Definition: Cap Cloud, a pileus cloud formed at the apex of a building, somewhat stationary, cumuliform cloud by moisture swept above the uprising expansion of air occuring from energy released from the latent heat of condensation in the presence of surrounding wind. As the prevailing wind is pushed up and over the apex, the capping occurs at the apex in a "Pileus," "Lenticular," or "Cap Cloud" form. This is known as a Cap Cloud. If high enough, to be at freezing level, 10-15000ft in this area, the Cap Cloud may be crystalline, i.e. ice crystals, but below freezing level it may appear as similar to swept virga or cumuloform cloud in a lens shape being pushed up above the rising apex. A similar phenomenon may occur at the apex of a mountain in the presence of upswept air containing moisture with dewpoint occurring at mountain top, this is also known as a Cap Cloud. Just as lenticular clouds may form in the absence of mountain wave, so may cap clouds form in the absence of mountains.
Related Meteorology, local: seabreezes are drawn inland and converge above the high central ground of north central Florida under solar heating thermal conditions. With the high humidity and lapse rate in this area, and the general upwelling of air under these conditions in north central Florida, thermal soaring flight is very good except for the frequent rainshower development which often shuts it down to a large extent post shower or under the overcast of cumulonimbus blow off. Where cumuli form and grow vigorously staying relatively stationary over ground the prevailing wind may be caused to sweep up and over and around the cumuli as if it had mass. There is a certain mass in the water of cumuli and upon condensation to cloudform there is additional heat energy released which further pushes up moist air above the condensation dewpoint level. When this becomes quite active in the presence of prevailing wind then the Cap Cloud may appear.
Experience and Contact: I have watched these beautiful clouds for years. They are hard to touch but on two different occasions I had the fascinating experience of reaching them. I was thermal soaring high about 5500 ft agl (6700ft amsl) just above Dobbins AFB, keeping eyes peeled for the near vertical Navy, Air Force, and Air National Guard fighter departures which were common there, and the cumulus were high and well formed without chance of overdevelopment. I was flying there in a "vfr-legal squeeze place" between the top of Dobbins AFB airport control area and the Atlanta TCA layer which definitely came down about there. I got to the sunward upwind side of cumulus and was able to climb not only up it but found lift above the top as Cap Cloud was forming there. I was able to fly to the Cap Cloud. What a sensation and what a view, 17 mtrs of brilliant creamwhite smooth glass flapped high performance wing flying in great magnificence, nose cocked into the wind from the northwest and climbed to 8800ft agl. Thermal climb had been good at 3.50-4.50 knots (350-450fpm) average to cloud base; just on the upwind side of cloud it was around 2.0-2.5 knots, and gradually decreased to nothing at the top of climb just at Cap Cloud on the forward side of it, there we perched in the sun above the bright bright white cumulus, on a day with beautiful blue sky marked by well defined cumulus, on top above the cumulus, with the Cap Cloud. I finally turned half-cocking downwind to go feel in the Cap Cloud and went thru maintaining visibility as it was not thick, but we were sinking as we went. I came back into the clear and went to front of the cumulus now, as we had lost altitude, and we could not re-do the same climb. I could not make it happen. So before we got way down to near cloudbase I headed out from about 7500 ft agl for a really beautiful glide north, leading on toward Rome Ga vicinity, fast to distant cumulus arriving at them 600ft below cloudbase for easy climbs the rest of the day in the normal working zone of no lower than 1500ft below cloud bases.
I have watched these Cap Clouds here in north central Florida much. They are abundant in this area. The conditions in which I have seen them here are not quite the same as on those days I went to the Cap Cloud in the Atlanta area, but it may be that I may contact one here someday. Maybe as rare as soaring with a bald eagle, but someday possible by the grace of God.
The times when climb up the side of cumulus may occur or to go to Cap Cloud are fairly rare. Many have never done it. When it happens it happens. You gotta be there, get some hints from feel and experience about a possibility for such a climb, and just do it...right time, right place, right equipment, and right desire, and other times you you just can not do it. It is not like centering a thermal and riding it up which is so common.
Those few times one may accomplish it, or similar unusual soaring flight, shall burn in memory. It is special to, and obtained by, only a few. We are fortunate to be in a place for cap cloud soaring, perhaps, and here in central north Florida we can watch the beauty of their formation and thirst for a contact someday, sometime.
Jim Culp USA
email: culpusa@hotmail.com
tel: 352 367 8608
| Dr. Günther Eichhorn | Springer 233 Spring Street New York, NY 10013 USA, email me |