UPDATE 7/11/2011: NCAR has released new research which confirms that precipitation is generated by propeller planes at major airports -- but only 6 percent of the time. Snow rates up to 1 inch per hour were observed, but total ground accumulation was not studied.

The complete PDF study states "Hole punch clouds are therefore not likely the result of contrails." and explains why although it also shows a shot of the contrail left by the plane that was shown to create the hole-punch cloud in Fig. 6.

The elongated clouds are called "canal clouds" and are produced by planes as well. Here is a radar image showing the precipitation falling from the hole-punch cloud to the ground:

There's also a "distrail" where the plane eats up the cloud as it passes through and leaves a blank path behind it.

ORIGINAL REPORT: In the past I have posted pictures of "hole-punch clouds," most recently last fall after witnessing one form over AccuWeather HQ (photo below). This week new research has come out that the precipitation (ice crystals called "virga") that "rains" out of the hole has been documented reaching the ground as significant snow.

I posted the research from UCAR on my Facebook Page earlier this week. Today FoxNews created a terrible headline saying "Planes Can Control the Weather, Say Scientists". Here's the video from the guy who did the research explaining what they found (the actual video shot from the plane is not online, but I have requested it).

There are three important points to remember in light of some of the media hype (disclaimer: these are my own and may not represent those of AccuWeather, Inc.):

1. I'm still not sure how the clouds form. Here UCAR has documented one case where planes flying through clouds can cause hole-punches, and that the precipitation can reach the ground (as two inches of snow did in that case). I still wonder if they can't also be caused by a jet contrail falling through the cloud, as I observed last fall. Note the elongated hole-punch clouds shown on satellite below -- more likely caused by a contrail descending through the cloud deck than a plane flying along at the exact level of the cloud, in my opinion. I suppose it's possible that a plane also flew through the cloud at the same time that I witnessed the hole-punch cloud, fooling me and I'll admit I was putting two and two together - clearly I have less documentation than what UCAR did.

2. I think FoxNews is overstating the possibility that the precipitation rained out of the cloud can reach the ground. I've seen plenty of photos of hole-punch clouds and have witnessed them myself, and have never seen evidence that the virga reached the ground. These clouds are typically very high and the precipitation would normally evaporate before reaching the ground, I would think.

Since obviously hole-punch clouds don't happen every day (or we'd see them all over Twitter & Facebook) the specific conditions to even get a hole-punch cloud are rare. I would think the conditions where the precip would reach the ground would be even more so (in fact if the ice crystals turned to rain with warmer air before they reached the ground they might have evaporated). In other words: Every plane flying through a cloud isn't going to do this so it's not something the average person needs to fear on the ground.

3. Cloud seeding has been going on in many parts of the nation for decades. UCAR equates the effect of the hole-punch cloud case they observed with a typical cloud-seeding operation. These are ongoing in at least (as of 2007) 11 states and 43 countries. We already knew that seeding worked (probably - depends on who you ask), we just didn't know that it could be occasionally happening unintentionally. I suspect that hole-punch clouds cause a tiny fraction of the beneficial rainfall of what actual cloud seeding does, so again let's not blow this out of proportion.

Here's a list of my previous blogs on this topic:

- Hole Punch Clouds in Mississippi 1/30/2007
- Hole-Punch Clouds in Florida 11/24/2008
- Hole-Punch Clouds in Pennsylvania 10/22/2009
- Russian "UFO Cloud" Was Really Hole Punch

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