Thunderstorms Monday were very slow to develop

I'm sure after the severe weather events that occurred across the middle of the county over the weekend and our own severe weather Sunday night, everyone was a little more 'aware' of the severe potential going into Monday afternoon.  However, storms were really lacking through much of the day and when they finally did arrive the strongest storms missed us to the east and south.  In the end, this left some wondering exactly what happened.

In order to answer that we need to look at what's occurring above our heads in the atmosphere.  The day started off a little cloudy with a few showers but those were quick to leave mid-morning.  While the dynamics of possible severe weather were there in the atmosphere we were also lacking a few things as well. 

Each and every day, morning and evening, National Weather Service offices across the U.S. will launch upper air balloons to try and gain a better idea of what's occurring aloft.  Attached at the bottom is a little data box - radiosonde-  that records temperature, dew point, wind speed/direction, humidity, etc.  This data is then feed into our weather forecast models (along with many other calculations, buoy data, surface data, etc) to try and accurately forecast the weather.  If there is the potential for severe weather, or in the winter time a big snow storm, the National Weather Service will do what they call a 'special' upper air balloon launch which is usually done around Noon or 1pm.  Just like with the morning and evening launches the data from the special launch is fed directly into weather forecast models.  It also allows forecasters to see just how potentially unstable the atmosphere may be getting.  For example, the afternoon sounding out of Oklahoma City showed an incredible amount of instability in the atmosphere which in turn fueled the storms, and tornadoes, across the state. 

The closest NWS office to the N. IL that conducts upper air launches is the Quad Cities forecast office in Davenport, IA.  They, too, launched a special upper air balloon but it showed a completely different type of atmosphere in place across the Stateline.  The image on the left is their 1pm launch.  First, a couple of things to note on the image - the green line indicates dew point temperature, the red line is temperature, the blue line is a 'theoretical' parcel of air rising through the atmosphere.  Wind speed and direction through the atmosphere are found on the right hand side with height on the left and at the bottom is temperature (°C).  At a first glance there are a couple things that stand out...one would be the drier air in place.  The green and red lines are a decent distance apart from each other with the dew point actually dropping slightly with height.  The second would be the slight inversion, or cap, between 850 mb and 900 mb.  A cap, while not too significant on there, will act as a lid on the atmosphere keeping storms from developing.  This is found when there's warmer air above the surface.  Also, there doesn't appear to be much instability in the air despite all the sunshine we had.  Those few factors along with others really didn't make the atmosphere ideal for thunderstorm development.  In order to get storms in the Stateline we had to wait until forcing within the atmosphere, what caused the storms in the central Plains, to arrive and that wasn't until 9pm/10pm Monday night.  There were, however, strong storms just to our south and east towards central Illinois and Chicago but this was tied to better moisture and lift in the atmosphere.  Another indicator of the atmosphere lacking instability would be to look at the height of the cumulus clouds in the sky.  If they don't seem to be growing much in height it's likely due to a little more of a stable atmosphere.  However, if you notice that they continue to grow taller and taller you're likely going to get rain and possibly storms soon. 

Looking at today you may notice a little more humidity in the atmosphere due to the recent rainfall and those puffy, cotton ball type, clouds growing some in height.  With the humidity levels (dew point values) up slightly from yesterday we could see a few storms develop this afternoon as a weak front pushes in from the west.  Severe threat does remain limited for this afternoon.