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Why are our PM air masses always so moist/saturated?

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  • 02-01-2021 10:00am
    #1
    Nqp15hhu
    Banned (with Prison Access) Posts: 2,254 ✭✭✭


    I refer to Polar Maritime as that is where the majority of our cold air is sourced from, either Eastern Canada, Greenland or Iceland.

    Anyway, what I have noticed is that these air masses that flow in from Canada/Greenland etc almost always have high humidity values of 85%-100%. This airmass right now is such an example with humidity values of 95%+ in all lower layers. And this is why our chance of snow is always so low too.

    Now, I question this because other maritime air masses don’t bring such high humidity. A typical summer TM airmass might bring humidity values of 70%, maybe 60%.

    Is this difference down to increased warmth and vapour holding capacity?


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    #2
    Gaoth Laidir
    Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    Nqp15hhu wrote: »
    I refer to Polar Maritime as that is where the majority of our cold air is sourced from, either Eastern Canada, Greenland or Iceland.

    Anyway, what I have noticed is that these air masses that flow in from Canada/Greenland etc almost always have high humidity values of 85%-100%. This airmass right now is such an example with humidity values of 95%+ in all lower layers. And this is why our chance of snow is always so low too.

    Now, I question this because other maritime air masses don’t bring such high humidity. A typical summer TM airmass might bring humidity values of 70%, maybe 60%.

    Is this difference down to increased warmth and vapour holding capacity?

    It's just to do with the long sea track. From NW Ireland to Greenland is 1800-2000 km. Cold dry air will modify much more quickly than warmer moist air from lower latitudes. That's why the stronger the winds the better in that setup as there is less time for modification

    In many instances when we get a northerly it's not a true northerly-sourced northerly, rather a returning northerly.

    A northeasterly is normally the best for us as it's source is continental rather than marine.


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