Clouds have finally moved into the region after a weak offshore low helps steer up a moist and unstable flow up from the south. Record high temperatures will continue on Saturday, although the earlier appearance of clouds on Sunday might crimp that back a bit into the upper-90s. The odds of those clouds turning into showers or thunderstorms is about 20% through Tuesday, and those odds increase to about one in three for the second half of next week. One of the big concerns for the next week is the chance of seeing dry lightning, as many of the thunderstorms that do develop could form without producing much if any precipitation.

So what’s a better way to cool your house, a swamp cooler or a conventional Air Conditioner? As with most things, it all depends on what you are looking for. The air coming out of a standard air conditioner is colder than that out of a swamp cooler, so you need to move less air to get the same amount of cooling in your house, and you are less likely to feel the “draft” that a swamp cooler can give you. And since the swamp cooler works by evaporating water, the air out of a standard AC unit is much drier… a benefit to some.

But the swamp coolers have a lot going for them. First off, in our dry climate, they are extremely efficient. Because the only electricity needed is to run a fan and a small water pump, they cost about a tenth as much to operate as a standard unit, which spends most of its juice running compressors. Swamp coolers also do a pretty good job of flushing out stale air inside your house, and they add a little moisture to the air, but not so much as to create any mold problems if you keep a window open when in use. And since the air is drawn through moist pads, the water takes most of the pollen and dust out of the air.

While swamp coolers are a perfectly viable (and in my humble opinion, preferable) option here in Nevada, you wouldn’t want to try and use them in, say, Houston. Since swamp coolers cool by utilizing the heat taken out of the air to evaporate water, it stands to reason that there will be less cooling if there is less evaporation. In areas of high humidity, when the air is nearly saturated, there is little impetus for liquid to turn to vapor, and swamp coolers just pump hot, muggy air into your houses.

So how would you know whether they could work where you are? While there’s no hard and fast rule, it’s good to keep in mind the air coming out of a swamp cooler can be no cooler than what is known as the “wet bulb” temperature. The wet bulb is a measurement obtained by wrapping a wet cloth around the bulb of a mercury thermometer, and swinging it around in a device called a “sling psychrometer.” By measuring the temperature drop (due to evaporative cooling) from ambient temperature, the psychrometer can be used to calculate the dew point. If you know the dew point and you know the outside air temperature, you can estimate the temperature of the air coming out of a swamp cooler (the wet bulb temperature) by splitting the difference between the two.

Stay cool!