Ag Weather Update

Matt Dixon, Meteorologist, UK Ag Weather Center

Updated July 20, 2021

Past Conditions

As a meteorologist, I’ve enjoyed the past couple days, which have given me a break from an active weather pattern. Just last week (data below), the state averaged another 1.5 inches behind multiple rounds of showers and storms. Those storms were capable of producing very heavy rain during a short period of time, which led to some localized flooding. It was the third straight week with above-normal average rainfall (chart below), marking only the second time that has happened in 2021.

We started off the growing season with fairly dry weather in place, but that trend has gone in the opposite direction for the summer months. Since July 1, Kentucky has averaged 4.78 inches, which is over two inches above normal for that time span. Just to put the rain into perspective, normal rainfall for the month of July in Kentucky is 4.86 inches.

Rainfall Departures

Data for the Past 7 Days

7-Day Observed Precipitation

Forecast

We had a dry start to the workweek and, for the most part, that will continue through Thursday. If you need to spray fungicides or make another cutting of hay, the window is now. Even moving forward, models don’t predict much rain through the weekend. Isolated to scattered chances enter back into the picture starting on Friday, but once again, I believe most will stay dry. This will be more of the diurnal activity with shower and storm coverage peaking during the afternoon and evening hours and then tapering overnight. The lack in rainfall is supported by the forecast 7-day rainfall map below from the Weather Prediction Center, which shows most of the area staying under a half-inch for the week.

Heat and humidity stay with us during the week, increasing into the upcoming weekend. Models show that temperatures across Western Kentucky may be in the middle 90s again late in the week. The heat will keep the livestock heat stress index in the “danger” category during the afternoon and evening hours. While confidence isn’t particularly high, outlooks hint that above normal temperatures and below normal precipitation will be the trend through the end of July and early stages of August.

Read the Kentucky Ag Weather Synopsis

Relative Humidity and Dewpoint –

What's The Difference?

I get asked the difference between relative humidity and dewpoint frequently. Both provide a perception of how we feel at any particular time of the year (most notably during the summer months), but they are different.

Dewpoint is essentially a measure of how much moisture is in the air. When dewpoints rise into the middle 60s and even into the low 70s (what we typically see over the summer), it starts to feel quite sticky and humid. Most of this higher moisture is pumped into the Bluegrass State on a southerly flow from the Gulf of Mexico. When dewpoints go in the opposite direction, it feels much more comfortable. You may have noticed this change over the past couple days as winds have shifted to the north-northeast and ushered some drier air into the region from Canada, bringing a more refreshing feel to the air.

Relative humidity, on the other hand, is a measure of saturation. How close is the air to becoming saturated? Once again, relative humidity tells us whether it is comfortable outside. Typically, the closer the dew point and air temperatures reading, the higher the relative humidity. When they diverge, we see relative humidity readings get lower. If they get low enough (typically less than 30%), the risk of wildfire rises.

Below is a look at various relative humidity/dewpoint levels and the varying human perceptions. In the end, dewpoint gives you a clearer idea of how humid or dry it feels outside.