Umbrellas required: Soaking rain chances ahead of fall cooldown

What's Ahead?:

Patchy dense fog may once again develop across the Stateline early this morning, potentially leading to reduced visibility for those traveling. Any fog or low clouds should gradually lift as we approach the mid-morning hours, but our attention then turns to our next storm system. Moisture will continue to spill in Tuesday evening into Tuesday night, allowing rain to become likely by Wednesday morning. 

Timing Out The Rain:

Scattered showers and periods of steady/heavy rain are expected both Wednesday and Thursday as the cold front approaches from the west. While severe weather is unlikely during this stretch, a rumble of thunder or two cannot be ruled out. 

Current forecast guidance continues to point towards the heaviest rain arriving Wednesday morning, with another round pushing in as we inch closer to midday Thursday and into Thursday afternoon. There is also some indication that tropical moisture could become involved with this incoming rain. The reason why?  The jet stream is expected to pick up the remnants of former major hurricane Polo and swing it in our general direction, helping boost rainfall efficiency and totals across portions of the Midwest. 

It's safe to say you'll want to keep an umbrella handy both Wednesday and Thursday. Most locations could receive more than an inch of rain by the time this system exits into the Great Lakes, while isolated areas may pick up as much as 2"+ where the heavies bands of rain persist. While the exact amounts will continue to be refined over the next 12 to 18 hours, confidence is growing for another soaking rain. 

Beautiful late September afternoon

 

After a rather chilly and foggy start Monday morning temperatures were able to warm nicely for the afternoon, reaching a high of 77 degrees in Rockford. While not too far above the average high of 71, it has been nice to have some warmth following the cooler and wet weather a week ago.

High pressure will still hold strong through the night which will help keep our skies clear, allowing temperatures to once again fall back into the upper

40s. Similar to Monday morning areas of fog are likely to develop early Tuesday, with some locally dense fog possible overnight. Clouds will be on the increase through the afternoon and evening Tuesday, but despite that temperatures are expected to warm back into the mid-70s. Skies will cloud over Tuesday night with temperatures holding right around 60 degrees. Rain will then move in during the day Wednesday, with some heavy rainfall possible through Thursday night.

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.