Additional showers and embedded thunderstorms are moving across the Stateline now, with heavy rain and more lightning/thunder. We expect at least widely scattered showers and thunderstorms to persist throughout the day today as a weak area of low pressure associated with storms from yesterday move through the region.
An upper-level low lifting in from the south will bring a bit more active weather to the Stateline, helping bring scattered shower and thunderstorm chances as we begin the new work week. With plenty of moisture in place, some of these storms could produce heavy rain, though severe weather will not be on the table. Despite the clouds and occasional rain, temperatures will still climb into the low 80s.
Looking ahead, we'll begin to see a low-end severe weather threat develop Tuesday. Storm Chances will be isolated, but for some, may present the potential for damaging winds and large hail. Areas south and west of Freeport and Rochelle have been placed under a level 1 of 5 Marginal Risk. The strongest potential Tuesday will actually be up in the Upper Great Plains, focused in North and South Dakota.
The severe potential ramps up noticeably as we head into the middle of the work week. A surface low lifting into Minnesota will drag a cold front closer to the region, setting the stage for storms to develop along that boundary. These storms are expected to push east into the Stateline Wednesday evening into Wednesday night, posing a risk for all severe hazards including damaging winds and isolated tornadoes. For now, the Storm Prediction Center has much of northwest Illinois and southern Wisconsin under a level 3 of 5 enhanced risk for severe weather.
Active Stretch Continues:
Please make sure to keep an eye on the forecast for not only Wednesday, but also Thursday as the surface low will likely contribute to potentially another round of significant severe weather.In their latest round of severe outlooks, the Storm Prediction Center has put the region under a 30% risk, which is equivalent to a level 3 of 5 enhanced risk.
Like Wednesday, a very moist and unstable airmass will allow all severe weather hazards to be on the table. So again, today, tomorrow, and even Wednesday morning will be a good opportunity to review your severe weather safety plan and make sure you are prepared ahead of time. With the potential for strong to severe storms increasing by midweek, having multiple ways to receive warnings and knowing where you would go pending severe weather makes all the difference.
Several pockets of heavy rain were realized Sunday afternoon with the isolated storms that developed late morning through early afternoon. Most did not see more than a few tenths of an inch of rain, but a couple locations across Ogle, Lee, and Jo Daviess County saw more than an inch of rainfall!
Similarly heavy rain may be possible in another isolated to scattered fashion Monday afternoon. This time around, rainfall should be a bit more widespread for more of the area compared to the little coverage from Sunday. Strongest storms will still be capable of producing strong downpours and some gusty winds, but the severe weather threat is limited.
The reason behind the limited severe weather risk has been a lack of better organization in the storms. So far, many of the storms have shown pulse-like, popcorn behavior. That is good for producing very heavy rainfall, but severe storms need more of a driving force in the upper levels to sustain them.
Such a pattern may develop toward the middle of the week as an upper-level trough slides overhead. This interaction between the extremely humid air mass ahead of it and the increased dynamics will allow for a few more chances for organized and possibly severe storms to develop later this week.
Much of our daytime hours Tuesday and Wednesday may end up dry, but isolated to scattered storms may pose a risk for severe weather late Tuesday evening, then again on Wednesday and Thursday. Each wave timing will depend heavily on the one before, but the ingredients are there for a mentionable risk for severe weather both Wednesday and Thursday in particular. For now, keep tuned to the forecast as we will be sure to bring you the latest!
While storms have been relatively isolated in nature lately, chances will be higher Sunday and Monday. A large-scale upper level low pressure system will force abundant and rich Gulf moisture our direction, resulting in continued humidity and increased rain and storm chances. Water vapor imagery shows this feature very well, with the dry slot across Texas already getting filled in by thunderstorms.
So what does that mean for our local area? As the increase in moisture reaches Northern Illinois, isolated to scattered thunderstorms will be possible. There will be lots of dry time, but any time of the day may feature a gusty downpour with some lightning possible. The overall severe risk will remain relatively limited, but a couple storms may be able to pulse up to produce localized instances of 60 mph winds or quarter sized hail.
Sunday's storm coverage looks overall similar to Saturday, with a few more storms compared to the relatively dry Saturday. Higher coverage looks to be possible early afternoon through evening, but only 30-40% coverage may be realized at the highest. Strongest storms may be able to produce gusty winds and heavy rain, but the severe threat will remain very limited.
Monday will bring a bit higher coverage of storms, meaning there will be less dry time and fewer dry areas. Highest chances for rain and storms will again be centered around the afternoon and evening hours. Similar to Sunday, strongest storms may produce gusty downpours, but widespread severe weather is not expected.
The majority of Tuesday will end up dry, but hot and humid like Saturday was. The change this time around comes with the potential for a round of storms late in the evening and into the night. These storms would hypothetically be in a weakening state but could have better organization and higher risk for severe weather compared to Sunday or Monday.
Regardless of storm coverage, humidity will not go anywhere. Dew points will likely rise near or above 70 degrees each day, keeping the uncomfortable feel to the air mass. Temperatures may temporarily drop with any storms, but humidity will not.
[12AM Saturday] This line of storms stretching across Central Winnebago, Boone, and McHenry Counties is producing lightning and heavy rain. While not severe, it may have some pockets of very heavy rain along with gusty winds possibly near 40+ mph. Storms are moving East around 20-30 mph. There has been some back building of these storms, which may enhance rainfall totals in a narrow, localized area. Flash flooding is not a concern yet, but some ponding on roads and low-lying areas may occur where rainfall is heaviest.
[11:15PM] The line of storms in Wisconsin has shown signs of weakening, now producing an outflow boundary in advance of the storms. That should work to aid in the weakening trend, but some pockets of 40 mph gusts may remain possible as storms move Southeast at around 30 mph.
[10PM] While not severe, this storm in Western McHenry County is producing lightning and heavy rainfall. Wind gusts may be able to approach 30-40 mph as the storm moves East at around 30 mph.
[9PM] Thunderstorm coverage is expected to gradually increase overnight as two regions of storms move toward the Stateline. Region 1 is diving out of Central Wisconsin with a few severe storms associated with it as of 9PM. Region 2 is a newly developing cluster of storms in SE Wisconsin, which should track along or just South of I-88 through the night.
Another round of widely scattered storms may be possible Friday night into the early hours of Saturday morning. While much of Friday evening has remained dry following the morning round of rain, additional activity will begin to develop late this evening.
Storms currently positioned in Central Wisconsin will dive Southward tonight, reaching Northern Illinois as early as 12AM. Another wave of storms may develop across Southeast Iowa and slide Eastward along I-80/I-88 corridors through that time as well. Between both rounds of storms, coverage is not expected to be very high, with several locations ending up dry throughout the night.
But those who do see storms may experience some very heavy bursts of rain, along with a few instances of gusty winds and small hail. The overall severe threat is not very high as storms will struggle to organize themselves. But be prepared in case any warnings are issued!
The heavy rainfall mentioned above will not be for everyone. In fact, only a few isolated pockets may pick up much rainfall at all. Where the clusters of storms form, a narrow axis of 0.5-1.0" may be possible. Elsewhere, only 0.25-0.5" may come down where isolated storms move overhead. There will be parts of the Stateline that end up totally dry overnight.
The overnight storms will push the most favorable environment to the South for Saturday afternoon. While most of the area will remain dry, a few isolated storms may be able to develop along remnant outflows from the overnight round. The best chance for this would be along and South of I-88. Where dry conditions remain, it will be a hot and humid day with temperatures reaching the upper 80s in many spots.
Thunderstorm chances are back in the forecast today, and it all ties back to something we call an M.C.V, or Mesoscale Convective Vortex. This is essentially a leftover spin in the atmosphere that develops within a cluster of showers and storms. Even after the main storms weaken or move out, this compact area of low pressure can linger and act like a spark for new storm development. The added spin from an M.C.V could also enhance the threat for weak tornadoes.
As for the severe threat today, areas south of highway 20 in northern Illinois are under a level 2 of 5 - slight risk for scattered strong to severe storms. It's not a slam dunk setup, though. Earlier rain and storms have worked the atmosphere a bit, which could limit how much additional thunderstorms is able to develop later on. That said, if storms could tap back into some of the available storm fuel, a few could become strong with gusty winds and heavy downpours. And while the overall threat remains on the lower end, it's still worth keeping an eye on, especially in the slight risk area where the spin will be enhanced due to the incoming M.C.V.
Thunderstorm chances on Saturday look to be more isolated and pulse-like, meaning we're not expecting much in the way of severe weather. Instead, a few individual storms could quickly pop up during the heat of the afternoon, briefly intensify, and then fade just as fast. So hit-or miss. Some will see rain and others will not. Most areas however will stay dry with highs climbing into the mid 80s. As we head into Sunday, most of the daylight hours should stay dry with a mix of clouds and sunshine. Rain chances hold off until later, with the next opportunity for showers and thunderstorms arriving during the overnight hours Sunday night.
May was an exceptionally dry month in the Stateline, for Rockford in particular. Only 0.52" of rain came down all month at the Rockford airport, making it the second driest May on record. It was similarly dry across much of the region as well. Maps below show the accumulated rainfall and percent of normal over the last 30 days, highlighting much of the Stateline region that has been exceptionally dry over the last month. Some locations have only seen less than 1/4th of "typical rainfall over the last 30 days!
Last week, the Climate Prediction Center indicated that much of the area was under risk for "Rapid Onset Drought". Just a week later, much of that same area is now under a Moderate Drought from the latest Drought Monitor. This has been rapidly expanding, given that just 3 weeks ago only a small part of Northern Illinois was considered "Abnormally Dry".
Some much-needed rain may soon be on the way, with repeated rounds of showers and thunderstorms starting Friday morning. While the rain will not be uniform and soaking rain for everyone, the additional waves will result in higher rainfall potential for everyone. Latest forecast models and the Weather Prediction Center suggest around 0.5-1.0" may be possible over the last 5 days, with higher amounts within scattered thunderstorms that may develop. Not totally drought-busting, but it would be more rainfall than we've seen in quite a while!
