Pleasant start to the week before a multi-day rain threat returns

Patchy Morning Fog:

Some patchy dense fog is beginning to develop just before the start of the morning commute. Morning meteorologist Owen Szarley mentioned that the fog was particularly dense in DeKalb County during his drive into the station. While no dense fog advisory has been issued at this time, those traveling should be prepared for fluctuations in visibility. Allow for a little extra time, keep your low-beams on, and be prepared for pockets of thick fog. 

Pleasant Monday:

High pressure anchored over the western Great Lakes will make for a pleasant start to the week. Any fog or low clouds lingering from this morning will gradually lift, giving way to a mix of clouds and sun. Afternoon highs will end up back  into the low 70s, a touch above late-September standards.  

 

More Fog Potential:

High pressure will also promote a very dry and quiet atmosphere overnight into Tuesday. Combined with a light easterly to southeasterly wind and mainly clear skies, that could set the stage for another round of fog during the early morning hours Tuesday. Currently, guidance suggests the best chance for travel impacts will be east of I-39, though areas outside of that area could still see localized fog. 

Rain Chances Increase:

Tuesday will remain dry through the daylight hours, but changes will begin to take shape as moisture will gradually increase across the region. Expect clouds to build through the afternoon and evening, with skies becoming mostly cloudy late. Rain chances will ramp up shortly after midnight as the next disturbance approaches from the west. This will mark the start of a more active weather pattern, with steady/heavy rain being a possibility through Thursday.   

Second half of this week more active with frequent rain showers

 Very pleasant, but warm fall-like weather has been the trend this weekend and will continue to be for the first half of the week. But a pattern change is on the way for the second half of the week, including a potential for some pockets of heavy rainfall.

There are still a number of moving parts to the forecast because of a complicated upper-level pattern involving an outgoing Nor'easter to the East and remnants from tropical systems to the West. Because of this, there are some uncertainties that remain. First off, we are confident in the more active pattern as a whole with increasing moisture Tuesday night and Wednesday, with pockets of steady or heavy rain through at least Thursday. But the exact placement of the cold front each day and where the heaviest rain will set up is still in question.

The system has been trending to arrive later and later over the last few days, resulting in a now dry forecast through at least Tuesday evening. Initial showers may not even arrive until Wednesday morning with drier air still in place ahead of the cold front.

But the slow-moving nature of the front will allow moisture to build in along it, producing pockets of steady to heavy rain particularly Wednesday night through Thursday. A few locations may be able to see more than an inch of rainfall, especially if the cold front stalls out overnight. Showers will eventually exit the area as higher pressure arrives from the Northwest, bringing an end to the rain by Friday afternoon. Cooler air will then follow with afternoon highs in the mid-60s next weekend.

Pleasant, fall-like conditions into early week

 Large-scale blocking will prevent much change in the weather pattern over the coming days, with more sunshine and pleasant fall-like weather continuing. The strong Nor'easter over the Atlantic Coast will keep this block in place through the next few days, limiting daily changes in the weather conditions.

We have a nearly a copy and paste forecast over the next few days as a result, with afternoon highs in the low 70s and overnight lows in the upper 40s to low 50s. A few patches of fog may be possible each night, but we will stay dry through Tuesday afternoon. Later in the evening and into next week will bring a more active pattern with more frequent chances for rain.

Weekend mostly dry, active pattern sets up again next week

 Moisture and dry air continue to play tug-of-war over the region this weekend, but drier air seems to win over locally. While an isolated sprinkle or two may be possible from time to time, most of Northern Illinois will remain dry this weekend with highs near 70 and lows near 50. Better chances for light showers will be possible to our West, mainly across Iowa.

A much more active pattern will then develop toward the middle and end of next week. A series of low pressure systems will each bring more widespread rain chances with it, including the potential for some locally heavy rainfall. The first cold front will slide over the region Tuesday evening and overnight, with at least scattered showers.

That front will then stall down to our South as another low pressure system lifts the moisture back our direction later in the week, continuing the active streak. The exact placement of this front is still in question as to where the heaviest rain may fall, but we do look to remain rather active through the end of the week. Widespread rain with a few embedded thunderstorms could be possible Tuesday evening through at least Friday.

A perfect balance of light: The equilux explained

What is the Equilux?:

While the fall equinox marks the official start of the astronomical autumn season, it is not the day where we receive exactly 12 hours of daylight and 12 hours of darkness. That distinction belongs to what's known as the equilux, which means "equal light". 

The equilux is the day when sunrise and sunset are separated by almost exactly 12 hours, resulting in an equal balance of day and night. Because of the Sun's size and the way Earth's atmosphere bends sunlight, the equinox and equilux do not occur on the same day. For instance, Rockford's spring equilux took place on March 17th, while the autumn equilux is scheduled to occur tomorrow, September 26th. Our sunrise is at 6:47AM and sunset is at 6:48PM, giving that equal split in day and night. Once the equilux passes, daylight hours continue to shrink, allowing nights to grow longer. 

Dry air gains ground as rain chances across northern Illinois fade

Shower Chance Early:

Over the next few days, we'll continue to watch a bit of tug-of-war unfold across the region as dry air anchored over the Great Lakes battles increasing moisture trying to push in from the west. Right now, moisture is winning out, leading to sprinkles, and even an isolated shower to start the day.  

Fortunately, any rainfall over northern Illinois will remain light, with no heavy rain expected. In fact, the best chance for any rain will be during the morning hours, primarily before 9-10AM. After that, dry air will take over as high pressure inches west, allowing conditions to gradually dry out and skies to transition to a mix of clouds and sun. Temperatures remain on the cool side, topping out in the upper 60s, while a light easterly wind keeps the early-fall feel. 

Dry Weekend Ahead:

High pressure will continue to inch closer to the area through the weekend, allowing dry air over the Great Lakes to win out. As a result, rain chances remain slim and very limited, with Sunday presenting the only weekend opportunity for rain in the form of a brief sprinkle. Otherwise, the persistent push of dry air from the east will make it difficult for moisture to successful spill into the region. Temperatures remain comfortable, hovering around 70 degrees. 

 

 

Active pattern brings more frequent rain chances to close out September

 After a very wet weekend, the last few days had been a nice break from the rain. But another active pattern will bring us better chances for rain again toward the middle and end of next week, right in time for the flip of the calendar into October.

It all starts with a shift in the upper level pattern over the next week. This coming weekend, blocking between high pressure over the Great Lakes and a strong Nor'easter will keep rain chances to a minimum. But once that pattern releases, a stronger jet will draw more frequent low-pressure systems our direction, beginning Tuesday and Wednesday.

The stronger Southwest direction to the winds near the surface and aloft will work to draw in that much more moisture. As a result, it will be much more abundant compared to this weekend, resulting in better coverage and intensity of rain. Rain chances will begin Tuesday afternoon and could continue on and off through the end of the week. A few thunderstorms may also be possible, with stronger dynamics in place.

The active pattern may continue into the first few days of October as well. The Climate Prediction Center gives Northern Illinois around a 50-60% chance to see above average precipitation between September 30th and October 4th, likely owed to the more active jet stream mentioned above. Looking further ahead to mid-October, we typically get at least one or two shots of chilly fall-like weather, with the first potentially set to arrive around October 5th-8th.