Watch NBC Action News HD for the latest on the Excessive Heat Warning for the area!
I hope everyone found a way to stay cool on a very oppressive day with heat indicies as high as 118 across parts of the area. Air temperatures ranged from the upper 80s in Chillicothe to the upper 90s in Lawrence. Here is a look at some of the high temperatures around the region today followed by the highest recorded dew point.
- Lawrence, KS T=98 D=78
- KCI Airport T=95 D=79
- Olathe JC Executive Airport T=94 D=79
- Knob Noster, MO T=92 D=82
- Chillicothe, MO T=87 D=75
Here is a look at the heat indices across the region at 4 p.m. today. The highest values were right over our immediate viewing area.
Temperatures in the 90s or even low 100s are very common each summer in Kansas City, but the thing that makes this heat wave stand out is the very high dew points and the time of year that they area occurring. Typically soils are drying out this time of year and as a result there is not as much lush vegetation to give off water vapor. The overall wet summer combined with recent heavy rains from the remnants of Dolly have supplied an abundance of soil moisture to continue to supply plants the needed water to grow. The process that plants release water into the atmosphere is called transpiration. This process adds moisture to the air and in turn results in higher dew points.
Here is the definition of Transpiration:
Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. Transpiration is essentially evaporation of water from plant leaves.
When I was growing up in southwest Minnesota dew points around 80 were not that uncommon because of the abundance of moisture that was given off by a thriving corn crop. Outside of the Gulf Coast and coastal locations of the Pacific Northwest some of the highest dew points each year occur in the corn belt of the nation's mid-section.
Below is some other information regarding transpiration that you may find interesting.
Atmospheric factors affecting transpiration
The amount of water that plants transpire varies greatly geographically and over time. There are a number of factors that determine transpiration rates:
- Temperature:Transpiration rates go up as the temperature goes up, especially during the growing season, when the air is warmer due to stronger sunlight and warmer air masses. Higher temperatures cause the plant cells which control the openings (stoma) where water is released to the atmosphere to open, whereas colder temperatures cause the openings to close.
- Relative humidity: As the relative humidity of the air surrounding the plant rises the transpiration rate falls. It is easier for water to evaporate into dryer air than into more saturated air.
- Wind and air movement: Increased movement of the air around a plant will result in a higher transpiration rate. This is somewhat related to the relative humidity of the air, in that as water transpires from a leaf, the water saturates the air surrounding the leaf. If there is no wind, the air around the leaf may not move very much, raising the humidity of the air around the leaf. Wind will move the air around, with the result that the more saturated air close to the leaf is replaced by drier air.
It really is fascinating how much of an impact plant moisture can have on sensible weather conditions, but this is one reason why the dew points have been so high and will likely continue to be for the next several days.
As the dew points remain in the 70s the actual air temperatures will begin to make a run at 100 degrees. I think here in the metro our best chance of hitting 100 will occur on Monday. Olathe or Downtown KC could touch 100 on Sunday, but chances are much better on Monday. Dew points in the 70s and temperatures in the 90s to around 100 will keep the heat index at 105-115, or in the dangerous category.
I know many have heard or seen the heat related safety tips over the years, but if you want to refresh your memory please check out the quick story I posted to the web today.
http://www.nbcactionnews.com/content/weathernews/story.aspx?content_id=f708c75f-feea-42c3-9a18-6535d08d3776
And finally, it's not the heat...but the humidity. Here is a comparison of the air temperature, dew point, and resulting heat index today from Las Vegas and Kansas City.
Las Vegas T=108 D=30 Heat Index=100
Kansas City T=95 D=79 Heat Index=113
Have a great night and try to stay cool!
Jeremy