Severe Storms & Measuring the Humidity

What a last week and half of June when it came to severe weather in the Badger State!  All in all during that span of time there were 7 days in a row with severe weather watches or warnings and as you can see below, plenty of reports of storms producing wind damage, hail and tornadoes.  Fortunately for us in North Central Wisconsin, the worst of the weather included just 3 reports of significant wind damage from downed trees, power lines and one instance of a boat that was apparently turned on its side.  Compare that to tornadoes that ranged in scale from EF0 to EF2 in nature across parts of southern Wisconsin.

The official tornado count for the year in the Badger State currently stands at 15 as of July 1st, which can be found on the
NWS Green Bay website.  So at this point we are just 6 short of the average number of tornadoes for Wisconsin in a year, which is 21.  As you'll note on the NWS Green Bay page, June is typically the most active month for tornadoes with approximately 6 on average, while July is right behind with about 5 in an average year.  The past several days have featured a nice break from the wet weather, however the July 4th holiday weekend could end with a bang on Sunday the 4th as a cold front slowly slides in our direction.

Another aspect of summer when it comes to the storms and the heat, is the humidity.  Yes you hear us talk on occasion how the dew point readings are on the rise and will make it feel muggy or oppressive outside.  But what exactly is the dew point?  The definition is the temperature at which the air would have to cool to for saturation to occur.  Simply put, if the air temperature dips to 65 and the dew point is also 65, then dew would form on the grass, and also odds would be good that fog would materialize.  Also if the dew point is within a few degrees of the air temperature, any rain on the radar is likely to lead to some wet times.  In the cold weather months, we usually have to wait for the air temperature to drop closer to the dew point before those flakes of snow or other frozen precipitation make it to the ground, since the air tends to be a lot drier.  Think of how much more static electricity you encounter during the winter.  In the summer, warmer and more moist air tends to get transported up in our direction from the Gulf of Mexico and thus there are a number of days when the dew point climbs from the comfy range in the 50s to the 60s and even 70s.  Check out the graphic below which spells it all out.

Every once in a while, we will hear from folks that would rather us focus on the relative humidity value instead of the dew point. It is true that you calculate the relative humidity by taking into account the air temperature and dew point temperature. Certainly when we show current conditions in Wausau or in other local spots, we include all of this data along with the winds and barometric pressure.  However the relatively humidity does not give you a good idea of how humid it feels on a summer day.  Here's a couple cases in point. 

1.  It is a summer day in July with the temperature in Wausau at 89 degrees and a relative humidity of 50%.  Other than being rather warm, doesn't sound so bad, right?

2. It's still summer in July and a couple days later the mercury in Wausau is sitting at 72 degrees with a relative humidity of 45%.  Certainly not a huge difference in the humidity and yes I know the temperature is lower, but how humid would it feel outside then in comparison?

Had enough time to think about it?  Well here's the answer to the above questions.  In the first scenario (1.) the dew point would be at 68 degrees and needless to say you would be grateful to spend time in an air conditioned location, because it would be downright oppressive.  In the second case (2.), the dew point is checking in at 50 degrees, which as you'll note from the chart above is by far in the comfortable range.  So sunny and 72 on that July day would be just about perfect. 

For the complete mathematical breakdown of how the relative humidity and dew point are determined, check out this link

Enjoy the holiday weekend and stay safe!

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