An upper level high pressure will remain parked over the central US through the week. This will allow the heat to build across much of the central US today and gradually spread east through the end of the week. Dangerous heat index values of over 100 will occur from North Dakota to Texas and east into Indiana through Alabama.
With surface high pressure dominating the Southern and a part of the Central Plains, temperatures will soar in the upper 90’s to around 100 F today. These temperatures combined with dew points in the 60’s and 70’s will cause heat index values to be in the lower and middle 100’s this afternoon.
There will be two areas of slight reprieve which include the high plains and parts of the central and northern Mississippi River Valley. For the High Plains, dew points in the lower 40’s which will allow relative humidity to fall into the 30% range and less during the mid and late afternoon hours. These lower relative humidity values will allow for the apparent temperature to be lower than the actual temperature as an individual will be able to cool with evaporation. The second area of reprieve will be for locations along and north a warm front extending across South Dakota and into southern Iowa and northern Missouri. Ongoing showers and thunderstorms along this boundary will cool the air. However once the clouds break, temperatures will quickly warm.
The 100 plus heat index values will expand north into the Dakotas and east into Indiana Kentucky, Tennessee and Alabama on Wednesday. Unfortunately even overnight lows will not provide much of a reprieve as they will only drop into the 70’s for most areas.
Thursday and Friday
Sadly little change is in sight as the upper level pattern will remain stagnant through the end of the week allowing the heat to continue to expand. Afternoon highs in the mid 90’s to lower 100’s with heat index values over 100 will be common from the Plains to the Great Lakes/Ohio Valley and Deep South through Friday. With overnight lows in the 70’s, individuals without air condition will have little relief.
Heat Related Watches/Warnings/Advisories
With these high heat index values, the National Weather Service has issued Excessive Heat Warnings, Watches and Heat Advisories and for North and South Dakota, Minnesota and Wisconsin south through Kansas, Missouri, Oklahoma and Texas, to locations as far east as Indiana, Tennessee and Mississippi. Most of these Warnings, Watches and Advisories extend into Friday.
Human Heat Impacts
If you must be outside in the warmest part of the day, drink plenty of fluids. Limit the intake of carbonated beverages and alcohol. Take frequent breaks and if you do start to feel the signs of heat stress or stroke which include heavy sweating, fatigue, low blood pressure, dizziness and muscle cramps, seek medical help. The Mayo Clinic has more information on heat exhaustion.
Livestock Impacts of Heat
Our animals will also fell the stress of the heat especially in since overnight lows will provide little relief. The USDA Livestock Heat Stress Index for Wednesday (7/20/16) shows Danger to Emergency conditions for the entire Central US and most of the Mississippi Valley and Deep South.
Livestock owners are encouraged to check on their cattle and other animals through this warm stretch to ensure that they have fresh and if possible cool water as well as shade. If livestock are in pens/close proximity provide fans to increase circulation and for dairy operators ensure that your misting systems are working In addition, if possible delay feeding until this evening/tonight during the cooler part of the day.
The Missouri Extension office has more tips on how to help cattle manage the heat.
The team at WxIntegrations will continue to provide relevant information and resources to help you better understand and prepare by incorporating weather impacts into your planning and response.