Thursday, July 7, 2011

Time Zones and Temperatures

I am easily confused in time zones checking weather forecasts.
For Example in the NWS Winds Aloft forecast data is in Zulu time, also know as Universal Time, UTC, or GMT (Greenwich Mean Time).
The forecast is based on data from Zulu time, for sometime in the future also Zulu time. Moving from timezone to timezone and getting thoroughly confused I decided I needed to help myself out. I've also been learning some JavaScript. That's what the numbers are in aide of top right of blog.

And what do the NWS winds aloft forecast numbers mean anyway ?

SFO 2507 2508+21 2412+15 2309+08 2607-08

at 3000ft MSL wind is from 250 degrees (WSW)
at 6000ft MSL wind is from 250 degrees (WSW) 21'Celcius
at 9000ft MSL wind is from 240 degrees (SW) 15'C
at 12,000ft MSL wind is from 230 degrees (SW) 8'C
at 18,000ft MSL wind is from 260 degrees (W) -8'C
DALR (Dry Adiabatic Lapse Rate) is 9.8°C /km
or ~1°C per 100m
or 5.38°F /1,000ft

If it is drier the Lapse Rate is less (maybe 4°F /1,000ft)
If it is wetter the Lapse Rate is also less (maybe 3°F /1,000ft)

So as soaring pilots we are always looking for those "popcorn skys"
Indicators of the desired humidity and lapse rate as well as to the location of lift.
Of course clouds tell a much more detailed story, but that's another story for another day.

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