would someone like to help me to understand how to interpret weather models?

[NCsandhills]

i would love to be able to engage in the conversations in the SE subforum, but for some reason google searches arent helping me to understand how to read these. i try to look at the GFS models but i cant make any sense of it. i see all the high and low pressure systems, and i know generally what that means, but how can one tell if it's going to cause storms? remember last april, 2011 with the AL, MS tornado outbreak...it was predicted several days in advance that it would be a severe outbreak with several long track, strong tornadoes. how does one see that on the map? what do you look for? and which model? also, i've noticed no one on here ever mentions the NAM model - why is that? is it not very accurate? i only see GFS and Euro being mentioned on here.

here is one from the model center here from this site. the 474-600 colored legend on the left - what does it represent? what is the difference between 00z, 6z and 18z, and why do they all have 0-384 as different maps? i understand that this is a lot to explain so i wont be surprised if i receive no answers, but i would GREATLY appreciate it if someone could.

[catoctin wx]

Well...there certainly are a ton of questions in your post so I will just try to answer a couple of them and leave some for others. I'm not a forecaster and don't wade into the specifics of the models often, so there are many others who are more qualified than myself to answer detailed questions.

i would love to be able to engage in the conversations in the SE subforum, but for some reason google searches arent helping me to understand how to read these. i try to look at the GFS models but i cant make any sense of it. i see all the high and low pressure systems, and i know generally what that means, but how can one tell if it's going to cause storms? remember last april, 2011 with the AL, MS tornado outbreak...it was predicted several days in advance that it would be a severe outbreak with several long track, strong tornadoes. how does one see that on the map? what do you look for? and which model? also, i've noticed no one on here ever mentions the NAM model - why is that? is it not very accurate? i only see GFS and Euro being mentioned on here.

Storms are most always associated with a surface low of some kind. Low pressure at the surface leads to air moving upwards, which causes the air to cool, condense, and eventually rain/snow.

If you are looking for severe storms (like the tornado outbreak you referenced) you (generally) want to see a very strong cold front moving into an area of moist, warm air. This cold front causes the lift that is required for storm formation. Of course storms develope in the absence of a cold front (called air mass thunderstorms), but speaking in general, that is what you look for. You can usually see that at the lower-to-mid levels of the atmosphere (850 mb = ~1500 meters agl; 700 mb = ~3000 meters agl; 500 mb = ~ 5000 meter agl). The NAM is not a good model for longer range forecasting (outside of a few days), so it's not used much.

here is one from the model center here from this site. the 474-600 colored legend on the left - what does it represent? what is the difference between 00z, 6z and 18z, and why do they all have 0-384 as different maps? i understand that this is a lot to explain so i wont be surprised if i receive no answers, but i would GREATLY appreciate it if someone could.

The map that you posted is a 500 mb height map with surface pressure denoted and marked by the white lines. You can use the 500 mb map to determine troughs and ridges at a midlevel of the atmoshere (approx. 500 meters). The legend on the left (and hopefully I am right about this, or I fail as a met) is in decameters. Meaning that the 540 (light blue) line corresponds to a height of 5400 meters. This means that the 500 millibar surface is at 5400 meters. Since you know the height, you can make a determination on the temperature in the entire column below that point based roughly on gas laws (a warmer gas will take up more volume than a colder gas, which is why lower heights are associated with colder air). As a rule of thumb, the 540 line is the "rain/snow" line, meaning the temperature in the column averages 0 degrees C.

The 00Z,6Z,12Z, 18Z denotes what time the model is run and the Z is zulu-time (or Geenwich Mean Time). Right now 6Z refers to 1 a.m. EST, 12Z is 7 a.m. EST, 18Z is 1 pm EST, etc. The 0-384 you ask about is the forecast time and refers to how many hours into the future the forecast is for. Since 384 hours is 16 days, you could say the 384 hour forecast is for 16 days from now, just as you would say that 72 hour map is for 3 days from now.

Also, take some time to look at the different maps available to see what each of them are reflecting. Generally the 850 mb map will show you 850 mb (~1500 meter agl) temperatures, rain totals for the period and surface pressure (mslp). 700 mb is generally the surface to look at for relative humidity in the midlevels. 500 mb is good for seeing vorticity (the amount of rotation in the atmosphere), 200 mb and 250 mb levels are looking at winds very high up, so you can determine jet stream patterns amoung other things.

One suggestion is to go through as many COMET modules as possible on this stuff, they are really great at explanations. Also, you should become as comfortable as you can at looking at the atmosphere on pressure levels. Eventually looking at things in millibars will become as second nature as looking at temperature in degrees F.

edited for clarification upon further reflection.

[catoctin wx]

That's my best shot for now on your questions (during my lunch break time). If you have any others, feel free to ask. Other mets, please correct me where I am wrong, I am not a model person.

[Disc]

i would love to be able to engage in the conversations in the SE subforum, but for some reason google searches arent helping me to understand how to read these. i try to look at the GFS models but i cant make any sense of it. i see all the high and low pressure systems, and i know generally what that means, but how can one tell if it's going to cause storms? remember last april, 2011 with the AL, MS tornado outbreak...it was predicted several days in advance that it would be a severe outbreak with several long track, strong tornadoes. how does one see that on the map? what do you look for? and which model? also, i've noticed no one on here ever mentions the NAM model - why is that? is it not very accurate? i only see GFS and Euro being mentioned on here.

Here's a 500mb map from the RUC (now known as the RAP model) from April 2011 if you were wondering what it looked like on the models. I know this might not really answer your question, but it gives you an idea what it should look like if you want a significant tornado outbreak. On the right side in the smaller boxes is helicity. Generally, if you have high helicity values such as the ones modeled below in a very unstable atmosphere, you have the possibility for strong tornadoes. There are many more indices that are used to predict severe weather/tornadic conditions such as these: http://www.theweatherprediction.com/severe/indices/

Maybe someone can elaborate on what I said and correct me if I described anything incorrectly. Also, does anyone have any other archived models from April 2011 or any good site where I could find such things?

[NCsandhills]

Well...there certainly are a ton of questions in your post so I will just try to answer a couple of them and leave some for others. I'm not a forecaster and don't wade into the specifics of the models often, so there are many others who are more qualified than myself to answer detailed questions.

Storms are most always associated with a surface low of some kind. Low pressure at the surface leads to air moving upwards, which causes the air to cool, condense, and eventually rain/snow.

If you are looking for severe storms (like the tornado outbreak you referenced) you (generally) want to see a very strong cold front moving into an area of moist, warm air. This cold front causes the lift that is required for storm formation. Of course storms develope in the absence of a cold front (called air mass thunderstorms), but speaking in general, that is what you look for. You can usually see that at the lower-to-mid levels of the atmosphere (850 mb = ~1500 meters agl; 700 mb = ~3000 meters agl; 500 mb = ~ 5000 meter agl). The NAM is not a good model for longer range forecasting (outside of a few days), so it's not used much.

The map that you posted is a 500 mb height map with surface pressure denoted and marked by the white lines. You can use the 500 mb map to determine troughs and ridges at a midlevel of the atmoshere (approx. 500 meters). The legend on the left (and hopefully I am right about this, or I fail as a met) is in decameters. Meaning that the 540 (light blue) line corresponds to a height of 5400 meters. This means that the 500 millibar surface is at 5400 meters. Since you know the height, you can make a determination on the temperature in the entire column below that point based roughly on gas laws (a warmer gas will take up more volume than a colder gas, which is why lower heights are associated with colder air). As a rule of thumb, the 540 line is the "rain/snow" line, meaning the temperature in the column averages 0 degrees C.

The 00Z,6Z,12Z, 18Z denotes what time the model is run and the Z is zulu-time (or Geenwich Mean Time). Right now 6Z refers to 1 a.m. EST, 12Z is 7 a.m. EST, 18Z is 1 pm EST, etc. The 0-384 you ask about is the forecast time and refers to how many hours into the future the forecast is for. Since 384 hours is 16 days, you could say the 384 hour forecast is for 16 days from now, just as you would say that 72 hour map is for 3 days from now.

Also, take some time to look at the different maps available to see what each of them are reflecting. Generally the 850 mb map will show you 850 mb (~1500 meter agl) temperatures, rain totals for the period and surface pressure (mslp). 700 mb is generally the surface to look at for relative humidity in the midlevels. 500 mb is good for seeing vorticity (the amount of rotation in the atmosphere), 200 mb and 250 mb levels are looking at winds very high up, so you can determine jet stream patterns amoung other things.

One suggestion is to go through as many COMET modules as possible on this stuff, they are really great at explanations. Also, you should become as comfortable as you can at looking at the atmosphere on pressure levels. Eventually looking at things in millibars will become as second nature as looking at temperature in degrees F.

edited for clarification upon further reflection.

excellent, excellent, so much help in this post. few more questions though!

bold part, number 1: i thought 500mb meant a certain height in the atmosphere, or does that legend mean that at that point in the air (5400 meters, 540 light blue line) is where the atmospheric pressure equals 500mb, as opposed to the 1000mb we would see at the surface?

i have indeed been looking through all the maps, GFS and Euro mostly as i see the most mentioned on here.

also, here is a screenshot of the GFS 00z 204 hr forecast. that low pressure system there on the east coast with the 546 color going as far south as NC, does that mean there is a winter weather event may occur?

also, i'm looking at a current GFS map and where i see Low pressure systems in the country, according to the weather channel cities in those areas are not receiving precipitation. how can you tell on these models whether or not that low pressure system will produce precipitation, especially that many days out?

i'm sure i'll think of more questions but i'm trying to not do too much at once haha.

[JoMo]

arwx,

The map you posted above is a 500 MB heights map. It doesn't show precip or the various layers of the atmosphere. It does have surface pressures plotted.

There's easier maps to interpret for beginners. The ones at http://www.instantweathermaps.com for instance.

Go to Maps > GFS Conus > Multi-Variable (NCEP Clone) > Precip/Pressure/2m Temps

This map shows the precip, pressure and temp and the wind. Anything behind the blue 0 degree line will be frozen. That should get you started.

[catoctin wx]

excellent, excellent, so much help in this post. few more questions though!

bold part, number 1: i thought 500mb meant a certain height in the atmosphere, or does that legend mean that at that point in the air (5400 meters, 540 light blue line) is where the atmospheric pressure equals 500mb, as opposed to the 1000mb we would see at the surface?

The bolded part is correct. The lines (and heights) indicate the height in the atmosphere that is equal to a pressure of 500 mb.

i have indeed been looking through all the maps, GFS and Euro mostly as i see the most mentioned on here.

also, here is a screenshot of the GFS 00z 204 hr forecast. that low pressure system there on the east coast with the 546 color going as far south as NC, does that mean there is a winter weather event may occur?

Well the rain/snow line is typically 540 mb, not 546. However, it's important to remember that this is just a rule of thumb and there are many other variables in play. Especially in the south, the surface is likely to be warmer, so the 540-line rule doesn't hold as true. To get an idea of the precip type you would also want to look at the lower levels of 700 mb, 850 mb, and the surface. Ideally you would look at a skew-t diagram or a radiosonde balloon measurement to determine the temperatures at the different levels.

also, i'm looking at a current GFS map and where i see Low pressure systems in the country, according to the weather channel cities in those areas are not receiving precipitation. how can you tell on these models whether or not that low pressure system will produce precipitation, especially that many days out?

i'm sure i'll think of more questions but i'm trying to not do too much at once haha.

Not sure what level you are looking at, but as JoMo pointed out, the 500 mb maps do not depict precipitation. For precip, you will want to look at either the surface (10 meter temp, wind, and precip) or 850 mb (850 temp, MSLP, and precip if looking at the NCEP maps). Not all low pressure systems produce precip, it also depends on the amount of moisture available.

[wxmeddler]

This is a good website to start out and get the basics. I highly recommend.

Fundamentals: (You don't have to know the meteorological equations, though some of the interpretations are useful)

http://www.theweatherprediction.com/basic/

Once you've looked over that you can go onto the rest of the site, there is link after link to click and learn about (500+ different topics)

http://www.theweatherprediction.com/habyhints/

[Great Snow 1717]

A good book to have is "Weather Maps, How to Read and Interpret All the Basic Weather Charts" by Peter Chaston

[weatherbob1234]

This is a good website to start out and get the basics. I highly recommend.

Fundamentals: (You don't have to know the meteorological equations, though some of the interpretations are useful)

http://www.theweatherprediction.com/basic/

Once you've looked over that you can go onto the rest of the site, there is link after link to click and learn about (500+ different topics)

http://www.theweatherprediction.com/habyhints/

I agree this is the best website i have found if you are just starting out. Me myself i use Penn state e-wall because i took online weather forecasting there. But it as alot of great models and maps and it has help guide to help you understand some of the models!!!

[NCsandhills]

I forgot I started this thread.  Thank you, everyone for your replies. I've gotten a bit better at it.  But I have more q's

 

When looking at this website's 500mb heights on the GFS or ECMWF etc and we're looking for a trough or a ridge, do I look at gray or red circle in my attached image?  I'm assuming red.  but it the grey circle not considered a trough?  because i thought ridges were associated with high pressure, troughs low pressure...

 

also, positivite/neg/neutral vorticity...that is talking about the direction of the tilt of the center of the low pressure system?  a tilt towards the right is positive, neutral is straight and negative is towards the left, right?  what causes this and what is the significance of it?

 

also, with the 500mb heights maps...i know that this means how high up in the atmospher the pressure equals 500mb as opposed to the ~1000 we experience on the surface, but again what is the significance in knowing how high the 500mb area is?  

 

so the lower the heights the colder it is right?  is this because cold air is denser so since the 500mb height is lower, the air is more..."squished" (for lack of a better word) making it more dense?  or am i completely off base?