Intense heat takes a back seat as July comes to a close

Hottest Day of the Year:

Monday (as of right now) is written in the books as the hottest day of the year for northern Illinois and southern Wisconsin. Temperatures soared into the mid to upper 90s for most locations. Combined with the tropical humidity and dew point temperatures in the upper 70s, heat indices climbed to very dangerous levels between 110° and 120°.  

While yesterday's heat sure was extreme, it's not the hottest we've been in recent years. For example, the Rockford airport recorded its first 100-degree day in a decade when the temperature reach 100 degrees on June 14th, 2022. Prior to that, the city had not hit or seen the century mark since 2012. 

  

Cooler, Less Humid Tuesday:

The good news is that yesterday's intense heat appears to be the peak of this most recent stretch, as afternoon highs are set to take a "chill pill". Thanks to a cold front that swept through the region Monday evening, highs today will be much closer to where they should be for late July, topping out in the low 80s. While the day will begin on a muggy note, noticeably drier air will filter in behind the front. 

Rain Chances Increase Late:

This stretch of comfortable weather should make for a rather great start to the Ogle County Fair, which gets underway Wednesday, July 29th, with dry conditions expected through the first few days. As we head into the latter half of the week, however, rain chances will begin to creep back into the forecast. Days 3 and 4 of the fair, along with days 1 and 2 of Festa Italiana at Boylan High School, could see a few showers as a weak system tracks to our south and west.  

Limited thunderstorm chances Monday evening

 

Numerous severe thunderstorms moved around the Stateline late Monday morning and afternoon, prompted several severe thunderstorm and tornado warnings. The storms formed along the outer edges of the high heat, humidity, and instability and were very quick to intensify across Wisconsin and northeast Illinois. There were several reports of large hail, damaging winds, and tornadoes. This left the majority of the immediate viewing area high and dry, and just plain hot and humid! Peak heat index values reached upwards of 115 degrees during the afternoon, with a couple sites even coming close to 120!

While our focus has been on the heat and humidity this afternoon, there are a few showers that are starting to develop along a couple outflow boundaries this evening located across Rock County. A few showers have popped between Janesville and Beloit and are drifting to the south/southeast.

Should the showers continue to develop there is still enough heat and instability to allow for an isolated storm or two through 9pm. And with the amount of instability a severe storm or two cannot be ruled out. So, with that I think our highest chance for thunderstorms (still around 20-30 percent coverage) will be along and east of I-39 through late evening. Should any storm reach severe limits, strong wind gusts and very heavy rainfall can't be ruled out. I'll be keeping a close eye on radar over the next couple of hours.

  

Extreme heat, storm potential also on the table across northern Illinois

Extreme Heat Warning:

Along with the dense fog potential, we also have extreme heat and the threat for strong to severe storms on the table today. Storms will be possible during the morning hours, with a secondary round potentially developing during the late afternoon hours. 

In addition, Winnebago, Stephenson, Jo-Daviess, Carroll, Ogle, Lee, DeKalb, and Whiteside County are under an extreme heat warning until 9PM, where heat index values could climb well into the triple-digits. The rest of the Stateline, including Boone and McHenry counties in northern Illinois as well as much of southern Wisconsin, have been placed under a heat advisory.  

Hot & Humid Monday:

Temperatures are expected to soar into the 90s once again today, and when combined with dew points in the mid to upper 70s, it will feel even hotter outside. These tropical levels of humidity will push heat index values into the 105 to 115 degree range this afternoon, creating dangerous conditions for anyone spending long periods of time outdoors. 

If you do have outdoor plans today, be sure to drink plenty of water, even if you don't feel thirsty. Take frequent breaks in air-conditioned buildings or shaded area, wear lightweight clothing, and avoid strenuous activities during the hottest part of the afternoon.  

Severe Storm Update:

Today's severe weather threat will be fueled by the extremely warm, humid, and unstable air in place ahead of southeastward-diving area of low pressure and the associated cold front. 

With lots of moisture, instability, and lift in the atmosphere, the environment will be conducive for a few strong to severe storms. Though there isn't much going on across Wisconsin at the time of this article, we'll still going to keep a chance for a few isolated storms during the early morning hours. However, forecast models have shifted the main thunderstorm potential towards the midday and early-afternoon hours. The Storm Prediction Center has placed much of the Stateline under a level 3 of 5 Enhanced Risk, indicating the potential for numerous severe storms capable of producing damaging winds and an isolated tornado or two. Make sure to stay weather aware throughout the day and have multiple ways to receive severe weather alerts.   

Dense fog advisory for all of northern Illinois until 8AM

What's Ahead: 

It's a busy start to the work week across the Stateline, and it all begins with very dense fog. 

 

 

   

Dense Fog Advisory:

A Dense Fog Advisory is in place for the entire area until 8AM, with visibility dropping to a quarter mile or less at times. The thick fog will make for difficult travel conditions during the morning commute, so be sure to slow down, use low-beam headlights, and allow for extra travel time. Conditions will gradually improve after sunrise as the dense fog begins to lift and visibility improves.  

Strong thunderstorms possible Monday morning, humid afternoon

 Strong to severe storms still remain possible overnight into early Monday morning. With the lack of a trigger, the atmosphere has remained calm so far today. But a complex of storms may dive across the area around 5-9AM, bringing strong winds and heavy rain. There is still a low-end chance we see something develop before then, but the main wave looks to arrive early Monday morning.

Models have a very hard time pinpointing exact timing of these sorts of patterns, so do not take this Futurecast picture as gospel. Chances for storms will increase after 5AM, and a severe storm may be possible through the course of the day. Be sure to have multiple ways to receive warnings and a plan to carry out should a warning be issued.

The influence from that morning complex will determine what, if anything, we see for Monday afternoon. Remnant boundaries, including a lake-enhanced boundary, may induce extra spin to allow for an isolated tornado threat to develop, should any storms form Monday afternoon. Once the cold front clears toward late evening, we will be done with the severe threat.

Outside of the storm potential, it will be another very hot and humid day. Confidence on heat index pushing 105°+ area-wide is not as high Monday as it was Sunday, so the heat advisory was allowed to expire for most. For NW Illinois, it remains in effect through Monday evening. Those who do not see any storms will likely see a heat index well over 100°.

Some wildfire smoke will make a return Monday evening, especially aloft. If any gets trapped under the incoming high pressure Tuesday, we could see some minor air quality concerns. But for now, that smoke does not appear to be all that dense, with forecast air quality in the "moderate" category.

Clusters of storms possible within oppressive humidity Sunday and Monday

 Oppressive heat and humidity will soon fuel thunderstorm chances Sunday and Monday. While both days will feature many dry hours, but the storms that develop will likely be strong to severe. Sunday will start with a weakening complex of storms from the West. This will arrive after 5AM and could produce gusty winds and heavy rain. Much of Sunday afternoon will be capped and dry, with higher coverage of storms arriving during the evening and into the night. Monday will depend heavily on what happens the day/night before, as leftover boundaries may develop storms around midday. By Monday evening, storms will be clearing out with higher pressure arriving.

Futurecast shows these scenarios playing out well but is still just one of many computer models that try to predict the future and should be taken with a grain of salt. Early-day round of storms will weaken upon arrival but still could pose a risk for gusty winds. Much of Sunday afternoon will then be capped and dry, but an isolated storm cannot be ruled out with extreme levels of energy in place for storms to utilize.

Better coverage of storms will arrive Sunday evening and Sunday night from the North. This looks to be the best chance for any severe weather locally with damaging wind gusts being the main threat. Storms should arrive after 9-10PM if not later Sunday night.

Storms will remain possible Monday, but the confidence on placement or timing is much, much lower. It depends heavily on the evolution of storms from the day before, so remain tuned for updates! Monday evening will begin the calmer stretch with higher pressure taking hold.

In addition to the storm potential, it will also be extremely hot and humid. Heat indices will likely push above 100 degrees much of the day Sunday and could reach 105-110 degrees in several locations. A Heat Advisory will go into effect for much of the area through Sunday evening, while an Extreme Heat Warning is the alert for Whiteside County with the higher confidence of 110°+ heat index. Additional alerts will almost certainly be needed Monday, but storms may give temporary reprieve from the humidity, placing less confidence in the heat index forecast for Monday.

Heat index pushes 100°, fuels thunderstorm chances this weekend

 Oppressive heat and humidity will return this weekend, with afternoon high temperatures pushing the low 90s Sunday and Monday. Factoring in the heat index, it will feel much closer to 90 degrees Saturday afternoon, and into the low triple digits Sunday and Monday.

That humidity will not only feel uncomfortable, but it will also provide the necessary fuel for thunderstorms. Ingredients for severe storms include moisture, instability, lift, and wind shear. We will have abundant moisture and instability, characterized by the mid-70s dew points. But lift and wind shear will be the limiting factors. Without a trigger to initiate storms, the fuel will remain untapped.

Even subtle waves can fire off strong storms with such high levels of energy, though. These small waves are hard to predict placement and timing ahead of time. If storms develop in such an environment, they will turn strong to severe rather quickly. The first opportunity for some severe storms would be Sunday afternoon, but limited forcing may keep many spots dry. Strongest storms will be capable of damaging wind gusts and very heavy rain.

Clusters of storms may redevelop along remnant outflows left over from previous storm complexes, particularly Sunday night into Monday. Overnight storms would be capable of gusty to damaging winds, heavy rain, and potentially large hail. Additional storms will be possible Monday afternoon, with highest coverage East of I-39 and across Michigan.

Both Sunday and Monday are under a highlight from the Storm Prediction Center for severe weather, with a Level 2/5 Slight risk Sunday and an equivalent 15% outlook for Monday. Exact timing of storms will become clearer as the waves and associated small-scale details come into focus. At the moment, coverage and duration of storms will be small, with many dry hours each day. But if you have any outdoor plans, be sure to keep an eye on the radar and be ready for any warnings that are issued!