Ulysses contains many weather references but as the sun sets on Bloomsday, let's dive into Met Éireann’s historical records for June 16th, 1904 to see what the weather in Dublin was actually doing that day.
This is what weather data looked like in 1904 - observations in the Phoenix Park were taken twice a day at 9 a.m. & 9 p.m. and recorded details for weather parameters including pressure, temperature, cloud, wind and humidity as well as a little one-line descriptor that gives us a sense of the day. Rain was measured once every 24 hours at 9 a.m.
The observer describes June 16th as a cloudy day and the code symbols indicate heavy rain between the hours of 3 p.m. and 8.30 p.m., which makes it sound a lot grimmer than the nuances of data suggest.
The cloud observations recorded at 9 a.m. indicate that just four tenths of the sky was covered in cloud, which suggests a pretty bright morning and chimes with what the narrator describes in the opening chapters of the book. The data for "duration of bright sunshine" indicates there were 12.2 hours of it, so it seems it was a reasonably pleasant summer’s day.
The details recorded for wind and rain suggest that a front passed through overnight as 0.21 inches or 5.3 mm of rainfall were recorded on the morning of Bloomsday. We also see that the winds have shifted to a more westerly direction, which is what we’d expect once the rain had cleared eastwards into the Irish Sea.
What normally happens next in our Irish climate is that showers follow from the Atlantic, often not reaching Dublin on the east coast until afternoon or evening. We can see from the data that the pressure has risen through the day (29.648 inches of mercury or 1001 hectopascals at 9 a.m. to 29.839 inHg or 1007 hPa at 9 p.m.) and the winds have fallen off light - form Beaufort force 4 to force 1 - so the heavy rain reported by the observer between 3 p.m. and 8.30 p.m. could well have been slow-moving heavy showers. And the 89% humidity he measured at 9 p.m. means that late evening was mostly cloudy and felt heavy and uncomfortable - with a chance of the thunder described in Oxen of the Sun.
The Phoenix Park observer records the maximum temperature on June 16th, 1904 as 63.1F (17.3C) but the weather report in The Evening Telegraph reports a temperature of 70F (21.1C) being recorded at 1.30 p.m. on Grafton Street. The discrepancy between the two figures could be accounted for by the urban heat island-effect of the city centre, or perhaps the measurement was taken in the sun (all meteorological air temperatures are recorded in the shade).
Either way, the day was warm enough to explain Bloom’s need to regularly remove his hat and wipe his brow.