Colder Weather Next Week…and What Makes Fall Fall? (Final)

As we say goodbye to September we will see a cooling trend settle in, although conditions won’t be too extreme. Sunny weather will move in over the weekend after Friday’s cold front has passed. Saturday’s high temperatures will reach the mid-70s and slide to the low 70s on Sunday. Another stronger cold front will move in to the region the first of next week, dropping highs Monday and Tuesday into the low 60s and upper 50s. The front won’t have much moisture, so showers are going to be limited, but it will bring some cloudiness.

autumnal-equinox-explainer

Yesterday, I gave the astronomical definition of the equinox. From an earthbound perspective, here’s a way to visualize what’s happening. If you extend the equator of the earth out into space, the line traced across the sky is called the celestial equator. During the summer months the sun always appears above (or to the north) this line as it crosses the sky. The path the sun appears to take can be considered the ecliptic. But as summer wanes and fall approaches, the sun drops lower (southward) and eventually crosses the celestial equator, marking the beginning of fall.

 

Advertisements

Temps Top Out Friday…and What Makes Fall Fall? (Pt 1)

While there is a dry cold front coming through the region that will bring us a few clouds and cool us off over the weekend, it doesn’t look like we will see anything but shade out of those clouds. Friday will turn breezy in the afternoon, and high temperatures will top out near 80 degrees with some cloudiness. By the weekend, the clouds should clear out and high temperatures will fall back to the mid-70s, and then continue to slide into the 60s for the first half of the work week. While it won’t be as cool as our last day of summer, it will feel fall-like.

Fall Leaves

I mentioned the last day of summer. For those of you keeping score at home, last Friday at 1:20 pm our time, summer officially ended and fall began. What is so magical about that exact moment? Technically, it is the moment of the autumnal equinox. Or if you prefer an ever geekier definition, it is the moment the ecliptic intersects the celestial equator… the sun having a southerly motion. (When the sun has a northerly motion and crosses the ecliptic, that’s the spring equinox.)

autumnal_equinox

I realize that this may peg the “Huh?” meter for most of you. Tomorrow, I’ll tell you what it all means.

 

Dry End to September…And The End of a Long, Wet Water year.

It looks like September will go out on a seasonably warm not this weekend. A ridge of high pressure will continue to shift to the east over us, peaking on Friday before a dry cold front passes over us, kicking us some strong breezes Friday night. High temperatures under sunny skies Thursday will result in a high in the upper 70s, and should top out around 80 on Friday with a few clouds coming though in the afternoon. Temperatures fall back into the mid-70s with sunny weather returning through the weekend.

tahoe dam1

A lot has been made about this winter, and by any metric, it has truly been historic. This Sunday, we will end the 2016-2017 water year, and the numbers are such as we’ve never seen before. Assuming we don’t get any more rain (a safe assumption), Reno will have recorded a water year total precipitation of 15.95”.  The average is 7.45”. The old record (which we had broken before the winter was even over) was 12.72”. And the story is the same in the mountains. Total average rainfall in the Tahoe basin is just shy of 90”…more than 10” greater than the old record.

 

How Warm Will We Get?…And Just How Does Buoyancy Work? (Final)

A building ridge of high pressure will keep our skies sunny and our temperatures rising through the end of the work week. Winds will be generally light in the morning with an east breeze coming up in the afternoon. High temperatures will rise to the mid-70s Wednesday and should land on the 80 degree mark by Friday before falling back to the lower 70s by Sunday.

duckling

So how does buoyance work? Fluid dynamics insist that the pressure around any submerged body presses in from all sides… and also pushes out from the inside. It’s the difference between these forces that determine whether the object floats, sinks or stays where it is. If an object is lighter than the volume it displaces, the overall force pushing up under it will be greater than that pushing down, and it will move upward.

Buoyancy-force

Tom Ballow, author of the book “The New Science of Flight and Movement”, has another way of looking at it. He explains a floating balloon by saying that gravity is pulling down on both the balloon and the air around it. Since the balloon is less dense, the gravity pulls down less on it, and it rises relative to the air surrounding it.

Not a bad way of looking at it.

 

Seasonably Warm Week…And Just How Does Buoyancy Work? (Pt 1)

After a quick shot of wintry weather to end summer last week, it looks like we will ease back into a seasonably warm early fall pattern for the rest of this week. A broad and stable ridge of high pressure will continue to move onshore giving us sunshine with high temperatures rising from the low 70s Tuesday to near 80 degrees by Friday and through the weekend.

duckling

Last time I mentioned that hot air is buoyant. Buoyancy is a topic that most everybody accepts (if it’s lighter than water, then it floats), but few actually understand the nitty-gritty of how it works. Here’s a simple definition of the effect of buoyancy: When the weight of the balloon (or ship) weighs less than the weight of the displaced fluid (air or water) – the thing “floats.” But the forces that cause this are a little tougher to explain.

It’s a tough subject to describe in this forum, since a detailed explanation involves drawing vector forces, but that’s never stopped me in the past. Tomorrow, I’ll give it a shot.

 

 

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”.

 

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.