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Interesting Temperature Fluctuations At Dublin Airport Yesterday
Topic Started: April 12 2011, 11:13 PM (394 Views)
Fergal (IWO)
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http://www.irishweatheronline.com/news/interesting-temperature-fluctuations-at-dublin-airport-yesterday.html

It is interesting to note the effect that passing showers had on temperature readings at Dublin Airport yesterday afternoon. Such were the temperature fluctuations that the observer on duty chose to highlight them on the hourly SYNOP reports (see the IWO Guide to Decoding Synops). Amazingly the temperature fell by 5°C in less than an hour, and rose again by 3°C in just 10 minutes!

A strong cold front had passed eastwards across the country overnight Sunday and Monday morning, leaving a cool blustery Polar Maritime airmass in its wake. This classic April setup caused showers to form as the sun heated the land, and the first of these started affecting Dublin by late morning. The graph below summarises the conditions at Dublin Airport for the period from 1100 UTC (midday local time) to 1500 UTC (4pm local time), based on the hourly Synop reports, listed here. The graph also includes dewpoint and mean windspeeds.

1100 AAXX 11111 03969 41464 72708 10115 20057 30128 40232 52011 72582 873//

333 82918 83823 85657 98180 98380 98780=

1200 AAXX 11121 03969 11480 72909 10137 20050 30130 40233 51009 69921 70186 873//

333 81918 83823 85657=

1300 AAXX 11131 03969 41486 52811 10122 20033 30135 40239 53011 71622 85930

333 81918 83647=

1400 AAXX 11141 03969 41475 72813 10075 20052 30140 40245 53012 78082 8793/

333 83918 85646 91119 99705=

1500 AAXX 11151 03969 41484 32908 10105 20057 30139 40243 50009 72581 81302

333 81918 83070 90710 99603 91313 90409 91308=

Posted Image

Temperature, Dewpoint and Mean Windspeed at Dublin Airport, Monday afternoon, 11th April 2011.


At 1400 UTC the temperature fell five degrees from 12.2°C to 7.5°C as a light rain shower passed through. The wind increased to 25 knots, with gusts to 37 knots. This was probably due to cold downdrafts from within the cumulonimbus clouds reaching the surface. These downdrafts are caused by evaporative cooling of the air, in which latent heat energy is taken from the air to evaporate water from the surface of the rain droplets. This air becomes colder and hence denser than the surrounding air, and descends towards the surface, a bit like the cold air you see sliding downwards out of your freezer when you open the door.

The most notable effect, however, was the sudden rise of 3°C in just 10 minutes up to 1500 UTC (shown by the 90710 99603 groups). This would have been caused by solar heating after the passage of the shower and its downdrafts, and is a reminder of the increasing strength of the sun as we head towards summer. Also notable is a sudden decrease in windspeed from 25 to 16 knots at 14:09 (shown by the 90409 91308 groups), which is further indication of the passage of the shower. Also, I suppose, a reminder that we are in the month of April, where if you don’t like the weather, just wait five (or ten!) minutes!
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