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!