Indeed it has been a while since the Rockford area has observed a high in the 70s. In fact, the last 70° day at the Rockford International Airport was 180 days ago on October 10th, where temperatures climbed into the low 70s. I am happy to say that we are going to see this streak come to an end later today.
As a warm front continued to lift into northern Illinois this morning, a thick layer of fog formed across the Stateline. It became dense enough in a to the point where visibility dropped below a half mile in a few locations. Fortunately, we are starting to improvement now that the fog is beginning to lift. You may still encounter areas of patchy fog if you set to drive during the mid-late morning hours. If you do see any fog, drive with caution, and use those low beam headlights.
Once this fog fully burns off, leftover cloud cover will clear up a bit leading to some sunshine for the afternoon. Following the warm frontal passage this morning, strong southwesterly winds at the surface, along with the additional sunshine, will help temperatures climb into the low to mid 70s for highs. This afternoon will provide a good amount of time to head outside, grab some fresh air, and enjoy the spring-like heat. The one component that we need to keep our eyes peeled for is the potential for strong to severe storms late this afternoon and into this evening.
An approaching cold front diving in from the northwest is going to be the main feature that brings the potential for severe weather. As of 8 AM this morning, the Storm Prediction Center has left a majority of the Stateline under a marginal risk (level 1 of 5) for severe weather. They also expanded the slight risk (level 2 of 5) a bit westward to include southeastern Dekalb county. This morning’s warm front is going to help pull in a good amount of moisture and instability ahead of the system’s cold front. In other words, the environment over our region is going to be conducive for severe storms later today. There’s just one component that is going to severely limit our potential for strong storms is something we know as “the cap”.
The good old cap, a storm chasers nightmare. Typically in a normal atmosphere, temperature decreases with height. But sometimes, you have a warm layer of air that situates itself in the low-levels (normally around 850 mb or ~5,000 ft). This layer of warm air acts as a blocker that stops moisture from rising higher up in the atmosphere, and limits any thunderstorm from fully maturing. Model soundings did show a strong cap in the low-levels this evening. The timeline for the severe potential begins at 5PM and will end around 10PM. As the cold front slides through the region, it all comes down to if the storms can overcome the cap. If they do, any storm that does end up being severe will have the capability of producing large hail and damaging winds. With that in mind, bee sure to keep updated with the forecast, and to have multiple ways to get watches and warnings.