Increasing coverage of thunderstorms early in the week, humidity remains

 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.

Another round of widely scattered storms possible Friday night

 [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.

Scattered storms possible today, hit-or-miss this weekend

What is an M.C.V?:

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. 

Today's Severe Threat:

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. 

For those who miss out on any of the scattered storms this afternoon and evening, it'll be a different story. Conditions will stay dry, partly cloudy, but noticeable more humid, with that muggy feel really settling in. Even without the rain, it'll be a summer-like finish to the day with afternoon highs in the low 80s and dew point temperatures in the upper 60s.  

  

Weekend Outlook:

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. 

Drought conditions expand across Northern Illinois following dry May

 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!

Thunderstorm chances increase Friday morning

 

Our stretch of comfortably warm weather will soon come to an end as a more summer-like pattern is set to return heading into the weekend. This means temperatures will not only remain in the 80s through the weekend, but we'll soon feel the return of higher humidity.

For the rest of Thursday evening clouds will slowly increase but our skies will remain dry. A line of non-severe thunderstorms stretches from northern Wisconsin back southwest through Iowa and northwest Missouri and will slowly move east through the night. High pressure over the Great Lakes has kept quite a bit of dry air in place as moisture continues to build west of the Mississippi River. Eventually, that moisture will move east which will lead to those storms moving into northwest Illinois around daybreak Friday. While in an overall weakening trend can be expected, the scattered showers/storms will move across northern Illinois and southern Wisconsin through late morning.

Friday afternoon will likely see some dry time as only an isolated threat for a storm or storm will be possible. Surface winds from the southwest will keep temperatures in the low 80s but push dew points into the 60s. This will make the afternoon feel quite a bit more humid than what it has the last several days.

The rain during the morning won't be evenly distributed across the region, leaving some to receive totals nearing a half an inch to three quarters of an inch while others may not get quite as much. The next chance for showers and thunderstorms will return late Friday evening from what develops to our west and northwest during the late afternoon and evening. The highest threat for strong to severe storms will remain west of the Mississippi River during that time, but the remnants of those storms could move in our direction Friday night posing at least an isolated risk for a strong/severe storm or two. Because of this northern Illinois and southern Wisconsin remain under a 'marginal risk' for an isolated strong storm or two.

Warm, breezy today—storm chances return Friday

Warmup Continues: 

Yesterday was another beautiful day, though it gave us a true taste of summer with highs climbing into the low to mid 80s across the region. Today, we turn up the heat a bit more as southwesterly winds become better organized, helping boost temperatures even higher for our Thursday. Expect afternoon highs to top out around 87 degrees beneath a partly cloudy sky. It'll be a bit breezy at times, with gusts reaching up to 25 mph this afternoon.  

Rain Chances Increase:

Cloud cover will begin to increase this evening as our next system organizes to the west. Even so, forecast models continue to slow down the eastward push of developing showers and thunderstorms, keeping most of the activity just out of reach through much of the night. As it stands now, the better chance for rain looks to hold off until closer to daybreak tomorrow morning, when that line of showers and storms finally works its way into the Stateline. 

Severe, Flash Flood Potential:

Another round of showers and storms is expected to fire up over Iowa by Friday afternoon, and where these storms form and track will be key for us here in the Stateline. That placement will play a big role in both our severe weather potential and the risk for flash flooding heading into Friday night and Saturday morning. Right now, the Storm Prediction Center has much of the Stateline under a Marginal Risk (isolated threat) for strong to severe storms, while the Weather Prediction Center has placed half the region under a Slight Risk (15%) for excessive rainfall and possible flash flooding. Precipitation chances should diminish or taper off Saturday morning as the main upper-level feature pushes to the east of the area.    

 

Prospects for much-needed rainfall increase into the second week of June

 While the last month plus has been rather dry across the Stateline, but we may begin to see more of a pattern change on the way before too long. We will see a few chances for at least scattered showers starting late this week and toward the weekend, particularly over Friday.

Another favorable window for some downpours or storms will arrive early next week. Abundant gulf moisture will inch Northward after Sunday, bringing increased rain chances toward Monday-Tuesday in particular. The deeper "Precipitable Water" values indicate more moisture than could be rained out given the right conditions.

Even subtle waves in the atmosphere will be able to produce scattered downpours, and that looks likely between Monday and Tuesday. That rainfall may not be widespread for everyone at any given time, but more locations than not should be able to see some of the beneficial rainfall early next week.

Rainfall coverage will be key in determining how much of the Stateline sees this soaking rain potential versus those who don't. Monday and Tuesday will probably be between 40-60% coverage, meaning only around half of the area will see rain at any given time. I'm not expecting the rain to be overly widespread, meaning there should be at least some dry time between waves of rain.

Even though the rain will not be overly widespread for everyone, the rich moisture will result in heavy downpours when rain does fall. Through the week, that will begin to add up with some rainfall for many locations around the region. Computer models may not have an easy time predicting how much widespread rainfall we will see this far out due to the scattered nature of the showers and storms. That said, there is an increasing chance for most of the area to see a half inch or more of much-needed rain through mid-next week.