Aircraft contrail altitude

[lukemc]

As I know, aircraft contrails normally form above about 25000 feet or snow, but watching the aircraft over my house last Friday (12th February) I was surprised to see persistent contrails forming at an altitude as low as 12000 feet - a Flybe Dash 8 flying from Manchester to the IOM was contrailling persistently at 15000 feet (FL150).  I have read that for contrails to form the air temperature has to be around -25C or so but 10000feet or so corresponds to the 850HpA level and even though we had cold upper air around last Friday it would not the temps at 10000 feet-15000 feet be no less than about -8C or so? So can anyone explain why I saw contrails at pretty low altitude last Friday? I know humidity is also involved so maybe something to do with the humidity of the air - I might expect a contrail forming at 10K feet when we are under an airmass with -25C 850s or below but why so low trail level on Friday 11th?

 

Luke 

[Chris.R]

37 minutes ago, lukemc said:

As I know, aircraft contrails normally form above about 25000 feet or snow, but watching the aircraft over my house last Friday (12th February) I was surprised to see persistent contrails forming at an altitude as low as 12000 feet - a Flybe Dash 8 flying from Manchester to the IOM was contrailling persistently at 15000 feet (FL150).  I have read that for contrails to form the air temperature has to be around -25C or so but 10000feet or so corresponds to the 850HpA level and even though we had cold upper air around last Friday it would not the temps at 10000 feet-15000 feet be no less than about -8C or so? So can anyone explain why I saw contrails at pretty low altitude last Friday? I know humidity is also involved so maybe something to do with the humidity of the air - I might expect a contrail forming at 10K feet when we are under an airmass with -25C 850s or below but why so low trail level on Friday 11th?Luke

The 850 level is around 4200 feet (FL42  1300m)  varying by around 100 feet  depending on air-mass.  That's what I thought anyway. Look up partial thickness which is very similar. Even so,  I would have thought even at FL150 it would still be warmer than -25c  so it's strange. Maybe because it was very dry Continental air as you say?

Edited February 17, 2016 by Chris.R

[Nouska]

1 hour ago, lukemc said:

As I know, aircraft contrails normally form above about 25000 feet or snow, but watching the aircraft over my house last Friday (12th February) I was surprised to see persistent contrails forming at an altitude as low as 12000 feet - a Flybe Dash 8 flying from Manchester to the IOM was contrailling persistently at 15000 feet (FL150).  I have read that for contrails to form the air temperature has to be around -25C or so but 10000feet or so corresponds to the 850HpA level and even though we had cold upper air around last Friday it would not the temps at 10000 feet-15000 feet be no less than about -8C or so? So can anyone explain why I saw contrails at pretty low altitude last Friday? I know humidity is also involved so maybe something to do with the humidity of the air - I might expect a contrail forming at 10K feet when we are under an airmass with -25C 850s or below but why so low trail level on Friday 11th?

 

Luke 

With the caveat that this is a subject I know nothing about - other than to use the WAFC charts for Cb forecasting.

This is archived chart for 3pm on the 12th of February - icing warning at FL140.

 

 

 

[johnholmes]

Not got time to explain this but when back from holiday will do so. Contrails are dependent on hot exhaust gases from either piston or jet aircraft and whether they form contrails or not is governed by the actual air temperature at the time and the degree of moisture in that air. Prediction of them is a fairly easy matter, rare in meteorology, and is provided by scanning skew-t or t-phi plots. Will iluustrtae later this month.