Dropping humidity, rising pressure

This happened just after midnight. Might explain why yesterday we reach 25C and today we will reach only 19. (but I’m not a meteorologist. I need to learn this stuff :wink: )

Added an animated graph of the humidity.


A roll cloud at the leading edge of a cold front. Down this side of the planet often but not always accompanied by a southerly wind, so up your side I guess you had a northerly change. In the northern parts of Australia gliders soar the roll cloud which comes with a different wind than the cold fronts. A bigger story…

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This map from Surface Pressure Charts - Met Office from 00 UTC shows an imminent cold frontal passage (FROPA). The cold front is associated with an occluding extratropical cyclone centered west of Nortern Ireland. So, yesterday, you were in the warm sector (see the warm front in the North Sea) and should have been seeing winds with a southerly wind component (which were likely advecting warmer continental air from Africa) … after FROPA, your winds should have acquired a more westerly component, which, in your location, should be advecting air from a “maritime” air mass, which, in that area is probably a pretty chilly air mass, so, without doing a detailed analysis, I would expect lower temperatures today.

And, yeah, the roll cloud pointed out by @iladyman is pretty cool :slight_smile:


your analysis is spot on. The interesting roll cloud was the reason for posting it as I don’t think we have those that often. Also a bit showing of my new camera that makes nice color pictures even at midnight. Just looking up, one would probably not have been able to see this very clearly.

I have mostly seen roll clouds here in the US associated with a strong thunderstorm gust front … rarely associated with a synoptic cold front. The ones that occur with thunderstorms can be rather dramatic (some times low enough to easily see the rolling motion with the naked eye and almost “ground scraping” :slight_smile: ).

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there wasn’t any lightning detected around midnight. There was a 2 degree temperature drop associated with the passing of the rolling cloud, but that drop only lasted about half an hour.

They can and do occur with cold front passage (see https://www.washingtonpost.com/weather/2020/03/12/breathtaking-roll-cloud-tumbled-over-nebraska-thursday-morning-heralding-cold-front/ ), but, they are most often associated with thunderstorms in most parts of the US.

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other phenomena but as visible on charts for me last night, wind swapped after it piked up and pressure suddenly goes up and humidity drops


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