I learned something

[AuntPeggy]

NWS talk at BDR/Gama 20 Aug 2012

• If the edges of a cumulus cloud are well defined then it will continue building. If the edges are torn or indistinct then it will not build.
• Updrafts in large storms may exceed 50 kts. If a strong updraft is close enough to the ground it may evolve into a tornado.
• There is no lightning without ice.
• Ice will form in cumulus clouds 3,000 to 5,000 feet above the freezing level.
• Lightning is possible from the anvil well after the storm has passed.
• Internet lightning reports are only for cloud-to-ground. Most lightning is inter-cloud.
• Thunderstorms can form well in advance of a cold front because of compression induced instability.
• Thunderstorms rarely last more than 1 hr but can pop up in minutes (literally, between Nexrad scans).
• The accuracy (observed vs forecast) of TS forecasts in the first 3 hours of a TAF are about 20% and drop rapidly after that.
• TS do not have intensity, +TSRA refers to heavy rain.
• IFR forecasts are about 30% accurate, MVFR about 60% and VFR 90%, i.e., the better the forecast, the more likely it is to be true.
• PROB30 will not appear in the first 9 hours of a TAF.
• TEMP refers to an event with a probability of at least 50% and lasting at least 30 minutes during the forecast period.
• RA is forecast only if the POP is at least 50%.
• Radar return intensity is, in part, based on the size of water droplets. Cumulus clouds tend to form larger droplets than do stratus so the returns may show a higher intensity for the same total amount of water.
• Radar shows only precipitation so there is no way to know if a storm is convective or not.
• Radar is line-of-sight so 100 miles from the installation Nexrad may be reporting no lower than 5,000 feet.
• Composite Nexrad uses the highest intensities found in any scan.
• Nexrad dishes rotate at 2 rpm increasing azimuth by 1/2 degree after each rotation. It takes 4 1/2 minutes for a complete scan.
• Some TAFs are issued every three hours, although they may not have changed.
• For TAFs, the "terminal area" has a radius of 5sm, "vicinity" has a radius of 10sm.
• ATC does not understand that TAFs are only for the terminal area and may fly you into bad weather on approach.
• Birds perching on ASOS equipment may alter the readings significantly.
• ASOS wind is a 2 minute average and gusts are the highest in 10 minutes.
• Only 15% to 20% of weather balloon instrumentation is ever returned.
• Balloons are inflated to 5 to 6 feet in diameter on the ground and rise to 100,000 feet where they may expand to as much as 20 feet in diameter before they fail.
• Balloons rise about 1,000 fpm.
• There are no known aircraft collisions with weather balloons.
• The reason that POU and SWF TAFs are so different is that they are authored by different people.
• Read the discussions to determine how accurate the meteorologist thinks the TAF is.
• NWS has run out of cloud posters because of budget cuts.

 

[Velocity173]

The TEMPO group is used for any conditions in wind, visibility, weather, or sky condition which are expected to last for generally less than an hour at a time (occasional), and are expected to occur during less than half the time period.

This is how I remember TEMPO. Not sure if it is the most current definition though.

 

[numl0ck]

Very cool stuff. Thanks for posting!

 

[Hobobiker]

The more I read your post, the more I realized I have a LOT to learn about weather...

 

[Rigged4Flight]

Very nice post. I'm going through the King weather DVD right now - I could actually follow along with most of what you posted!

 

[\__[Ô]__/]

Thanks for posting this!

"Birds perching on ASOS equipment may alter the readings significantly."
Have never thought of this, but it could explain some bizarre reports i've heard.

 

[AuntPeggy]

Thanks for posting this!

"Birds perching on ASOS equipment may alter the readings significantly."
Have never thought of this, but it could explain some bizarre reports i've heard.

It does indeed. For example, a bird landing on the wind detector might produce a 100mph gust.

 

[Rigged4Flight]

It does indeed. For example, a bird landing on the wind detector might produce a 100mph gust.

One of my guys (a great practical joker) climbed up on the roof with a can of canned air (the kind you blow dust out of keyboards with). Practical joker + canned air + anemometer = FUN TIMES!

He proceeded to give the guys in the ground control station heart attacks as they saw winds go from calm to tornado in seconds. Of course it only lasted for a few seconds. Just long enough for jaws to drop open and eyes to bug out!

 

[dell30rb]

NWS talk at BDR/Gama 20 Aug 2012

• Radar shows only precipitation so there is no way to know if a storm is convective or not.
  

If its a storm, it is convective.

You can generally tell from a radar signature if you are looking at a storm cell or just a rain cloud. If the precip intensity change is gradual and is not heavier than moderate (yellow) rain you're (usually) looking at a rain cloud. If the change in precip intensity is sharp, it is a storm cell.

 

[AuntPeggy]

If its a storm, it is convective.

You can generally tell from a radar signature if you are looking at a storm cell or just a rain cloud. If the precip intensity change is gradual and is not heavier than moderate (yellow) rain you're (usually) looking at a rain cloud. If the change in precip intensity is sharp, it is a storm cell.

• Convection denotes vertical motion.
• Advection denotes horizontal motion.

 

[AuntPeggy]

• Wind is the most frequent component in weather-related aviation accidents/incidents.
• Wind is the most frequent component in weather-related aviation deaths.
• The FAA is requesting further information and concentration on wind.
• Unscheduled TAF updates occur when the wind changes by more than 10 knots.

 

[MAKG1]

• Convection denotes vertical motion.
• Advection denotes horizontal motion.

Hmm, I'm curious where that came from.

Convection and advection are different processes, and they can overlap. Convection is heat-driven motion. It's usually vertical, but doesn't necessarily need to be; a commonly observed horizontal convective phenomenon is the sea breeze. Advection just means having features hauled around by the flow. For instance, if there were a wildfire feeding a convective cell, the smoke would be advected along the cell as well.

Advection in weather often shows up as moisture being hauled around by wind, but that's not the only type of advection.

Both convection and advection play a role in thunderstorm formation.

 

[DouglasBader]

Ice will form in cumulus clouds 3,000 to 5,000 feet above the freezing level.

Ice will form a lot higher than that. The ideal range for icing in clouds is +5 deg C, to -15 deg C.

We used to do most of our initial thunderstorm penetrations and weather penetrations in the -10 to -15 level(s), picking up more ice there than most other places in the cloud, in terms of speed of buildup and the amount of ice.

Supercooled water can be found to -40 C, as high as 40,000'.

If the edges of a cumulus cloud are well defined then it will continue building. If the edges are torn or indistinct then it will not build.

That's somewhat of a general rule of thumb, but not accurate. A glaciated cell or one that's dying will tend to feather out, and one that is building generally does appear more crisp, but it's very possible to have a cell build up through the dying one, and to have very strong updrafts on the upwind or upshear side of the cell. From one angle it may appear to be dead or dying, but that may be very deceptive. Additionally, what the cell appears to be on the outside may not at all be what it is on the inside, and the cell may not be exhibiting further vertical growth, but may still have considerable activity inside.

 

[Threefingeredjack]

A glaciated cell or one that's dying will tend to feather out, and one that is building generally does appear more crisp, but it's very possible to have a cell build up through the dying one, and to have very strong updrafts on the upwind or upshear side of the cell. From one angle it may appear to be dead or dying, but that may be very deceptive. Additionally, what the cell appears to be on the outside may not at all be what it is on the inside, and the cell may not be exhibiting further vertical growth, but may still have considerable activity inside.

There is only one hard rule about thunderstorms that can be universally applied: they eat small airplanes, so stand clear. Some of the most "interesting" times I have had in the air have been working under squall lines in underpowered helicopters.

 

[azure]

NWS talk at BDR/Gama 20 Aug 2012

• ATC does not understand that TAFs are only for the terminal area and may fly you into bad weather on approach.

This one makes no sense to me. Why would an approach control facility rely on a forecast to tell what is going on right now? Don't they generally have weather radar?

Birds perching on ASOS equipment may alter the readings significantly.

As may helos crossing slowly directly over the sensor...
(happened recently at VLL)

 

[Everskyward]

This one makes no sense to me. Why would an approach control facility rely on a forecast to tell what is going on right now? Don't they generally have weather radar?

As may helos crossing slowly directly over the sensor...
(happened recently at VLL)

Also clouds of dry snow in the process of being plowed...

 

[DouglasBader]

There is only one hard rule about thunderstorms that can be universally applied: they eat small airplanes, so stand clear.

They eat big ones, too.

 

[Threefingeredjack]

They eat big ones, too.

True, but as this is a GA forum I went small. Maybe an edit to remove "small" would have been appropriate.

 

[Velocity173]

This one makes no sense to me. Why would an approach control facility rely on a forecast to tell what is going on right now? Don't they generally have weather radar?

As may helos crossing slowly directly over the sensor...
(happened recently at VLL)

I agree. This sounds like it's coming from a weather guy and not an ATC guy. When I worked approach I knew what a TAF was. We get extensive wx classes plus we work with the weather and FSS guys hand and hand. I'll say I didn't pay much attention to the TAF though.

1. It's the pilot's responsiblity to get the TAF not mine.
2. Could careless what the forecast is, I cleared people based on actual or PIREP conditions.
3. Had radar to vector aircraft around areas of precipitation.

This is still a lot of good info Peggy and appreciate you posting it.

 

[DouglasBader]

True, but as this is a GA forum I went small. Maybe an edit to remove "small" would have been appropriate.

No, I think it's good as-is. Everyone here flies small airplanes (or helicopters). Some fly gliders, some fly professionally, but everyone here is either interested in, enthused by, or a participant in general aviation in some way, shape or form.

When it comes to weather and meteorology, there are forces that far exceed any of our abilities to handle or cope. In the face of a thunderstorm and it's associated byproducts, we are gnats under the finger of God.

No degree of structural integrity, no amount of raw power, and special, intensive piloting training or skill is any match for what lies therein. It's good to remember that perspective, especially when considering taking flight in tube and fabric, or riveted aluminum, or wraps of e-glass and epoxy, or wood and glue and ply. We fly kites, and the wind is far stronger than we.

 

[AuntPeggy]

>Ice will form in cumulus clouds 3,000 to 5,000 feet above the freezing level.

Ice will form a lot higher than that. The ideal range for icing in clouds is +5 deg C, to -15 deg C.

We used to do most of our initial thunderstorm penetrations and weather penetrations in the -10 to -15 level(s), picking up more ice there than most other places in the cloud, in terms of speed of buildup and the amount of ice.

Supercooled water can be found to -40 C, as high as 40,000'.


That's somewhat of a general rule of thumb, but not accurate. A glaciated cell or one that's dying will tend to feather out, and one that is building generally does appear more crisp, but it's very possible to have a cell build up through the dying one, and to have very strong updrafts on the upwind or upshear side of the cell. From one angle it may appear to be dead or dying, but that may be very deceptive. Additionally, what the cell appears to be on the outside may not at all be what it is on the inside, and the cell may not be exhibiting further vertical growth, but may still have considerable activity inside.

Yes, that was not intended to be a range. Ice (as in hail) forms somewhere at 3000 and above the freezing level.

 

[dell30rb]

When it comes to weather and meteorology, there are forces that far exceed any of our abilities to handle or cope. In the face of a thunderstorm and it's associated byproducts, we are gnats under the finger of God.

No degree of structural integrity, no amount of raw power, and special, intensive piloting training or skill is any match for what lies therein.

Just a note

If you happen into a thunderstorm, you have put yourself in great danger and should not be there in the first place.

But all hope is not lost. In all of the material I have read about airplanes (big or small) being torn apart in thunderstorms, all of them are preceeded by LOC and the aircraft exceeding turbulence penetration speed. So fly attitude and cross your fingers

 

[DouglasBader]

If you happen into a thunderstorm, you have put yourself in great danger and should not be there in the first place.

But all hope is not lost. In all of the material I have read about airplanes (big or small) being torn apart in thunderstorms, all of them are preceeded by LOC and the aircraft exceeding turbulence penetration speed. So fly attitude and cross your fingers

In my case, thunderstorm penetration was my assignment, and no, we didn't put ourselves in a great deal of danger. It was our job: atmospheric research. Specifically, thunderstorm research.

I don't know how many thunderstorms you've experienced from the inside, but keeping your speed within a given range may not be as easy as you might imagine. Trying to maintain a lower speed may place you in a stalling range, with associated control issues, and maintaining a safe margin above that may result in frequent excursions into overspeed.

Flying a thunderstorm is most definitely not about crossing one's fingers and relying on luck. You're absolutely right that most people shouldn't be in them in the first place, and frankly, unless I have a dedicated reason to be going there, you won't find me in one, either.

Yes, that was not intended to be a range. Ice (as in hail) forms somewhere at 3000 and above the freezing level.

Ice and hail form above and below the freezing level, especially in a thunderstorm. The range of altitudes for ice formation can be quite large, and supercooled water can exist above and below the freezing level. Further, freezing can occur on the airframe, especially a precooled airframe, at lower altitudes, or freezing rain can cause icing well outside of where one might expect ice, based strictly on the freezing level.

Supercooled water can be found to -40 deg C, and as high as 40,000'.

 

[jnmeade]

Many regional weather offices conduct severe weather training in the spring of the year, preparing for tornado and thunderstorm season. It's a two hour presentation that is interesting and educational. It's not aviation weather but a pilot can get a lot of good out of it. I go every year or two. Go the the regional or district NWS web site and look way down the left side for Storm Spotter or anything similar to that (I've seen them called different things in different places).
You learn that the southwest quadrant of a cell is usually the one with strong updrafts (not always, and they tell when not). I think it helps me look at a cell and decide how far to avoid it in which direction.