Gwinnetians woke to almost two thirds of an inch of rain on Sunday morning, ending Atlanta’s driest start to the month of May since recordkeeping began in 1878. Through Friday the 13th, Hartsfield Airport had recorded only a trace of rainfall for the month, while here in Lawrenceville, I recorded .04 of an inch of precipitation. According to the National Weather Service, the previous record was set in 1932, when .01 inches of rain fell.

The rain will also mean a break in the above normal temperatures recorded last week. While none of the region’s official temperature readings broke 90 degrees, Charlie Brown Field saw 89 on Thursday and Friday, while the temperature topped out here at 87 degrees on Thursday. These 5 to 8 degree above normal temperatures are likely the warmest weather we’ll see for the rest of the month.

Clearing skies Sunday afternoon will usher in pleasant weather to start the week, with normal high temperatures around the 80 degree mark, and lows in the 50s. A chance of rain returns on Thursday, then by the weekend, we may see cooler than normal temperatures, with highs in the mid 70s. Additional storms are possible on the 24th and 25th, and again on Memorial Day weekend.

This week, I added three additional sensors to my weather station — soil temperature, soil moisture, and leaf wetness. You can see the readings for these sensors on the weather details page, and graphs on the weather charts page.

While primarily used by farmers monitoring crop growing conditions and the need for irrigation, the data produced by these sensors can also be useful for homeowners. The soil temperature, measured six inches below the ground, can be used as a guide for when to plant annuals. Leaf wetness uses a scale of 0 through 15 to measure water on leaves and foliage, with 0 meaning completely dry, and 15 meaning completely wet.

Soil moisture is calculated by measuring the electrical resistance in centibars between two probes set underground. Because water is an electrical conductor, lower resistance indicates a greater amount of soil moisture. A soil moisture reading below 20 indicates extremely wet soils, a range between 40 and 70 indicates that the ground is dry enough to water, and readings above this indicate extremely dry conditions.

Of course, the moisture readings show what’s going on in my yard - when I turn on the sprinklers, soil moisture will go up for me, but not for areas that didn’t receive the benefit of my watering. However, the readings will give you some idea of how quickly the ground is drying out, and whether you need to water. If you haven’t been watering and see a soil moisture reading in the 50s, it might be time to think about pulling out the hoses.

The relatively dry weather over the past two weeks got me itching to turn on the sprinkler system and water the lawn. Keeping in mind the gardening advice that lawns should receive an inch of water a week, it would seem to make sense to water, since we haven’t had a one week period with an inch of rain since March.

I decided to use a soil moisture tester I have before watering. It showed that 3 or 4 inches below the surface, there was actually plenty of moisture — and no need to water.

We have abundant soil moisture, despite the lack of recent rain, for several reasons: First, we had plenty of rain during the last week of March, and much of that rain is still in the ground. Trees draw plenty of water from the ground once they are fully leafed out, but not as much when they are bare. Finally, our cooler than normal temperatures have kept soil temperatures around 60 degrees, by my records, about 6 degrees cooler than what it’s been on May 7th over the last few years. The cooler temperatures also tend to keep moisture in the soil.

Last week’s cooler than normal temperatures are going to be replaced by normal to slightly warmer than normal weather during the upcoming week. The first week of May saw average temperatures about 7 degrees cooler than normal, accented by lows in the 40s. Lows this week will be about 15 degrees warmer than last.

High pressure to our east will bring winds from the southwest, bringing in more humidity as well, adding to the impression that things are much warmer than they have been so far this season. This high pressure will also keep the effects of a low over the upper Midwest away from Georgia, at least through Monday. Midweek, things are a bit more unsettled, as there is a chance of rain Tuesday and Wednesday, and again towards the weekend. For the week of the 15th, we’re likely to see temperatures returning to a more normal range, with highs in the upper 70s, and about a normal chance of precipitation.

If temperatures warm as expected next week, and if we are able to avoid rain, it might be time to water by next weekend, but I’ll use my moisture tester to make sure.