If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
cloud base forecasting question
I'm not a pilot, but I've got a question pertaining to aviation
forecasts. I'm a mountain climber who has recently discovered aviation forecasts that could be very useful in determining cloud base heights. The idea being that alot of times I'll see a forecast that calls for rain yet I find out on my climb that I'm easily above the clouds for great climbing weather. My question has to do with interpreting cloud base forecasts. For instance, at http://usairnet.com/cgi-bin/launch/c...nge +Location, I note that on Saturday at 11:00 am they are calling for a cloud base of 3000-6500'. I'm assuming (maybe I'm way off, but that's why I'm asking) that this means if I was climbing a mountain at 10,000', I'd likely be above the clouds. Yet at 11:00 am on Friday at http://usairnet.com/cgi-bin/launch/c...nge +Location, I note a forecast for clear skies and a cloud base of 12,000' to "unlimited." I'm not sure what this means, does this mean that even though it is supposed to be sunny, I may encouter clouds above 12,000'? Can someone set me straight on what this data is supposed to mean? |
#2
|
|||
|
|||
"William_F" wrote in message
... [...] Can someone set me straight on what this data is supposed to mean? To understand, you should probably look at two things: the raw data, and the NWS explanation of the raw data. All that the web site you're looking at does is map the NWS raw data to plain English, essentially by just using the tables the NWS provides in the first place. You can find the raw data by clicking on the links near the bottom of the pages you provided. The key for that data can be found he http://www.nws.noaa.gov/mdl/synop/mavcard.htm As far as your specific questions go: First, it's important to understand that the forecast beyond about 6 hours or so is extremely unreliable, especially with respect to cloud coverage and heights. Second, clouds can and often do come in layers. A cloud base of "3000-6500 feet" does not preclude the possibility of clouds above that height. Note also that the range is quite wide; the reason being that there's a very wide range of uncertainty in the forecast. They aren't saying that the bases will actually range from 3000 to 6500 feet on that day; they are saying that the bases, which will generally be relatively uniform, will be at a height that is somewhere in or near that range. Likewise, the "12000' to Unlimited" describes a potential range of conditions. They are basically saying there won't be conditions favorable for low clouds, but that there may be middle-altitude or higher clouds, or there may be no clouds at all. So, during a time period for which clear skies are predicted, the "Unlimited" (which is really just a misleading transcription of the NWS term "unlimited ceiling") is the more likely condition to prevail. On the other hand, on a day when cloudy skies are predicted, the "12000'" (with the implied "or higher") is the more likely condition to prevail. So, if you want to know whether you'll see the sun, look at the "Sky" category. If the "Sky" category indicates clouds, you can learn more detail about the predicted lowest cloud heights in the "Cloud Base" category (but it won't tell you how high the clouds are likely to go). A forecast for low clouds could mean you'd be above the clouds on your climb, or it could mean clouds extend all the way from below your climb to well above it. There are other aspects to interpreting weather forecast information that would give you more detail with respect to the extent of the clouds, but the data you're referencing right now won't provide that. As pilots, especially those flying recreationally, are painfully aware, any forecast a day or more in the future is not to be relied upon. It gives you a vague sense of what the most likely weather conditions may be, but that forecast is almost never exactly correct. Even large scale questions like "will there be rain?" or "will it be sunny?" can be wrong either in terms of degree or time of occurrence, and fine details like temperature, wind speed, cloud bases, and the like are almost impossible to predict with any accuracy that far in advance. For your purposes, I think the most useful information is "sunny or cloudy" and "low clouds or high clouds". Looking for more detail than that from these forecasts is likely to simply lead to disappointment. Pete |
#3
|
|||
|
|||
William_F wrote:
I note a forecast for clear skies and a cloud base of 12,000' to "unlimited." I'm not sure what this means, does this mean that even though it is supposed to be sunny, I may encouter clouds above 12,000'? The aviation weather people typically don't provide info for clouds above 12,000'. Basically what they're saying is that they aren't forecasting for clouds to occur, but maybe there will be some above 12,000'. George Patterson Why do men's hearts beat faster, knees get weak, throats become dry, and they think irrationally when a woman wears leather clothing? Because she smells like a new truck. |
#4
|
|||
|
|||
"George Patterson" wrote in message
news:y4nue.4801$PZ6.2791@trndny08... The aviation weather people typically don't provide info for clouds above 12,000'. Basically what they're saying is that they aren't forecasting for clouds to occur, but maybe there will be some above 12,000'. That's not what they are saying. If they forecast no clouds, then they are forecasting no clouds. There's no "maybe there will be some", except inasmuch as the forecast itself is subject to being inaccurate. Pete |
#5
|
|||
|
|||
Thanks for the advice, Peter. I thought I had stumbled on some secret
weapon that would allow me to pick my climbing days while friends sat at home because rain had been forecast. I guess it's not that simple. Oh well. |
#6
|
|||
|
|||
Start with temperature and dew point at ground level, apply standard lapse
rate to both until the expected temperature and dew point are the same or within about 2degrees Celsius of each other.. That would be the "expected cloud base" if clouds were to form. Depth of clouds or vertical development and resulting rain depend on other criteria, such as instability in the atmosphere, upslope winds, amount of moisture in the air, there may be enough for cloud development but not for rain. BT "William_F" wrote in message ... I'm not a pilot, but I've got a question pertaining to aviation forecasts. I'm a mountain climber who has recently discovered aviation forecasts that could be very useful in determining cloud base heights. The idea being that alot of times I'll see a forecast that calls for rain yet I find out on my climb that I'm easily above the clouds for great climbing weather. My question has to do with interpreting cloud base forecasts. For instance, at http://usairnet.com/cgi-bin/launch/c...nge +Location, I note that on Saturday at 11:00 am they are calling for a cloud base of 3000-6500'. I'm assuming (maybe I'm way off, but that's why I'm asking) that this means if I was climbing a mountain at 10,000', I'd likely be above the clouds. Yet at 11:00 am on Friday at http://usairnet.com/cgi-bin/launch/c...nge +Location, I note a forecast for clear skies and a cloud base of 12,000' to "unlimited." I'm not sure what this means, does this mean that even though it is supposed to be sunny, I may encouter clouds above 12,000'? Can someone set me straight on what this data is supposed to mean? |
#7
|
|||
|
|||
On Wed, 22 Jun 2005 16:33:19 -0700, William_F
wrote in :: I'm a mountain climber who has recently discovered aviation forecasts that could be very useful in determining cloud base heights. The idea being that alot of times I'll see a forecast that calls for rain yet I find out on my climb that I'm easily above the clouds for great climbing weather. It seems to me, that you are interested in cloud tops as well as cloud bases. Cloud top forecast information is difficult to find, but pilots often report observed cloud top altitudes in what are known as Pilot Reports (PIREPS). NOAA makes that information available he http://adds.aviationweather.noaa.gov/pireps/java/ |
#8
|
|||
|
|||
try this:
http://www-frd.fsl.noaa.gov/mab/soundings/java/ once you learn to interpret skew T plots you can accurately forecast cloudbase and get a good guess on top heights. I use it every day as a soaring forecast tool. "William_F" wrote in message ... I'm not a pilot, but I've got a question pertaining to aviation forecasts. I'm a mountain climber who has recently discovered aviation forecasts that could be very useful in determining cloud base heights. The idea being that alot of times I'll see a forecast that calls for rain yet I find out on my climb that I'm easily above the clouds for great climbing weather. My question has to do with interpreting cloud base forecasts. For instance, at http://usairnet.com/cgi-bin/launch/c...nge +Location, I note that on Saturday at 11:00 am they are calling for a cloud base of 3000-6500'. I'm assuming (maybe I'm way off, but that's why I'm asking) that this means if I was climbing a mountain at 10,000', I'd likely be above the clouds. Yet at 11:00 am on Friday at http://usairnet.com/cgi-bin/launch/c...nge +Location, I note a forecast for clear skies and a cloud base of 12,000' to "unlimited." I'm not sure what this means, does this mean that even though it is supposed to be sunny, I may encouter clouds above 12,000'? Can someone set me straight on what this data is supposed to mean? |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
I want to ask you the most important question of your life. | Douglas Olson | Owning | 1 | May 22nd 05 05:15 AM |
Base reflectivity versus composite reflectivity | Peter R. | Instrument Flight Rules | 14 | May 20th 05 05:34 PM |
182RG question | Paul Anton | Owning | 11 | May 16th 05 09:45 PM |
Good morning or good evening depending upon your location. I want to ask you the most important question of your life. Your joy or sorrow for all eternity depends upon your answer. The question is: Are you saved? It is not a question of how good | Excelsior | Home Built | 0 | April 22nd 05 01:11 AM |
Question about Question 4488 | [email protected] | Instrument Flight Rules | 3 | October 27th 03 01:26 AM |