What determines the saturation profile of an airmass?

#1 · 09-04-2021 2:33am #1

This evening we had a cold front pull through, this brought in an Arctic sourced air mass. The 850hPa temperature will be around -9c at their lowest with thickness values around 516 decametre. This is slightly warmer than the airmass we had at the beginning of the week.

What has struck me is the high saturation and Relative Humidity in this airmass. After the cold front passed humidity levels actually rose.

Right now I am sitting with a temp of 3c and a relative humidity of 91%. The prior airmass had humidity of around 60-70%.

As the air masses are both sourced from the same place and travel over the same length of water, why such a change in humidity and saturation levels?

Nqp15hhu · 09-04-2021 5:02am

Now it is 1.9c and raining...

Gaoth Laidir · 09-04-2021 8:00am

Relative humidity is meaningless when there's a change in temperature. You need to look at dewpoint instead. What did it do?

Even if the dewpoint doesn't budge, the r.h. will increase if the temperature decreases. Saying it's 91% now and was 60-70% earlier tells us nothing unless you state the temperature at these times.

Oneiric 3 · 09-04-2021 9:08am

This latest front did not clear in a clean fashion as it had warmer, moister air still clinging on well to the back of it:

The real Arctic air mass (such as it is) won't really make any meaningful inroads over Ireland until later on today.

Gaoth Laidir · 09-04-2021 10:07am

Last weekend's airmass was sourced from northeastern Canada (Baffin Island area), whereas this most recent airmass is more from eastern Greenland, and is therefore more ocean-influenced and hence higher dewpoints.

Last week's source (NE Canada)

This week's source (eastern Greenland)

What determines the saturation profile of an airmass?

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