shower early in the day, rain chances should stay quite low as we wrap up the work week. Overall, the pleasant stretch of weather continues into Friday with a mix of clouds and sun, afternoon highs near the 80-degree mark, and comfortable humidity. In fact, dew points will remain in the upper 50s, making for another refreshing summer day.  

Warmer Weekend:

Moving forward to the weekend, we'll begin to see a ridge of high pressure strengthen across the central plains and Midwest. That, combined with a return to southwest surface winds, will allow summer heat and humidity to gradually build back into northern Illinois and southern Wisconsin. Temperatures will wind up back in the low 80s Saturday, with highs in the 90s scheduled for Sunday and Monday.  

Heat and humidity set to return by the weekend

 The cool and comfortable weather is a welcomed sight while it lasts, but humidity will be back in the picture by the weekend. Wednesday morning's low temperatures ranged from the low to upper 50s, while the afternoon only returned to the mid-70s.

A building ridge of high pressure across the Western and Central United States will push an increasingly warm and humid air mass our direction through the weekend. The Northwest flow in the jet stream overhead will quell some of that in the near term, but the spreading heat dome will win out by Sunday.

As a result, afternoon high temperatures will keep climbing each day, reaching into the 80s by Friday and Saturday, then 90s Sunday and Monday. Humidity will also accompany the heat, with dew point temperatures pushing well into the 70s. Heat index could approach the triple digits again by Sunday. That will also begin to fuel some isolated to widely scattered thunderstorm chances, but a large majority of the area will remain dry on any given day.

The pattern of Western U.S. ridging will remain locked in place for a bit longer. The long-term outlooks from the Climate Prediction Center continue to feature above average temperatures for much of the country, including a slight lean toward warmer than average for the Upper Midwest. This would take us into the first few days in August. That ridge will flatten a little bit into early August, but most days look to be on the warmer side until at least then.

Cool and comfortable across northern Illinois moving forward

Air Quality Update:

After battling hazardous and unhealthy air quality at times late last week and again on Monday, conditions have improved dramatically across the area. In fact, Tuesday's air quality was what the doctor ordered, with most Stateline locales spending most of the day in the "good" to "moderate" range. The good news is set to continue as the air quality index (AQI) both to start our Wednesday and for this afternoon is expected to remain near or below 50. 

Much Cooler Wednesday:

If that news wasn't enough, how about improvements in the temperature department? That's right. The cool air filtering in behind Monday's cold front will be sitting directly overhead today, limiting afternoon highs to the low 70s. This is below late-July standards and much cooler than last Wednesday. Today's cooler weather does come with a dry outlook as an area of high pressure sits close to the Stateline.  

Staying Cool:

After dropping into the low 50s overnight, we can expect this cooler-than-average weather to stay put for Thursday and Friday. A wind change to the south and southwest will bring afternoon highs up a few degrees, landing us in the upper 70s Thursday and then back near-seasonable Friday. The only chance for rain we are tracking during this stretch is on Friday and it's a very slim chance. Chances should remain slim through Saturday.      

Pair of cold fronts usher in cooler and pleasant stretch

 This morning's cold front resulted in a few of the storms we saw during the day yesterday but has since settled well South of the area. It is now producing severe weather across the Ohio River Valley into the Northeast. Our second cold front in 18 hours will slide overhead this evening, and that one will be the main driver behind the cooler more comfortable air ahead.

A cold front is typically associated with cooler temperatures but can also bring drier air with it. We will get both behind this front, with dew points settling into the low 50s for a couple days amid strong Canadian high pressure!

The drier air will result in some very pleasant and cool nights ahead, especially for July standards. Typical lows are in the mid-60s, but a couple nights will be in the mid-50s starting tonight! We keep the comfortable air through Friday night, but humidity and summertime heat will soon return by the weekend. Enjoy the pleasantly cool weather while it lasts!