A few isolated to storms may begin the day Sunday, but the afternoon will dry out and warm up once again. High temperatures will likely push well into the 80s, similar to if not warmer than Saturday. Once again like Saturday afternoon, the humidity will fuel a lot of storm energy. But storms are unlikely after mid-morning with a lack of a trigger mechanism to initiate storms. Some shower and storm activity is possible to the North along a warm front.
While the afternoon will remain dry, it will be rather humid with dew point temperatures pushing the low to mid-60s: similar to if not a little higher than Saturday. Winds will increase feeding into the aforementioned warm front, with some Southerly gusts pushing 30 mph at times through the day.
Better coverage of rain and storm potential will arrive toward Monday morning. A few of these storms may pose a risk for gusty winds and small hail, but the severe threat early in the morning should be somewhat limited.
Monday afternoon could be a different story, however. Following that morning round of storms, the atmosphere could become primed for more storms with high levels of instability once again. But very similar to Saturday and Sunday, the atmosphere is lacking a trigger mechanism. Storm development during the afternoon will hinge heavily on that forcing (or lack thereof) and how morning storms evolve. Stay tuned!
With as warm and humid of a day it has been, we have remained remarkably dry. This despite a lot of uncapped instability, or storm energy, sitting overhead, fueled by the humidity at the surface. Usually, with an uncapped environment, you would see several storms develop using up all of this fuel.
But moisture and instability are just two ingredients for storm development. Storms also need something to jumpstart the process with a boundary or lifting mechanism along with wind shear to keeps the storms going. We do not have strong lift or shear right now, which is why we have remained dry so far Saturday evening.
But an outflow boundary/weak frontal boundary is sitting nearby with all that instability. That boundary may provide just enough of a trigger to get some isolated thunderstorm development between now and 12AM. Any storm that fully develops may pose a risk for gusty winds and some small hail, but the severe threat is not very high.
Slightly higher coverage of showers and storms may be possible after 12AM, with isolated to scattered activity carrying over into Sunday morning. The severe threat does not appear to be very high with the overnight storms, either. A large majority of the area will likely remain dry through at least most of the night.
Thunderstorm chances persist through much of the weekend, but there will be many dry hours between waves of showers and storms. The outflow boundary from Friday night's storms will be a potential focal point for additional showers and storms Saturday afternoon. The large majority of the area and time will remain dry, but an isolated storm or two remain possible through the day. Higher coverage of storms may be possible toward Saturday evening/night.
The Storm Prediction Center has maintained their Level 1/5 Marginal Risk for severe weather, indicating one or two storms may reach near severe limits. Limited forcing and shear will prevent more widespread and organized severe potential during the daytime. Better organization looks possible with the evening wave.
Another threat for severe weather exists Sunday. This will be more of a "watch and see" event compared to Saturday, as it depends on how Saturday night's storms evolve. Similar to Saturday, the large majority of Sunday should be dry, but any storms that develop from the West may pose a risk for severe weather as they progress East across the area. This may be another late evening risk, like Friday night.
Both days this weekend will be very summer-like with warm and even humid conditions. Afternoon highs will push into the mid-80s. Isolated storms remain possible each day, but both afternoons appear to be relatively dry compared to the evening/nighttime windows.
[2:00AM] Round 1 of storms is now exiting the area, leaving some gusty outflow winds (30-40 mph) in its wake. Round 2 is developing in Eastern Iowa and will move toward the Stateline after 4AM. While widespread severe weather is not expected behind round 1's outflow, some isolated pockets of stronger thunderstorm winds may be possible toward daybreak.
[1:30AM] Along and behind the outflow boundary from the storms, winds have been gusting near 25-35 mph in some spots. While it may remain breezy through the night, the severe weather threat is ending for our Western Counties.
[1:25AM] While not severe, this storm in Central Boone County has perked up a little and may be capable of producing penny to nickel sized hail as it moves Northeast at around 40-45 mph. Poplar Grove, Capron, Chemung, and Harvard may experience some hail with this storm.
[1:15AM] This storm centered over West Rockford has been able to produce at least pea sized hail and very heavy rain over short bursts. Storm is not severe at this time, but is moving Northeast at around 45 mph.
[1:00AM] The Monroe airport measured a wind gust of 47 mph as storms passed through. A severe thunderstorm warning remains in effect until 1:30AM for Green and Rock Counties with 60 mph wind gusts possible.
[12:25AM] A severe thunderstorm warning has been issued for Green and Western Rock Counties in Southern Wisconsin until 1:30AM. These storms are capable of producing 60 mph wind gusts and penny sized hail as they move East at 60 mph. A tornado is also possible, but not imminent at this time.
[12:15AM UPDATE] Storms have moved into SW Wisconsin with a few areas of rotation and associated tornado warnings. Storms are generally moving East at around 30 mph. Additional cells have begun producing lightning in NW Illinois in a more isolated fashion. Weakening trends will continue with Eastward extent, but it is unclear how quickly they will weaken. Right now, the highest chance for anything severe over the next few hours is primarily across Southern Wisconsin, but far Northern Illinois may get clipped by a strong storm or two. Highest threats will remain with damaging wind gusts, followed by very isolated spin-up tornadoes, then small hail.
[10:45PM UPDATE] A severe thunderstorm watch has been issued for Northwestern parts of the Stateline until 5AM Saturday. Storms out in Iowa have been holding together to an extent as they move East with a few severe warnings along the line. Primary threats would be damaging wind gusts and some instances of small hail. Our primary storm window will be through 2-3AM, exiting East after 3-4AM.
Scattered storms have developed in Iowa with several severe thunderstorm warnings. This line of storms will continue to progress Eastward, reaching NW Illinois after 10-11PM. Storms will be on a weakening trend but could still produce some damaging wind gusts and hail.
The current late evening SPC outlook has expanded the Level 2/5 Slight risk further East across a large portion of the Stateline now. Storms will be possible from 11PM-3AM, so be sure to have ways to get warnings should any be issued that late!
Talk about a flip of the switch. Just weeks after seeing the 7th wettest April on record, the Stateline has done a complete 180- May is now trending as the 4th driest on record so far. From soaking rains and multiple episodes of severe weather to extremely dry conditions, it's been a dramatic shift in our pattern, and one that's been felt by many.
Dry & Warm Friday:
We did see a weak system come through overnight, bringing us a few light showers. A lingering shower and some early clouds will hang around for the start of the day, but improvements are on the way. Sun gradually breaks through as we get into the afternoon hours. That, along with a increasing wind out of the south will result in a warmer and above-average end to the work week with upper 70s.
Overnight Storms:
Our attention will then turn to the west where storm are expected to develop across Iowa. Those storms could organize and maintain some strong to severe characteristics as they track east over the Mississippi River. While they may gradually weaken, strong winds, heavy downpours, and hail will be the primary concerns with any severe storm.
Weekend Outlook:
The rest of Saturday aims to remain dry. After early-day clouds give way, we'll stay dry through the afternoon with highs climbing into the mid 80s - a very summer-like afternoon.
That said, the quiet stretch won't last long as another round of storm chances arrive late Saturday into Sunday. This may end up putting a lid or cap on the atmosphere for the rest of the afternoon and evening. Even so, we'll need to keep an eye on things as we do have a warm front lifting through late Sunday morning into Sunday afternoon. The highest potential as of this morning comes in on Monday as a strong low and a cold front enter the equation.
Humidity is not something we have needed to talk about for a while, but this weekend will bring a very muggy feel compared to average conditions for mid-May. Dew point temperatures will surge all the way into the 60s beginning Saturday afternoon, until a cold front swings through Tuesday.
Moisture is just one ingredient for thunderstorms, though. Instability is a measure storm energy, describing how quickly air will rise and form an updraft. Saturday through Tuesday will bring substantial amounts of instability nearby and especially to the West, but the main question is if there is enough forcing to develop storms.
Each day Friday through Tuesday features at least an isolated severe weather potential nearby. Friday night and Saturday both have Level 1/5 Marginal risk for parts of the area, indicating an isolated severe storm may be possible, primarily in the evenings.
The Storm Prediction Center has 15% risks nearby or overhead (Monday) each of Sunday, Monday, and Tuesday. Monday has the best environmental conditions for severe storms, but each day may feature some strong storms. The exact timing of each wave will be hard to pinpoint until closer, as previous waves will determine outflow boundaries and other small-scale features that will impact storm threats.
Following a very wet April the first two weeks of May have been exceptionally dry. With only 0.05 inches of precipitation being recorded at the Rockford Airport this May, month to date, is the second driest start to May since records began in 1905! It follows 1958 and ties with 1928 - two years that were a long time ago.
The surplus of rainfall during the month of April helped bring northern Illinois and southern Wisconsin out of drought conditions but it has really dried out over the last two weeks, even though it has also been a cooler start to the month. Rain chances do look to ramp up heading into the weekend thanks to a more active pattern that'll start to take shape Friday night.
Skies will remain mostly clear through Thursday evening as high pressure hangs on across the eastern Great Lakes. You'll start to see an increase in some higher-level clouds, already moving in across northwest Illinois, through sunset. These will thicken up as a warm front moves a little closer. There are a few showers and thunderstorms ongoing across Iowa and Minnesota but those will continue to fizzle as they encounter the drier air to the east. Late Thursday night an upper-level disturbance will move in giving us a chance for a few passing showers into Friday morning. Any steady rain and thunderstorms will likely miss us to the south over central Illinois.
The warm front will pass to our north Friday afternoon as southerly winds increase, gusting around 30 mph. This will help push afternoon temperatures into the mid and upper 70s. Most of the afternoon will remain dry but the chance for showers and thunderstorms is set to return Friday night with the arrival of a cold front. While not much cold air is behind this front, it will be the focus for showers and thunderstorms heading into the weekend.
Strong to severe storms are likely to our west Friday afternoon and evening, and that's where we find a 'slight risk' for severe storms - centered over southern Iowa, northwest Missouri and southeast Nebraska. Further east, a 'marginal risk' for isolated strong to severe storms can be found over most of northern Illinois and southern Wisconsin. This would be for any storms we get overnight Friday. The main risks with those storms would be primarily hail.
The front will stall over the region Saturday afternoon and will be the focus for additional showers and thunderstorms during the afternoon and evening.
