Frosty start to the weekend, increasingly mild next week

 After a chilly and windy Friday, the overnight time frame will see clouds and winds ease substantially. Temperatures will continue to fall under a clear sky, down into the low 30s by morning. Our first freeze of the season is likely as a result, with a freeze warning beginning late tonight across the entire Stateline. Freezing temperatures will be delayed a few hours for North Central Illinois, so the freeze warning will not begin until 5AM for some.

The deep trough responsible for the chilly weather will lift back North again over the weekend, bringing strong high pressure. It will remain cool Saturday with highs in the 50s despite the abundance of sunshine. But Sunday onward will be again milder than average with highs back in the 60s and 70s. This also comes with a drier pattern as well, with very limited rain chances throughout the next week.

Freeze warning issued for all of northern Illinois

Blustery Friday:

Strong winds will be the story today, and they'll play a big role in ushering in a much colder air mass for the start of the weekend. Northwest winds to start will gradually turn northerly by this evening, gusting up to 25 mph early before increasing to 30 to 35 mph this afternoon. The persistent wind will keep temperatures in the low 50s despite any sun. A few showers may accompany today's gusty wind as the storm system from yesterday continues to pull away. 

Frost Likely:

Winds will begin to ease this evening while staying out of the north and northwest overnight. Combined with clearing skies and a fresh surge of chilly air, temperatures will tumble to their coldest levels of the season thus far by Saturday morning. Many locations are expected to wake up in the low 30s, making it feel much more like mid-October.  

This colder air will also bring the likelihood for frost by Saturday morning. Because of that, the National Weather Service has placed the entire area, including our three counties up in southern Wisconsin, under a FREEZE WARNING. For northern Illinois, this will be in place from 5AM-8AM. Temperatures will be cold enough to damage or kill sensitive vegetation if left unprotected. Before heading to bed this evening, be sure to bring any potted plants indoors or cover them up to protect them from the frost. 

Weekend Outlook:

The rest of the weekend looks dry, with temperatures gradually warming after the chilly start. Despite lots of sunshine on Saturday, highs will remain stuck in the 50s thanks to the cooler air in place. By Sunday, winds will shift to the southwest and begin to pick up a bit, helping temperatures climb back into the low to mid 60s. The warming trend continues into Monday, when highs could approach 70 degrees. 

Cold and blustery Friday, hard freeze possible Saturday morning

 Rain showers will continue to linger through the evening Thursday, but some drier air will bring an end to the steady rain after 9-10PM. As the "dry slot" of the system passes overhead, coverage of rainfall will wane. But winds will pick up, with Northwest gusts approaching 30 mph at times.

Temperatures will fall to the 40s to start out the day Friday but won't warm much from there with a stout Northerly wind. Afternoon wind gusts could push 30-35 mph, which will limit high temperatures to the low 50s. A few light showers will be possible from time to time, but only a couple tenths of an inch of additional rain will be possible.

Winds will ease substantially overnight into Saturday morning, but temperatures will continue to fall under the influence of high pressure. By daybreak, most will be in the low 30s with potential for the first hard freeze of the year. A freeze watch is in effect for far Northwestern Illinois and Southern Wisconsin. Be sure to protect any sensitive plants from the likely frost and freezing conditions!

Wet Thursday ahead, frost threat looms by Saturday morning

Wet Thursday:

After a stretch of dry weather, you'll want to keep the rain gear handy on Thursday. A seasonably strong area of low pressure moving into Illinois will bring the chance for isolated showers during the morning hours, but the wetter part of the day arrives later on. Rain coverage is expected to become much more widespread by midday, with periods of steadier and occasionally heavier rainfall continuing through the afternoon and evening. 

If you have to be out and about, be prepared for wet conditions, allow for extra travel time, and keep an umbrella and rain jacket nearby. While temperatures won't be especially cold, the combination of the rain, the cloud cover, and east-southeast wind will limit afternoon highs to the low 60s. 

Most locations should pick up a beneficial rainfall from this system, with amounts generally from 0.25" to 0.75" by the time chances end.

Cooler Times Ahead:

Scattered showers will linger through the first half of the night Thursday, before tapering off behind the associated cold front. In the wake of this cold front, winds will increase and usher in a quick shot of much cooler air. Temperatures are expected to tumble into the low 30s by Saturday morning, allowing frost to be likely. If you still have sensitive outdoor plants, be sure to bring them indoors or cover them up before heading to bed Friday evening.

Strong fall system to bring widespread rain, then fall chill

 A seasonably strong weather system will push through the Stateline before the weekend, bringing widespread rain then a sharp cool down between Thursday and Friday. We will start off Thursday with pockets of light to steady rain, lasting through the duration of the day. There is potential for some pockets of heavier rain embedded within, where some may pick up an inch of rain. The tail end of the system will likely wrap additional showers through the area, but not as widespread as Thursday. Winds will be much stronger from the Northwest or North, holding temperatures in the 50s with frost potential overnight into Saturday.

The initial push of rain will arrive after 5-6AM, with scattered and light showers at first. Through late morning and early afternoon, coverage will become more widespread with pockets of moderate or even heavy rain. That band of heavier rain will be fairly narrow on the Northern edge of the low pressure, resulting in more sporadic rainfall coverage over parts of Northern Illinois. Where that narrow band sets up will bring better chances for the soaking rain of up to an inch.

Additional wrap-around showers will be possible into Friday afternoon with more subtle moisture rotating around the center of the low-pressure system. This will also be accompanied by stronger Northwest to North winds, gusting around 30 mph or greater at times. Temperatures may struggle to reach the 50s in a few spots during the afternoon and continue falling at night, down into the 30s. It does appear increasingly likely that we will see our first frost of the season Saturday morning!

Rain returns Thursday, frost possible by Friday night

Quite The Drop:

Monday's record-breaking high of 88° is feeling like a distant memory. A cold front and departing storm system have helped usher in a much cooler air mass, sending temperatures back to where should be for the middle of October. Instead of flirting with records, afternoon highs will top out near 67°, much closer to seasonal averages. We're also trading yesterday's sun for a bit more cloud cover as clouds look to linger behind the departing storm system. 

Thursday's Rain:

From there, the forecast turns a bit more unsettled as another area of low pressure lifts into Illinois from the southwest. Rain chances increase shortly after midday Thursday, with widespread showers, possibly a few thunderstorms, expected through the afternoon and into the early evening hours. 

 

Conditions gradually dry out Thursday night, though winds will become quite gusty behind the departing system, helping pull in cooler air. Overnight lows are expected to fall into the low to mid 40s by Friday morning, with even colder temperatures arriving by Friday night. In fact, lows are expected to drop into the low to mid 30s, which could bring the potential for frost across parts of the area. Keep tabs on the forecast as you might have to cover sensitive outdoor plants before heading to bed Friday. 

As for rainfall totals, most locations should pick up between a quarter to three-quarters of an inch, though a few spots could wind up near 1". A strong area of high pressure will push in for the weekend, keeping us dry but chilly with highs in the 50s.  

 

  
 
 

Frost/freeze potential in northern Illinois Friday night

 

We've enjoyed quite the stretch of mild and mostly dry fall weather over the last week to week and a half, but a return back to reality and more of an 'October-like' feel will greet us by the end of the week.

For the remainder of Tuesday evening, we'll see a mix of sun and clouds as a few weaker upper-level disturbances move across the Midwest. A couple of those disturbances have produced a few showers and thunderstorms west and south of the Stateline. The shower activity across central Illinois isn't anything we need to be concerned with and will mainly remain to the south. But the cluster of thunderstorms moving through northeast Iowa will continue on their northeast trek, reaching southern Wisconsin around 7pm-8pm. Additional isolated thunderstorms will remain possible across northern Illinois after 8pm-9pm.

Wednesday will feature more clouds than sun which will hold afternoon temperatures in the mid-60s. Winds will turn to the north and northeast. Widespread rain returns Thursday with increasing moisture and low pressure sliding just to our south. Northern Illinois will remain north of the low which will keep afternoon temperatures in the 50s and low 60s, but south of the low (in the warm sector) afternoon temperatures will climb into the 70s and 80s.

Following the passage of the low a strong cold front will sweep across the Midwest and western Great Lakes Friday morning. This will pull a considerably cooler air mass down into the Stateline Friday afternoon. Afternoon temperatures will fall through the 50s, remaining in the 50s, during the afternoon. This will also come with a rather strong north wind with gusts 30-40 mph. Following some of the record heat from Monday afternoon it will feel rather chilly Friday afternoon.

By Friday night the winds will ease some as high pressure slides a little close to the Stateline. This will cause temperatures overnight Friday into Saturday to plummet down into freezing territory Saturday morning. This could lead our first fall frost/freeze this season.

As the mercury drops it'll be pretty much right on target for when we typically average our first fall freeze, which for Rockford is around the 13th of

October. Last year the temperature fell to 30 degrees on October 23rd. The earliest fall freeze was back on September 13, 1975, and the latest was the 11th of November back in 2016.

Warmth fades as rain chances rise later this week

Rainfall by Month:

While October hasn't been especially wet overall, the rain we picked up on the very first day of the month has done a lot of the heavy lifting. That early-soaking rain was enough to keep rainfall totals running above-average, even as we've settled into a remarkably dry and sun-filled stretch since then.  

 

Few Evening T-Storms:

Rain chances begin to increase from here, but not before one more mainly dry day. In the wake of this morning's cold front, skies will remain partly cloudy with afternoon highs landing in the upper 70s, close to the 80 degree mark. While this is a step down from the record-breaking warmth we had yesterday, it's still above mid-October standards. 

The cold front from this morning along with upper-level support being filtered in from the southwest will help stir up a few showers and thunderstorms this evening into the first half of tonight. IF we end up seeing a severe thunderstorm, large hail would be the primary concern. Overall, the better chances for rain seem to remain south of Rockford, mainly along and south of the I-88 and I-80 corridors. Coverage should gradually diminish after midnight, with activity becoming a bit more isolated. 

Rain Likely Thursday:

By the morning commute Wednesday, any lingering rain will have move out, but clouds will be slow to clear the Stateline. In fact, mostly cloudy skies are likely to stick around for much of the day. Combined with a cool east-northeast breeze, afternoon highs will be limited to the upper 60s.    

A low-pressure system arriving Thursday will bring our next significant chance for rain, along with the potential for a few thunderstorms. The greatest coverage appears likely during the afternoon and evening hours as deeper and rich moisture moves into northern Illinois and southern Wisconsin. While the details are still being fine-tuned, many areas may see a beneficial rainfall with the heaviest right now trending to the south. Because of the rain pushing in during peak-heating hours, afternoon highs will be limited to the low 60s.

Isolated thunderstorms return late Tuesday night

 

Temperatures Tuesday won't be quite as hot as they were Monday, but they'll remain close to 80 for some into the afternoon. A cold front passing through the Stateline Tuesday morning will shift winds from the southwest to the northwest. There isn't much cold air initially behind the front which is why afternoon highs will remain above average.

Most of Tuesday will see dry, and likely, sunny conditions. But clouds will increase through the evening as a surge of moisture returns late Tuesday night. This moisture will arrive with increasing winds from the low-level jet (stronger winds a few thousand feet above the surface). The front from Tuesday morning will have settled to our south, sitting roughly across central Illinois. Showers and thunderstorms will develop after sunset (between 8pm and 11pm) across southern Iowa, moving towards northern and central Illinois around Midnight - and beyond.

The Stateline will sit on the northern edge of the thunderstorm activity, and north of the front, which will help keep the highest risk for widespread thunderstorms to the south. But a few of those thunderstorms could reach some of the region, mainly in the form of elevated thunderstorms. With just enough instability the strongest of the storms could produce some locally large hail (quarter of an inch, or greater) along with gusty winds late Tuesday night. Because of that risk the Storm Prediction Center has placed areas along and west of I-39 in northern Illinois under a 'marginal risk' for isolated severe storms. At this point it doesn't look to be anything too widespread, but something we'll need to keep an eye on heading into Tuesday night. 

Record heat for Rockford Monday afternoon

You may have had to do a double take when looking at the calendar this afternoon. Temperatures across northern Illinois and southern Wisconsin felt more like July or August and not the middle of October. That's because afternoon highs warmed well above the average high of 64 degrees, climbing into the mid and upper 80s! Rockford's high officially reached 88 degrees! That's 24 degrees ABOVE AVERAGE!

Not only is that warmth incredible for October it was also record breaking. The previous record for October 12th was 85 set back in 2008, as well as in 1930. On average, Rockford's last 85-degree recorded temperature (or higher) is around the 19th of September. Not only did today's high surpass that it is also the warmest temperature this late in the season since October 15th, 1947, when the high that day reached 89 degrees! Simply put - this type of warmth doesn't happen very often and is definitely rare.

We'll see a few clouds roll through the region through the evening with mostly clear skies expected for the night. Temperatures tonight will fall to around 66 degrees. A cold front will slide through the region Tuesday morning shifting winds to the northwest. There isn't much cold air behind this front initially, so afternoon highs are likely to warm back close to 80. But moisture surging north Tuesday night will likely lead to a few elevated showers and thunderstorms after Midnight, into early Wednesday.

80s in October? Record highs could fall across northern Illinois today

What's Ahead:

Remember when 90° heat was stealing the headlines at the start of September? Now, just a few weeks later, we're talking about possibly record-breaking warmth as we head into the middle of October. That's where this week's weather story begins! 

 

Record Warmth:

The reason for the potential record warmth today comes down to a favorable setup ahead of our next cold front. Conditions remain very dry across the region, and a strengthening southwest wind will help transport much warmer air into northern Illinois and southern Wisconsin. With plenty of October sunshine and little chances for rain, temperatures will have no trouble climbing into the mid 80s. That puts today's record high of 85° from 2008 in jeopardy.  

Forecast models continue to show our next cold front pushing through early Tuesday morning, but with very little moisture available, its expected to sweep through dry. We do on the other hand see a round of slightly cooler air push in behind it. However, we're still expecting temperatures to climb to mild levels, landing in the upper 70s. As for the record books, the standing record high for tomorrow of 87 degrees will remain intact for another year. 

Rain Chances Rise:

As we move into the second half of the work week, temperatures will begin to cool while rain chances start to increase. A surge of atmospheric moisture is expected to move into the region on Thursday, giving us the ingredients for showers. Heaviest seems to occur to the south of I-88, but it will be important to keep up with trends the next few days.    

Steady decline from record warmth to fall chill this week

 It was a warm weekend across the Stateline with 2 days reaching the 80-degree mark or warmer in Rockford. We will make it a streak with a 3rd day in the 80s Monday, with a forecast high of 85! That would tie a record high set in 2008. But it is all downhill from there, with afternoon highs dropping each day until we reach the 50s on Saturday!

This will come with a few chances for rain, notably with a chance for a few elevated storms Tuesday night. These will not be overly widespread, but a couple of the strongest storms may pose a low-end risk for some gusty winds and severe hail. The Storm Prediction Center has placed a Level 1/5 Marginal Risk over parts of West Central Illinois, up to around I-39/I-88.

Wednesday will be largely dry, but more widespread and steady rain will be possible Thursday with our last push of moisture before a strong cold front arrives. This could bring some pockets of 0.5-1.0" rainfall totals, with some locally heavy rain, especially South of I-88. Behind this weather system, much cooler and drier air will take over into the following weekend.

Warmth continues with near records possible, but not for long

 It was a remarkably warm Saturday in the Stateline as afternoon high temperatures reached into the low 80s! We will be similarly warm over the next couple of days, with plentiful sunshine. Mild nights will also accompany this warmth, but changes are on the way toward the end of the week.

Temperatures will be closer to average through the early half of next week, with more sporadic chances for rain, especially Tuesday night and again Thursday. A much stronger cold front will usher in our first true taste of fall chill with afternoon highs in the low 60s or 50s by Friday and Saturday!

Why does the wind seem stronger during the day than at night?

 Continuing with our Answering Viewer Questions series, Susie asks why it seems like the wind is stronger during the day than at night. Outside of the influence of storms, our winds are typically a bit stronger during the day compared to at night. This is because stronger winds found just above the surface can be mixed down to the ground a little easier during the day.

This can be visualized using an atmospheric sounding, or a vertical profile of a column of air above one single point. The red line plotted below is the temperature, while the green line is a dew point. The bottom of the plot the surface, while the top of the chart is typically miles up in the sky.

A typical daytime sounding has strong "lapse rates" in the lower levels. Simply put, the air cools quicker over short distances. This steeper slope allows the air above to easier mix down toward the ground unimpeded. And often stronger winds -- commonly referred to as the "low-level jet" -- are found just above the ground. These winds are also mixed down to the ground, producing stronger winds during the day.

Compare this to a nighttime example. The only change from the last sounding to this one is the temperature in the lower levels near the surface. Since we cool off quickly at night with the loss of solar radiation, the temperature at the surface becomes cooler than that above. This is called an "inversion" where there is no longer cooling with height. This layer of relatively warmer air prevents that mixing mentioned above, which typically results in lower wind speeds at night compared to the day.

To summarize: stronger winds during the day are a result of deeper mixing, where air above the surface is easier transported down to the ground. While the loss of daytime heating prevents that mixing effect.

Summer-like weekend ahead, cooler and active pattern returns next week

 Hurricane Isaias is just hours away from making landfall near Pensacola, Florida as a strong hurricane. Sustained winds as of 6PM Friday are near 115 mph as the center of the storm is moving North at 18 mph. Storm surge, heavy rain, and tornadoes will accompany the storm across the gulf coast as it makes landfall Friday evening, with impacts carrying over into Saturday.

Locally here in Northern Illinois, we will see a very summer-like weekend with limited influence from the tropical system to the South. A weak blocking pattern aloft will keep us dry, as the rain shield will stay off to the Southeast. A few upper level clouds will spread over the area Saturday, but we will remain rain-free with highs near or above 80 degrees. Chances for showers and even a few storms will begin to move in later in the week, with the initial cold front arriving Monday night.

Showers will be higher in coverage toward the middle of the week, as the upper-level pattern brings several waves our direction. With varying degrees of moisture, we may not see widespread and heavy rain potential locally. But a cooler pattern with more frequent chances for rain will take over the second half of next week.

Isaias strengthens, but a warm and dry weekend remains on track

Showers Friday:

It's been a beautiful stretch of weather across the area so far this week. Sunshine has been plentiful, and our temperatures have consistently climbed into the 70s, ranging from the low 70s early in the week to the upper 70s more recently. 

Combined with low humidity and dry conditions, it's made for a fantastic first full week of October. But as the saying goes, all good things must come to an end. Fortunately, our interruption from the sunshine will be brief as our weather pattern aims to dry back out for the upcoming weekend.  

Today's rain showers are tied to a weak disturbance and accompanying warm front lifting east across the Central Plains. Over the past 24 hours, this system has sparked several severe thunderstorm warnings and flash flood warnings across Iowa. As it continues its eastward trek, it will bring an opportunity for a few showers, possibly a rumble of thunder around or just after the midday hours. Amounts should be light for most locales, and once this system moves through, clouds will decrease into the night. 

Latest on Isaias:

Since our last update, Isaias has continued to gain strength as it spins over the central Gulf, reaching category 2 status with maximum sustained winds of 105 mph. At the same time, its central pressure has fallen to 972 millibars. Landfall remains expected sometime late Friday evening along the Gulf coast, possibly still as a category 2 hurricane.  

Weekend Outlook:

The core of Isaias is still expected to remain well to our southeast after landfall, keeping the heaviest rain and strongest winds away from northern Illinois. That said, we may see some of the system's influence in the form of high-level clouds late Saturday into Saturday night as tropical moisture spread north into the Great Lakes. Even with those clouds, a ridge of high pressure positioned to our north will help keep our weather dry and summer-like with afternoon highs landing in the upper 70s and low 80s. Saturday looks to be the warmest day of the stretch with highs topping out around 81 degrees. This warmth aims to linger into the start of next week.