I'm wondering how daft an idea this is because of the heat.
There's a plan afoot to ride on motorbikes down through Spain and cross to Morocco on 1st July.
Stay at Chefchaouen & Midelt.
Ride over to Boulmane dades but
camp at the highest spot past Tighadouine
Marrakesh via the Tizi pass.
Casablanca then ferry back to Spain on the 7th July.

I'm mostly concerened about the heat.
Can anyone tell me what temperatures I'm likely to find at different stages of this route?

We haven't much choice with the time of year so if it's too mad then we'll have to turn left and head for Eastern Europe instead...

Life obviously goes on through the Moroccan summer so as long as you plan accordingly there's no reason why you shouldn't join in. It's no more than you might encounter during a Spanish heatwave.
Temps will jump south of the Atlas - Ouarazazate is especially hot and it's at over 1100m (I am sure you can find climate data online).
Once the ambient temp exceeds body temp (as it will in the south in July), on a bike the faster you go the quicker you dehydrate. You will have to zip up against the heat and any exertion will become draining. Drinking litres of water a day is necessary obviously, but taking rehydration tablets (like Nuun or Zero - from pushbike shops) makes a real difference if you're not to end the day feeling crook. Sugar and salt @ 8:1 is similar.
A sensibly scheduled road ride is surely possible in such temps, but will it be much fun? If you are tackling Trans Atlas via Agoudal (MH1) I would factor in an extra day and expect to get home quite weary if not even a little ill.

Note too that you will be in Morocco for the last week of Ramadan by which time some locals might be getting quite cranky.

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Morocco Overland 4 pre-order for Xmas • Trans Morocco Trail

Today I set out on a 200km offroad loop wearing jacket with liner with heated jacket underneath. Before long the heated jacket was switched off. An hour later I took the heated jacket off. An hour later I removed the liner. An hour later I opened all the zips of my jacket, but was still hot. And this is January.

July is possible, but can be difficult. Weirdly Marrakech is often hotter than Ouarzazate, either because it's lower (550m vs 1200m) or because of the effect of a big city. Marrakech holds the record of 49.7ºC for the whole of Morocco.

The two problems are (1) shade temperatures and (2) the effect of the hot sun.

Shade temperatures
20ºC typical English summer day
24ºC English heatwave
28ºC lovely--warm enough to ride in T-shirt
32ºC about as hot as I like it. Take lots of water, sugar, salt
36ºC getting silly, especially mid summer, head for a swimming pool
40ºC TURN BACK, head for the coast or mountains

(note my table stops at 40ºC, but it can get hotter)

In summer months the temperature typically decreases by 0.5ºC for every 100m of altitude, so going from Marrakech (550m) to Imlil (1750m) will reduce the shade temperature by maybe 6ºC.

Effects of sun
Right now in January, taking a white object from the shade to the full sun raises the temperature 12ºC. So you can imagine the effect in July with a black object—maybe 25ºC, probably more.

My main suggestion is DO NOT WEAR BLACK and invest in a light-coloured 'air' jacket. Take a buff to protect your face and don't forget sun cream for your nose!

When it's really hot get on the road as soon as possible (dawn temp might still be 25ºC). Stop for the day somewhere with a swimming pool by 2pm before it really gets hot around 3-4-5pm. Cool down when riding by dousing your clothes with water, this dramatically increases the wind chill.

At nighttime sleep under a wet towel if necessary. I carry a 100ml perfume atomiser that I fill with water and have a small battery fan. If I awake hot, I can spray myself and use the fan to chill me.

.

__________________
"For sheer delight there is nothing like altitude; it gives one the thrill of adventure
and enlarges the world in which you live," Irving Mather (1892-1966)

I went in late July /August in 2012. The hottest temperature was in Fez, where my bike registered 43*C!

I found several things useful. My hydration pack was a life saver; excellent bit of kit. Also, I rode down from the UK, so the I discovered that the time spent riding down through France and Spain acclimatised my body to these temperatures. I think if I'd flown there and ridden, or even sailed to Spain and then bombed down, I wouldn't have coped nearly as well. I wore fully vented clothing, so whenever I rode cool air kept me feeling OK. I didn't ride off road as much as perhaps I might have liked, and I think this is the only real caveat. Serious off roading, dropping and picking the bike up again and again would cause real problems in the heat. I've read of serious problems caused by this in the past.

I remember asking Tim at a HUBB meet just before I went about the heat, and his expression said everything! Personally, I do find that I cope better in the heat than the cold. Why am I here in the UK in winter then? Good question . . . .

Ha, I grew up in Peterborough, before it was one of the new towns. Used to go fossiling in the open cast clay pits when I was a kid.

__________________
"For sheer delight there is nothing like altitude; it gives one the thrill of adventure
and enlarges the world in which you live," Irving Mather (1892-1966)

Thanks for the tips. I guess we'll probably go anyway.
Maybe head back along MH2 and head back via Fez?

So we went. Two of us. Had a couple of days over 45 degrees but by then we'd already had a few days in Spain at 40 plus. I think we go acclimatised!
Ignored some advice but followed most. Black helmets, black bikes and rode all day but did wear vented jackets and had hydration packs.
I loaded mine with electrolyte tabs and made sure I sipped it all day.
Doing cirque de Jaffar we managed to drink 5 litres of water during the day!
Couldn't make it through to Imilchil from Midelt as rains (!) had washed the road out East of Imilchil. So we left the panniers in Midelt and did the cirque and back.
Lots of washed out sections covered in soft gravel even so.
Popped down to Erg Chebi and then passed back over the Atlas via todra gorge. Ran out of time to do Marrakesh, Casablanca etc.
Had an excellent trip, no big problems with Ramadan; in fact we got invited to a Berber guys house to break fast (although it proved to be a long winded carpet selling game) which was excellent.

I had a blast and now I've got the hang of it; I'll be back soon, maybe when its cooler though!