Effect of inversion - Winter gnd windspeed

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R055YB0Y95 avatar
1 month ago #2
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Guest111 wrote:

Yo rossybot
Do not expect you to believe anything as there may be fairies at the bottom of your garden and Santa may deliver you a new wing for Christmas.
I also know that the last time you posted was not the 15 of December as this forum seems to suggest........that is the problem with this forum along with an inability in posting on the correct threads.

Whilst we are it what do you think of statement
"Significant Inversion forecast due to warm front approaching Scotland from the NW"
Prize for pointing out the elementary error.

All the best

Hello guest111 long time no hear. A few points the warm front coming from the NW causing the inversion perfectly matches everything I've seen today both whilst out flying and based on the spot winds, surface pressure and weather forecasts issued by the met office so I'd say that statement is/was correct.

As for old Saint Nick brining me a new wing whilst I would love that I highly doubt that's going to happen. but if you or anyone else is offering i'll have a skywalk chili 4 in orange size XS.

MurrayHay avatar
1 month ago #3
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Hi Ross FYI the troll G111 has not been away... this troll posts here using other 'identities' as well....

For non UK pilots information:

I've attached today's F214 & F215 showing the significant inversion, the MET Office forecasts giving experienced UK pilots (especially those who took the time to get qualified in Aviation MET!) probable warning of the risk almost calm LOW level conditions etc DESPITE the 15-20kt predictions for the 1,000ft level.... suggesting bigger sites likely to be 'blown out'.. as I'd indicated in a early morning Twitter post

MurrayHay avatar
1 month ago #4
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(Murray in teaching mode)

The Aviation section of the UK MET Office forecasts includes form 'F214' which is described as "Low Level Spot Wind". What this 'Low Level' refers to is the "lower flight information region" i.e. basically when below 24 thousand feet (above sea level) so part of the information is a prediction of temperature against height. To understand the benefit to glider pilots of having an indication of the days 'actuals' (when other MET information is factored in) PG pilots need to understand some basic Fluid Physics (air is a fluid). As air rises due to the lower pressure, it expands, as energy can't be destroyed a 'bubble' of air once higher, takes up a larger volume, hence the energy is spread over the new volume resulting in a reduction in temperature.

The mathematical 'perfect' (no mixing with surrounding air/no forming of clouds etc) change in temperature with variations in altitude is known as DALR (Dry Adiabatic Lapse Rate) and is 3* C per 1,000ft. Once the RH (Relative Humidity) reaches 100% cloud forms, then due to the Physics of Air»Liquid or Liquid»Air once cloud comes into play instead of DALR we see SALR (Saturated Adiabatic Lapse Rate) which is at 1.5*C per 1,000ft.

So back to the forecast charts I've posted earlier, a 'normal' or average temperature profile (based on starting at 5*C at 1,000ft) would see +2*C at the 2,000ft and -7*C at 5,000ft, -22*C at 10,000ft etc..... hence the effect of the Warm Front over Scotland see which has arrived from the NW as shown on the F215 is clearly seen 😄

Clearly for PG pilots interested in the stability or lack of stability of the atmosphere being able to anticipate (factoring in info from F215 and TAF's etc) what makes a good 'Thermal Day' or (especially for lower airtime PG pilots wanting a non-thermal ridge soaring day to practice take off's and landings) a good (safe) day for windy flying practice!

Murray Hay

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