Weather Question: forecasting clouds

I've been wondering about this for a while now, and am sure someone here
will know...

How can I find/figure out what the forecast cloud bases will be 3 or 4 days
out? I've looked on ADDS, AOPA's weather, NOAA.gov, etc but not found
anything.

In other words, if I'm going flying in a few days, And I go to weather.com
and see 'mostly cloudy' in the forecast, how do I know if that's "2000'
better-file-an-ifr-flight-plan Cloudy" or "10,000' VFR-is-no-problem"
cloudy?

I've tried looking at forecast temperatures and dewpoints, and using lapse
rate calculate cloud bases, but that hasn't worked out.

Are there any sites which give this info? or other info I could use to
figure this out?

TIA for your help

-Jonathan

"Jonathan" wrote in message
news:cPand.115563$R05.55665@attbi_s53...
How can I find/figure out what the forecast cloud bases will be 3 or 4
days out?

Three or four days in advance? Forget it. It is impossible to KNOW what
the weather will be that far in advance.

I empathize with your desire to be able to better plan your flights. I wish
I could do the same for mine. But the truth is that there's simply no
reliable way to predict. The most practical solution is to simply plan the
flight as if the weather will be good enough, and provide yourself with a
backup plan in case the weather's not good enough.

Ultimately, the ONLY thing that matters with respect to a particular flight
is what the weather is doing right that moment. Even short-term forecasts
are frequently wrong, and the long-term forecasts you're talking about are
just plain unreliable.

There's a reason that official aviation weather services don't provide cloud
height forecasts three days in advance. The only reason that the commercial
services do is that the public loves to be told what will happen, even if it
turns out to be wrong. For some perverse reason, that's more acceptable
than being told "I don't know what will happen" (probably because being told
an incorrect forecast gives an individual the "right" to blame the bad
weather for their plans on the meteorologist).

Pete

I'm sure that there are NWS meteorologists who would love to know the answer
to your question. Kind of hard to anticipate moisture content, air mass
movement, and lifting force with any degree of accuracy that far in advance.

Bob Gardner

"Jonathan" wrote in message
news:cPand.115563$R05.55665@attbi_s53...
I've been wondering about this for a while now, and am sure someone here
will know...

How can I find/figure out what the forecast cloud bases will be 3 or 4
days out? I've looked on ADDS, AOPA's weather, NOAA.gov, etc but not
found anything.

In other words, if I'm going flying in a few days, And I go to
weather.com and see 'mostly cloudy' in the forecast, how do I know if
that's "2000' better-file-an-ifr-flight-plan Cloudy" or "10,000'
VFR-is-no-problem" cloudy?

I've tried looking at forecast temperatures and dewpoints, and using lapse
rate calculate cloud bases, but that hasn't worked out.

Are there any sites which give this info? or other info I could use to
figure this out?

TIA for your help

-Jonathan

On Fri, 19 Nov 2004 00:07:37 GMT, "Jonathan"
wrote:

I've been wondering about this for a while now, and am sure someone here
will know...

How can I find/figure out what the forecast cloud bases will be 3 or 4 days
out? I've looked on ADDS, AOPA's weather, NOAA.gov, etc but not found
anything.

In other words, if I'm going flying in a few days, And I go to weather.com
and see 'mostly cloudy' in the forecast, how do I know if that's "2000'
better-file-an-ifr-flight-plan Cloudy" or "10,000' VFR-is-no-problem"
cloudy?

I've tried looking at forecast temperatures and dewpoints, and using lapse
rate calculate cloud bases, but that hasn't worked out.

Are there any sites which give this info? or other info I could use to
figure this out?

TIA for your help

-Jonathan


Try this site....
http://www.usairnet.com/cgi-bin/laun...nge +Location

It has been pretty good for me......

I know you mentioned the NOAA site, However, I find the 7-day forecast at

http://www.hpc.ncep.noaa.gov/medr/medr.shtml

To be pretty useful when I'm trying to look a bit further into the future.
You get the standard forecast weather chart - its up to you and your
knowledge of the area to work out what that will mean for flying. As pilots
we get quite a lot of weather training and there is a real incentive to get
familiar with these charts and try to interpret then correctly. For example,
a few days in advance of a XC flight I start looking at the charts for the
day of flight. I try and estimate what the weather will be like and then
each day reassess how I think its going to turn out. Finally, I either get
to fly or not depending on what actually happens. After you do this a few
times you start to get better at knowing what a particular weather pattern
on the chart will translate into as actual weather in you home area.

Having said that, however, I tend to flight plan to fly IFR anyway (use
airways with transitions to IAF for IAP). So I'm usually really interested
in where the freezing level is likely to be and if there is any risk of
embedded thunderstorms. I'm only interested in ceilings if they are likely
below minimums when I want to land.

-Brenor

"Jonathan" wrote in message
news:cPand.115563$R05.55665@attbi_s53...
I've been wondering about this for a while now, and am sure someone here
will know...

How can I find/figure out what the forecast cloud bases will be 3 or 4
days out? I've looked on ADDS, AOPA's weather, NOAA.gov, etc but not
found anything.

In other words, if I'm going flying in a few days, And I go to
weather.com and see 'mostly cloudy' in the forecast, how do I know if
that's "2000' better-file-an-ifr-flight-plan Cloudy" or "10,000'
VFR-is-no-problem" cloudy?

I've tried looking at forecast temperatures and dewpoints, and using lapse
rate calculate cloud bases, but that hasn't worked out.

Are there any sites which give this info? or other info I could use to
figure this out?

TIA for your help

-Jonathan

"Jonathan" wrote in message
news:cPand.115563$R05.55665@attbi_s53...
I've been wondering about this for a while now, and am sure someone here
will know...

How can I find/figure out what the forecast cloud bases will be 3 or 4
days out? I've looked on ADDS, AOPA's weather, NOAA.gov, etc but not
found anything.

In other words, if I'm going flying in a few days, And I go to
weather.com and see 'mostly cloudy' in the forecast, how do I know if
that's "2000' better-file-an-ifr-flight-plan Cloudy" or "10,000'
VFR-is-no-problem" cloudy?



Peter is pretty close in his "forget it" point-of-view, but there are a few
things you can do if you want to try a guess.

The best, of course, is to be able to talk to the government's forecast
office. They have an idea of why they would have said "mostly cloudy". The
problem with this approach is.... 20 years ago, you could do just that for
free. These days, you get a free recording, but if you want anything more,
you have to go to a 3rd party fee-for-service provider. Canada used to have
a 1-900 fee-service to talk to a forecaster, but I don't see it advertised
anymore.... they just seem to say "go to the private fee-for-service
provider".

The next best thing is to know what the forecast situation is going to be.

(I digress, but frankly, I am amazed at the poor quality of Meteorological
training that ground-school seems to provide. In some ways, boaters get a
better course from the Power Squadrons. The "Meteorology" chapter of one of
the most popular Basic Training text in the US, written by probably *the*
most well known instructor in the country, has a few rather bizarre sections
in it. ... but I digress)

Back to topic:
In Canada and the US, the Computer-produced forecast runs are done twice
daily at 0000Z and 1200Z (available several hours after the nominal
run-time). The Canadian version is available on-line at
http://weatheroffice.ec.gc.ca/model_.../global_e.html ... I don't know
about the availability of the US version on line, but the Canadian one
pretty much covers all of North America.

The forecast charts from the 00Z run goes out to 144 hours, and from the
12Z run out to 72 hours.

Now, if you look at the surface-pressure forecast in the top-right panel of
each chart, you might be able to get an idea as to what the Pressure pattern
is expected for your date and place of interest.... (use the black&white
charts at the bottom of the page, the colored ones at the top are
useless.... and don't forget that the valid time: 0000Z "Tuesday", means
MONDAY EVENING in most of North America)...

All of us should have been watching the weather daily, since ground school,
and comparing it to the CURRENT surface analysis every day. By now, we
would have a pretty good idea what sort of weather we get in various
pressure regimes. All we would have to do is look at the FORECAST pressure
chart for the day in question, and we would have a pretty good idea what to
expect.

For those of us who didn't, here are a few rules of thumb to make some sort
of guess:

If the forecast chart puts you immediately to the west of a low pressure
system, or in the north or northwest flow of what appears to be cold air,
then probably 2-3 thsnd agl stratocumulus, most probably MVFR or better, but
NOT 10 thsnd.

If they are calling for isolated showers in such a flow, then probably
generally VFR cumulus except for IFR in the showers...

If closer to the centre of a High, but still in the northerly flow, probably
Cumulus so something like 3-5 thsnd VFR.

If immediately northeast of a low, especially if precipitation is being
called for, then probably IFR.

If still quite a distance northeast of a low, they are probably forecasting
the onset of the storm but it will not be there yet, so probably middle to
high cloud, like 8 thsnd or more.

The dotted lines on that chart are somewhat representative of temperature.
If they are close together, that will probably be a front. If it looks like
the wind direction is pushing such a front from the north (cold front), then
they are probably thinking thunderstorms, or at least some sort of lift
along the front, MVFR, probably IFR in any precipitation.

If southerly winds pushing the front up from the south (warm front), could
be just middle cloud 8-thousand plus, unless they calling for
precipitation... in which case likely IFR.

In the southerly, southwesterly flow south of a Low pressure system in
summer, probably Cumulus, maybe towering cumulus or isolated CB. Probably
4-5000 plus, except in the isolated showers. Also probably reduced vis in
haze, if nothing else.


In general, immediately northeast or east of the low pressure system, look
for greater possibility of IFR.
West, southwest of the low, greater possibility of VFR.
Cumulus in cold northwesterly flows might be slightly lower than cumulus in
the hot southerly flows. And cloud in the northerly flows, west of a low,
will rarely be on the deck. The hot southerly flows will produce more
severe thunderstorms out of the CU later in the day.

Also watch the catch-phrase "afternoon cloudiness". That is almost surely
an afternoon-convective-cumulus kind of day, VFR.

In poorly-organized pressure regimes, lacking a distinct low-high pressure
pattern, the forecaster is probably looking at some sort of upper
disturbance or convective instability. The upper disturbance will give you
higher cloud (8thsnd plus), the convective instability will give you patchy
towering Cumulus or patchy thunderstorms. Either case will be usually VFR
except IFR in precipitation.

All of the above are my own opinion, and working meteorologists are free to
disagree... I will not rebut. YMMV.... a lot. All kinds of complications
with mountain areas, upslope flows, etc... if you are in the foothill states
and the forecast is for an easterly or northeasterly flow, then probably
IFR.

And of course, if the forecast pressure pattern does not come to pass as
forecast, then all bets are off.

But it turns out that the computer models forecast surface pressure pretty
well. In fact, quite often the forecast is better for the third or fourth
day than it is for today. The reason is that the forecaster has no desire
to do much "interpretation" in the third or fourth day...he basically makes
a quick assessment of what the forecast model told him and he puts down
"rain" (or whatever). (In fact, it is quite probable that the text for 3rd
and 4th days is directly generated by the computer from the model).

But as that day comes closer, facts get in the way. The morning of, he is
expecting this rain, but maybe the METARs are not showing it yet. He starts
to have doubts. Maybe the lift is not quite enough to produce rain. Let's
just call it cloudy.... sure enough, three hours after his "cloudy" forecast
gets distributed to the media, the rain starts, and his "cloudy" forecast is
blown.

Hi Jonathan

Two things that you need to know -
1, Anyone can forecast 3-4 days ahead,
2. They are usually wrong

Tony

--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE


I've been wondering about this for a while now, and am sure someone here
will know...

How can I find/figure out what the forecast cloud bases will be 3 or 4 days
out? I've looked on ADDS, AOPA's weather, NOAA.gov, etc but not found
anything.

In other words, if I'm going flying in a few days, And I go to weather.com
and see 'mostly cloudy' in the forecast, how do I know if that's "2000'
better-file-an-ifr-flight-plan Cloudy" or "10,000' VFR-is-no-problem"
cloudy?

I've tried looking at forecast temperatures and dewpoints, and using lapse
rate calculate cloud bases, but that hasn't worked out.

Are there any sites which give this info? or other info I could use to
figure this out?

TIA for your help

-Jonathan

www.farmersalmanac.com

Peter Duniho wrote:

Three or four days in advance? Forget it. It is impossible to KNOW what
the weather will be that far in advance.

No, don't forget it. Yes, it's impossible th *know*, but there are some
astonishingly accurate mathematical models out there. Depending on the
situation, their predictions are valid for several days, even
cloudbasewise, and they are becoming better as the models are refined
and the computing power grows. Of course, you'll never *know* in advance.

An example of a usually very accurate two days prediction (yes, only two
days, but they are working on it) can be found he
http://www.unibas.ch/geo/mcr/3d/mete...nmm2/BASEP.htm

I don't know an easily accessible source for such predictions concerning
the USA, but I would asssume that they exist.

Stefan

In article cPand.115563$R05.55665@attbi_s53, Jonathan wrote:
In other words, if I'm going flying in a few days, And I go to weather.com
and see 'mostly cloudy' in the forecast, how do I know if that's "2000'
better-file-an-ifr-flight-plan Cloudy" or "10,000' VFR-is-no-problem"
cloudy?

You can guess that sort of order-of-magnitude quite easily yourself.

What sort of weather system is generating the "Mostly cloudy" forecast?
Cold front? Warm front? Occlusion? A marine air-mass? That'll give you a
pretty good idea of what to expect.

What are the places that are currently in the weather system that's
moving your way like? Of course it might change by the time the airmass
reaches you (and depending on where you live there may be several
factors which could change it significantly), but if you see low clouds
and ceilings advancing on you - well, that mostly cloudy is probably
gonna be the low stuff.

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"