Determining Mountain Clouds, Winds and Temps

Determining Mountain Clouds, Winds and Temps

Page Type Page Type: Article
Activities Activities: Mixed


There was a thread in the forums recently asking if there was a way to determine the elevation of cloud layers in the mountains(current and/or forecast). Generally speaking, yes, there is. In fact, you can determine more than just cloud information. You can find wind and temperature information also.

Hopefully this article will give you some basic techniques to head for the mountains perhaps a little more prepared for the weather that awaits you. However, I caution you that Mother Nature is unpredictable, weather forecast models are not 100% accurate, and mountains do indeed form their own micro-environments at times. So use this information to plan, but as always, be prepared for the worst.

Obtaining an Upper Air Sounding

RUC SoundingsRUC Soundings Interface

Go to to reach the page in the image above. We will use this interface to obtain an upper air sounding for a location.

You can use this interface to obtain the most recent sounding or forecast soundings for locations in the U.S. Unfortunately the forecast soundings time period does not go out very far on this site. But, the most recent soundings are reliable and they have a handy Java function we will use later.

To obtain a current sounding, select RAOBs in the initial data source block. Leave Start Time at Latest. Number of hours doesn't matter (unless you are trying to get forecasts). Then enter the identifier for the location you are trying to retrieve. You can find location identifiers at Generally speaking, any place with an airport will have an identifier. Finally, obtain the sounding by clicking Java-based plots.

Making Sense of an Upper Air Sounding

KTFX Skew-TUpper Air Sounding for Great Falls, MT

The image above is a plot of an upper air sounding for Great Falls, MT. This is a representation of the state of the atmosphere displayed in the vertical. The information used to make this plot is the raw information obtained from the release of a weather balloon.

At the top of the image we can determine that this sounding is for Great Falls, MT (TFX), and it is from 7 Jun 2006 at 1200 GMT. Note this info is repeated in the lower left.

Along the left margin you can see the pressure level in millibars. Note the pressure decreasing with height. Pressure levels generally correspond to certain heights but will vary with atmospheric conditions. There are some basic reference points though, as follows:

925mb - 2,000 ft MSL
850mb - 5,000 ft MSL
700mb - 10,000 ft MSL
500mb - 18,000 ft MSL
400mb - 24,000 ft MSL

You can also see heights generally corresponding to these pressure levels on the right side of the chart above the label Press Alt (Kft).

The thick red line and thick blue line in the middle of the chart are the temperature and dewpoint traces (red is temp, blue is dewpoint). These are plotted using the thin red lines oriented from bottom left to top right of the chart and correspondingly labeled with red numbers near the bottom of the chart in degrees Celcius. So for instance in this sounding, the temperature at 600mb is 0 Celcius and the dewpoint is -8 C.

Along the right side of the chart is a series of lines with other lines and pendants sprouting off of them. These are the winds at altitude. The tail of the wind line will point to the direction the wind is blowing from. On the sounding up is north, down is south, right is east, left is west. The barbs and pendants protruding from the wind line represent the speed. A half barb (line) is 5 knots, a full barb is 10 knots and a pendant (triangle) is 50 knots. On the example chart above, the wind at 15,000 ft is from 250 degrees (WSW) at 30 knots. Bear in mind these are steady state winds and will not include gusts.

Finding Cloud Layers

KTFX Cloud BaseTFX Cloud Bases

Once you obtain the sounding, you can click inside the image to activate Java tools. These are the lovely lines and numbers in the image above showing the height (mbs and ft) and the temp, dewpoint and winds at the level where you are holding your mouse pointer.

To identify cloud layers on the sounding, your first visual clue should be finding areas where the temp and dewpoint lines come close together. Clouds usually occur in areas where the dewpoint depression (the difference between the temp and dewpoint) is 5 degrees F (2-3 degrees C) or less. This also corresponds to a relative humidity of 70% or more. So to define cloud layers, moving vertically from bottom to top, we want to identify areas where the RH first exceeds 70% to determine the cloud base, then, proceeding vertically, goes back below 70% to determine the top of the cloud layer.

In the image above the base of a cloud layer has been identified at 15,974 feet, where the temperature is -4.9 C.

KTFX Cloud TopsTFX Cloud Tops

In the above image the top of the cloud layer has been identified at 19,094 feet, where the RH has dropped below 70% to 66%. The temp at this level is -11.9 C and the winds are from 255 degrees at 39 knots.

You Try!

KUIL Skew-TUIL Sounding

Above is a sounding for UIL, Quillayute, Washington from 7 Jun 2006 at 1200Z. Can you find the cloud layers?

KUIL Cloud BasesUIL Cloud Bases

The base of the first layer of clouds is at 3133 feet. Temp 4.8 C, RH 94%. Probably raining. Anything over 90% generally indicates precipitation.

KUIL Cloud TopsUIL Cloud Tops

The top of the first cloud layer is at 4,304 feet. The RH is down to 61%.

KUIL Cloud Bases 2UIL Cloud Bases Layer 2

Proceeding upward, we find another cloud layer with bases at 20,981 feet. RH at 71%, temperature is -22.5 C.

KUIL Cloud Tops 2UIL Cloud Tops Layer 2

Proceeding ever upward, we find the top of this second cloud layer at 23,816 feet. RH is still at 71% but drops sharply above.

Here is the surface observation from Quillayute around that time.

KUIL 071153Z AUTO 00000KT 10SM SCT030 10/08 A3007 RMK AO2 SLP182 T01000083 10122 20100 52001 TSNO

The observation reports scattered clouds (3 to 4 eighths of the sky covered) at 3,000 feet (SCT030). Pretty much what our analysis of the sounding told us. Note that it does not report the higher cloud layer we found. There is a reason for this. Notice this station says it is an automated station (AUTO). I can tell by looking at the remarks section (RMK) that this automated system is an AO2 system. Thus only equipped with cloud detectors that reach only to 12,000 feet. So this station is not capable of detecting the clouds we detected on the sounding up near 20,000 feet.

How Do I Use This?

So how can you put your new found skills to use?

You can use a current sounding (if your excursion is happening soon and quickly) or a forecast sounding (for future, longer excursions) to get an idea of what conditions on your mountain of choice may be like.

The following site can be used to access forecast soundings. It is a little more user-friendly and reliable than the RUC site, but it doesn't have the Java tools. But you don't need those because you have skills now.

So you get to the site.

Storm MachineStorm Machine

And follow the steps.

Step one, pick a model. I like NAM or GFS. Some models may be right some days and wrong others. Compare a couple. If you see two alike, they are probably right.

Step two, choose a forecast time. This is trial and error. You usually just have to poke, then look at the first image you get then adjust your time to what you really want.

Storm Machine 2Storm Machine 2

Step three, decide data output. Leave it on Skew-T diagram.

Step four, decide on Metar Site. Pick a place close to where you are going to climb. For this example, our burly climber is headed up to do the Upper Exum on the Grand Teton. So, he has wisely chosen Jackson, WY to look at.

Step five, background color. Whatever floats your boat. White is easier to read.

Jackson SoundingJackson Sounding

So here is the forecast sounding for Jackson, WY valid at 1200GMT on Friday 9 June. Notice the sounding doesn't even start until around 750mbs or roughly 7,500 feet, this due to the high elevation at the Jackson Airport, so we know we are in the right place.

It doesn't do us much good to look above 600mb, or roughly 14,000 feet, since the Grand is 13,770 feet. So, proceeding up to 600mb, I don't see any areas of dewpoint depression less than 2 to 3 degrees Celcius, so it should be relatively cloud free. There are some higher clouds up around 400mb, but not of concern to us.

I also see a surface temp of around 9 C with winds from the WSW around 15 knots. It looks like summit temp will be about -2 C with steady state winds from the WSW around 20 knots. All in all, not a bad day to be trying to negotiate that step across at the end of Wall Street.


Post a Comment
Viewing: 1-11 of 11

Charles - Jun 9, 2006 12:53 pm - Voted 10/10


I´ll need some time to digest this!




dadndave - Jun 13, 2006 11:37 am - Voted 10/10


Now that's what I call answering the question. Can't get the links to work at present but I'll come back to it later. Interesting stuff. I seems there are 500 of these stations worldwide.


mvs - Jun 14, 2006 7:53 am - Voted 10/10

awesome article

Great tutorial format, thank you!


Fettster - Jun 14, 2006 3:07 pm - Hasn't voted


Thanks for taking the time to put this together! I was able to try it out last weekend with some success. It will take some more practice to get used to examining the data.

Thanks again!

montana boy

montana boy - Jun 16, 2006 4:01 am - Hasn't voted


This is fantastic information. Thanks!


TempestPeace - Jun 20, 2006 7:21 pm - Hasn't voted

Very interesting

That is very very interesting information..But I must ask Where is that Pic that is displayed on the next to the Article on the Homepage?

wtfo - Jun 22, 2006 5:21 am - Hasn't voted

Re: Very interesting

I don't know. One of the site admins must have attached that image for use on the front page. The primary photo I used is courtesy of Natural. I would assume it is in Brazil.


joegrim - Jul 7, 2006 11:21 pm - Voted 6/10

Not quite right

wtfo, I commend you on putting a lot of effort into this. By reading this article, I can tell you have spent some time studying the weather. However, as a meteorologist myself, I have to make the following comments on the content.

These guidelines you are showing are useful as rough estimates for determining if clouds will be present and at what level. However, I think you should mention that these are rules of thumb and are not strictly based on pure science.

For example: In order for a cloud to be present, the relative humidity MUST reach 100%. You state that a relative humidity of 70% should be used to determine if there is a cloud. This appears to be misleading, as the pure science says this is impossible. In reality, humidity can vary over short distances so that one spot can have 100% and a cloud, while the nearby sounding may have 90% humidity at that level and no cloud. Therefore, your 70% threshold can be used to find the "possibility" of clouds. However, I personally would use a threshold of 80 or 90%. One other thing, 70% humidity usually corresponds to a dewpoint depression of about 10 F (not 5F). I assume this might have been a typo.

Anyway, there are several other "rules of thumb" that you use that would better be explained as such. (e.g., finding out if a cloud is raining.)

Thanks for your hard work on this article!

wtfo - Jul 10, 2006 10:21 pm - Hasn't voted

Re: Not quite right

First thing to consider here is that this quick lesson is intended for the layman to use, not a meteorologist. My 5F, 70% method is a quick rule generally applicable at all levels of the atmosphere. Of course these numbers change some with temperature, but I was trying to simplify for average folks. Second, I don't know where you got the 100% RH necesssary for cloud formation figure from, but I assure you that the 70% threshold is and has been the accepted threshold (at least in my 20 years as an aviation met and operational met). I believe I proved this in my Quillayute example above. Saying 100% RH is a requirement for clouds is like saying the same for fog formation. And that is totally untrue. If you adopt a 100% RH threshold to locate clouds, you will miss more than you find.


Proterra - Oct 28, 2007 6:25 am - Voted 10/10

Re: Not quite right

Although Joegrim is right, that you need 100% RH for clouds to form, it depends on other factors as well. For example, in rising air parcels, it's just all too possible that at say, 10,000 foot, such a pocket will be 10C with a RH of 70%, where the surrounding air will have a T of 5C with an RH of 90%. When that parcel will cool off, you'll have nice cumuli forming, because the air gets oversaturated with moisture. In this not too uncommon instance, there are spots where the RH reaches 100%, whereas the surrounding air never gets over 90.

I think this is a good and usable article, because it explains a few guidelines that folks, who don't know shite about the physics of weather systems, are being explained what to look for. In essence, it can prevent people from doing stupid shite.

About Quillayute, i tend to follow this rule: "If it's not raining right now, it will in a wee bit" From September to June, that rule tends to have a higher success rate than any other weather model.

It wouldn't mind to make that link work, btw.

wtfo - Jul 11, 2006 5:31 pm - Hasn't voted

Re: 100% RH is required

I have been using soundings for operational forecasts for a long time. If I waited for 95% or higher RH to forecast clouds, I would be wrong way more than right. The balloon would have to go right through the cloud to pick up the 100%.

Viewing: 1-11 of 11