Wednesday evening weather update

 

Temperatures warmed into the mid and upper 80s, low 90s, Wednesday afternoon following the non-severe thunderstorms that moved through during the morning. Heat index values have also gone up, reaching the mid-90s thanks to dew point temperatures reaching the upper 60s and low 70s. Dry conditions will remain for the rest of the evening, but the chance for showers and thunderstorms will begin to increase during the overnight.

Severe thunderstorms tied to a couple storm complexes over the Plains will continue to move east through the evening, impacting the Stateline early Thursday morning. Storm coverage is expected to expand through Iowa, moving closer to the region after 2am/3am. While some of the energy needed for strong to severe storms will decrease through the night, enough will be present to hold on to the chance for a few stronger wind gusts with any of the storms that move through.

The storm threat will last through 9am, with drier conditions expected by late morning and early afternoon. Breaks in the cloud cover will allow temperatures to warm back into the mid and upper 80s, with heat index values reaching the mid-90s once again Thursday afternoon.

An incoming low-pressure system (currently over the Plains Wednesday evening) will move into southern Wisconsin Thursday afternoon. Instability will once again increase ahead of the low allowing thunderstorms to redevelop after the 2pm/3pm time frame. With just enough instability in place, and likely outflow boundaries left over from the morning activity (think of these as little mini cold fronts), some of the storms could turn strong to severe later in the afternoon. Because of that the Storm Prediction Center has placed most of north-central Illinois under a 'slight risk' for severe storms, primarily with a hail and wind threat. 

Heavy rainfall will also be a concern given the high amounts of moisture in the atmosphere, but the risk for flooding will remain low. The storm threat will come to an end Thursday night as low pressure moves across Lake Michigan. We may still see a few lingering showers, and isolated storms, Friday but drier conditions are expected into the weekend.    

Temperatures won't cool off much as we remain in the mid and upper 80s. Highs could even approach 90 degrees once again Saturday.  

Active, hot and humid pattern to carry on into the start of August

The Stateline missed out on yet another opportunity for strong to severe storms as the main storm track remained to our south and west. 

No complaints here, especially after all the major flooding that occurred around the Rockford area during the middle of the month. In fact, one of Tuesday's complexes was long-lived, leaving behind a 750+ mile path of wind damage reports stretching from central Iowa to northern Georgia.

Skies this morning are quiet, though another potent M.C.S is underway in southeast Iowa. This one should take a similar track to the one previously mentioned from Tuesday, leaving us mainly dry. However, we'll have to monitor any outflow or storms that form on the complex's northern side as that could possibly spell a thunderstorm chance by the time we reach the mid-morning hours. 

For this, the Storm Prediction Center does have most of the region under a level 1 Marginal Risk, mainly for the threat for damaging winds. Portions of Jo-Daviess, Carroll, Whiteside, Ogle, and Lee County are under a level 2 Slight Risk. This is also for strong winds but also a tornado or two. 

Otherwise, expect a dry, but hot and humid afternoon with temperatures peaking near the 90° mark. Heat indices will likely be near the triple digits again. Storm chances spike again after midnight tonight as a line enters the Stateline from the west. These will likely be in a weakening phase, though still could pose the risk for damaging winds, heavy rainfall, and frequent lightning into hours leading up to the morning commute. Overnight lows will stay warm, landing in the low 70s. 

An upper-level low approaching from the northwest will provide us with another window for scattered storms Thursday afternoon. 

The strength of this round will be dependent on how quick conditions are to dry out. If we're able to tap into daytime heating a little bit more, expect storms to have more of a fuel source once they form. As of this morning, the severe threat appears to be highest to the south and east of the Stateline, closer to I-80 and Indianapolis. Of course, this is subject to change based on how things trend between today and Thursday morning.

Periodic waves of storms possible through Friday

 So far, the humid Tuesday afternoon has yielded us no storm activity. But that has been a very different story across SE Iowa and Central Illinois. Our focus now turns well Northwest where our next potential round of storms has begun developing in the Northern Plains.

Our main 3 windows for storm chances in the next few days set up like this. We are watching trends to the Northwest for our next waves of storms as they move through the unstable environment to see where and when they may reach our general vicinity. Same deal for Wednesday as the afternoon looks dry as of now once lingering storms from the morning round clear out. This will produce the hot and humid weather like what we saw on Tuesday. Our next upper air wave looks to move in by the early overnight hours, producing our next chance at some storms. By Thursday, we will see better forcing with an upper level low ahead, leading to scattered storm chances during the afternoon, some of which may be strong to severe.

Ahead of the storms developing in the Northern Plains Tuesday evening, a tricky environment is set in place. There is still a lot of instability set up across the area for these storms to work with, but there is not a lot of upper air support to steer them. Because of this, the exact track and timing of these storms reaching the Stateline is still in serious question. The best chance for them arriving would be just before dawn tomorrow, as I currently favor a dry forecast through 5AM. These storms may be capable of damaging winds and heavy rain when they arrive.

Following the overnight/early morning round of storms, the environmental looks to destabilize for Wednesday afternoon, leading to more storm threats into the late evening again. With the lack of storms during the daytime, heat and humidity will build up, with heat indices likely near the triple digits again. This will be the fuel for the storms later in the evening. The exact timing of when this round of storms initiates to the West is still uncertain, but likely would be between 8PM-2AM window before progressing East through the Stateline shortly after initiation. Stay tuned with the forecast for this threat heading into tomorrow!

Another round of storms may be possible Thursday afternoon with the upper level low nearby. Any daytime heating between lingering morning storms and afternoon initiation will determine how strong the storms would be. As of now, the threat appears to be highest to the South and East of the Stateline, closer to Indiana, but this is subject to change based on how things trend between tonight and tomorrow night.

Note, so far all of the storm complexes have followed a very similar track just to our Southwest and South. There is a chance this could happen with both the chances Tuesday night and Wednesday night, which would keep us completely dry through Thursday morning. Nonetheless, I maintained our storm chances mainly during the evening and nighttime hours Tuesday night and again Wednesday night, with scattered storms possible Thursday into Friday as the upper low swings overhead. We dry out a bit into the weekend, but temperatures do not fall far, only back into the low/mid 80s.

Disclaimer: Forecasting multiple complexes of storms in weather environments like this one is not easy. Particularly with computer modelling, one of the biggest tools used to predict storms like these. In situations featuring extreme instability and multiple storm complexes, computer models can very quickly get off track. Think of it like a row of dominoes. Each complex of storms is a domino cascaded on by the previous round. It is difficult for the computer model to determine how quickly the atmosphere may recover following a round of storms, and this is only exasperated when there are multiple rounds of storms each throwing a wrench into the weather model that just ran based on current conditions as of an hour ago. Sometimes even miniscule details such as a change of a dew point temperature by 1-2° can set the line of dominoes on a completely different path, throwing off the entire rest of the forecast. That is where good human forecasting comes into play. A good forecaster looks at all the different scenarios based on current radar data and makes a determination of what might actually happen.

Long stretch of heat and storms begins today, lingers into Friday

Monday could have been a bit more active if it wasn't for the showers and storms that passed through earlier in the day. What that basically did was push the severe weather threat to our south and east, leaving conditions dry and clear overnight. 

However, this was just the first of multiple chances that northern Illinois has to see storms this week. Especially now that conditions are to be a bit more hot and humid moving forward. 

Tuesday begins with patchy fog and temperatures in the upper 60s. If you plan to be out for the morning drive, take it slow if you do encounter any areas being impacted by lower visibility. 

Aside from an isolated afternoon shower or storm, a good chunk of the day aims to remain dry with temperatures peaking in the upper 80s. With a light southwest wind in place, expect heat indices to make the jump into the mid 90s. 

Towards the evening, our attention will turn to our northwest as storm evolution will determine who will see the highest coverage for strong to severe storms and flash flooding. Earlier this morning, the Storm Prediction Center placed areas stretching from southeast South Dakota to northern Georgia under a level 2 Slight Risk for severe weather. This does include our areas that hug the Mississippi River, mainly for damaging winds. The rest of the region is under a level 1 Marginal Risk.

A few more uncertainties will be in play Wednesday, such as the state of the "cap" or lid on the atmosphere as well as the position of the warm front. Right now, the Storm Prediction Center has the entire area under a level 1 Marginal Risk. Again, this would be for strong winds and heavy rainfall. 

A more organized storm system will then slide to our north by Thursday afternoon, continuing the potential for storms and flash flooding. Headlines also include additional heat and humidity as Wednesday and Thursday could feature heat indices near 100 degrees. As previously mentioned, check the forecast frequently and make sure to take the necessary steps to keep yourselves and your loved ones safe from severe weather and from the grueling heat. We do see this weather pattern simmer down a bit by the weekend as an area of high pressure introduces northwest flow.

Multiple rounds of storms possible this week

 We may be in for an active week ahead with multiple chances for storms. There are a lot of moving parts in the forecast going forward, but here are the basics: Multiple waves of storms may be possible within the next few days, some of which may pose a risk for severe weather. Our first window is early Tuesday. This wave will develop from decaying storms forming in the Dakotas Monday night. The track of this wave is still uncertain but will dive Southeast close to the Stateline likely before 3PM. If these storms were to remain intact through the area, it would limit the next potential wave. Conversely, if those storms were to fall apart before reaching the Stateline, chances for strong storms late Tuesday evening would be higher. Similar uncertainties remain in place later in the week, but conditions appear favorable for a few waves of storms within the general region.

Right now, my thinking is that the first wave of storms will pass just to the Southwest, possibly clipping portions of the viewing area along the Mississippi River and just East. If things play out like that, the instability gradient would be shunted Southward, keeping the next wave late Tuesday night also to the South. Note: In this scenario, Rockford and areas Northeast would remain completely dry. My confidence on this scenario is low-medium at this time.

The Storm Prediction Center agrees for the most part with this assessment, placing only SW portions of the viewing area under a Level 2/5 Slight risk. Meanwhile, the rest of the Stateline only under a Level 1/5 Marginal risk. The main risk would be for damaging winds and heavy rain.

Regardless of how Tuesday plays out, Wednesday looks to build that instability gradient back up, but the afternoon should remain capped with a lack of upper air forcing to break through it. That said, another passing wave late into the evening may bring the next complex of storms after 8/9PM. With the uncertainty still in place, SPC has placed the whole Stateline under a Level 1/5 Marginal risk. Like Tuesday, the main risk would be for damaging winds and heavy rain.

In addition to the severe threat, we may also see multiple rounds of heavy rain especially if the storm complexes track over the same areas over and over again. With abundant moisture aloft, the storms will be very efficient rain producers, with 1-2"/hr rainfall rates possible. If storms were to backbuild or train at all, the risk for flash flooding would be higher. The Weather Prediction Center has placed the Stateline within the slight risk for flash flooding Wednesday into Thursday, noting a 15% chance for flash flooding guidance to be met.

Active weather with very hot and humid afternoons will continue for a few more days, with weaker scattered storms Friday before drying out into the weekend with highs back near average and less humidity.

Northern Illinois to enter a more active weather pattern this week

The Stateline is waking up to the sound of rain and occasional thunder this morning as a compact storm system slides in from the west. 

Showers will remain a possibility in a scattered fashion into mid to late morning. If they do end up lingering this long into the morning, this would limit the potential for storms locally later on by pushing the greater instability to our south and east.

There is kind of a hint that this scenario will play out as the Storm Prediction Center did place areas from southeast Illinois to central Kentucky under a level 2 Slight Risk for severe weather. 

Locally, we're under a level 1 Marginal Risk, mainly for damaging winds. Any chance that develops will linger into the first few hours of the night tonight, with some clearing taking place.

This clearing looks to be enough for Tuesday to begin with some patchy dense fog. Use extra caution if you have to be on the roads Tuesday morning. The rest of Tuesday will remain fairly dry as the focus for storm development will be to our northwest. Evolution from there remains highly unclear at this moment in time as we'll have to see what happens or where this activity tracks once it does form and mature.

It will also depend on where a boundary sets up. Either the boundary slides through in time so that we miss out on the brunt of the rain and storms. Or, the boundary plants itself over northern Illinois, allowing a strong line or M.C.S to slide through, elevating the risk for flash flooding and strong storms. 

Be sure to check the forecast frequently over the next 24 hours as finer details come about. Also, practice your severe weather safety plan just in case. As far as temperatures are concerned, highs will reach the low 80s today, then upper 80s, close to the 90° mark Tuesday and Wednesday. Humidity levels will likely climb as well, allowing heat indices to approach the century mark at times. This is especially for those afternoons that feature limited or nonexistent storm chances.

Severe storm chances through the week ahead

 As I am very quickly reminded many times, the weather is sometimes quite unpredictable. This is the case especially heading into the week ahead with multiple chances for strong to severe storms, but very low confidence on each one. There are a number of factors that play into how a storm complex will develop, but oftentimes it is hard to tell how one will develop until the previous round has moved out. This will be evident many times this week, starting with tomorrow morning. The shower coverage (or lack thereof) will heavily impact how strong our next potential round of storms may be. That will determine where any boundaries or outflows get placed, along with how much instability (storm energy) may build back in for the afternoon. Similar uncertainties exist with each storm chance through mid-week, but we do look to remain under an active pattern throughout that time with multiple storm complexes passing through the Midwest region this week.

Starting with Monday, our morning shower activity may inhibit the destabilization of the atmosphere heading into the afternoon. Some computer models are much more bullish on this than others, but generally speaking, a lack of mid/late morning storms will enhance the risk later in the day. We also have to watch upstream for any developing waves aloft that will provide the forcing and shear for storms to develop. With the uncertainties in place, the Storm Prediction Center has a very broad area under a Level 1/5 Marginal risk for severe weather.

Similar uncertainties exist for Tuesday, but this time around more storm energy appears to be available for any storms to use. Fortunately, the upper-air support may be slower to arrive, approaching from the West after sunset. In theory, this would limit the overall severe risk if it were to play out like that. As of now, the afternoon appears very hot and humid with late evening storm chances rising. SPC once again has a broad region under a Level 1/5 Marginal risk.

On each day, if storms were to remain limited or nonexistent, the heat and humidity would likely build up, with heat indices approaching 100° at times. This is especially true for Tuesday through Thursday. I maintained our storm chances on the forecast, with highest confidence as of now within the Monday evening/Tuesday night windows in the short term. Lower confidence exists with our next possible storm window between Wednesday and Thursday. A general drying trend will be present into the weekend, with slightly cooler afternoon highs back in the mid-80s.

Sunday morning weather update

 Over the next few days precipitation and thunderstorm chances will continue to rise as a ridge of upper-level winds begin to make its way into the region. Right now, though an upper-level low pressure system is bringing increased humidity, moisture and precipitation to the state line this morning and afternoon.

Currently a wide band of light rain is occurring in the southern tier of counties of the state line with rain to continue to move to the northeast through the morning. Although not heavy this rain will stick around for at least the few hours of the morning until clearing with clouds and some sunshine make an appearance later in the late morning.

However, depending on atmospheric recovery behind the rain some showers and thunderstorms may develop through the afternoon today as well. Depending on how much sunshine we get through the morning this will either increase or decrease or thunderstorm risk. Right now, not much destabilization or sunshine is expected to occur however even with that some scattered thunderstorms are still expected to develop this evening with quick downpours and possibly some gustier winds.

As the evening approaches though instability will quickly decrease along with thunderstorm chances.

Into Monday morning though, showers and thunderstorms begin to move into the state line once again. This is due to a small warm front lifting north through the morning, with some instability clearly present, some rumbles of thunder cannot be ruled out early tomorrow morning. This round does look to be more widespread with some heavier rain so through the morning especially during morning travel time keep an eye out for widespread downpours and rumbles of thunder.

But, after the morning round on Monday, skies are expected to clear behind the line with instability rapidly increasing through time Monday evening. The sunshine is the main cause of increasing unstable air so with more sunshine expect more unstable air and possibly stronger storms. Currently the storm prediction center has us under a 1/5 marginal risk for severe thunderstorms through Monday. This marginal risk is for all hazards however as of now damaging wind gusts seem to be the highest peril into tomorrow.

Expect thunderstorm chances to continue through the week this week as enhanced upper-level winds, high humidity, and higher temperatures return to the Midwest.

Scattered storm chances next week starting Sunday

We have remained dry over the past few days with high pressure overhead the Stateline, but that is beginning to change as we head into Sunday morning. Clouds have already been on the rise with our next chances for rain moving in shortly after. This will keep our overnight low a bit warmer, only reaching the mid-60s. 

Light rain may be the onset into early tomorrow morning, starting just before or near sunrise. Pockets of light to steady rain may last for a few hours before rain becomes a bit more scattered toward the afternoon. A few breaks in the clouds may also appear, helping promote a few thunderstorms. Scattered showers and storms will then last into tomorrow evening before we lose daytime heating. Within any spots that see sunshine, temperatures may rise into the low 80s. Otherwise, many will be stuck in the upper 70s.

Our next potential for some strong to severe storms come shortly after, and multiple rounds may be possible over the week ahead. The first of which comes Monday, as the Storm Prediction Center has placed us under a Level 1/5 Marginal Risk for severe storms. Scattered storms may be possible through the afternoon, but the highest risk for any strong or severe storms looks to come late in the evening, when better ingredients come together. For details on the science behind the ingredients of our severe threat, visit here: The science behind Monday's severe weather threat (mystateline.com).

A few isolated storms may be possible into Tuesday, but another chance for stronger storms returns Wednesday into Thursday. Heat indices may push the upper 90s most days especially when storms do not form (particularly Tuesday afternoon). Overall, a gradual drying trend will filter in toward the end of the week, while temperatures remain near to just above average.

Increased precipitation chances next week

 As the past two weeks now have been seasonably cooler and relatively dry in terms of precipitation we can start to look into this weekend and next week when the pattern begins to change. Through the past week or so high pressure has dominated much of the lower 48 causing calmer and drier weather which has fueled some of the fires out West. But expect that to change at least in the Midwest as upper-level winds and increased moisture will increase thunderstorm chances.

Over the next week these two main ingredients will combine almost daily to bring higher precipitation chances to the Midwest nearly every day. Showers and thunderstorms need three main ingredients those being, moisture, lift and instability. Over the next week two of the three boxes will be checked off as moisture and lift will be present but depending on instability from day to day can increase or inhibit thunderstorm development.

This pattern starts to take shape Monday as upper-level winds from the northwest (Northwest flow) from a ridge is set to move over the Midwest. With those enhanced winds deep moisture from the Gulf of Mexico will be funneled northward giving two things we need for storms. Instability Monday is a very big factor as of now as the Storm Prediction Center has the entire state line under a level 1/5 marginal risk for severe thunderstorms. If instability is realized a severe thunderstorm threat may develop as the "special" ingredient for severe weather is present being wind shear which is the change in wind direction with height. This wind shear helps organize thunderstorms and cause them to be longer lasting and taking in more instability helping them become severe.

This pattern continues into Wednesday then as more enhanced upper-level flow is still over the region with ample moisture. Wednesday and much of the rest of the week will be days to watch for scattered thunderstorm develop as once again two of the main ingredients are present. Instability rides normally on how much sunlight we can get, as sunlight heats the surface and makes it more unstable through time with moisture. If instability is realized throughout the week expect near daily thunderstorm, chances moving ahead.

With daily near daily thunderstorm chances, this will also increase total rainfall through the week. That being said, more rainfall may be coming for an already wet season! The crops are sure loving this rainfall but be on the lookout once again for flash flood warnings if days of rainfall occur. 
 

Active weather returns with more storm chances next week

It has been quite the "cool" stretch lately in the Stateline, with much of the last month lacking the heat and humidity we are typically accustomed to most summers. The last time the temperature reached 90° in Rockford was June 25th, more than a month ago! We haven't even seen the mid-80s in about a week and a half.

But that stretch of cooler-than-average highs ends tomorrow with afternoon highs likely reaching the mid-80s under plentiful sunshine once again alongside a gradual increase in cloud cover through the evening.

The cloud cover will be the precursor to our next rain chances that will enter the region Sunday morning. This weather system will bring widespread cloud cover and spotty showers, along with a couple embedded thunderstorms. Soaking showers will be possible, but they will be scattered. It will not be a washout by any means, but multiple waves of showers will be possible through the evening.

Looking ahead into next week, an active pattern aloft will develop with persistent flow out of the West Northwest. This will funnel multiple disturbances our way through the week, increasing our storm chances. Our proximity to a developing ridge of high pressure will also bring some heat and humidity back into the region, including our next shot at seeing 90° again. The combination of the warm and humid airmass along with the active flow aloft will bring periodic storms our way through next week.

We have one more sunny and warm day before humidity and storm chances increase starting Sunday. Higher potential for strong storms appears to be on Monday and Wednesday as of now, but there is still plenty of time for this to shift as ingredients become clearer. Afternoon highs and overnight lows will also climb into mid-week, reaching the upper 80s and near 70-degrees, respectively.

Pleasant, sun-filled weather lingers into the weekend

Felt great to have the windows open huh? Well, if you loved Thursday's weather, then you'll be a big fan of what I have to say about today! 

Friday's forecast gets a perfect 10/10 as high pressure to the east will continue to keep skies sun-filled to conclude the work week. With a more southeast wind in place, highs will end up a degree or two warmer than Thursday, but still comfortable. 

Perfect for that daily run, grilling, City Market, or if you're heading to either the Stephenson County Fair or the Lee County Fair and 4-H Show! Skies will stay mostly clear overnight, with temperatures falling into the upper 50s by daybreak Saturday.

Saturday will also be rather pleasant as sunshine aims to dominate our skies for most of the day. It's not until we reach the evening hours that clouds will begin to increase as a broad area of low pressure drifts into the Midwest from the southern plains.

Eventually, this will lead to our next chance for rain which may begin as early as Sunday morning. The chance for scattered rain will be present for most of the day, though there will be dry time mixed in. Thanks to the expansive cloud cover, temperatures shouldn’t climb higher than the mid 80s. As things stand now, the best chance for showers and storms will come Monday into Tuesday. Severe weather and even flash flooding will be possible.