Packing for summer

this may provide some help

https://www.ricksteves.com/travel-tips/packing-light

By "Northern France", do you mean Normandy and/or Brittany? Although you may well encounter hot weather, most of the places you are visiting can also be chilly and wet during the summer. I am very cold-natured, and when I travel north of the Alps, my suitcase includes the following (in addition to some lighter-weight clothing):

1 set of light polypro long johns (seldom used, but always needed on my very long trips)
1 cotton turtleneck top (the only top that works with the long johns)
1 pair of slacks that are heavier than summer weight (uncomfortable if it's hot)
1 light fleece jacket
1 unlined rain jacket/windbreaker

Otherwise, my clothing is summer-weight (3 other pairs of pants and 4 other tops for a 4-month trip). For sun protection I prefer 3/4-length or long sleeves even on the hottest days, but I go with what I have in my closet that mixes and matches; this year 2 of my tops are short-sleeved.

The long johns would be overkill for some folks, but I find rainy days in the northern part of Europe are often chilly, and the long johns have helped keep me comfortable in downpours when my slacks were soaked through. My rain jacket is very short.

The weather in Europe isn’t following any normal pattern this year, so it’s harder than usual to predict what you will experience.

I spent last June in northern France and we had everything from a sweltering 37 degrees in the shade to a week of near gale force gusts, rain and 9 degrees daytime temperatures. That’s difficult to pack for, which is why I always take a large bag!

Like acraven, I'm very cold-natured. What exactly is a "set of polypro long johns"? Can you share a brand or merchant?

I agree that at least for those of us who don't like cold, packing something lightweight for cold in northern France and the Netherlands could be very important.

nthompson, polypro(pylene) is a term for long underwear made with a synthetic wicking fabric. Look at REI.com for "base layers" or at Columbia, Patagonia, Lands End, or just about any store that sells outdoor and sports clothing. Silk long underwear works too.

PS to the original question, if it were me, I'd check the medium-term weather forecast the day before leaving, and pack accordingly. A long sleeve t-shirt is pretty versatile, but long-johns? Only if it was likely to be cold. Even then, I might get them there if it turned out I needed them.

The plastic underwear comes in various weights. The thinest, lightweight, "wicking" version is part of my kit in shoulder season, though I usually only bring the bottom half. Don't get warmer weights unless you are staying in an ice hotel.

It is great stuff, packs down to nothing and adds warmth outdoors without bulk. Indoors it adds nearly nothing, another plus if you don't plan to spend the entire day out in the cold.

The weather is so weird all over this year. It's really hard to even try to predict anything.

I started out using silk long johns, but they were pretty fragile even if hand-washed, and sometimes the colors ran. I now use Cuddl Duds. They're often on sale around Christmas time, and as of a couple of years ago they had a less expensive line available at either Walmart or Target. They dry very quickly and can be used as pajamas in a pinch.

My Cuddl Duds allowed me to salvage an utterably miserable day in southern (!) France last May. Heavy rain was forecast and materialized, but I was able to forge ahead with a planned day-trip that would have been difficult to reschedule.

It's hard to predict the weather, but for me It's best to pack some shirts trousers,cardigans a pair of flipflops and some personal necessities.

Take a look at the average temperatures for that time of year and pack accordingly. Pack lightly with a light rain jacket and a lightweight cover along with your "normal travel clothes". Just plan on doing some laundry or having it done along the way. Your luggage is 22x14X9 so you have a lot of room!