Mild Start, Stormy Finish To the Week… And Just What Is A Rain Shadow?



We have a few nice mild days of weather this week before the pattern begins to shift back into a more active one. For Tuesday and Wednesday, high temperatures will warm to near seasonable levels, and while we will have a few clouds that will drift in and out of the area, conditions will stay dry. By late Wednesday, the next storm front comes through the region, although at this time it looks pretty weak. A slight chance of valley rain and mountain snow Thursday through early Saturday will take a short break Saturday afternoon. Then a series of potentially stronger storms start to move into the region Sunday into Monday.

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I talk about the “rain shadow” a lot around here… not surprising since we are on the lee side of a major mountain range. If you have ever wondered why we are in a desert environment on this side of the mountains and things are a lot more lush (lusher?) on the west side, but never really understood why, tune in tomorrow I’ll tell you why.




Strongest Storm of the Season Yet…And What Is a Blizzard?



What is likely to be the strongest storm of the season is bearing down on the area. Strong winds and heavy snow will create blizzard conditions in the mountains (a Blizzard Warning is in effect from 10 am Thursday to 1 pm Friday), making travel over the mountains tough if not impossible during that time frame. Mountain snowfall totals over the next three days could range from 2-5 feet depending on location, with the valleys seeing significant amounts, but significantly less than the mountains. Rain and snow mix in the valleys Thursday morning should turn to snow at all elevations by Thursday evening. A valley Wind Advisory kicks in early Thursday, and a Winter Weather advisory starts up after 4 pm Thursday into Friday morning. Valley accumulations will vary greatly depending on elevation and location (east-west) in the valley, but by Saturday could range from an inch or two to over 6 inches in some places. Temperatures will be in the 40s Thursday before dropping to the 30s Friday and Saturday.


And in case you are wondering, a blizzard doesn’t just entail heavy snow. In order to be a blizzard, a storm has to have winds 35 mph or higher, reduce visibility to ¼ mile or less, and last a minimum of three hours.


Strong Winter Storm Headed Our Way



Well, it’s taken almost all winter, but we do have a pretty impressive winter storm lined up to arrive late Wednesday (in the mountains) and sticking around in the form of several waves through Saturday.  For Wednesday, temperatures will climb into the mid-40s ahead of the cold front, and by late in the day the mountains could start to see some snowfall. Winds will be pretty high ahead of the front, gusting Thursday to as high as 50 mph in the valley.

Snow levels will start out at or a little above the valley floors Thursday, and with the wind I would expect to see a fair amount of rain shadowing Early Thursday. As the wind eases, cold air will move into the region turning precipitation to snow at all elevations, and travel over the mountains will be challenging from Thursday through Saturday.

Total snow amounts in the valley will likely range from an inch or two on the low end to a half a foot or more, especially in the western foothills. This will be spread over a few days (Thu-Sat). The3 mountains could see anything from a foot to 5 feet over the same time period.



Winter Storm…And A Thermometer Doesn’t Always Measure Air Temperature



Winter weather comes back to the area, with snow showers likely in Reno starting early Thursday. Valley accumulations could range from trace amounts to a few inches, with approximately twice that amount possible for the mountains. High temperatures will drop to the 30s through Friday, before climbing back into the 40s for the weekend. Another storm series come through at the first of next week.


Yesterday I said the air temperature in and out of the sun is nearly the same. For those that do object, you might seek to prove your point by taking a thermometer and laying it in the sun. See?! Look at how the reading immediately rises when it is in the sun. The air must be warmer.

Thermometer in the sun

Au contraire! While the reading on the thermometer will be much higher in the direct sunlight, that doesn’t mean the air temperature is higher, only that the temperature of the thermometer is higher. Just as the sun’s radiation heats your skin and makes it hotter than the surrounding air, so also it heats the thermometer casing. That’s why it is so important to place your thermometer in a well ventilated, shaded location in order to assure an accurate air temperature reading.

Thermometer box


Another Moderate Storm…And Radiation Vs. Conduction

While I don’t see a real wet storm in the short term, we should be able to squeeze some more snow out of the weather before we say goodbye to February. Another low pressure center will drop down out of the north, bringing some more light to moderate snow to the region late Wednesday through Thursday. Temperatures will nudge upward into the low 40s Wednesday, but will still remain well below average. After a drying out over the weekend, another trough of low pressure brings scattered snow back early next week.

Radiation 2

While warm air can heat you up by conduction, the sun is a lot more efficient at transferring energy to your skin by radiation. Radiation from the sun travels through air relatively unscathed (the air only absorbs a minor amount of the sun’s radiation), and when it hits you, it excites the molecules of your skin, generating heat. That’s why you feel so much hotter if you are in direct sunlight as opposed to being in the shade. Even though it may not seem like it, if you measure the air temperature in and out of the sun, there’s almost no difference. You may disagree with that. Tomorrow, I’ll tell you why you’re wrong.



Cold Week…And A Hot Question About the Sun

Cold…that’s the main weather word for the week. Tuesday morning lows could dip into the single digits in some valley locations as our skies clear out. Sunny skies on Tuesday won’t warm us up much, with all areas struggling to get over the freezing mark. Another wave moves through the region early Wednesday, bringing back a chance of snow showers through Thursday. Weak systems pass through off and on through the rest of the week, with high temperatures varying from the mid-30s to the mid-40s.


Since it’s so cold this week, let’s warm things up with this question: Our high desert summer sun is intense. What is it about the sun that makes it so physically draining while one is lounging about in a deck chair, but when the temperature is only 80 degrees?”  I’ll refrain from talking about spending too much time lounging in deck chairs, and tell you why direct sunshine feels so hot.

The sun can heat you up in two ways. First (and this is how it heats thermometers that read that 80 degrees mentioned above), the sun can heat the air, either directly or indirectly, and then the air transfers that heat to your body by direct contact. That’s called heat transfer by conduction. But the air isn’t really that efficient in conducting heat. Tomorrow I’ll tell you a better way.




Get Ready For Some Cold Weather…And Different Types of Jet Streams

We have some big swings coming our way weatherwise. Saturday will bring mostly sunny skies and warm temperatures (highs in the lower 60s in Reno) before a cold front drops in Sunday, bringing gusty winds, cooler temperatures and a chance of rain turning to snow.  Scattered snow accompanies even colder temperatures on President’s Day Monday with the high barely clearing the freezing mark. Conditions dry out Monday afternoon and Tuesday, but temperatures remain very cold through the first half of the week.

hadley ferrel polar cells

We’ve been talking about the jet stream. And even though we often talk of the jet stream as a single entity, there are really four of them typically circling the globe. There’s a polar and a sub-tropical jet stream in each hemisphere, each generally following a sinuous path from the west to the east. The polar jets are lower in the atmosphere (generally 25-35,000’ altitude vs. 35-60,000’ for sub-tropical jets), and they tend to be stronger in the winter when the contrast of the polar and tropical airmasses is the greatest.

low level jet stream

And at times you can get other types of jet streams, including one in the summer that goes the opposite direction (east to west) down in the tropics, and low-level jet streams can affect the strength of winter storms hitting the west coast. That’s one kind of jet stream on which the land does have a large effect.


Cold Hit Next Week…And How Does Land Affect Jet Streams?

Temperatures will warm up quickly over the next couple of days as a ridge of high pressure moves into the area… but then they will fall even quicker as we head into the end of the weekend and the first of next. Sunshine Friday and Saturday will be accompanied by highs in the 50s to low 60s, but the cold front coming in Sunday will drop temperatures back into the 40s, and then plunge all the way into the 30s Monday and Tuesday with a slight chance of some light snow Sunday and Monday. Things stay relatively cool through the rest of the week.

hadley ferrel polar cells

Does land affect jet streams? Land receives and releases heat from the sun more rapidly than the oceans do, and therefore the vertical convective air currents (called Hadley, Ferrel and Polar Cells) which on a large scale help form somewhat stable weather patterns will have differing strengths over the oceans versus over continents. The continents can have an effect on the positioning of large scale persistent weather patterns, which also help determine the strength and position of the jet streams. But in terms of direct interaction between land and jet streams, there’s very little. Since the jet stream is usually found above 25,000’ of elevation, you’d have to get to the Himalayas before the land has any real touch on the jet.


Roller Coaster Temperatures… And Does Land Affect Jet Streams?

While there is no single storm headed our way, the temperatures will roller-coaster somewhat over the next week. After a cold front passes through the area Wednesday night, Thursday will clear out and cool down to the mid-40s. The ridge of high pressure builds back in Friday and Saturday, bumping the high back to the 60 degree mark. Another cold and mostly dry low drops back down late Sunday into Monday, bringing at most some isolated snow and dropping the highs all the way down into the 30s on Monday and Tuesday.

Earth wind patterns, artwork

Joe wondered if the landmasses in the southern hemisphere affected their jet streams. It’s kind of hard to answer that in real simple terms, because if you really want to get down to brass tax, anything anywhere that touches air can have some effect on the chaotic system that is the atmosphere. “If a butterfly in Tokyo flaps its wings, it can cause rain a week later in New York” is an old adage that at least holds some truth in theory, if not being absolutely provable. Having said that, landmasses do have a limited effect on jet streams. I’ll tell you how tomorrow.


Warming for the Weekend…And Does the Southern Hemisphere Have Jet Streams?

While we have a slight chance of seeing a few isolated snow showers Wednesday night, for the most part, the forecast will dry out and warm up as we head into the weekend. A weak low will once again drop down from the north late in the day Wednesday, increasing clouds and winds, but it appears the bulk of that system will pass to our east, with us here in Reno only getting a slight chance of a snow shower.

After it passes, skies will clear out on a cool Thursday (high in the mid-40s) and things will warm back up to the low 60s on Saturday before the next weak storm tries to move in Sunday.

Earth wind patterns, artwork

Earth’s wind patterns, schematic view. Atmospheric circulation in each hemisphere consists of three cells. The Hadley Cell (labelled) dominates the tropical atmosphere and is intimately related to the trade winds, tropical rain belts, subtropical deserts and the jet streams. The Polar Cell (labelled) produces the polar easterlies. The outflow from the Polar Cell creates waves in the atmosphere known as Rossby waves which play an important role in determining the path of the jet stream. The polar cell also balances the Hadley Cell in the Earths energy equation. The Ferrel Cell (labelled) is dependent upon the Hadley Cell and the Polar Cell and just as the trade winds can be found below the Hadley Cell, the westerlies can be found beneath the Ferrel Cell. *** THIS PICTURE MAY NOT BE USED TO STATE OR IMPLY ESA ENDORSEMENT OF ANY COMPANY OR PRODUCT ***

Joe wondered: “Is there a corresponding jet stream in the southern hemisphere? Do large land areas that are not present in the southern hemisphere affect the jet stream?”

Yes, there are corresponding jet streams in the southern hemisphere, and they act much like the ones up here do. They even flow the same way (generally west to east.)

As for the land masses (or lack thereof) in the south affecting the jet, that’s a little more complicated to answer, and I’ll tackle that tomorrow.