Now that the severe thunderstorm watch has come to an end, we can take a look at the storm reports from Sunday evening/night. Again, with the early round of showers and storms pushing through, the atmosphere didn't really become active until after sunset as a lifting frontal boundary provided the lift needed for additional development. Several reports were received across northern Illinois, including a few tornado reports. One possible tornado was reported in Lee County, while another touched down closer to I-80 near Atkinson and Annawan.
Northwest Flow Continues:
While the northwest flow pattern aloft isn't as strong as it was over the weekend, it is keeping the jet stream positioned almost directly at the western Great Lakes. That setup will allow a few more disturbances to ride southeast over the next several day, bringing periodic chances for showers and storms. As a result, we will need to keep tabs on the forecast during the first half of the week as some thunderstorms could entail the potential for severe weather.
Daily Severe Potential:
A portion of the Stateline, particularly areas south and east of Rockford, remains under a level 2 of 5 Slight Risk for scattered severe weather. While coverage is not expected to be widespread, any thunderstorm that develops and moves through will be during evening and early overnight hours. The primary threat will be damaging winds, though the environment may also support an isolated tornado or two.
Tomorrow brings much of the same, though timing appears to be much earlier. Another disturbance riding along the jet stream will likely spark a round of the thunderstorms and showers late tonight into tomorrow morning, with the resulting cluster pushing into the Stateline Tuesday morning, with chances possibly stretching into the midday hours.
Given the amount of instability of storm fuel in the atmosphere, a few of these storms could once again be strong to severe, with damaging winds being the primary concern. Similar to today, make sure to keep tabs on the forecast while also having multiple ways to receive watches and warnings.
[12:10AM] Lingering storms remain in Eastern Walworth County, but we are severe storm free now. Likely, much of the night ends up dry, with increasing thunderstorm chances again Monday evening. Flash flood warning for Lee County remains in effect until 1:15AM, but rain is finished there for now.
[10:50PM] The Tornado Warning for Lee County has been canceled.
[10:25PM] The initial tornado warning that had been issued for Lee County has expired at 10:30pm, but a new tornado warning is now in effect for eastern Lee County until 11:30pm. This storm is currently moving towards I-39. The rotation within the storm has broadened out a bit, but still capable of producing a tornado. Heads up if you are in the Paw Paw area as the main area of location is now over Compton, heading towards Paw Paw. Localized flooding is also possible with a Flash Flood Warning in effect until 1:15am for eastern Lee County.
[10:05PM] Tornado warning continues for Lee County IL until 10:30PM. Mid-level rotation remains strong over Shaws, and a tornado could develop at any time. Storm is moving East at 20 mph. Seek shelter now if you're near Shaws, Brooklyn, or Compton!
[9:50PM] A tornado warning has been issued for Central Lee County until 10:30PM. This storm has been elevated but is right along the warm front, helping to enhance some rotation. This part of the storm is moving East at 20-25 mph.
[9:40PM] A new severe thunderstorm warning has been issued for Lee County until 10:45PM. These storms are capable of producing 60 mph wind gusts, quarter sized hail, and very heavy rainfall as they track East at 15 mph. Be on the lookout for flooded roads, as 1.5-2" of rain has already fallen in spots!
[9:35PM] New cells are developing West of the current severe warned storm in Lee County. With cells that train, or track over the same areas, we could see enhanced flash flood potential. Very heavy rainfall rates and slow movements have already allowed for over 1" of rain to fall in some spots. Watching very closely over the next 30 mins to an hour for flooding threats in Central/Eastern Lee County. If you come across any flooded roads, be sure to turn around!
[9PM] All of Northern Illinois is now under a severe thunderstorm watch until 4AM. Storms have begun developing along the previous outflow boundary, including the severe thunderstorm warning for Lee County. Along and North of the boundary closer to I-80, storms will likely be elevated in nature, limiting the tornado threat. Hail and damaging winds will be the primary concerns with any severe storms locally.
[8:50PM] A severe thunderstorm warning has been issued for Lee County in Northern Illinois until 9:45PM. This storm is capable of producing half dollar sized hail and gusty winds under 50 mph. Storm motion is only 15 mph to the East, so very heavy rainfall will also be a concern. Take shelter if you are within this warning!
While most of the Stateline did not see the strong storms or heavy rain from the midday round of activity, another round may still develop later tonight, likely along the outflow/effective warm front from the previous round of storms.
The more favorable environment for strong to severe storms remains near and South of I-88 Sunday evening. Elevated storms remain below severe limits along the I-39 corridor in Northern Illinois and Southern Wisconsin but are within the less favorable environment. With little daytime heating left, I don't expect that front to lift much further North than I-88.
The evening storms will likely develop along this front after 7-8PM, producing the potential for heavy rain, gusty winds, and small hail. The strongest storms may produce some instances of damaging wind gusts, but this would be rather isolated in nature. I suspect some, if not most locations in the Stateline will remain dry tonight.
Multiple rounds of showers and storms will be possible between Sunday morning and Monday, each bringing the threat for severe weather. The first wave of storms won't arrive until midday Sunday, with renewed development into the evening and then again Monday. The main threats will be damaging winds and heavy rain, but an isolated tornado will be possible, particularly Sunday evening where surface convergence sets up following the first round of storms.
SPC has the Level 2/5 Slight risk over most of the area for both Sunday and Monday, indicating the chance for a few severe storms both days. Where thunderstorms track over the same areas over and over, very heavy rainfall will be possible with a risk for flash flooding.
As typical for these types of patterns, there are a LOT of moving parts, so be sure to stay tuned to the forecast for the latest! Each round of storms heavily dictates what happens with the next, so the forecast is going to be rather fluid over the next 48 hours.
Our weather pattern will become a bit more active as we head into the weekend and next week. A ridge of high pressure building over the western United States and Rocky Mountains will place the Stateline under a northwest flow pattern aloft. That setup often acts as a conveyor belt of quick-moving disturbances to slide southeast through the Midwest.
While the weekend doesn't look to be a total washout, these disturbances will introduce periodic chances for showers and thunderstorms. Starting with today, the best potential for thunderstorms with disturbance #1 will be to the west and northwest of Rockford, across Wisconsin, Minnesota, and Iowa, hence the Level 1 of 5 Marginal Risk for severe weather. Locally, most of the daylight hours will be dry with showers, and possibly the chance for an isolated thunderstorm or two, sliding in late into Friday night.
Weekend Forecast: Saturday looks to stay dry for the most part, with high temperatures climbing into the low 80s. The next low is set to move through the northwest flow pattern does not appear particularly strong to start, though forecast models do show it sparking off a round of scattered showers and thunderstorms to the northwest of the area into Sunday. Some of which may track into the Stateline as we approach midday.
The Storm Prediction Center does have the entire area highlighted under a level 1 of 5 Marginal Risk for an isolated strong thunderstorm or two. Given the time of year and atmospheric profiles, damaging straight-line winds will be the primary concern with any severe storm. Temperatures should remain either near or just above-average in the low 80s.
The typical summertime humidity will not go anywhere through the weekend and into early next week. Dew points will hover between 65 and 75 throughout nearly all of the next week. While this will not come with oppressive heat alongside, it will feel quite muggy for the foreseeable future.
That humidity will allow for some patches or areas of fog to develop potentially each of the next few nights. Rain chances will also be on the increase heading through the weekend and into early next week. While the daytimes of Friday and Saturday will both likely be dry, Friday night may produce a few storms along a passing cold front. Any severe threat is positioned Northwest of us at this time, but showers and a stray storm may be possible after Friday evening and then again Saturday night into Sunday morning.
The sky will also have a bit more of a haze to it, with a continued feed of Pacific Northwest wildfire smoke. While this smoke will not result in air quality concerns in the near term, the smoke aloft will allow for a milky or hazy sky to take full effect, especially on Saturday when we would see otherwise sunny conditions.
Daytime windows of Friday and Saturday will be dry, but warm and humid with a bit more sunshine compared to recent days. Both Friday and Saturday nights will feature isolated to scattered rain chances, with a few storms possible as well. Sunday and Monday may have more widespread rain and storm chances, including the potential for a few stronger storms.
With that secondary batch of scattered showers and storms moving through late Wednesday afternoon and evening, plenty of moisture leftover has once again allowed fog to develop. This morning however, the fog may become a bit more impactful than what we encountered Wednesday morning. Extra travel time should be built into your morning routine as visibility will fluctuate from locale to locale.
Once the fog lifts, quiet weather settles into the area behind yesterday's cold front. A stray sprinkle or brief shower can't be ruled out early in the day, but most locations should remain dry. Clouds will gradually decrease as we approach midday, giving way to a mix of clouds and sun for the afternoon. With cooler, less humid air filtering in, temperatures will top out near the 80-degree mark. Expect overnight lows to drop into the low 60s with patchy areas of fog once again being on the table Friday morning.
Active Northwest Flow:
Looking ahead, the overall weather pattern turnsa bit more active as we fall under a northwest flow regime aloft inthe atmosphere. This setup will allow a series of quick-moving disturbances to slide southeast across the western Great Lakes, bringing multiple opportunities for rain from time to time through the weekend and into early next week.
The first wave is expected to arrive Friday evening into Friday night, presenting the chance for a few showers, followed by the second late Saturday into Sunday. The third disturbance then looks to move through late Sunday into Monday, bringing a slightly higher chance for isolated storms.
After the oppressively hot and humid end to July, August has started on a bit of a cooler note. Only one day so far has reached above the "average" high, with Tuesday reaching 85°. Part of the reason for this subtly cooler stretch has been the pattern aloft.
A Northwest flow has been the dominant feature in the jet stream, resulting in more frequent rain chances and not nearly as much heat and humidity. This type of pattern typically keeps the warmest air locked up over the Southern Plains and Southwest with more prolonged heat below that ridge. On the outer edge, we have frequent waves bring us more chances for rain.
This pattern looks to persist awhile longer into mid-August, as backed up by the Climate Prediction Center outlooks. The outline of that Northwest flow looks to keep subtly cooler than average temperatures along the Great Lakes and Northeastern United States, while most of the country experiences more heat.
Weather systems like to travel along the edge of this pattern, bringing more frequent rain chances along with it. Overall, we might see a little more rainfall than typical between the 11th-15th, similar to the on and off showers we have seen over the last few days.
