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.

Summer-like, humid pattern with isolated storms next week

 While the warmth over the last week has not come with much humidity, that is about to change in the coming days. While Saturday will remain somewhat comfortable with clouds and slim chances for rain, the humidity really builds in after Sunday.

Sunday will begin the first of several hot and humid days, with temperatures pushing into the mid-80s. The heat index will make it feel a bit warmer, possibly near 90. Monday through Wednesday will be even hotter, with near 90-degree highs possible each day. The peak heat index will likely be well into the 90s, and possibly close to 100 degrees at times.

Normally when you have excessive heat and humidity like this, you will see storm chances not far away. The Stateline will be right on the edge of the more active jet stream aloft. This acts like the highway for storms to form and maintain themselves on. South of us, the atmosphere will likely remain capped each day, preventing storm activity. With the active jet centered mostly around Central and Southern Wisconsin, the Stateline itself will have a chance for rain each day, but the highest concentration of storms may remain just to the North. If this jet stream were to shift South even a bit, storm chances will increase each day with slightly lower concerns about the heat.

Increased clouds limit temperatures with light rain possible Saturday

 A line of decaying storms will approach the Stateline by mid-day Saturday, bringing the potential for at least some light showers mainly between 11AM and 5PM. The threat for thunder will be near zero, but a few pockets of rain may bring a brief steady shower. Outside of that, light sprinkles will be the primary form of precipitation. Any rain we do see will begin to clear by 5-7PM. The bigger impact the rain will have is on the temperature. We may not quite reach the 80s with the clouds in place during the peak heating hours of the day.

The rain that does fall will not amount to much, with most seeing under a tenth of an inch. Better chances for 0.1-0.2" of rain will be primarily Northwest of Freeport. Some locations in the Stateline may not even see any measurable rain at all. Higher chances for rain and storms may be possible toward the end of next week, following increased heat and humidity.

Meteorological fall across northern Illinois begins with a summer-like sizzle

Pleasant Friday:

Mother nature really delivered this week, treating the Stateline to several comfortable days with afternoon highs settling in the low to mid 80s. We'll wrap up the workweek on a similar note, with skies remaining dry and partly cloudy and temperatures climbing into the low 80s, right around 83 degrees.  

Even better, Friday evening/night plans look weather-friendly. Unlike last week, there are no thunderstorms or rain in the forecast, meaning high school football games across the area should kick off and finish without interruption. The dry and pleasant conditions are also great news for anyone heading downtown for City Market, with comfortable temperatures lingering into the early overnight hours. 

 

Weekend Outlook:

This quiet weather pattern won't disappear entirely over the weekend, but most of us will stay dry. Our next disturbance arrives around or just after midday Saturday, bringing the chance for an isolated shower or two during the afternoon. 

Even so, the better rain chances and moisture will stay north of the Stateline, focused across central and southern Wisconsin. As a result, many location across northern Illinois may end up seeing a few clouds and a sprinkle. Sunday brings a similar setup, though temperatures will be a touch warmer as a ridge of high pressure aloft pushes east across the midsection of the lower 48. This will allow highs to climb into the upper 80s. A pop-up shower or isolated thunderstorm cannot be ruled out, but rain isn't expected to be widespread. If you have outdoor plans, keep an eye on the heat but also the radar. 

Meteorological Fall:

As we turn the calendar from meteorological summer to meteorological fall on September 1st, the weather certainly won't be following suit. In fact, the average high for early September hovers around the 80-degree mark, but temperatures will run well above that mark as an upper-level ridge settles across the Tennessee Valley and the Deep South States. 

That ridge will allow summer-like heat to build into the Stateline at the start of next week, sending highs back near the 90-degree mark.
   
 
 

Tonight's full Sturgeon Moon comes with a bonus: A partial lunar eclipse

Dry & Pleasant:

Despite a cold front sliding through during the late morning hours yesterday, temperatures still managed to climb into the mid 80s. The front itself wasn't particularly strong, but it came through early enough to where the severe potential was shoved to our south and east, leaving us dry and warm.

 

Today will feature a much more comfortable setup as high pressure settles into the region. Dry conditions are expected from start to finish, with a mix of clouds and sun present for our afternoon. The drier air will keep the area's humidity in check, while afternoon highs will top out in the low 80s.  

 

  

August's Full Moon:

Tonight, high pressure will also keep us dry, giving us a great view of August's full moon. Also known as the "Sturgeon Moon", this full moon earned its name from Native American tribes, as late summer was traditionally one of the best times of the year catch Sturgeon in lakes and rivers. With only a few passing clouds and calm winds in the forecast tonight, we should be in for a show when peak illumination occurs at 12:18AM Friday morning. 

Partial Lunar Eclipse:

Tonight's full moon is extra special as it coincides with a partial lunar eclipse. A lunar eclipse occurs when the Earth passes between the Sun and the moon, causing the Earth's shadow to fall across part of the moon's surface. The partial eclipse will begin at 9:33PM, reaching its maximum eclipse at 11:12PM, then ending at 12:51AM Friday. 

Summer-like heat set to return next week

 While much of the region has enjoyed some cooler days and refreshing nights as of late, a more summer-like pattern featuring heat and humidity will return starting this weekend. The upper levels of the atmosphere have been favorable for cooler, more comfortable weather as of late, with a Northwest direction to the flow aloft. This has kept a lot of the typical summertime heat and humidity away from us across the Western United States.

But as that ridge begins to shift East, it will bring a lot of the heat with it. As the jet stream flows North of the Stateline, summertime heat and humidity will build up across the Plains and into the Midwest. This will push temperatures into the upper 80s and near 90 some days next week, beginning Sunday and Monday. Isolated to scattered thunderstorms will be possible each day, with higher confidence on storms along the higher concentration of jet stream winds across the Northern Plains and Upper Great Lakes.

It does appear this pattern will stick with us a bit longer, as the Climate Prediction Center is giving us a 70-80% chance we will see above average temperatures to start the month of September. Average highs for this time of year are closer to the low 80s and upper 70s, so it appears likely we will see more mid to upper 80s if not a couple 90s thrown in there.

High pressure builds back in following Wednesday's cold front

 

8pm Update: Just a few very isolated showers moving across the region as the last few pieces of energy rotate around the upper-level low over the Great Lakes. Skies will clear this evening with a little patchy fog possible early Thursday morning.

A line of thunderstorms continues to develop from Michigan down through east-central Illinois Wednesday afternoon, ahead of a cold front that moved across northern Illinois during the morning. Precipitation chances remain limited locally with the front well to our east, but with still a little moisture around and some instability it isn't completely out of the question that an isolated shower or two may still occur through sunset.

Temperatures have warmed into the low 80s with just a touch of humidity as dew points have reached the low to mid-60s this afternoon. Skies should begin to clear with high pressure settling back in Thursday. Temperatures Wednesday night will sit right around 60 degrees with highs on Thursday warming into the low 80s. Thursday night should be good sleeping weather with lows dipping back into the upper 50s. Friday will remain mostly dry with high pressure still over the Great Lakes, but a return to southerly winds Friday night into Saturday will slowly begin to set the stage for the return of not only a rise in temperatures, but also a climb in humidity and thunderstorm chances across the Midwest through early next week.