Warm days and cool nights this weekend

 A broad region of higher pressure and drier air will slide overhead into the weekend. This will lead to many warm afternoons and cool nights. Afternoon highs will reach the low 80s while lows tag the 50s through this weekend. There is a chance for patchy fog a few nights, especially Saturday morning.

Relative humidity is forecast to be around 95-100% early Saturday morning, which could enhance some of the fog potential. There is a bit of uncertainty on coverage and thickness of the potential fog, but the threat for areas of fog seems to be highest Friday night into Saturday compared to other surrounding days.

The warm and dry pattern sticks around throughout the entire week ahead. Very little of the Central U.S. will see any measurable rainfall through at least the middle of next week. Zero rainfall is forecast in Rockford through at least Thursday. However, significant rainfall may be possible across the Carolinas with a tropical system. This system will likely strengthen into Tropical Storm "Imelda" within the next few days, according to the National Hurricane Center's latest forecast.

 

Above average temperatures with very little precipitation to come

After yesterday gave us a bit of a break from 80-degree temperatures we will see much of the same stick around into today. Temperatures today will be slightly warmer thanks to more sunshine while conditions at the surface remain comfortable, calm and dry!

Heading into the next few days temperatures will slightly warm as an upper-level ridge will set in over the Midwest allowing slightly warmer temperatures to creep northward. By the beginning of next week temperatures will be summer like, however with the humidity thankfully!

Although temperatures will be slightly warmer, we won't have to worry about precipitation ruining outdoor events over the next week. As mentioned, humidity won't be the biggest concern as we'll see temperatures be summer like, but our atmospheric moisture will stay dry over the next week. Combine that with very weak upper-level winds, there won't be much forcing or lift available to create showers/storms.

This may sound great to some; however, the drought monitor for Illinois has begun to look a bit concerning as we've gone through the month. Luckily for Northern Illinois we've been able to receive some rainfall during the late summer however areas further south may feel bigger impacts with the dry pattern setting in. 

 

Unseasonably warm and dry stretch to close out September

 After a brief stretch of cooler and cloudy weather, we will see a return to summer-like warmth to take us through the last week of September. The upper level pattern will flip on its head over the weekend, bringing another ridge of high pressure over the Central Plains and Midwest.

This will boost our temperatures back to the 80s over the weekend and much of next week. Average high temperature this time of year is near 70 degrees but forecast highs will be about 10+ degrees above that into the weekend.

Only 4 years in Rockford's history have seen the last week average an 80-degree high: 1897, 1905, 1953, and 2021. This year could become the 5th to average an 80-degree high, as our current forecast would result in an average of exactly 80 degrees over the last week of September.

5 days this week are forecast to reach at least 80-degrees. Only 2 other years have seen 5 days reach 80 in the last week of September: 2014 and 2021. Again, 2025 could add to this list as Friday (26th) through Tuesday (30th) are forecast to reach 80 or higher.

This warm pattern also comes with a lack of rainfall. Many computer models are forecasting zero rainfall across Northern Illinois through at least next Wednesday, if not longer. The upper-level ridge may finally start breaking down toward the end of next week, signaling an eventual pattern change after the first few days of October.

High pressure to keep our weather warm and dry into next week

Cloud cover, and a little bit of fog kicks off what is to be a rather seasonable day. Skies will clear up as the morning progresses, leaving us partly cloudy by midday and for this afternoon. 

Temperatures, thanks to a light northeasterly wind, will be end up a little different from the previous few days, landing in the low 70s which is on par for late-September. Conditions then remain quiet overnight as high pressure settles over the Midwest, allowing overnight lows to fall into the low 50s.  

Forecast models then show the upper-level low over the Great Lakes progressing eastward, allowing a ridge to develop out west. This ridge will then shift east, displacing the jet stream north into Canada over the weekend into next week. 

 

  

What does that mean? That means this long-lived summer-like stretch isn't going to back down one bit as we turn the page into October. 

High temperatures to round out the work week will hover around the 80° mark, then climb further into the low 80s Saturday, Sunday, and Monday. Compared to average, this winds up 10° to as much as 13° above late-September standards. 

Rain chances remain very very slim during this stretch. Even with a cold front sliding through late in the day Saturday, it won't have the supply of moisture needed to produce any rainfall. 

Isolated thunderstorms remain likely along advancing cold front

 

A few isolated showers and thunderstorms have developed along a southward advancing cold front Tuesday evening, stretching mainly from Whiteside into Lee County. These storms will continue to move south through the rest of the evening as slightly drier, and cooler, air moves in from the north.

Temperatures are already beginning to fall north of the front with a few locations falling into the upper 60s under a northeast breeze. As the evening settles in there may be some clearing but moisture moving in from Lake Michigan will cause cloud cover to fill back in along with the development of a little fog. Temperatures tonight will fall into the upper 50s, warming into the low 70s Wednesday afternoon.

The precipitation expected for Tuesday night will remain isolated and should quickly weaken as we near sunset. Cloud cover will be slow to clear which will lead to a mostly cloudy, and potentially foggy, start Wednesday.

Summer-like air to stay as we enter the final days of September

While Monday marked the seasonal transition from summer to fall, it has felt anything but fall-like here in the Stateline the past 2 weeks. 

That trend is not only set to continue this weekend, but also into the final days of September. 

Now, we do have a cold front sweeping through this morning, which will leave highs somewhat cooler in the upper 70s. Compared to late-September standards, this ends up 4° above-average.  

 

 

Cloud cover hangs tight and with that cloud cover may come a few showers and thunderstorms. Unlike Monday, any thunderstorm that does manage to form will showcase non-severe characteristics. Overnight low temperatures will end up a smidge cooler in the upper 50s. Some may even wind up in the mid 50s IF a fog layer can become established. If so, you may need to give yourself a few extra minutes for travel for tomorrow morning's commute.

On the backside of today's cold front, low pressure sweeping to our south will keep surface flow out of the northeast, so off Lake Michigan. This will help bring afternoon highs down closer to average for not only Wednesday but also Thursday. Depending on the northern extent of the precipitation shield, we could see a few showers Wednesday. 

The midweek cooldown is brief as summer-like air makes a quick return for the weekend. There is a cold front that forecast models bring in during the first half of our Saturday. However, there isn't much cool air that comes along with it, which will leave afternoon highs near 80° into next week.

Weather to remain somewhat unsettled for the first few days of fall

Astronomical fall begins today at 1:19PM. That is the moment when the sun's light crosses the celestial equator, resulting in nearly equal amounts of daylight and darkness for all parts of the Earth. Sunrise will be at 6:44AM while sunset will be at 6:52PM.

With the first afternoon of fall comes above-average temperatures as well as the chance for additional rainfall. Chances will be isolated and low during the day, though coverage will increase after sunset as our next cold front approaches. Especially for those north of the Illinois/Wisconsin border.

  

For that, the Storm Prediction Center has placed areas north of Freeport, Savanna, Rockton, and Poplar Grove under a Level 1 Marginal Risk. The biggest concern with any storm that becomes severe will be hail up to quarter size in diameter and winds up to 60 mph. By Tuesday afternoon, the focus for further development along this boundary will shift south of I-88. But just to be safe, I did leave an isolated chance for a shower or thunderstorm. 

Temperatures will end up cooler and not as summer-like, landing in the upper 70s today and tomorrow, then in the low 70s by Wednesday. Overnight lows will be rather comfortable, dropping into the low 60s the next few nights before dropping back down into the upper 50s Wednesday night.