Summer humidity returns to Minnesota this week

(KMSP) - For the first time in 2018, it’s going to be HUMID. With a predominantly southerly flow at nearly every level of the atmosphere, not only will temperatures rise significantly, but so will humidity levels.

So far this month, we’ve been more than six degrees above average. Even though we’ve dabbled with some really warm days and dabbled with what felt like, some pretty significant humidity, it’s just nothing compared to what is on the horizon. We have just scratched the surface at how hot and humid Minnesota can get in the warm season.

It has certainly felt warm at times this month, and already felt humid at times, but that’s mostly because we just aren’t used to it yet.  It’s like comparing a 60 degree day in March to a 60 degree day in September.  On paper, they are the same, but as we all know, we’d be singing praises and wearing shorts in March, but bundled up in pants and a hoodie in September.  Temperature and humidity are entirely relative.

To be as consistent as we can, and take most of the relativity out of the equation, we have something called the dewpoint. The dewpoint is a standardized number that shows us how much moisture is in the atmosphere. The higher the number, the more moisture can be found in the air and generally the more uncomfortable it becomes.

While there is always a dewpoint number, we really don’t begin to “notice” moisture in the air until we get dewpoints into the 50s. That’s when you can begin comparing one day to the next on what it actually feels like. For example, you may have a dewpoint of 25 degrees one day and 45 degrees the next, but you’re not really going to notice because even though the level of moisture in the atmosphere went up, it wasn’t high enough in either instance to really “feel”. But things change when your dewpoints get higher. In the middle of the summer, dewpoints in the 50s seem comfortable, often times because we seldom see levels this low. But in the spring, dewpoints in the 50s actually feels a little humid. Again, much of weather is on relative terms. These 50 degree dewpoints that we have experienced so far this season seem humid for us right now, but not on the grand scale of summer.

What’s headed in our direction is far more humid. On Monday morning, dewpoints were in the very comfortable 40s, but rising to the 50s by the afternoon. We will then continue the steady climb into the low 60s on Wednesday, considered to be humid, and then mid to upper 60s Thursday and Friday which is considered very humid.

When you get dewpoints into the 70s, it’s considered to be a tropical air mass, or something you would experience in the middle of summer in someplace like Florida or the Caribbean.  But often times, that’s as far as the scale goes. Unlike temperatures, which in theory can go well over 120 degrees, dewpoints can’t get much passed 75 on any more than rare cases. Even on the most humid day in the summer, the dewpoint rarely gets passed the low 70s in the metro. The all-time record highest dewpoint in the metro was back in the summer of 2010, when the Twin Cities reached an earth shattering 84-degree dewpoint. Combine that with afternoon temperatures in the mid 90s, and the heat index was the highest I had ever seen in the Twin Cities at 126 degrees.

The world record highest dewpoint was actually set just last year in Kuwait. While it’s in the very dry Middle East, it’s position right up against the Persian Gulf can give it some of the most extreme humidity in the world. The dewpoint skyrocketed passed 90 degrees for the first time ever recorded, with a dewpoint of 92 and a heat index of a skin melting 165 degrees.

At least it won’t be that hot around here, at least not yet.