A brief storm threat gives way to comfortable August weather

What's Ahead:

1. Storm chances increase this afternoon and evening, with an isolated risk for severe weather

2. Dense fog will be a possibility for those traveling Wednesday morning. 

3. Temperatures trend cooler, with the most noticeable drop arriving over the weekend.  

Isolated Severe Tuesday:

The Stateline may see a few showers with the first of two disturbances around the midday hours. However, it is the second wave arriving this evening that will bear watching as the associated cold front could fire up a few thunderstorms, some of which may be strong to severe. While severe weather is not expected to be widespread, an isolated threat does exist, with strong winds being the primary hazard. 

Drying out Wednesday:

Any chance for rain or thunderstorms should come to an end before midnight, leaving us with the potential for dense fog Wednesday morning. If planning to be on the roads, travel with caution.  

After the morning fog lets up, Wednesday is shaping up to be a quiet and pleasant day, with skies turning partly cloudy by the afternoon. Behind tonight's cold front, winds will shift back to the northwest, helping usher in a cooler air mass. That will keep afternoon highs in the upper 70s, providing comfortable conditions for mid-August. 

Winnebago County Fair:

It's also welcoming news fore the final county fair of the summer, the Winnebago County Fair. The chance for rain throughout the fair will be low, allowing most events and activities to stay dry. The only opportunity for rain arrives late Friday into early Saturday as a second cold front sweeps through. Otherwise, expect dry but also cooler-than average conditions as highs remain in the upper 70s into the weekend. 

Scattered storms Tuesday evening, comfortable pattern sticks around

 A couple strong to severe storms may be possible Tuesday evening and the comfortable pattern is here to stay for a bit longer. Starting Tuesday morning, decaying showers and storms may push into the region between 6-9AM but should clear out by midday. Threat for any storms during this time is very low, and most in the region may actually stay dry.

How fast the clouds clear out will determine the severity of the storms into the late afternoon and evening. The main window for storm activity arrives after 2-3PM, continuing through the evening. The strongest storms may be capable of wind gusts around 50-60 mph along with downpours.

Overall severe risks remain limited locally, with the entire Stateline under a Level 1/5 Marginal risk for severe storms. That indicates an isolated storm or two may be able to pulse up near severe limits, but a widespread severe threat is not expected. A few showers and storms may persist into Tuesday night, but even less of a severe risk after 12AM.

Behind that weather system, afternoon high temperatures will hover in the upper 70s each day forward. This will begin a streak of sub-80 degree highs, the first 5+ day stretch since late June! As we get closer to the end of summer, 70s will become much more common than 80s, as the pattern looks to remain near or below average for much of the next couple weeks.

Comfortable air settles in before storm chances return Tuesday

Pleasant Monday:

Temperatures and dew points have taken quite the tumble overnight, providing a refreshing start to both Monday and the new work week. After the recent stretch of muggy conditions, dew points are sitting in the low 60s, with air temperatures also settling into the low 60s early this morning. The result is a much more comfortable feel in the air. 

The pleasant conditions will stick around through the afternoon as an area of high pressure remains firmly in place to our west across Iowa. Aside from a few fair-weather cumulus clouds bubbling up during the peak heating of the day, skies will stay dry and feature a mix of clouds of sunshine. A light northwest breeze will continue to usher in less humid air, helping afternoon highs remain in check. Highs are expected to barely reach the 80-degree mark. 

Storm Chances Return:

Much of Tuesday looks to remain dry as the effects of this high pressure system lingers. That said, changes begin to arrive later in the day as a fast-moving system approaches from the northwest. 

Clouds will gradually increase through the afternoon, with storm chances returns very late in the afternoon and during the evening hours. While widespread severe weather is not expected at this time, a few storms could be strong to severe. As of this morning, the Storm Prediction Center has the entire Stateline under a level 1 of 5 Marginal Risk for severe weather, with damaging winds being the main concern. Conditions should rapidly improve once the disturbance is through, resulting in a quiet but possibly foggy start to our Wednesday. 

 
 

High and dry Monday, storm chances return Tuesday afternoon

 Behind Sunday's cold front, dew point temperatures were dropping into the low 60s and upper 50s through the course of Monday. This much more comfortable air mass will be accompanied by an area of high pressure, keeping us dry through early Tuesday. Afternoon high temperatures with more bountiful sunshine will push back into the low 80s, but without the humidity of Sunday, it will feel much more pleasant.

Our next round of thunderstorms looks to develop Tuesday. An elongated area of low pressure and associated weak cold front will bring a threat for scattered thunderstorms during the afternoon and into the evening. A few of those storms may be strong to severe, with the primary risks of damaging winds and heavy rain.

Scattered storms, heavy rain, and areas of fog possible Saturday night

 [10:40PM] Scattered storms with pockets of heavy rain are developing along a line from about Savanna to McHenry in Northern Illinois. Strongest cells have lightning and rainfall rates above 2" per hour. Storms are moving East at around 15-20 mph. Severe weather is not a concern, but ponding on roadways and low-lying areas will be possible where heaviest rain falls.

[9:50PM] A severe thunderstorm warning has been issued for Southern Whiteside County, IL until 10:45PM. This storm is capable of producing 60 mph wind gusts and very heavy rainfall as it moves to the East at around 45 mph. Worst of the storms will stay along and South of I-88, but isolated pockets of heavy rain will be possible locally as well.

Another round of thunderstorms is developing in Southeastern Iowa, tracking along I-80 once again. A few pockets of heavy rain may lift North of that and into Southern portions of the Stateline through 10PM-1AM. Heavy rain would be the primary threat, with rainfall rates near 1-2" per hour.

Some locations near and North of Rochelle received 2" of rain last night, so flooding threats would be highest if any storm were to pass over that same region again. After 1AM, coverage of rain will wind down, with only a few isolated showers to follow the rest of the night.

Patches or areas of fog will then be possible into Sunday morning. Visibility may be limited at times, with pockets of locally dense fog. Temperatures will return to the mid-80s Sunday afternoon as a cold front clears out some of the cloud cover by the evening.

Heavy rainfall, flash flooding possible tonight for parts of Northern Illinois

 [11PM] With only light rain showers so far North of I-80, our flash flooding threat will be a bit lower tonight. On and off showers remain possible with some pockets of heavy rain, but that will be rather isolated in nature with a lower risk for flooding.

[9:45PM] Latest model runs have been coming in, suggesting that the heaviest, most intense rainfall may end up South of I-80 now. That does not quite put us entirely out of the woods in Northern Illinois, but we are trending in the right direction. Light to steady showers will remain possible at times through the night with some pockets of heavy rain. The significant flash flooding will likely be a big concern South of I-80, though. Many locations already saw very heavy rain last night, with another few inches of rain possible over already saturated soils. If you know anyone in Central Illinois, make sure they are aware of the weather forecast and have steps to keep themselves safe if a flash flood warning were to be issued.

Heavy rainfall and flash flooding could be on the table for parts of Northern Illinois this evening and overnight. Our next wave of showers and storms is currently taking shape this evening in Iowa and will slide our direction along I-80 tonight.

Isolated pockets of showers will remain possible this evening, but higher coverage will arrive after 10PM-12AM. The due Easterly trajectory of this system will keep the heaviest rain just South of the Stateline, and potentially South of I-88 or even into Central Illinois. Nonetheless, strongest storms will be capable of rainfall rates near 1-3" per hour.

Back-building and training thunderstorms will quickly produce 3"+ of rainfall and develop a flash flooding threat. Luckily for Northern Illinois, I believe that threat to remain highest South of I-88 and maybe even South of I-80. We may still have pockets of heavy rain with 1-3" possible in isolated spots, but the widespread flash flooding threats should remain just to our South.

A flood watch will remain in effect through Saturday morning for Carroll, Whiteside, Ogle, Lee, and DeKalb Counties, where the locally higher risk is for flash flooding concerns. That said, be sure to heed any warnings that are issued, and I'll be sure to keep you updated through the night!

Heavy rain threat returns to northern Illinois this weekend

Flood Watch Cancelled:

The flood watch that had been in effect for our areas to the south has been cancelled as the heaviest rain has shifted well south of the Stateline. While a few lingering showers will be possible as we approach the midday hours, the threat for widespread flooding has diminished. A few light showers will also be possible this afternoon as our next system approaches. Nothing to the extent however that would increase the threat for flash flooding across the Stateline area. 

Saturday's Rainfall:

Speaking of that system, that is where our focus will turn to for the start of the weekend. Forecast models are in agreement on the track of the low, bringing it in to the Stateline prior to sunrise. From there, we could see the opportunity for additional showers and storms, though severe potential should be low. Heavy rainfall however will be on the table until about 9AM, with rainfall totals end up between .75" to 1.5". 

The Weather Prediction Center has placed portion of central and southeast Iowa, along with west-central Illinois, under a Moderate Risk for Flash Flooding. This area extends into parts of northwest Illinois, including most of Whiteside County. These locations will sit closest to the deepest plume of atmospheric moisture over the next 24 hours, resulting in rainfall totals between 2" to 3". 
 

Once the low is positioned to our east, we dry out for the rest of our Saturday. Aside from a stray sprinkle or shower, skies will turn partly cloudy with high temperatures landing in the low 80s. 

 

  

Another weak disturbance pushes in overnight into Sunday, though the bulk of the heaviest rain should remain south of the Stateline area. That is good news for those attending the final day of the Boone County Fair! Temperatures to round out the weekend will end up seasonable, in the low 80s.