Monday's system moves out, sunshine returns for 815 Day

815 Day Forecast:

After a mainly dry start to August, a slow-moving storm system brought a dose of much-needed rainfall to N. Illinois and S. Wisconsin Monday. Of the weather stations across the area, Galena came in with the most rainfall at 3.2", followed by Savanna with 1.7", then Rockford with 1.08".

 

With yesterday's rain-maker still in close proximity to the region, we may awaken to some lingering cloud cover. However, sunshine is to emerge as the day progresses, with highs peaking in the upper 70s. For those doing the math, that's roughly a 10-degree difference from highs Monday. 

Also present will be a breeze out of the north, which will be the big reason why we will end up below Mid-August standards. All in all, a great forecast for anyone celebrating 815 Day!

Seasonable Wednesday:

Forecast models then show an area of high pressure diving to our south overnight. This will leave conditions dry into Wednesday, with temperatures falling into the upper 50s. Wednesday will also be dry. But this time around, a southwesterly wind will be in place, allowing temperatures to climb back into the low 80s. Even with our next cold front coming in sometime Thursday morning, highs Thursday and Friday will peak in the low 80s.

Isolated severe/heavy rainfall possible Monday

Unusual Timing:

The workweek kicks off on a busy note thanks to a upper-level disturbance diving in from our neighboring states to the northwest. 

This will bring not only the low risk for isolated severe, but also the potential for heavy rainfall throughout the day. As this low dives southeastward, it'll draw an occluded/warm front northward, along with a little more moisture.  

Severe Risk:

That front is likely to stall very close to the Stateline just as the low will be moving through. The end result could be a increased risk for a few isolated tornadoes, with gusty winds and hail up to 1 inch in diameter being secondary concerns. Again, the risk is low, which is why the Storm Prediction Center has the entire region under a Level 1, Marginal Risk. 

The one key factor into determining where exactly we have the highest potential for rotating storms will be track of the low, but it does appear to be very close to the region. And because the threat is during a time in which is not typically known for tornadoes, make sure you're on your A game, staying updated on the situation. Be sure to have multiple ways to receive watches and warnings, whether that be from a NOAA weather radio, your cell phone, or by watching us on Eyewitness News! 

Flooding Concerns:

Another big concern with Monday's rain chances is the potential for flash flooding, especially for areas north of Interstate 88. As of this morning, only Green, Walworth, and McHenry Counties have been placed under a Flood Watch. It's in these areas where 2" to as much as 4" of rain could fall. 

For areas along and on either side of I-88, rainfall totals could range from 1"-2". As the low begins to slide east of the region, rain and storm chances will lower into the overnight hours. We do look to keep a bit of cloud cover overnight, with some clearing taking place towards sunrise. Clearing will continue Tuesday morning, resulting in a less active a more sun-filled day for Tuesday. Even though we get in on a good amount of sunshine during peak-heating hours, highs will be limited to the upper 70s thanks to a lingering northerly wind.

Isolated severe risk Monday morning

 
You'll want to make sure you're paying attention to the forecast Monday morning as there is a low-end risk for severe thunderstorms during that time. Now, a low-end risk may not sound too exciting, but the threat for the severe weather will occur from roughly 6am-2pm, not typically a time that we are used to severe weather.

A portion of southern Wisconsin and most of northern Illinois are under a 'marginal risk' for severe thunderstorms Monday morning. This is on the lower end of the spectrum, but the risk is there. A strong upper-level low pressure system currently located over the Upper Midwest will dive southeast towards the Stateline Monday morning. As it does, it'll draw northward an occluded/warm front, along with a little more moisture. That front is likely to stall very close to the region just as the low will be moving through. The end result could mean an increased risk for any storm that develops to spin, producing the risk for isolated tornadoes. The track of the low will ultimately be key in determining where exactly we have the highest potential for the storms to rotate, but it does appear to be very closer to the region.

We should start to see shower and storm activity increase after 6am, focusing on the 8am-2pm time frame. Isolated tornadoes and damaging winds will be the greatest threats. It's important to make sure that you are paying attention to the forecast before heading out tomorrow morning, and throughout the afternoon.

As the low passes to the east during the afternoon, the threat will shift to heavy rainfall. Right now, a FLOOD WATCH has been issued for Rock and Walworth counties in southern Wisconsin beginning Monday morning. This will last until Monday evening. The heaviest rain threat, and flooding risk, appears to be located over Wisconsin but totals of 1-2 inches are not out of the question for areas south of the state line. It's possible a watch could be issued further south.

There is a lot that'll take place with the weather Monday, both in the morning and evening. Please make sure you check the forecast when you get up, and throughout the day, for updates. And make sure to have a way to receive any weather updates if you're out. Remember - our window for severe weather will be from about 6am-2pm, shifting to a heavy rain threat through the evening.

Two rounds of storms possible today, drying out into Saturday

Few Uncertainties:

As we discussed on Thursday, the severe potential that is in the works for today has a few uncertainties to work through. All of which have to do with the cluster of showers and storms that are pushing through eastern Iowa this morning. 

First, how much of a cap or "atmospheric lid" develops following this morning's thunderstorm chances. Secondly, if this cluster were to produce an outflow boundary (a boundary consisting of rain-cooled air being pushed down from a thunderstorm), where would it exactly set up. These are questions that will be answered as the day progresses, which is why it's going to be important to be weather ready this morning and then again as we inch closer towards dinnertime. 

Today's Severe Threat:

Of the two rounds that are possible today, the early round features the lowest threat for severe weather. As for timing, guidance brings the early round through between sunrise and noon, with heavy downpours, gusty winds, and frequent cloud to ground lightning being the biggest concerns. 

If we do manage to get in on the second and stronger round late this afternoon into early tonight, damaging winds and large hail will be the bigger threats. Again, the tornado threat is low, but will be highest along any outflow boundary. Overall, the severe outlook locally hasn't changed much over the last 24 hours as the Storm Prediction Center kept all of N. Illinois and S. Wisconsin under a level 2 slight risk. Highs will end up a degree or two warmer than Thursday, with most in the upper 80s. 

Weekend Outlook

The associated cold front slides into the region early tonight, with dry conditions filtering in behind it. This will leave us with a good amount of sun, with high temperatures landing in the mid-80s. 

Clouds increase Sunday as our next storm system dives into the western Great Lakes. But it won't be until Sunday evening into early Monday morning where we see a chance for a few showers, possibly a few isolated thunderstorms enter the equation. Highs due to the increased cloud cover and rain chances will only peak in the low 80s, cooling into the upper 70s for Monday and Tuesday. 

Northern Illinois placed under another dense fog advisory, severe storms possible Friday

Another Dense Fog Advisory:

In a similar fashion to Wednesday, the day is starting off with a Dense Fog Advisory. This time, the advisory is for all of our northern Illinois counties, and it runs until 9AM. Visibility in these areas will fluctuate, registering less than a 1/2 mile at times. If you plan to be out on the roads during the morning commute hours, please make sure to remain focused and use extra caution. 

Once the fog fully lets up, expect a mix of clouds and sun into the afternoon. Despite a decent breeze out of the northwest, high temperatures for most will climb into the mid to upper 80s. 

Even though we see an uptick in our temperatures, today's northwest wind will help keep humidity-levels comfortable. As our next frontal boundary sinks into the region from the north, skies will turn mostly cloudy for the overnight hours. 

Friday's Severe Potential:

It's during this time in which we will have to monitor the position of the front, as well as a storm complex that develops to the west. This complex will be weakening as it approaches the Stateline, but it may hold together long enough for us to see a few showers and storms early in the day. 

While severe weather is not expected with this activity, this will play a role into the severe threat that comes about Friday afternoon into Friday night. Another factor that will determine Friday's severe threat will be the cap or "atmospheric lid" that will be present during the afternoon. This is a warm layer of air in the low-levels of the atmosphere that hinders thunderstorm develop. 

In their latest severe weather outlook for Friday, the Storm Prediction Center left all of northern Illinois and southern Wisconsin under a level 2 slight risk. Of the severe threats, straight-line winds and large hail are the biggest concerns. 

The tornado threat is low, but still present as there will be enough low-level shear (winds turning with height) in place. The associated cold front will pass through late Friday night into early Saturday, allowing dry conditions to settle in for Saturday. Despite Saturday's winds being out of the northwest, highs will climb into the upper 80s.

Dense fog advisory issued for some, heaviest rain stays south

Heavy Rain Stays South:

The rainfall department finally had something to be excited about as Tuesday's rainfall left behind almost a quarter of an inch at the Rockford Airport. 

On the flip side, the leftover moisture is one of the few reasons why some are waking up to dense fog this morning. For that, the National Weather Service has placed Winnebago, Boone, McHenry, Dekalb, Ogle, Lee, and Whiteside Counties under a Dense Fog Advisory until 8AM!

It's in these areas where we may see visibility drop to a .5" mile or less. If you plan to be out on the roads for the morning commute, please make sure to remain focused and use extra caution. Once the fog lets up, clouds will increase towards mid-day, resulting in a mostly cloudy sky for the afternoon. 

Forecast models show most of the heaviest rain falling to the south of the area, leaving us with just a few showers into the evening. If our area does see any rainfall, it will mainly be for those that live along and south of I-88. Chances will linger into the early stages of tonight, with skies turning partly cloudy into the early stages of Thursday. Expect lows to register in the low 60s. 

Mainly Dry Thursday:

Thursday looks to be a bit more pleasant, with partly cloudy skies and highs peaking in the mid-80s. While that does sound warm, the northwest breeze that will be in place will keep humidity-levels rather comfortable. It's at this time we'll be monitoring our next front as it sinks into the region from the north. This will be the focus for the potential for severe weather on Friday. 

Friday's Severe Threat:

Earlier this morning, the Storm Prediction Center placed the entire Stateline area under a level 2 slight risk for severe weather. As we go into Friday, this frontal boundary will stall nearby, and then lift northward as a warm front. 

Of course, there are a few uncertainties with Friday's severe threat such as a cap or atmospheric lid being present. But from what it looks like, damaging winds and large hail are the biggest threats. Tornado threat is low, but still present as low-level shear will be sufficient enough to support a tornado or two. For now, stay up to date on the forecast, especially if you have any outdoor plans. Models then show the associated cold front passing through Saturday morning, leaving conditions mainly dry for much of the weekend! 

Isolated rain possible during the first day of the Boone County Fair

Isolated Rain Tuesday:

Tuesday starts off dry under a mix of clouds and sun. By the afternoon, a weak upper-level impulse glides into Illinois, which may be enough to generate an isolated shower/storm during the afternoon. Keyword being isolated, meaning not everyone will be getting in on today's rain chance. 

But if you plan to attend the first day of the Boone County Fair, you'll definitely want to keep an eye on the radar. Any chance for a shower or thunderstorm does come to a close around sunset, leaving us dry and partly cloudy overnight. Expect temperatures to fall into the low 60s by sunrise Wednesday!

Scattered Rain Wednesday:

Clouds will thicken up towards mid-day Wednesday as a stronger disturbance moves into the Midwest. This will ultimately lead to a slightly higher chance for the Stateline to see some rainfall, mainly in a scattered fashion. However, it appears that the heaviest rain will fall to our south as the storm system moves through the southern half of Illinois. As for temperatures, both Tuesday and Wednesday are to feature highs in the low 80s.