Late-season heat fuels thunderstorm chances late this week

 The early September heat has really packed a punch, with two days each reaching into the mid-90s! That heat will fuel the potential for at least some isolated thunderstorms in the coming days, beginning Wednesday evening and overnight. While most will remain dry, a stray shower or storm may be possible from time to time. Outside of storms, it will remain very warm and humid, with overnight lows only dropping into the mid-70s.

Much of the daytime Thursday will once again be dry, hot, and humid. Afternoon temperatures will likely surge into upper 80s and low 90s for some. Isolated storms may be possible during the afternoon and evening, with highest coverage across Southern Wisconsin. Where it doesn't rain, heat index values will likely push into the triple digits again.

Any other chances for storms will depend on placement and evolution of previous rounds, but higher coverage looks possible Thursday night into Friday. There will be a fair bit of dry time in between rounds, but periodic thunderstorms are possible into the holiday weekend.

Future-cast has the Thursday night round mainly North and Northeast again, but the ingredients for a couple storms will be in place for much of the area. A few stronger storms may be possible, with a low-end risk for severe weather. Strongest storms may be able to produce damaging wind gusts and large hail, as the Storm Prediction Center maintains a Level 1/5 Marginal risk overhead for Thursday into Friday morning.

Showers and storms may be ongoing Friday morning and could persist into the daytime. If storms track over the same regions as the couple nights before, flash flooding may be a larger issue. If showers linger into the afternoon, temperature could be limited to the upper 80s Friday. But if things dry out quicker, another 90-degree day is on the table.

94° yesterday, triple-digit heat indices on the table again today

Second Heat Advisory:

Temperatures climbed to 94 degrees in Rockford on Tuesday, making it the hottest day of the year so far, and while today's high temperatures may end up a degree or two lower, oppressive humidity will keep conditions feeling much hotter. 

  

A heat advisory will once again be in place for all of northern Illinois from 12PM-9PM. Heat indices are expected to reach between 100° and 105°, possibly as high as 110° this afternoon, creating dangerous conditions for anyone spending time outdoors. Like yesterday, be sure to stay hydrated, take frequent breaks in the shade or air conditioning, and remember that little relief from the heat is expected overnight as temperatures only fall into the low 70s.  
 

Sizzling start to September: Heat Advisory issued for northern Illinois

Heat Advisory:

The heat and humidity are making a big comeback across the Stateline today, prompting a Heat Advisory from 12PM until 9PM for Winnebago, Boone, Ogle, Lee, DeKalb, McHenry, Carroll, and Whiteside Counties. As of this moment, the heat alerts do not extend into southern Wisconsin. 

  

Temperatures this afternoon will climb to around 90 degrees, but the bigger story will be the humidity. With dew points in the low to mid 70s, it feel considerably hotter, with heat index to 100 degrees or higher for several hours this afternoon. If you are spending time outdoors, be sure to take frequent breaks, stay hydrated, and limit strenuous activity during the hottest part of the day. Don't expect much of a cooldown tonight. Temperatures will be slow to drop, only settling into the low 70s. 

Hot Start to September:

The heat won't completely let up after today. A strong late-summer ridge will drift east but at the same time, leaving low-level flow out of the southwest. This will keep temperatures running well-above average through the second half of the week. 

Highs will end up in the low 90s Wednesday before easing slightly into the upper 80s Thursday and Friday. While air temperatures may come down a bit later in the week, the humidity isn't going anywhere. Heat index values are expected to climb into the 100 to 105 degree range on Wednesday, then remain above 90 degrees Thursday and Friday, making it feel several degrees hotter than the thermometer suggests. Again, be sure to practice heat safety during the prolonged hot stretch.  

Widely scattered thunderstorms occurring over northern Illinois Monday afternoon

 

A few non-severe thunderstorms have developed within the last couple of hours of over northern Illinois producing mainly locally heavy rainfall and frequent lightning. The threat for these storms to turn severe remains very low.

A weak little ripple, or upper-level wave, in the jet stream is currently moving across the Midwest and has provided just enough force in the atmosphere to allow some of these storms to develop. But with the atmosphere remaining 'capped' the threat for the storms to grow to severe limits remains very low.

These widely scattered thunderstorms will continue through this evening, roughly through 8pm or 9pm. Overnight there does remain an isolated chance for a couple storms, but we may see a better chance for more storm coverage late Tuesday into Wednesday.

Temperatures have warmed into the mid and upper 80s, with the heat index pushing the mid-90s in a few spots. But expect temperatures to briefly drop as the rain moves through. Unfortunately, it won't clear some of the humidity we are experiencing this afternoon. 

Hotter days ahead as the ring of fire pattern reemerges

"Ring of Fire" Returns:

We haven't used the phrase "Ring of Fire" in quite some time, but it makes a return as we round out the month of August and start September. What does this mean? Expect temperatures to climb close to the 90-degree mark through the first half of the week. Since we're positioned along the northern edge of the ridge, we'll also need to keep tabs on storm potential. Weak systems ridging around the ridge may occasionally trigger showers and marginally-severe storms. 

Current Heat Alerts:

As of this morning, no counties across the Stateline are under any heat-related alerts. However, the heat is becoming more intense farther to our south and west where Heat Advisories are in place. Again, pending storm chances, we may see that expand into northern Illinois but for now, we have no alerts.

 

Today's Heat:

For today, expect mostly cloudy skies to gradually become partly cloudy as the day goes on. A weak system arriving late in the afternoon and evening could be enough to spark up an isolated shower or storm after 3-4PM. Now, with the ridge anchored to our south, a large reservoir of warm air is spreading into the low levels of the atmosphere. 

That warm air acts like a cap, limiting thunderstorm potential for much of the day and keeping any storm chances isolated and confined to the late afternoon and evening hours. Temperatures will climb into the upper 80s, and with humidity continuing to increase, it will feel more like the low 90s. Overnight, storm chances will lower after midnight, allowing skies to turn partly cloudy with lows in the low 70s. 

Tomorrow's Heat:

Tuesday will bring another hot and somewhat humid day to the Stateline. Like today, high pressure and the cap will keep daytime storm chances at bay for the most part, allowing temperatures to climb close to the 90-degree mark. With dew point values sitting in the low 70s, heat indices could end up in the mid to upper 90s at times Tuesday afternoon. Forecast models do show a disturbance pushing through late in the day towards the evening. This could again be enough for us to see an isolated chance for a shower or thunderstorm.Wednesday may end up being the hottest day of this upcoming stretch as highs may end up a degree or two past the 90-degree mark. 

Shower and thunderstorm chances continue into Monday morning

 Showers have been a little more widespread this afternoon than I was expecting, limiting temperatures to the mid/upper 70s like yesterday. Many locations in the Stateline picked up between a quarter inch and an inch of rainfall from late Saturday night through Sunday evening, with light showers continuing for some as of 5:30PM.

We will keep the light showers with pockets of heavy rain into the evening and night, but likely in lesser coverage than the daytime. Temperatures will hold steady through the night, only falling into the low 70s.

Isolated thunderstorm chances amid increasing humidity next week

 Increasing humidity will bring a noticeable summer-like feeling this week, with isolated thunderstorm chances to boot. The heat and humidity will be characterized by a rise in dew points, pushing into the 70s at times. With a very warm air mass just above the surface, temperatures will rise near 90 degrees some days, pending thunderstorm development. As for storm chances, the daytimes will be mainly capped and dry each of Sunday, Monday, and Tuesday. The evening and overnight periods may bring slightly better coverage of rain. Whenever they develop, the strongest storms may be strong to severe.

But the storm development is far from a guarantee. This is because of that very warm air above the surface mentioned above, otherwise known as a "cap". This effectively acts as a lid on the atmosphere which can work to prevent thunderstorms from developing. If we were to be capped during the day, the temperature would likely be able to reach its maximum, pushing near or above 90 degrees. Conversely, if the cap is weaker or breaks, thunderstorms may be able to develop. This would promote slightly cooler afternoons with highs in the middle or upper 80s, but likely still rather humid.

Because of the small-scale nature of this cap, models will likely change a lot each day, promoting wildly different rain chances even within the same day. In short, we may see isolated thunderstorm development anytime starting Saturday night through Monday evening. But much of that time will be dry.

The first wave may arrive early Sunday morning in the form of some scattered showers and a few embedded storms. Depending on how long this lingers into the afternoon, temperatures may not quite reach as high.

Chances drop off for the evening a bit, but higher coverage may return overnight and Monday morning. Another chance looks to develop Tuesday morning. Similar to Sunday, the afternoon temperature depends on how quickly the clouds and rain thin out, and if the cap holds for the afternoon. If we remain dry, temperatures will likely push near 90 degrees Monday and Tuesday afternoons.