June in Leiria, Portugal, brings average daily highs of 24°C and overnight lows of 15°C in the 2016–2025 historical record. Pack clothes you can layer as conditions change. The average leaves room for both warmer and cooler days, so a flexible walking plan is more useful than deciding every outdoor stop before you arrive.
In the record, at least 1 mm of rain or snow falls on 5 of 30 days on average, a daily chance of 17%. Leave some freedom to swap an outdoor day with a sheltered one. There is no need to read the average as a fixed number of lost days; it says nothing about how long rain lasts on each occasion.
The calculated day length, sunrise to sunset, averages about 15 hours. Sunshine averages 14 hours a day. The longer daylight window gives you more choice about when to be outside; it does not mean every part of the day will be sunny. Sunshine is a separate measure, and those hours need not arrive in one uninterrupted stretch.
For a culture-focused visit, group the places you want to see into manageable areas, with time between stops. Check each venue's opening dates before fixing the order.
July has an average daily high of 27°C, 3°C higher than June. Its historical rain-day chance is 4%, compared with 17% this month. If your dates are flexible, compare those trade-offs with the kind of days you want. Neither set of averages predicts the conditions of one particular holiday.