Very Hot…And The Ins and Outs of Making Rain (Pt. 2)

It’s a pretty straightforward forecast…mostly sunny skies with mid-summer (plus) temperatures through the next week. Saturday will continue the dry and stable pattern with valley temperatures reaching the 90s. Sunday could bring an isolated mountain thunderstorm south of Lake Tahoe in the Sierra, and a few afternoon clouds could drift into the region as a result. Temperatures peak on Tuesday at somewhere around 100 degrees.

water cycle1

So how do you get water out of the ocean into the clouds? It’s all part of the water cycle. While we know that water (liquid) falls from the skies out of clouds, how does it get up there to begin with? Let’s start with liquid water in the ocean. On a molecular level, water can’t be transported into the air unless it turns into vapor, which is essentially the release of individual water molecules to float free in the atmosphere. If you heat liquid water, you increase the rate those water vapor molecules break away from the liquid ones. But clouds aren’t made up of water vapor. Water vapor is invisible… clouds aren’t. So in order to turn the water vapor back into liquid, you have to cool it. That’s the condensation part of the water cycle. But how do you cool water vapor in nature?

cloud condensation

The laws of physics state that if you reduce the pressure of a gas, it will get colder. The most natural way to reduce the pressure of a gas (air) is to take a chunk of it from a lower elevation and raise it to a higher one. As you probably already know, as you go up in elevation, the air pressure drops. That’s why your ears pop as you drive over the mountains. So if you lift air upward, it will expand and cool. With more lifting, more condensation occurs, and the little itty-bitty drops that make up a cloud and can remain suspended in the air currents become too large and heavy to stay up there, and you get rain.

I realize this may seem elementary to many of you, but it is a simple way of saying rising air means a chance of rain, while falling air equates with sunshine.


First 100s?…And The Ins and Outs of Making Rain (Pt. 1)

After our little dalliance with some wintry weather to start the week, it looks like we will start the next with a realistic shot at triple digit temperatures. A very strong and warm ridge of high pressure will boost temperatures into the low 90s on Friday, the mid-90s by Sunday, and a realistic shot at 100 by Monday and Tuesday. The overall flow pattern is fairly stable, so even with these very warm temperatures it’s not likely that we will see thunderstorms here in Reno, although an isolated thunderstorm in the mountains south of Lake Tahoe could be possible by the end of the weekend.

Water Vapor

When we last met I mentioned that precipitation and storms happen when air moves upward. Now while what I wrote is technically correct, it still didn’t answer why rising air should make a difference. To fully explain, you first need to look at water. It can exist in three forms: Vapor, liquid and solid (ice). For our purposes, we’ll lump liquid and solid together. The trick is getting water from liquid, to vapor, and back to liquid. Tomorrow, I’ll begin that journey.


Heating Up…And A Curious Question About Pressure (Pt. 2)

We are going from almost winter-like straight to mid-summer in the space of a few days. A ridge of high pressure will strengthen across the west coast, pumping our high temperatures into the 80s Wednesday in the valleys, and continuing into the 90s by Friday. By the first of next week, some of the warmer communities could see near triple-digit temperatures. Even with the heat, the flow pattern remains stable enough to keep the chance of thunderstorms at a minimum.

High and low

Bob, a golfer from Las Vegas, wondered why high pressure brought good golfing weather while low pressure brought the opposite. The answer isn’t as straightforward as I would like, but in a nutshell, it has to do with what highs and lows do with vertical movement of air. Clouds, and thus rain and other storminess happen when moist air is lifted upward. Lows at the surface cause air to converge, and up is the only place that air can go. So to over-simplify things: lows cause rising air, which in turn causes rain. Conversely, highs do just the opposite, causing air to descend, clouds to clear, and six-irons to travel straighter.



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Snow Monday, 90s Friday: Must Be Northern Nevada…And A Curious Question About Pressure.

Snow on Monday…90s by Friday…yep, we must be in northern Nevada. As quick as the warm temperatures disappeared into the rain and snow, they will come storming back, without the storms. The cold low pressure center will move out of the Great Basin on Tuesday, and a ridge of high pressure will quickly build back in, bringing sunny skies and much warmer temperatures. Tuesday’s high will pop back up into the mid-70s, Wednesday and Thursday will see a return to the 80s, and Friday will bring 90s that should stick around through the rest of the weekend.


Bob’s from Las Vegas, but comes to our area for about three weeks a year in order to play golf. He said he enjoys this column (whoda thunk?), and that he has lots of questions, but would only trouble me with one. “This high pressure-low pressure thing has me confused. While I associate high pressure with good golfing weather and visa-versa, why does it work that way? Does the low pressure suck out all the good weather, or does the high pressure simply force all the bad weather somewhere else to misbehave?”

Regardless of the answer, I love the way he looks at weather. I’ll answer tomorrow.


Cold Weekend, Warmer Next…And How Much Bigger is a 7.0 Earthquake Than a 6.0?

The first weekend of summer vacation will be anything but summer-ish, but warmer conditions will be returning to the region next week. A cold low pressure center will move slowly though the Pacific Northwest this weekend, keeping winds high and temperatures low. Saturday’s high will drop to the upper 60s, and then on Sunday that will fall to the upper 50s, with a chance of valley rain and mountain snow continuing into Monday morning. Skies will clear out by Tuesday, and temperatures will warm back up to the 70s on Tuesday and then climb into the 80s for the rest of the week.


We had a small earthquake (3.9) hit the Topaz Lake area earlier this week. Bob wondered: “How far away will a 7.0 earthquake affect, versus a 6.0 and 5.0? Thanks for any input you have.”

It’s hard to put into real precise terms, because the distance felt depends on several factors, including direction of the fault movement and the rock it is passing through, as well as the depth of the hypocenter and the surrounding geology. And the magnitude of an earthquake isn’t a measure of how far away it will be felt.


Loma Prieta Earthquake Damage, 1989

It also depends on how you define “affected.” The Loma Prieta (a 6.9- 7.1 quake, depending on measurement type) in 1989 centered in the San Francisco area could be felt by some people over here in Reno, but we weren’t really affected. But a 7.0 quake can cause damage 100-150 miles away. The distance shrinks very rapidly as the magnitude drops.

But can an earthquake far away affect the tectonics (earthquake potential) in another area? That’s another tough question. There’s no way to say for sure if the 6.0 earthquake that hit the Wells area back in late February of 2008 had any effect on the earthquake swarm in NW Reno which started a week later. It’s not likely that it did, but there’s no way to say for sure.

Earthquake Energy Chart

But here’s another way to compare one earthquake to another of differing magnitudes: A 7.0 earthquake releases about 30 times the energy than a 6.0 quake, which in turn releases 30 times the energy of the 5.0 earthquake. So a 7.0 earthquake has nearly 1,000 times the energy release that a 5.0 quake has.



Cold Start to Summer Vacation…And The Difference Between Isolated and Scattered

It somehow seems ironically appropriate that the first weekend of summer vacation for Washoe County students will be the chilliest we have seen in nearly a month. A low pressure center will send its first cold front through the region early Friday, dropping our highs to about 70 on Friday and Saturday. A second colder front moves in Sunday, bringing a chance of valley rain and high mountain snow, resulting in a Reno High of only about 60. Monday stays chilly but things will clear out and warm back up to seasonable levels near 80 by midweek.


Donna asks: “Can you explain to me the difference in “Isolated” Thunderstorms and “Scattered” Thunderstorms in the weather forecasts?  I know what the 2 words mean but not how they apply to WHERE thunderstorms are expected to appear.”

Actually, neither implies where they might occur, it only implies how likely it is you will see one. Isolated means you have about a 10-15% chance of getting under one, whereas scattered means about 20-50% of the region will have a thunderstorm. In addition, scattered suggests there will be several groups of showers going on at the same time, whereas isolated showers tend to be loners, with no or few neighbors.

High Fire Danger and Cooler Temperatures…And the Downside of Swamp Coolers

We have some big changes coming our way weather-wise. A cold front will move into the region Thursday, kicking up some strong winds (and likely kicking off another Red Flag Fire Warning). Here in the valley, the rain shadow will probably keep most of the rain from the system up in the mountains, but a little spillover on the west side of the valley is a slight possibility. Temperatures will fall to the mid-70s Thursday, and will struggle to get to 70 Friday and Saturday. Another cold shot of air moves in Sunday, dropping our temperatures further into the low 60s. The skies clear out by the end of the weekend, and sunshine returns next week with a warming trend.

avaporative cooler physics

We’ve been talking about the benefits of swamp coolers, but there are some drawbacks. Because they do move a lot of air, some may find them a little too drafty for their likes. If they are in-window units, they can be noisier than forced air systems. And if you really want them to run at full efficiency, you do need to do some periodic maintenance, since the minerals in your water will precipitate out on the pads, and they will need to be cleaned, replaced or otherwise treated.

Swamp cooler 1

All in all, I’m cheap enough to overlook their shortcomings.


Cooling Down…And Why I Like Swamp Coolers

We have reached the peak of our temperature curve for the next week, and as we head into the second half of the week, we will see a steady downhill slide to our high temperatures, culminating in a 20+ degree drop and a chance of showers by Friday.

For the short term, Wednesday will still be mostly sunny and warm, with a high temperature in the upper 80s. A cold front begins a slow transit across California Thursday, kicking up some gusty winds and dropping our high temperature to the upper 70s. By Friday, even though the rain shadow will keep most of the rain up in the mountains, we do have a slight chance of rain showers here in Reno and our high will barely make 70. The weekend dries up, but will stay cool with highs in the upper 60s.

Swamp cooler 1

If it isn’t obvious by this time, I’m a big fan of using swamp coolers in this part of the country. Besides the obvious cost savings (in addition to the power savings, they probably average less than a fifth of the cost initially), there are some other nice benefits. They move a higher volume of air and are designed to flush out the atmosphere in your home instead of just recycling stale air, so they may be helpful preventing summertime colds and flus. It also adds a little moisture to our desert-dry air, which is helpful to some who suffer from sinus irritation.

Hot Start, Cool Finish…and Let’s Talk Swamp Coolers

We are going to start the week off on a pretty hot note, but those temperatures will peak on Tuesday and will start a slow slide before bottoming out on Friday and Saturday. Look for highs to reach the low 90s in Reno on Tuesday with sunny skies. A sunny Wednesday follows with highs dropping into the upper 80s. A cold front starts to move onshore Thursday bringing some clouds, wind and cooling us to the upper 70s. The front passes over us on Friday, and scattered showers and/or thunderstorms come with it, with high temperatures falling to the upper 60s. The weekend dries up, but stays cool.

Swamp cooler 1

These warmer temperatures have many turning their swamp (evaporative) coolers back on. Now that we are in June it becomes less likely that we will get any freezes hard enough to do any damage to the units. The only downside is it could still get cool enough at night so that the house may get chilly at night as the cold air bleeds in through the open vents. But if you don’t mind that, it’s probably a good time to fire them up.

There are lots of areas across the country that get pretty hot where you would never find a swamp cooler. That’s because you also need low humidity in order for the physics to work out. A swamp cooler works because of the heat of vaporization. In order for liquid water to evaporate, it needs to take in energy to break the intermolecular attractions between water molecules. So liquid water absorbs heat from the air as it evaporates, cooling the air. A simple design allows swamp coolers to take advantage of this.

avaporative cooler physics

It’s basically a large box with three slotted air intakes, and one exhaust vent which blows into your house. A small water pump feeds a slotted trough above absorptive mats which cover the air intakes. Water trickles down through the mats, which are permeable enough to allow air to be drawn through. A simple squirrel cage fan draws the hot (dry) air through the soaked mats, evaporating the water and cooling the air which is then blown into your house. They are extremely economical, using about 10% of the electricity of a standard AC unit, and can make a house comfortable even in triple digit outside temperatures.




Warm and Windy Weekend…And Why Do Clouds Stick Together? (Final)

Temperatures will remain high on Saturday as the west coast ridge of high pressure stays put. A few clouds will likely run into the region Saturday afternoon as a very weak low bumps up against the ridge from the southwest, but high temperatures will approach the 90 degree mark before backing off into the low 80s on Sunday and Monday. The ridge strengthens by midweek sending high temperatures back into the upper 80s.

Sierra Wave 1

We’ve been talking about how clouds form. The famous “Sierra Wave” (or flying saucer shaped) cloud is always forming cloud on the upwind side, and evaporating (disappearing) on the downwind side. Think of a standing wave that forms on a stream that flows over a rock. The wave itself seems to be “standing still.” But it is always utilizing “new water,” that only stays in the wave itself for a very brief time. To the eye on the ground, a Sierra Wave cloud seems to be motionless. But each water droplet inside is generally zipping through the cloud at over 35 miles per hour.

So in a nutshell, it’s not the water that is “sticking together”, but rather the physical processes of cloud formation that is contained in a definable volume.

Of course, it’s always fun when those physical processes end up looking like a UFO.