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!

 

Heat, humidity, and storm chances slide back in over the weekend

Comfortable Friday:

This comfortable stretch of weather will carry us right through the end of the work week. While the day may begin will more clouds overhead, increasing sunshine will help temperatures climb a little higher the last few days, reaching around 80 degrees. 

Not only are we staying comfortable air temperature-wise, humidity levels will stay in check as well, with dew points temperatures holding in the upper 50s. In the end, this will be great weather for those attending the Woman's Baseball World Cup but also City Market this evening. As we head into the overnight hours, skies remain partly cloudy as a weak disturbance approaches from the northwest. Hi-res models suggest a very isolated sprinkle or shower may result late Friday night into early Saturday. Any shower activity that does manage to develop will be spotty and short-lived.

Weekend Outlook:

The combination of a strengthening high pressure system to our west and persistent southwest winds at the surface will lead to a noticeable increase in both the temperature and humidity departments. 

Afternoon highs are expected to climb into the mid 80s Saturday, then low 90s, while dew point temperatures surge into the upper 60s, possibly low 70s. This warmer, more humid air will provide the atmosphere with a tremendous amount of storm fuel. At the same time, disturbances riding along the northern edge of the ridge may track into the Great Lakes, providing that spark for storms to develop. Some of which may be strong to severe. 

Saturday's Risk:

Fortunately, for those heading to the Beloit Farmer's Market Saturday morning will only have to worry a out a passing sprinkle or shower. It seems the better severe thunderstorm ingredients will line up further to the north of the Illinois/Wisconsin border, in areas across central and northern Wisconsin. That is where a Marginal Risk is currently in place.   

Sunday's Risk:

As for Sunday, the Stateline remains under a risk for severe weather, a level 2 Slight Risk for some, and a level 1 Marginal Risk for others. However, there are still several uncertainties that need to be worked out over the next few days. 

The overall environment will be favorable for strong to severe thunderstorms, given the expected heat, humidity, and the large amount of atmospheric fuel in place. The questions marks however will be storm placement as capping will have a huge impact on Sunday's potential as well as the placement of any surface boundaries. Despite the uncertainty, remain weather aware. If the Stateline does see any clusters of complexes of storms move through, damaging winds will be the primary concern.       

Storm threat returns as heat builds back in for the weekend

It hasn't necessarily felt like late July the last couple of days as cooler air has settled into the region. Highs both Wednesday and Thursday warmed to the mid-70s, falling 10-15 degrees below the monthly average. While it may have felt nice it won't last as we feel a quick return to the late July heat and humidity by the weekend.

Skies will remain mostly cloudy Thursday evening as temperatures slowly fall back through the upper 50s/low 60s Friday morning. A few sprinkles may fall south of the viewing area during the morning but locally our skies are expected to remain dry. Temperatures during the afternoon will rise into the upper 70s, close to 80 degrees. High pressure will continue to slide further away from the area allowing a warmer and slightly more humid air mass to return to the Midwest and Great Lakes. This as a strong ridge of high pressure builds to our west where temperatures will reach well into the 90s, likely reaching the triple digit mark in many locations.

Locally, we remain on the eastern edge of the ridge. Close enough where temperatures are forecast to rise into the low 90s Sunday and Monday, but not directly under the ridge to heat us up any further. However, the location of the Stateline in proximity to the outer ridge could lead to a few storm complexes coming close to, or right overhead, the area Sunday and Monday.

As of Thursday evening, the Storm Prediction Center is already highlighting parts of the Midwest and Great Lakes as favorable areas for thunderstorms, some severe, both days. It's still too early to pinpoint exactly where storms will develop and who will see what, but the risk for thunderstorms will increase Sunday and Monday.