Incoming cold front brings thunderstorms Monday night; Isolated severe storms possible

 

A line of strong to severe thunderstorms continues to march east Monday evening, impacting much of southwest Wisconsin and northwest Illinois.

A TORNADO WARNING has been issued for northwest Green County until 10pm as a severe thunderstorm, capable of producing a tornado, was moving right over Blancharville, WI.  This storm is moving to the northeast at 40 mph, and away from the immediate area.  While radar indicates the rotation has weakened just a bit, very strong winds are possible as the storm passes.

Further south a few thunderstorms have been moving across the region, producing a bit of lightning and heavy rainfall.  Wind gusts to 30 mph will be possible with the storms moving into Stephenson and Ogle counties.  This line of storms extends all the way down through western Illinois into Missouri ahead of a cold front that will move through the Stateline early Tuesday.  

Ahead of the front isolated severe weather is possible as the low level jet increases from the southwest.  This is why we're seeing a few of these storms turn severe.  Thunderstorms will continue through roughly 12am-2am Tuesday before quickly shifting east by sunrise.  Winds will increase from the northwest gusting as high as 25 mph during the afternoon. 

Big Changes to Come Following Tonight's Cold Frontal Passage

Scorching Sunday:

The last weekend of summer went out with a bang as warm southerly winds and plenty of sunshine brought our afternoon highs into the low 90s. In fact, Sunday's high of 93-degrees at the Rockford Airport tied for the warmest September 19th on record, now tied with 1925, 1947, and 1948. Although not as hot, Monday remains warm ahead of a strong cold front that will help usher in big-changes by the fall equinox.

Few Morning Showers:

Believe it or not, the remnants of tropical storm Nicholas will be a big part of today's forecast. As the moisture associated with it slowly creeps northward, Monday begins with a chance for a few sprinkles and light showers. 

Otherwise, we remain dry and breezy into the afternoon, with gusty winds becoming a concern for those traveling late in the day. A stout southerly to southwesterly wind, which could gust to around 25-30 mph at times, will help push highs into the low to mid 80s. Winds remain out of the southwest but quickly will change to the northwest as a strong fall cold front slides through overnight. Along with this frontal passage does come the potential for strong to severe thunderstorms.

Overnight Storms:

In the latest outlook, the Storm Prediction Center has placed half the Stateline under a Slight Risk (level 2 of 5) for severe weather, with the eastern half under a Marginal Risk ( a category below). Storm looks to fire up along this frontal boundary late in the afternoon in central Iowa, and track eastward as we head into tonight. While it seems this line of showers and thunderstorms will be in a weakening phase on approach, gusty winds and heavy rainfall will be the primary threats. A few sprinkles may last into early Tuesday morning, with conditions drying out but remaining breezy into the afternoon.

Fall's Moving In:

Winds behind tonight's frontal passage will turn to the north-northwest, allowing a much cooler, more fall-like air-mass for the days to come. Highs look to drop significantly from the low 80s today to the low 70s by Tuesday afternoon. And if that wasn't cool enough, we see our daily highs drop even further as we head into Wednesday. 

You would have to all the way back to July 8th to find the last time Rockford observed a high in the 60s. Well, with this much cooler air-mass still sitting overhead, we may see the 60s return both Wednesday and Thursday. Along with cooler days comes cooler nights, as overnight lows moving forward look to fall into the 40s. A few isolated areas may flirt with the upper 30s early Thursday morning. Prepare yourselves, fall is coming! 

Record high temperatures Sunday; Big changes by midweek

 

The last weekend of summer definitely felt like it as the high temperature in Rockford reached 93 degrees Sunday. This tied the previous record high of 93 degrees for the 19th of September most recently set back in 1948, as well as in 1947 and 1925.  Sunday's high temperature wrapped up a very unseasonably warm weekend, but likely the last upper 80/low 90 degree high temperatures we'll feel this year.  A strong cold front coming in Monday night will bring temperatures back to, and slightly below, where they should be for late September.

 

Cloud cover will continue to increase Sunday evening as low pressure lifts north from the Gulf.  this low has a little more Gulf moisture associated with it, bringing in a slight chance for a few light showers Monday morning.  As that low moves over the Great Lakes late morning, drier air will briefly move in for Monday afternoon.  Temperatures may not be quite as hot as Sunday, but the humidity will be a touch higher thanks to increasing dew point temperatures.  Highs on Monday will warm into the low 80s - still above average.

A strong trough (dip in the jet stream) will continue to move east across the Plains and Midwest during the day Monday.  This will help pull a cold front closer to the area during the afternoon and evening.  A redevelopment of showers and thunderstorms are possible towards late evening, bur likely more-so during the overnight.  Some of those storms could be strong with gusty winds and heavy rainfall.  A drop in temperatures is then expected for Tuesday, falling even further Tuesday night and Wednesday.  Wednesday marks the official start to Fall, and right now the forecast high for the afternoon is currently 68 degrees.  Overnight lows Wednesday night will drop into the low to mid 40s.  Temperatures throughout the remainder of the week will remain in the 60s and 70s, coming back close to 80 degrees both Friday and Sunday.

Small Storm Chance Late, Remaining Summer-Like Over the Weekend

Sun-Filled Trend:

The Stateline has had no issues with seeing sunshine during the month of September. Including yesterday's wall-to-wall sunshine, the average cloud cover at the Rockford International Airport has come in under 50% 8 of the last 13 days. As we now prepare for the last day of the current work week, sunshine will kick off the day. However, a few more clouds and a small chance for thunderstorms can be expected later on as one of two cold fronts swings into the region. 

Small Storm Chance:

Our Friday kicks off in a similar fashion to the past couple of mornings, with plenty of sunshine and temperatures sitting somewhere in the 50s. Although we hold onto a good amount of sunshine into the afternoon hours, a cold front sinking don from the Upper Midwest will help bring a little more cloud cover to the area as we approach the evening commute hours. Along with the increase in cloud cover does come a small chance for a few isolated thunderstorms. Thankfully, no severe weather is expected. But it's definitely something to keep an eye on if you plan to attend this week's edition of Rockford's City Market or any of the high school football games. Chances look to come to an end well before midnight, with skies remaining partly cloudy into Saturday morning.

Seasonal Transition:

Summer will be in full force over the weekend and into the start of next week, with the hottest air arriving Sunday and Monday. With winds being generally out of the southerly direction, our daily highs look to top out in the upper 80s. A weak system moving in from the south may bring us a chance for a few showers and thunderstorms Monday, with a strong cold front continuing chances into early Tuesday morning. As we've been hinting at, this cold front looks to bring a taste of beautiful fall-like weather just in time for when we change seasons. Highs fall into the 70s, with overnight lows falling into the 40s. 

Comfortably Warm Thursday, Highs near 90-Degrees over the Weekend

Light Jackets Needed:

The best way to summarize Wednesday's weather is by saying it was a perfect 10 out of 10. As expected, the day was filled with plenty of sunshine as an area of high pressure moved overhead, with most of our local airports topping out in the upper 70s. 

With the atmosphere remaining very dry overnight, temps early Thursday morning have fallen into the upper 40s and low 50s. Similar to Wednesday morning, you'll likely want to grab a light jacket and a pair of sunglasses before heading out the door. The forecast remains sun-filled and pleasant, with temperatures gradually warming up as we move into the upcoming weekend. 

Comfortably Warm Thursday:

With this area of high pressure now sliding over the Great Lakes, winds moving forward will be more out of a southerly direction. Hence why the Stateline will see a warming trend in the days to come. Sunshine looks to dominate our skies once again, with a decent breeze out of the south-southeast lasting well into the afternoon hours. 

This will bring our highs up by a few degrees, with most topping out in the low to mid 80s. The heat doesn't really start cranking until Friday. With our surface winds being out of the south-southwest, temperatures will make a quick jump into the upper 80s by Friday afternoon. A frontal boundary sliding in late in the day will Friday bring one of our few chances for rain over the next 7 days. Clouds look to increase into the afternoon, with a few isolated showers and storms are possible. 

Fall Arriving Just in Time?

While it looks like the forecast will remain very summer-like into early next week, models continue to show a strong cold front sliding through during the day on Tuesday. The air-mass behind this frontal passage looks to put summer on vacation mode, dropping our highs from the low 90s on Sunday to the upper 70s by Wednesday. 

And guess what? This would come just in time for the Fall Equinox, which occurs Wednesday, September 22nd at 2:20PM. As I mentioned yesterday, we still have a week for this scenario to change. But models have been consistent with the timing of this system and the cooler temps that follow!

Meteorological Fall temperatures warm as climate change concerns continue to grow

 It should come as no surprise that our temperatures have continued to warm both at the local and regional levels, but also across the globe.  The beginning of Meteorological Fall in northern Illinois and southern Wisconsin was somewhat near average, with a few warm and cool days to average things out.  to date, however, our monthly temperature for the first two weeks of September is about two degrees above average, with no signs of slowing down (at least within the next week).  Today, Wednesday, was a 'cooler' day, but really only with the drier and less humid air mass.  The high in Rockford officially reached 81 degrees, which was still five degrees above the average high of 76 degrees.  And temperatures throughout the rest of the week will continue to run at least five to ten, even fifteen, degrees above average.

When we look at Meteorological Fall as a whole - September, October and November - the average Fall temperature has gone up nearly two and a half degrees in Rockford since the 1970s.  And on average, we've added roughly 10 more days where the high temperature warms above average during that same time.

 Nationally, the West, Southwest and Northeast have had a significant rise in their Fall average temperatures when compared to the Midwest.  The heat out West has also prolonged the wildfire season, with some of the worst fires in some of the western state's history occurring within the last year.  The high heat also means that the drought conditions continue and worsen, which in turn causes the heat to only grow more.

The extended period of warmth into the Fall months can cause the allergy season to last longer, as well as prolong the impacts from summer pests such as mosquitoes and ticks.  Prolonged heat can also increase the risk of heat-related illness and hospitalizations, especially in children, people over 65 and lower income communities.  Not only that, but it can also become a financial burden on many as air conditioners run later in the season, coasting you more and increasing the amount of greenhouse gas emissions into the atmosphere.  Impacts to animal hibernation fruit ripening, fall leaves changing and bird migrations can also be felt as the summer heat lasts longer and longer.

While some may enjoy the heat a little longer as the seasons begin their transition, it's important to remember that the choices we make now will impact further generations to come.  Winter is the fastest warming season, but the other seasons are quickly catching up.

Perfect 10 Out of 10 Today, Summer Quick to Return by the Weekend

Much Cooler To Start:

Tuesday was considered a "day of transition" as a much anticipated cold front marched through, allowing a much more comfortable air-mass to settle in. I mean, take a gander at how much cooler the Stateline is sitting this morning because of Tuesday's frontal passage. With most of our local airports sitting in the low to mid 50s, it might be a good idea to grab a light jacket before heading out the door. Otherwise, prepare for a sun-filled and refreshing day.

Perfect 10 Out of 10:

An area of high pressure over the Midwestern U.S will continue it's eastward journey, moving directly over the Stateline by this afternoon. With plenty of sinking air in our atmosphere, clouds will have a tough time popping up throughout the day. 

While a few fair-weather cumulus clouds cannot be ruled out this afternoon, sunshine looks to dominate our skies with highs topping out near the 80-degree mark. More of the same is expected for Thursday, with highs ending up slightly warmer in the low 80s. In my opinion, both days provide a great opportunity to enjoy the outdoors, and to give your air-conditioner a break. As this high pressure system shifts eastward, warmer winds will help summer make a quick return by the weekend, with the potential for a few 90-degree days included.

Summer Quick To Return:

Southerly to southwesterly winds look to help draw in a warmer, more moist air-mass from the deep south, bringing back that summer-like feel as early as Friday. Our daily high temperatures as of a result will end up on either side of the 90-degree mark through the upcoming weekend and into the early parts of next week. While the humidity isn't likely to reach uncomfortable levels, it’ll certainly be more than enough to force us to turn on the A/C once again. 

The Countdown Is On:

As of this morning, we are officially 7 days away from the fall equinox. Fall begins on September 22nd at 2:20PM CDT. Guidance does keep our weather pattern very summer-like into next Tuesday. But there was a hint of a cold front that may move in late Tuesday into Wednesday, possibly bringing us our next cool-down just in time for the beginning of the fall season. Still, that scenario has plenty of time to change.