Freeze Warnings, Warming Coming…And Why Do Hot Air Balloons Rise? (Pt 2)

Now that fall has officially begun, it looks like we will be on a slow boat to some warming temperatures. A stable ridge of high pressure is building back into the west coast, and we should have a steady rise in temperatures (low 60s Saturday, 70s by Monday, and the 80s by mid-week. While the days are warming, Saturday morning will be cold with widespread frosts and freezes, and a Freeze Warning is in effect until 9 am. Sunday morning could also have some freezes in the region as well.

Balloon races

So why does hot air rise? First, it’s better to describe hot air as being less dense instead of lighter. It’s a subtle distinction, but an important one. When one substance is less dense than its liquid or gaseous surroundings, that substance will “float”, just like Styrofoam (less dense) floats on water, while iron (more dense) sinks. So what makes hot air less dense?

Air Density

Think of it this way. The density of the air is determined by the number of molecules in any unit volume. Temperature is a measure of the average kinetic energy of the air. In simple terms, that means that hot air molecules are moving faster than cold ones. The faster the air molecules are moving, the more often they are bouncing off each other, and the further apart they become on average. If all the molecules are further apart, there are less of them in any given volume, ergo it is less dense. And your balloon floats. Another way to put it is to say the balloon is “buoyant”.

 

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Frigid End to Summer….And Why Do Hot Air Balloons Rise? (Pt 1)

Summer officially ends Friday afternoon, and it doesn’t appear that it is putting up much of a fight. Rain and snow showers (snow level down to the upper foothills) could last into Friday morning, but things will dry out as we go through the day, and mostly sunny conditions will carry us through the weekend. A high temperature near 60 on Friday will warm to the mid-60s Saturday and will likely reach the 70s Sunday or Monday. Summer may try and make a comeback late next week, with a return to the low 80s possible.

Balloon races

I don’t know how many of you had the chance to get over to Rancho San Rafael Park for the Great Reno Balloon Races earlier this month, but it was pretty spectacular. Images of hot air balloons soaring cause might some to wonder just how the darn things can get off the ground in the first place. Most everybody knows that hot air rises. But why? Well, because it’s lighter than cold air is the “Well…duh!” response. But have you ever wondered why it’s lighter?

Tune in tomorrow for an answer.

 

Summer Goes Out With A Whimper…And Could We Stop A Hurricane?

With some very chilly temperatures and a decent chance of high elevation snow on Thursday, it seems like summer’s last day is giving up without a fight. A second cold front will drop Reno’s high temperature into the upper 50s and will drop the snow level to just above Lake Tahoe. It’s not a particularly wet storm, and once it gets by things should dry up leaving Friday through the weekend dry with temperatures slowly warming back to about 70 by Sunday.

Hurricane-Bomb-Drop

Let’s entertain one more hurricane question, this one from Mary: “This may be a foolish question, but would it be possible to halt a hurricane from forming in its early stages with a squadron of cloud seeding planes or other means, e.g. explosives, just to break it up & disrupt the storm/rotation?”

Wouldn’t that be nice? For time immemorial, mankind has been frustrated by having to live under the old adage, “Everybody talks about the weather, but nobody does anything about it.” And as a result, many interesting proposals have been thrown out for ways to stop hurricanes (and modify the weather in other ways), but none are considered practical and/or effective. We don’t have the means to affect something as large and energetic as a hurricane. The power in a hurricane is so immense that blowing stuff up in them would really amount to spitting in the ocean, as it were.

 

 

Summer’s Exiting…And Can Two Tropical Storms Join Forces? (Conclusion)

Temperatures will continue to fall (no pun intended) as we say goodbye to summer later this week. A cold low pressure center will remain over the Pacific Northwest, sending another cold front through the region Wednesday, kicking up some strong winds and bringing some mainly mountain showers of rain, with some high elevation snow (above major pass level) late Wednesday into Thursday. High temperatures will bottom out in the upper 50s Thursday, and conditions should slowly clear and warm up as we head into the weekend.

Fujiwara 2

A reader wondered if two tropical storms could join and “combine forces.” That’s a good question. That can happen to any type of tropical cyclone. They often start to rotate around each other in something that is called the Fujiwhara effect. Named after Dr. Sakuhei Fujiwhara, he noticed the effect whenever systems of at least tropical storm strength get within about 900 miles of each other. Look at it as something akin to two bodies orbiting each other in space. It can lead to the storms merging and becoming one of catastrophic strength, but more often the larger of the two will tend to become the focal point, with the smaller orbiting around it until it gets drained of its energy.

fujiwhara-1-56a9e1543df78cf772ab3462

 

Getting Chilly…and Can Two Tropical Storms Join Forces? (Pt 1)

While the odds of getting any rainfall are slight, fall weather will definitely be felt from a temperature standpoint. A cold low pressure center is rotating through the Pacific Northwest, bringing a cold front through our region. Winds will remain brisk for the next couple of days, and high temperatures will fall noticeably. Tuesday will stay dry, but will cool to the low 70s, and temperatures will drop further to the low 60s with a slight chance of showers by Thursday. Skies will clear as we go into the weekend and temperatures will rebound to the low 70s by the end of the weekend.

170908-O-N0204-001

After 12 years without a major hurricane landfall, this season unfortunately seems to be making up for lost time. And Irma was closely followed by Jose and Maria, both of which fortunately seem to be turning away from the US mainland, although Maria is definitely threatening some already impacted Caribbean Islands. One reader asked: “With two tropical storms so close together in the Atlantic last week, is it possible for one to catch up with the other and merge to create an even bigger storm? And has that ever happened?” The answer tomorrow.

 

 

Drier Weekend…And A Different Kind of Lightning (Final)

It looks like the weather will clear up for the weekend, if you can ignore the smoke and haze from area fires. A stable ridge of high pressure on Saturday will result in mostly sunny and hazy conditions with temperatures in the upper-80s. The ridge will build over the next couple of days resulting in highs moving back into the 90s. By Monday, and especially Tuesday things destabilize enough to bring afternoon thunderstorms back into the mix.

positive-lightning

As I mentioned yesterday, positive lightning can be much more dangerous than negative (not that negative is anything to sneeze at.) First of all, a positive lightning bolt is generally much longer than a negative one, since it has to reach the top of the cloud instead of the bottom. This alone can add several miles to its length. Because of the greater distance the positive strikes travel, it takes a higher charge to complete the “circuit”, and positive strikes usually carry more current… up to ten times that of standard negative strikes. But what makes them even more deadly is their unpredictability.

Positive lightning strikes can hit more than ten miles away from the thunderstorm, and be literally a “bolt from the blue.” Because of that, the normal precautions that we might take as we hear thunder in the distance may not be there, because the first strike can come long before we would have heard any previous strikes.

To distinguish one type from another, positive lightning usually forks upward from the ground, while negative lightning forks downward from the cloud.

Friday Thunderstorms, Dry Balloon Race Weekend…And A Different Kind of Lightning (Pt 2)

It looks like we might see one more round of thunderstorms Friday before the weekend clears up. Temperatures will cool to the lower 80s as clouds increase and scattered thunderstorms form on the western side of the Silver State. Morning winds should be light enough to allow the launching of the Balloon Race craft through the weekend. A warming trend picks up over the weekend with high temperatures rising to the upper 80s Saturday and the low 90s on Sunday.

Lightning 3

Yesterday I mentioned that most lightning is considered “negative polarity”, but there is “positive” lightning as well. Instead of originating from the negatively charged base of the cloud, positive lightning starts from the positively charged top of the thunderstorm cloud, usually up in the anvil portion. That huge positive charge induces a negative charge from the ground, and the stepped leader flows upward from the ground, instead of the other way around. As it reaches near the top of the anvil, the return stroke hits downward from the top of the cloud.

Lightning positive

Positive polarity lightning often forks upward.

Positive lightning can be much more dangerous than negative (not that negative is anything to sneeze at.) I’ll tell you why tomorrow.

 

Calming Down?…And A Different Kind of Lightning (Pt 1)

Thunderstorm activity will calm down a bit over the next couple of days as the post-cold front flow becomes more stable. We could still see a few scattered afternoon thunderstorms Thursday and Friday, but they should be few and far between. Temperatures will cool to the low to mid-80s, before warming back to the upper 80s and low 90s over the weekend. At this point the weekend looks to be pretty dry with only a few clouds here and there.

雷

I’ve talked a lot about lightning and , and have given a quick and over-simplified explanation of how lightning occurs. Negative charges from the base of thunderstorms clouds induce a positive charge on the ground, and after a “stepped leader” forms out of the clouds, it causes a “return stroke” from the ground once the negatively charged leader gets close enough to the positive charges on the ground. This generally referred to as “negative” lightning, and is the most common kind. But it doesn’t always work that way… lightning can be positive as well.

Tomorrow I’ll tell you how nature sometimes turns the tables on lightning’s polarity.

 

 

Another Round of Thunderstorms…And Why Do We Round Off Temperatures?

A weak southerly flow will continue to bring up a moist and unstable airmass Wednesday creating prime conditions for thunderstorms again. A cooler airmass will also move into the region, dropping the highs to the low 90s Wednesday and the mid to lower 80s for the rest of the work week. There will be just enough heat and moisture around for a slight chance of mainly afternoon thunderstorms through the rest of the week.

thermometer digital

Here’re some reasons we don’t report temperatures to tenths of a degree. To begin with, the temperature around any thermometer probably varies a degree or two within just a few feet. The temperature of the air on the ground on a clear night can be 10 or more degrees cooler than the air at eye level (the approximate height where official temperatures are taken). And even at the same elevation off the ground the temperature can change several degrees in different spots in your yard, not to mention in varying places around town. So what makes the cubic centimeter of air around your thermometer bulb so special? It is only getting a representative sample of all the air at the measuring site. If all that air can vary by more than a degree, it is actually lass accurate to pretend a precision that you can’t reproduce.

And remember: Being more precise doesn’t mean you are being more accurate.

Cooler Temps In Sight…And Why Don’t We Report Temperatures More Accurately? (Pt 2)

After another string of triple digit temperatures, there will be a slow easing off of the heat as more moisture comes up from the south, giving us a few more clouds with scattered afternoon thunderstorms. The high Tuesday will still reach the upper 90s with a slight chance of thunderstorms, and will fall to the lower 90s Wednesday with our best chance of storms then. Temperatures fall off into the 80s for the rest of the week with only a slight chance of storms.

thermometer digital

So if thermometers can measure to tenths of a degree, why don’t we report temperatures to that?  Certainly we could report the temperatures to a more exact scale, instead of rounding off to the nearest degree. But the first question I would ask is “Why?” Can you feel the difference between 75.5 degrees, and 75.6 degrees? I can’t tell the difference between 72 and 75 degrees with any certainty, so will sticking in some decimal places do anything for the practical usage of the temperatures for me? But there are other reasons why rounding is actually just as accurate, and I’ll tell you those tomorrow.