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.

Flood Watches issued for some as heavy rainfall remains possible late Thursday night

 

11pm Update: A line of thunderstorms has developed along and south of I-80 late Thursday evening and will be the focus for potential flash flooding through Friday morning. The area outlined in white is where that greatest potential will be, including parts of Carroll, Whiteside, Lee, Ogle and DeKalb counties. This is where locally two (plus) inches of rain could occur through Friday morning. North of there will be isolated to scattered thunderstorms with locally heavy rainfall. Reminder - Flash Flood Watches are in effect for Ogle, Lee, and DeKalb counties until Friday evening and for Carroll and Whiteside counties until Saturday evening.

A steady rain came down for most Thursday as stronger thunderstorms slipped to our south through the afternoon. Most of the rain has come to an end, but a few showers extend along the Highway 20 corridor - slowly sinking to the south and southeast this evening. While scattered showers remain in the forecast through the evening the rainfall won't be widespread.

Flood Watches have been issued for Ogle, Lee, and DeKalb counties until Friday evening and for Carroll and Whiteside counties until Saturday evening for the potential of heavy rainfall, possibly over two inches, occurring late tonight. But the exact axis of that heavy rainfall is still a little bit in question.

Here is how things look going into Thursday evening:

Widely scattered showers will continue through the rest of the evening with a band of rain moving southeast of Highway 20 towards DeKalb County, and another band of rain developing just north of the Quad Cities. Those showers have developed along an old boundary that stretches across eastern Iowa and into western Illinois and *could be the beginning of the heavy rain threat later this evening. It's still a little unclear as to where exactly that band establishes itself over the next few hours, but if it continues to develop where it is at currently then areas in Carroll, Whiteside, Lee, southern Ogle, and DeKalb counties would stand the best chance for rainfall totals nearing, or exceeding, two inches through Friday morning. The probability for higher rainfall totals to the north of there is a little less with rainfall expected to range from a quarter of an inch up to an inch.

Scattered showers/storms will continue into Friday during the first half of the day with some dry time possible during the afternoon. Although, keep the umbrella handy as rain could occur at any one given point throughout the afternoon. Another round of heavy rainfall will then be possible late Friday night, going into Saturday morning.

Dense fog possible for the Thursday morning commute

Just like the past few mornings we're starting our day with some fog. However, unlike the past few days we're likely going to see widespread and much more dense fog through the morning today. The fog the past two days provided the fuel for incoming thunderstorms which will be a similar case today, however thunderstorm chances are much lower. Thanks to calm conditions along with plenty of summertime humidity, expect visibility to be quite low this morning.

The fog this morning is dense enough to require a Dense Fog Advisory to be issued for almost all of Northern Illinois outside of McHenry County. This advisory will last until 9 a.m. however surface conditions before may deteriorate rapidly. If you are heading out for your morning commute, make sure to give yourself extra time so you can drive slower in decreased visibility. Make sure to turn on those fog lights too!

Even before sunrise fog took over a few spots in the region. Areas closer to Highway 20 as of 4:20 a.m. seem to be getting in on the heaviest fog so far, however the expectation is that the fog will gradually spread around the region. Once again expects conditions to improve after sunrise closer to 9 a.m. this morning. 

 

Stormy weather pattern continues after Midwest derecho

Storm Reports:

Yesterday's severe weather event turned into something more significant than your typical summer thunderstorm complex. The line of storms that swept across the Midwest has been classified as a Derecho, or a long-lived wind storm. According to the Storm Prediction Center, damaging wind reports stretched from eastern Iowa to western Ohio.  

Storm Chances Continue:

Attention now turns to our next potential round of strong to severe thunderstorms which is currently pushing trough northeast Nebraska. Forecast models suggest this complex maintaining strength and tracking across northwest Illinois late this morning into the early afternoon. Depending on how far north this complex tracks, this could bring a portion of the Stateline the potential for damaging winds as well as heavy downpours and frequent lightning. 

For that, the Storm Prediction Center has the south and southwest portions of the Stateline under a level 2 of 5 Slight Risk for severe weather. Areas north of Savanna, Sterling, and Paw Paw are under a level 1 of 5 Marginal Risk for isolated severe storms. Again, we will have to monitor the track of this complex because any shift to the north will heighten the potential for damaging winds and heavy rainfall for areas closer to the Illinois/Wisconsin border. Afternoon highs should make the climb into the low 80s. 
 

Isolated thunderstorms possible once again Tuesday night

 

The storms that came through Tuesday morning were quick to move in, but also quick to move out. While the worst of the weather occurred closer to Chicago and over in Indiana, there were quite a few severe weather reports across northern Illinois. But by Noon, most of the storm activity had passed leaving mostly dry skies through the rest of the afternoon and evening.

However, similar to Monday night, the risk for a few isolated thunderstorms presents itself once again Tuesday night as a little upper-level disturbance - currently over Iowa - shifts east/southeast with time tonight. There have been a few attempts for some activity to blossom over north-central Iowa, but so far that activity has struggled just a bit to maintain itself.

If we were to see thunderstorms develop over the next couple of hours (now through 5pm) the storms would be elevated posing mainly a large hail risk. Although locally strong wind gusts can't entirely be ruled out.

As it looks right now the highest threat for thunderstorm development may fall just south of the Rockford area, lining up closer to the Quad Cities to south of Chicago. But radar trends will need to be monitored closely over the next few hours. With any thunderstorms that develop the risk will also be there for heavy rainfall, especially with any storms that move over the same areas repeatedly.      

Tracking Tuesday morning's severe weather threat

Low Chance for a Watch:

A mesoscale discussion has been issued by the Storm Prediction Center for a cluster of thunderstorms moving though central Iowa. In the discussion, it says there is a 40% chance a watch is needed, but while the storms may continue to organize, there remains uncertainty regarding how quick that organization will occur. This is something we'll need to keep an eye on as we approach mid-morning. 

Severe Weather Risk:

If organization does occur, damaging winds would be the primary threat as we head into the second half of our morning. Because the potential remains on the table, the Storm Prediction Center has placed nearly all of northern Illinois under a level 3 of 5 Enhanced Risk for numerous severe storms.   

 

Severe Watch Issued:

All of northern Illinois and southern Wisconsin have been placed under a SEVERE THUNDERSTORM WATCH until 2PM this afternoon.   

 

 

Looking back on previous August severe storms as severe chances loom

 

On this day 6 years ago one of the most infamous weather days in recent weather history occurred as a large complex of severe thunderstorms impacted much of the Corn Belt region. This day is remembered by many across the Midwest and even here in the state line as this complex brought winds over 100 mph and multiple tornadoes to the region. This of course caused heavy damaged to many buildings, farmsteads, and even cornfields as entire fields of crop were destroyed in many locations. This ultimately led to this complex being classified as the most expensive thunderstorm event on record totaling up to over 11 billion dollars. 

 

In total the 2020 Midwest Derecho caused 910 different reports of damaging wind gusts with some even up to 140 mph! Although damaging winds were the main headline, this complex was quite successful
at producing tornadoes as well with nearly 30 being reported as well! The craziest thing is, exactly one year later a very similar wind event occurred in the same region, thankfully nowhere near as strong. 

  

Derecho’s specifically MCS’ are quite common around the Corn Belt and Lower Great Lakes in the summertime. This is due to a common pattern in the summertime known as “Northwest Flow” which often sends many weaker disturbances our way. Those weak disturbances are usually our “spark” for showers and storms to occur, all we need in the summer is the instability.

Over the next few days, severe thunderstorm chances will stick around thanks to this Northwest Flow pattern or “Ring of Fire” with an active jet stream. Damaging winds, large hail, and a few isolated tornadoes can’t be ruled out, changes to areas of higher confidence may shift the next few days as well. 

 

Our jet stream pattern will continue to send weak disturbances while at the surface plenty of instability will be available thanks to a stalled boundary keeping summertime heat/humidity in the region. The heat and humidity will lead to daily instability values favorable for severe storms as well so all we’ll need is a spark to come through. Over the next few days, make sure to have multiple ways to receive watches and warnings!

 

Northern Illinois to see a few more severe opportunities this week

Sunday's Storm Reports:

Now that the severe thunderstorm watch has come to an end, we can take a look at the storm reports from Sunday evening/night. Again, with the early round of showers and storms pushing through, the atmosphere didn't really become active until after sunset as a lifting frontal boundary provided the lift needed for additional development. Several reports were received across northern Illinois, including a few tornado reports. One possible tornado was reported in Lee County, while another touched down closer to I-80 near Atkinson and Annawan.  

Northwest Flow Continues:

While the northwest flow pattern aloft isn't as strong as it was over the weekend, it is keeping the jet stream positioned almost directly at the western Great Lakes. That setup will allow a few more disturbances to ride southeast over the next several day, bringing periodic chances for showers and storms. As a result, we will need to keep tabs on the forecast during the first half of the week as some thunderstorms could entail the potential for severe weather. 

Daily Severe Potential:

A portion of the Stateline, particularly areas south and east of Rockford, remains under a level 2 of 5 Slight Risk for scattered severe weather. While coverage is not expected to be widespread, any thunderstorm that develops and moves through will be during evening and early overnight hours. The primary threat will be damaging winds, though the environment may also support an isolated tornado or two.  

Tomorrow brings much of the same, though timing appears to be much earlier. Another disturbance riding along the jet stream will likely spark a round of the thunderstorms and showers late tonight into tomorrow morning, with the resulting cluster pushing into the Stateline Tuesday morning, with chances possibly stretching into the midday hours. 

Given the amount of instability of storm fuel in the atmosphere, a few of these storms could once again be strong to severe, with damaging winds being the primary concern. Similar to today, make sure to keep tabs on the forecast while also having multiple ways to receive watches and warnings.        

Severe storm and heavy rainfall threat Sunday night

 [12:10AM] Lingering storms remain in Eastern Walworth County, but we are severe storm free now. Likely, much of the night ends up dry, with increasing thunderstorm chances again Monday evening. Flash flood warning for Lee County remains in effect until 1:15AM, but rain is finished there for now.

[10:50PM] The Tornado Warning for Lee County has been canceled.

[10:25PM] The initial tornado warning that had been issued for Lee County has expired at 10:30pm, but a new tornado warning is now in effect for eastern Lee County until 11:30pm. This storm is currently moving towards I-39. The rotation within the storm has broadened out a bit, but still capable of producing a tornado. Heads up if you are in the Paw Paw area as the main area of location is now over Compton, heading towards Paw Paw. Localized flooding is also possible with a Flash Flood Warning in effect until 1:15am for eastern Lee County.

[10:05PM] Tornado warning continues for Lee County IL until 10:30PM. Mid-level rotation remains strong over Shaws, and a tornado could develop at any time. Storm is moving East at 20 mph. Seek shelter now if you're near Shaws, Brooklyn, or Compton!

[9:50PM] A tornado warning has been issued for Central Lee County until 10:30PM. This storm has been elevated but is right along the warm front, helping to enhance some rotation. This part of the storm is moving East at 20-25 mph.

[9:40PM] A new severe thunderstorm warning has been issued for Lee County until 10:45PM. These storms are capable of producing 60 mph wind gusts, quarter sized hail, and very heavy rainfall as they track East at 15 mph. Be on the lookout for flooded roads, as 1.5-2" of rain has already fallen in spots!

[9:35PM] New cells are developing West of the current severe warned storm in Lee County. With cells that train, or track over the same areas, we could see enhanced flash flood potential. Very heavy rainfall rates and slow movements have already allowed for over 1" of rain to fall in some spots. Watching very closely over the next 30 mins to an hour for flooding threats in Central/Eastern Lee County. If you come across any flooded roads, be sure to turn around!

[9PM] All of Northern Illinois is now under a severe thunderstorm watch until 4AM. Storms have begun developing along the previous outflow boundary, including the severe thunderstorm warning for Lee County. Along and North of the boundary closer to I-80, storms will likely be elevated in nature, limiting the tornado threat. Hail and damaging winds will be the primary concerns with any severe storms locally.

[8:50PM] A severe thunderstorm warning has been issued for Lee County in Northern Illinois until 9:45PM. This storm is capable of producing half dollar sized hail and gusty winds under 50 mph. Storm motion is only 15 mph to the East, so very heavy rainfall will also be a concern. Take shelter if you are within this warning!

While most of the Stateline did not see the strong storms or heavy rain from the midday round of activity, another round may still develop later tonight, likely along the outflow/effective warm front from the previous round of storms.

The more favorable environment for strong to severe storms remains near and South of I-88 Sunday evening. Elevated storms remain below severe limits along the I-39 corridor in Northern Illinois and Southern Wisconsin but are within the less favorable environment. With little daytime heating left, I don't expect that front to lift much further North than I-88.

The evening storms will likely develop along this front after 7-8PM, producing the potential for heavy rain, gusty winds, and small hail. The strongest storms may produce some instances of damaging wind gusts, but this would be rather isolated in nature. I suspect some, if not most locations in the Stateline will remain dry tonight.

Scattered strong to severe storms possible Sunday and Monday

 Multiple rounds of showers and storms will be possible between Sunday morning and Monday, each bringing the threat for severe weather. The first wave of storms won't arrive until midday Sunday, with renewed development into the evening and then again Monday. The main threats will be damaging winds and heavy rain, but an isolated tornado will be possible, particularly Sunday evening where surface convergence sets up following the first round of storms.

SPC has the Level 2/5 Slight risk over most of the area for both Sunday and Monday, indicating the chance for a few severe storms both days. Where thunderstorms track over the same areas over and over, very heavy rainfall will be possible with a risk for flash flooding.

 

As typical for these types of patterns, there are a LOT of moving parts, so be sure to stay tuned to the forecast for the latest! Each round of storms heavily dictates what happens with the next, so the forecast is going to be rather fluid over the next 48 hours.