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Newbie weather and other questions


Ginx snewx

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We actually had a question thread a while back in this sub forum:

We can use this one as the new one though since its already started. But we've certainly been willing to answer questions and have a thread devoted to them as the link illustrates.

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at 5h I do understand what it takes to get a nice setup for us. The funny thing is I am confused as to what the energy actually is, physically. Also, how is the energy measured? I look at the bottom of the NCEP images and there is a color scale but no guide as to what it is measured in.

Also would like a detailed description of omega and snowgrowth regions. Where they are based on a skew and what makes up a good and bad snowgrowth region. ( I obviously know what good and bad snowgrowth in terms of the flake size themselves )

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at 5h I do understand what it takes to get a nice setup for us. The funny thing is I am confused as to what the energy actually is, physically. Also, how is the energy measured? I look at the bottom of the NCEP images and there is a color scale but no guide as to what it is measured in.

Also would like a detailed description of omega and snowgrowth regions. Where they are based on a skew and what makes up a good and bad snowgrowth region. ( I obviously know what good and bad snowgrowth in terms of the flake size themselves )

I am also curious about the bolded.

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I always hear the term bl, or B/L or boundary layer.. can you guys please explain what it means, why is importan and how to read it on a weather map or any other manner?

Thanks

Raul

BL or boundary layer is the lowest part of the atmosphere near the earths surface. I forget the mb it goes up to aloft, want to say the BL is between 1000mb and 900/950mb. Its simply important regarding temperatures in most situations like in snowstorms.

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Oh, I have so many newbie questions. Let me start with the "millibar". When someone posts data from the NAM or GFS they often refer to the 500, 850, 700 or some other mb. Is this a height or a measure of atmospheric pressure? What is the significance?

What are upper and lower levels?

There seems to be opinion about which is best, but maybe someone can just explain the fundamentals of what the GFS, NAM, and whatever else there is, is. For bonus points answer why they differ so. Do they not obtain the same data, from the same place, at the same time?

What is it when a storm bombs?

What is a trough?

Why does the radar sometimes show precipitation when nothing is happening (or just the opposite)?

When is 00, 06, 12, and 18Z in EST time?

Do readings (i.e. weather balloons) actually happen at each of these times or are these computer simulations? When are the actual readings and best data produced?

I've got more smile.gif

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at 5h I do understand what it takes to get a nice setup for us. The funny thing is I am confused as to what the energy actually is, physically. Also, how is the energy measured? I look at the bottom of the NCEP images and there is a color scale but no guide as to what it is measured in.

Also would like a detailed description of omega and snowgrowth regions. Where they are based on a skew and what makes up a good and bad snowgrowth region. ( I obviously know what good and bad snowgrowth in terms of the flake size themselves )

Dendrite seems to know a ton about snowgrowth and the physics behind it. The snowgrowth zone, as I can gather, is essentially the temperature at which dendritic growth occurs (-10 to -20C). You want to see maximum lift and saturation at this level for intense snowfall.

Check this out: http://www.erh.noaa.gov/er/hq/ssd/snowmicro/sld009.html

It's intense but you can probably get the just of it.

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Oh, I have so many newbie questions. Let me start with the "millibar". When someone posts data from the NAM or GFS they often refer to the 500, 850, 700 or some other mb. Is this a height or a measure of atmospheric pressure? What is the significance?

What are upper and lower levels?

There seems to be opinion about which is best, but maybe someone can just explain the fundamentals of what the GFS, NAM, and whatever else there is, is. For bonus points answer why they differ so. Do they not obtain the same data, from the same place, at the same time?

What is it when a storm bombs?

What is a trough?

Why does the radar sometimes show precipitation when nothing is happening (or just the opposite)?

When is 00, 06, 12, and 18Z in EST time?

Do readings (i.e. weather balloons) actually happen at each of these times or are these computer simulations? When are the actual readings and best data produced?

I've got more smile.gif

Millibar (mb) is a pressure level of the atmosphere...we are down low usually near 1000mb or higher unless a strong storm is near us then the sfc pressure gets down into the high 900s. The higher up you go in the atmosphere, the lower the pressure reading.

Upper levels are generally considered about 500mb and up....with low levels considered below 850mb...but its kind of subjective...those are often good guides to use. Mid-levels are frequently referring to levels between about 600mb and 850mb. (we'll often just use H7 or 7H as a references which stands for 700mb)

GFS and NAM (and other models) try to simulate the weather using complex equations and different ways of gridpointing data...so you will end up with slightly different (usually) solutions because of that. The ECMWF (the Euro for short) usually performs the best with its simulations which is why we are often worried about what it says. The models all obtain the same raob data but sometime they can have slightly different sfc obs and satellite assimilation data in there...the Euro seems to do this the best which is why it performs the best.

When a storm bombs it means it drops at least 12mb in 12 hours. A "Superbomb" is dropping 24mb or more in 12 hours...much rarer.

A trough is a dip in the jet stream or air flow aloft...it usually promotes storminess on the eastern side of it and general cold conditions anywhere under it.

Radar shows precipitation sometimes when its not falling because the radar is detecting precipitation as it falls from the clouds and often it can be falling a few thousand feet above our heads but it dries up before it reaches the ground if the lower levels are very dry. This is known a virga.

00z, 06z, 12z, and 18z, are 7pm, 1am, 7am, and 1pm respectively in eastern standard time...in the summer you have to move all those times forward one hour since there's no daylight savings in UTC (zulu) time.

RAOB launches usually only happen at 00z and 12z but some sites will do special ones at 06z or 18z if they are in an area of interest for high impact weather.

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For lots of these questions I posted a link that answers lots of them. May I suggest that you take the time to read that link and then if you have more questions ask.

For example this is one module out of thousands , each term is underlined and linked

When the height contours bend strongly to the south, (as in the diagram below), it is called a TROUGH. Strong troughs are typically preceded by stormy weather and colder air at the surface. Below is an example of a trough in an upper-level height field (red contours). The trough axis is denoted by the purple line.

a689895f-33d4-54de.jpg

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at 5h I do understand what it takes to get a nice setup for us. The funny thing is I am confused as to what the energy actually is, physically. Also, how is the energy measured? I look at the bottom of the NCEP images and there is a color scale but no guide as to what it is measured in.

Also would like a detailed description of omega and snowgrowth regions. Where they are based on a skew and what makes up a good and bad snowgrowth region. ( I obviously know what good and bad snowgrowth in terms of the flake size themselves )

We use the term "energy" to describe vorticity. For instance, you might hear us say, "there is a ton of energy digging on the backside of the trough." This means there is a lot of vorticity diving on the backside of the trough. It's easier and usually accepted to say "energy."

The snowgrowth thing is a little more complicated, but the powerpoint might help explain some of the concepts. Basically you want the air to rise in a layer that is saturated (or at least 80-90% RH) in a layer that is preferable between -12C to -18C. This is how you get those great dendrites to form, they love the -12C to -18C temp range...this is optimum.

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The snowgrowth thing is a little more complicated, but the powerpoint might help explain some of the concepts. Basically you want the air to rise in a layer that is saturated (or at least 80-90% RH) in a layer that is preferable between -12C to -18C. This is how you get those great dendrites to form, they love the -12C to -18C temp range...this is optimum.

Is the snow growth typically occurring at ~700h or at some other level of the atmosphere (or does it depend on where the lift is)?

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Is the snow growth typically occurring at ~700h or at some other level of the atmosphere (or does it depend on where the lift is)?

It depends on where the lift is. Usually, it's found within about 100mb of H7...but more typically 750-650mb.

There is more to it, but in general you want to find good lift and RH through the area near -12C to -18C, but it could extend to -10C in our neck of the woods.

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could someone explain a little aboubt the PV? This is a term that gets tossed around quite frequently...I don't have a good grasp of it yet...

Arctic and Antarctic variation

The vortex is most powerful in the hemisphere's winter, when the temperature gradient is steepest, and diminishes or can disappear in the summer. The Antarctic polar vortex is more pronounced and persistent than the Arctic one; this is because the distribution of land masses at high latitudes in the northern hemisphere gives rise to Rossby waves which contribute to the breakdown of the vortex, whereas in the southern hemisphere the vortex remains less disturbed. The breakdown of the polar vortex is an extreme event known as a Sudden stratospheric warming, here the vortex completely breaks down and an associated warming of 30-50 degrees Celsius over a few days can occur. The Arctic vortex is elongated in shape, with two centres, one roughly over Baffin Island in Canada and the other over northeast Siberia. In rare events, the vortex can push further south as a result of axis interruption, see January 1985 Arctic outbreak.

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could someone explain a little aboubt the PV? This is a term that gets tossed around quite frequently...I don't have a good grasp of it yet...

Polar vortex, here is an example from the GFS. It's basically a massive upper level low, but a true polar vortex is accompanied by extreme cold underneath the low.

post-33-0-50362000-1294022230.gif

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