Weather Explained: Why Is The Radar Is Always Green At Night?

If you look at the radar on a calm night, you might think that it's raining. But, upon a look outside, you see no clouds. But the radar is showing color everywhere, as pictured above. What is going on?

During the day, air rises as the sun heats the atmosphere. Whether a storm is coming or going, air is always rising during the day. This rising of the air actually affects the radar. A radar works by sending out a wave in all directions. This 'wave' then bounces off any clouds and back to the radar, telling the radar that it caught something. This 'catch' by the radar wave is how we see storms on the radar.

At night, the radar is still working, sending out beams in all directions. However, at night, air sinks if high pressure is in the area. This sinking of the air will take the radar 'waves' and actually push them to the ground. When they are pushed down, they hit houses, trees, anything and everything on the ground. This gives the radar a false idea that there is something in the area, hence the colorful display like the one above.

So when you're having an outdoor party and check the radar to see something like the above but see a clear sky, it's the radar beams hitting the ground thanks to sinking air.

Andrew

Weather Explained: Arctic Oscillation (AO)

Arctic Oscillation Positive/Negative phases.
Positive Phase on the left, Negative Phase on the right.

The Arctic Oscillation is an oscillating index based in the Arctic Circle region.
When the Arctic Oscillation is in a positive phase, a vortex in the upper regions of the Northern Hemisphere is strong and locks in cold air to keep it up north. This keeps the cold air up north as stated, and does not let the US get colder air.

When the Arctic Oscillation is in a negative phase, the vortex weakens, and the cold air locked in releases itself to more southerly regions of the North Hemisphere, typically affecting North America.

The AO can be a key player in winters when determining cold weather, and is an index that should be watched closely.

Weather Explained: Aleutian Low

The Aleutian Low is a semi-permanent low pressure system that sets up over the Aleutian Islands, Alaska. Below is an example of the Aleutian Low.

The Aleutian Low is most intense during the winter months, and can send energy towards North America that can eventually affect the US.

We are not publishing too much information on the Aleutian Low because we do not have enough information on it at this time.

Weather Explained: LRC

What is the LRC?

The LRC (Lezak's Recurring Cycle) is a pattern eagerly followed by many meteorologists and can be a key instrument in determining a winter forecast. Here are the guidelines:

-Pattern sets up between October 1 and November 10.
-Between this time, a certain atmospheric feature occurs that will reoccur over the winter, spring and into summer over a 40-60 day cycle.
-Pattern is never the exact same each year.

So, as an example, let's say a huge rainstorm came through the Ohio Valley on October 17th. Then, on November 30, another huge rainstorm came through the Ohio Valley. This may be considered a part of the LRC, if atmospheric conditions (similar strength, effects on atmosphere) agree with the October 17th storm.

Weather Explained: What does it mean when I see '12z' on a weather map?

Because there are so many different time zones in the world, it gets hard to track models- much more if some are made in different continents. For this reason, weather models are run on Greenwich time, which is the time equivalent of the world's clock, if you will.

Whenever you see 'z' next to a time (example: 12z, 18z, 0z, 6z) it means Noon, 6PM, midnight, 6 am, respectively, all in Greenwich time.

So let's say you live in Missouri. You saw a map with a forecast for rain in your area at 12z. You can subtract 5 hours or 6 hours (depending on daylight savings time) to get your local time in Missouri for when the rain will fall. If you subtract 5 from 12, you get 7 AM. The rain would fall at 7 AM in Missouri.

Weather Explained: Lower Level Jet Stream

What is a lower level jet stream?
It is a river of fast moving air in the lower level of the atmosphere, while toe big jet streams are in the higher atmosphere.

What does it do?
In the spring-summer time, the lower level jet stream will amplify itself and storms around it in the Plains at nighttime, explaining why storms are sometimes stronger at night.
It can rapidly transport moisture and warm temperatures from the Gulf of Mexico north.

So the only thing it does is use wind to make storms stronger at night?
With the rapid transport of moisture, it is able to quickly pump up storms and feed it until the jet moves away.

What does it look like?

The white area is the lower level jet stream.

Weather Explained: Types of Weather Fronts

About.com
1. Cold Front- A front with a following cold air mass.
2. Warm Front- A front with a following warm air mass.
3. Stationary Front- A front that is literally not moving.
4. Occluded - When a cold front overtakes a warm front. Usually, an air mass dries when an occluded front passes.
5. Trough- An elongated region of low pressure, usually associated with fronts.
6. Squall - A line of severe storms ahead of a cold front.
7. Dry Line- Separates humid air to the east and dry air to the west.
8. Tropical Wave

Weather Explained: Lapse Rates

What are Lapse Rates?

Lapse Rates is what tells the decrease of temperatures the higher you go in the sky. It is also a measure of instability. The more difference there is between levels, the more instability there is.

How can you tell if the atmosphere is unstable?

Values in images less than 5.5-6 degrees in the images are considered very stable, while values near 9.5 degrees is considered incredibly unstable.

Below is a Sample Image from March 18, 2011.

In this image, we definitely see good instability in the Plains into the Midwest.

Weather Explained: Pacific Ring of Fire

What is the 'Ring of Fire', and where is it?

The Ring of Fire is the edge of the Pacific tectonic plate. On those edges, other tectonic plates rub against each other. The earth is pushed up or down. Volcanoes are formed on the edge of this Pacific Tectonic Plate.

The Ring of Fire are the volcanoes surrounding the Pacific Ocean. Below is an image of the Ring of Fire.

Image from the USGS.

The red area are the edges of the tectonic plates.

Why is it called the 'Ring of Fire'?

Volcanoes produce fire and lava, and with so many volcanoes surrounding the Pacific tectonic plate in an awkward circle-like formation, it became known as the Ring of Fire.

Are these volcanoes active?

Some are very active, while others are dormant. Mount St. Helens in Washington State, US is included in this Ring of Fire.

Weather Explained: Shift in Earth's axis

(Note: The Earth's axis shifted 4 inches from the March 11, 2011 Earthquake and Tsunami)

So the axis shifted. Will the weather go crazy now?

No. Not at all. 4 inches compared to the Earth is incredibly small. Any changes would be unrecognizable to the human eye or experience (wind, rain, etc.)

For the weather to go crazy, the Earth has to pretty much turn upside down or shift an incredible amount more than 4 inches.

My weather seems to be different than forecasted. Is this due to the shift?

No. Meteorologists are not prophets, and likely never will be. It is expected for the temperature to be slightly different than forecasted or rain to occur even if it wasn't forecasted. Recently, Chicago had bands of heavy lake effect snow that weathermen did not forecast.

Weather Explained: QPF

What is QPF?

QPF is Quantitative Precipitation Forecast. It is a map depicting future precipitation for an area.

How can I read a QPF map?

It is very simple. Let's say the weatherman says rain. You find a QPF map. It shows 1.13''.

That means 1.13'' of rain will fall. It is just showing you how much rain will fall.

For snow, you can multiply a value by 10 to get an average snowfall amount. Below is a real-time QPF map.

What does a QPF map look like?

So, if we look in Mississippi (March 5th), we see the number 4.1 That means 4.1 inches of rain is predicted to fall.

Weather Explained: CAPE

What is CAPE?

CAPE is a measure of instability in the atmosphere. It is also called MUCAPE, which means Most Unstable Convective Available Potential Energy. Certain values indicate when severe storms can form. Typically, values of 2000 j/kg are the beginning of instability good enough for storms.

How unstable can CAPE values get?

The most I have ever seen on a map is 6000 j/kg. That is EXTREMELY unstable.

How can I determine if the atmosphere is unstable?

One you find a CAPE map, see the below table for guidance.

1-500 j/kg: Stable.

500-1000 j/kg: Relatively stable.

1000-2000 j/kg: Unstable.

2000-3000 j/kg: Very unstable.

3000-4000 j/kg: Extremely unstable.

4000+ j/kg: Rare. So unstable that a simple rain shower could make a tornado.

Where can I find a CAPE map?

1. Go to the Storm Prediction Center website.

2. Click 'Mesoanalysis'.

3. Click on the region where you live.

4. Mouse over the tab 'Thermodynamics'.

5. Click on 'CAPE- Most-Unstable / LPL Height'.

Weather Explained: Graupel

Graupel is a snowflake that is laden with supercooled water droplets.

It falls to the ground as white ball-shaped precipitation.

Below is a picture of Graupel.

image from jonschrage.com

You can see how the snowflakes are full of little balls of what look like snow as well.

Weather Explained: Snowdrift

What is a snowdrift?

When snow is falling and wind is blowing, the wind blows the snow against a wall or solid object. A snowdrift looks like a big hill. In the Blizzard of 2011, snowdrifts were as high as 5 feet and over.

Are snowdrifts dangerous?

Snowdrifts can bury cars, stop people from being able to open front doors, and be hazardous in general.

What does a snowdrift look like?

(image from kevinmd.com)

Weather Explained: Why Storms get Stronger on the East Coast

Storms get stronger on the East Coast because of the moisture in the Atlantic Ocean.

The moisture is open and feeding into the storm system, and the storm openly strengthens.

Weather Explained: Phasing

What is Phasing?

Phasing is when two low pressure systems combine into one low pressure system.

Is Phasing dangerous?

It is an atmospheric condition. While it is typically not dangerous, lows that combine can be stronger and more intense.

Under certain conditions, phasing lows can be dangerous.

Weather Explained: Shortwave

What is a shortwave?

A shortwave is an area of prolonged low pressures. They are not a low pressure system, but rather low pressure readings.

Can they cause precipitation?

Absolutely.

Are they dangerous?

Since shortwaves typically aren't as powerful as a low pressure system, not really.

What does a shortwave look like?

A shortwave can be identified by a series of millibar lines on a map pushed down.

See the lines pushed down in the middle of the country?

That's a shortwave.

Weather Explained: Supercell

What is a supercell?

A supercell is the most likely to become severe. It is isolated from other storms. Supercells are characterized by their rotation in clouds.

What does a supercell look like from the ground?

A supercell is defined by the almost circle-like formation in the clouds.

What does a supercell look like on radar?

Supercells are very well seen, like something is swirling the storm into one spot.

That is the most telltale sign in a supercell. If you see one, find cover immediately.

Are supercells dangerous?

They are the most dangerous of thunderstorms and have most potential to be severe.

Other information

Because the supercell shows a swirl, it is a very strong example of how a tornado forms. If you see that type of swirl, supercell or not, it has the most likely chance of being a tornado.

Weather Explained: Bow Echo

What is a Bow Echo?

A bow echo is a line of storms in a curve shape. Below is a picture.

It is a squall line that carries very intense winds.

What can a bow echo do?

Bow echoes are extremely windy. They are very similar to squall lines. They do have more potential to produce tornadoes, as the winds are higher and there is a curve in the line, which is conductive for tornado formation.

Are bow echoes dangerous?

Yes they are.

What can I do if I see a bow echo coming?

Take anything that can fly away outside inside. Bow echoes can topple trees and are associated with supercells, which will be in the next Weather Explained.

How will I see a bow echo on radar?

You will see a line of intense storms in a big curve.

Weather Explained: Squall Line

What is a squall line?

A squall line is a band of intense storms moving together in a line. They are associated with cold fronts, as cold air meets warm air.

What do squall lines do?

Tornadoes have been known to occur more often in single-celled storms. Squall lines are like a big line of single-celled storms. Squall lines are very likely to produce high winds, because they move so quickly and can be in a bow echo, which will be in the next Weather Explained.

Are squall lines dangerous?

Yes. They are very dangerous at times.

What do squall lines look like?

On a radar, they come up as a line of storms. Below is an image of a squall line.

You can see the leading edge of storms at the front, where the cold air first meets the warm air. Then, the cold air overtakes the warm air, and the storms die down after the first line of storms.