Temperatures are running a bit warmer than they were at this time yesterday. This is largely thanks to a blanket of cloud cover overhead but also a light but warm wind out of the south. Most Stateline locales are waking up roughly 10 to 15 degrees warmer, in the mid to upper 60s. There has also been a slight increase in humidity levels since yesterday as dew point are now sitting in the low 60s.
With the early arrival of our next cold front, there will be a chance for an isolated shower or thunderstorm from now up until about 9-10AM.
Once the cold front passes, winds at the surface will shift out of the northwest and gradually increase, helping to usher in slightly drier air for the rest of our "hump day". Expect partly cloudy with afternoon highs reaching the low 80s. Occasionally, wind gusts could top out around 20 mph.
Severe Potential Very Low:
It is also because of the cold front's early arrival that the severe weather threat today is expected to stay well to our south and east, even beyond the Chicago metro area. The Storm Prediction Center has placed portions of eastern Illinois, northern Indiana, and the southernmost areas of Michigan under a level 2 of 5 SlightRisk for scattered strong storms.
Once again, the atmosphere is setting upfavorably for some patchy fog to develop. Winds remain calm, the moon is shining overhead (meaning mostly clear skies) and temperatures are within 1 or 2 degrees of the dew point, allowing moisture to condense near the ground. The good news is that conditions don't appear to be supportive for widespread dense fog.
Once any patchy fog lets up, another pleasant late-summer day is in store across the Stateline. The same area of high pressure that brought spectacular weather Sunday and Monday will be parked to our east over the Ohio Valley, keeping conditions quiet with partly cloudy skies. Afternoon temperatures, thanks to a south to southwest wind, will end up a little warmer, pushing into the low 80s. Thankfully, it won't feel humidly warm as dew points should remain around the 60-degree mark. Great weather for Food Truck Tuesday over by the Conservatory.
Midweek Storm Chances:
At the same time, thunderstorms are expected to develop across northern Wisconsin and portions of northern Minnesota this afternoon. While that activity will be well to the Stateline's northwest initially, forecast models suggest some of those showers and storms could drift southeastward overnight. As a result, we could see a chance for a shower or storm after midnight, with the possibility of a few lingering into the Wednesday's morning commute.
Thunderstorm chances during the day all depend on the timing of our next cold front. It does seem the front pushes through without any worry, pushing the better environment for thunderstorm development to the south and east of the Stateline. For now, I've kept a chance for a few thunderstorms during the midday and afternoon hours. But again, it wouldn't surprise me if much of the day remained dry. Expect afternoon highs to land in the low 80s.
In their latest round of severe outlooks, the Storm Prediction Center has left the entire Stateline under a non-severe risk with the higher potential along the cold front being south and east of Chicago.
If you woke up Monday morning thinking it was a little on the cooler side, you'd be correct! Temperatures area wide fell into the low 50s, with a couple spots even dipping down into the upper 40s! But with the late August sunshine we warmed nicely during the afternoon reaching a high of 79 degrees in Rockford.
Rockford's low fell to 50 degrees, our coolest overnight low since the middle of June. Before Monday morning, our coolest August low temperature was 55 degrees reached on the 20th and 23rd. The average overnight low for late August should be around 61 degrees.
We've actually been running a bit on the 'lower' end with our overnight lows for the last week as a flip from above average lows to below average lows took place on the 17th. In fact, every night since the 17th has had a below average low temperature. Monday night will be cool once again, but not quite as cool as Monday morning. Temperatures will fall into the mid-50s early Tuesday. Low temperatures will slowly begin their climb as a southerly wind takes us through the middle to end of the week. This will also help bring in a little more moisture which will slowly cause the humidity to rise into the upcoming weekend.
Three years ago, late August was delivering some of the most dangerous heat of the summer across the Stateline region. Highs soared into the upper 90s, and when combined with tropical humidity, heat index values climbed into the 115 to 120 degree range. Fast forward to this year, and the weather headlines couldn't be more difference. Instead of extreme heat, we're looking at a much more comfortable stretch with afternoon highs in the upper 70s.
Those upper 70s will come with plenty of sunshine as a weak high pressure system continues to keep a firm grip on our weather pattern. With sinking air limiting cloud development and thunderstorm chances, expect there to be partly cloudy skies. Winds will also be lighter than they were on Sunday, further adding to the day's comfortable feel. As we head into tonight, skies will remain mostly clear thanks to that lingering area of high pressure. That will make for another cool start to the day with mid 50s for most.
Hit or Miss Chances:
Tuesday remains dry across the Stateline, though we will see signs of our next weather maker by the time we get into the evening. Forecast guidance shows a pocket of upper-level energy or spin tracking into the western Great Lakes by Wednesday afternoon. Ahead of it, we do see moisture spill inas the associated cold front approaches. This may result in the chance for rain after midnight while also fueling the chance for a few thunderstorms on Wednesday.
Because of that setup, the Storm Prediction Center has much of northern Illinois and southern Wisconsin under a level 1 Marginal Risk. It's still a few days away, but it's a setup we'll be keeping a close eye on as details continue to come in focus.
A typical summertime heat dome will set up across portions of the country next week, but the Stateline will be spared from the worst of the heat and humidity. The continued feed of weather systems across the Great Lakes and Northeast will keep the most oppressive heat away from the area.
Even so, we will still reach the upper 70s to low 80s each day this week. That's not very far from the typical highs this time of year! A bit of a humid feel returns Wednesday and Thursday with isolated or scattered rain chances, but we will stay dry through at least Tuesday evening.
An EF-0 tornado touched down Southern Lee County, IL during Friday evening's storms, the National Weather Service confirmed during a recent storm survey. The tornado touched down near Henkel, or about halfway between Sublette and Mendota, just before 6PM. It was spotted by storm chasers and reported to the National Weather Service but lifted shortly after and did not touch down again.
The Henkel tornado was only on the ground for 0.7 miles, producing estimated peak winds of 70 miles per hour. The tornado's maximum width was estimated to be 200 yards. Thankfully there was minimal damage and no injuries reported. There was a severe thunderstorm warning for Lee County at the time of this tornado.
[9PM] The last of our storms are pushing across Eastern Lee County and Southern DeKalb County this evening. There are still some pockets of heavy rain and lightning, but storms will remain sub-severe now that the sun has set.
[8:20PM] A severe thunderstorm warning is in effect for Southwestern Whiteside County until 9PM. This storm is capable of producing 60 mph wind gusts and quarter sized hail as it moves East at 25 mph.
[7:20PM] The Severe Thunderstorm Warning remains in effect for southwest Carroll and Whiteside counties until 8pm. Over the last few minutes, the storm has weakened some but still may produce some gusty winds and small hail.
[6:50PM] Storms are still producing a bit of lightning as they track Southeast at around 30 mph. Highest concentration of lightning will be with the cell in Carroll County, but a few strikes of lightning remain possible within any cell.
[6:30PM] Our lone severe thunderstorm is moving Southeast across Southern Jo Daviess County and is currently capable of producing 60 mph wind gusts and quarter sized hail. The warning is out for portions of Jo Daviess, Stephenson, and Carroll Counties until 7:15PM.
[5:50PM] Two active severe thunderstorms at this time. One for portions of Lee and DeKalb Counties until 6:30PM and the other for Jo Daviess County until 6:15PM. Both storms may be able to produce 60 mph wind gusts and quarter sized hail as they move Southeast at 20-30 mph.
[5PM] A severe thunderstorm warning has been issued for Eastern Ogle and Lee Counties, along with a portion of Central DeKalb County until 6PM. This storm is now capable of producing half dollar sized hail and 60 mph wind gusts. Storm movement is to the East-Southeast at around 20 mph.
[4:15PM] Our lone severe storm stretches across portions of Whiteside and Lee Counties, just North of Sterling. This storm is capable of producing 60 mph wind gusts and quarter sized hail as it moves Southeast at around 15-20 mph. This storm will pass over Dixon soon. Take shelter if you are ahead of this storm!
[3:45PM] A new severe thunderstorm warning has been issued for Winnebago and Boone Counties until 4:45PM. This storm is capable of producing 60 mph wind gusts and quarter sized hail as it moves to the East at 25 mph. There is frequent lightning on the West side of this cell, too. Take shelter if you are near this storm!
[3PM] With the main wave of storms still developing to our Northwest along a cold front, a severe thunderstorm watch has been issued for the entire Stateline until 10PM. Strongest storms will be capable of damaging wind gusts, large hail, and frequent lightning. An isolated tornado may also be possible. Main timing of storms is still expected between 5-9PM for local Stateline Counties.
[2:20PM] A severe thunderstorm warning has been issued for portions of Boone, McHenry, and DeKalb Counties until 3PM. This storm is capable of producing 60 mph wind gusts and ping pong ball sized hail as it moves to the Southeast at 25 mph. Heavy rainfall and frequent lightning is also possible.
For those heading out tonight for the first week of high school football, be prepared for some lightning delays and scattered storms. The wave of storms moving through this afternoon (radar as of 2PM) is sub-severe but may be producing 40 mph winds and small hail over Southern Boone County.
The main wave is Northwest along a cold front and will arrive after 5PM. Our main window of storms is 5-9PM. The primary concerns within strongest storms will be lightning, damaging wind gusts, and heavy rainfall.
Pockets of large hail and an isolated tornado cannot be ruled out, either. Once storms clear to the Southeast after 9PM, we will be drying out for the night. Temperatures will drop from the mid-70s by the time games are scheduled to start to around 70 by 9PM.
