Originally Posted by
GhostRider62
Could you explain the wind patterns for the dense (me).
Let's say I arrive Loudeac at 6 am and get to Brest at 1-3 pm, would I have the slight tailwinds until coming down into Brest down the "Roc"? And more importantly, would I expect a tailwind leaving Brest? In my three times (plus some touring in the area), it gets to 37-42F in the valleys especially Tintineac to Fougeres. Or would you advise taking an afternoon nap in Brest to profit from the wind later? The section 190km approx. from Brest to Loudeac tends to have a lot of climbing is probably the most wooded section whereas from Loudeac to Mortagne is pretty open going with wavy up and down rolling terrain w/o a lot of trees. In 2019, there was headwind in both directions on this Loudeac to Mortagne stretch and was kind of hard. I really did not think about wind that time and just rode how I felt.
Today, there’s a huge massive depression heading its regular way, West-> East, that storm has even been given a name : Gérard.
Strong wind which peaked at 160km/h 99.41 miles/h South of Brest.
Not a single chance for a coastal effect.
If you have a similar, even weaker, weather system in August, it’ll take the upper hand over the Coastal Effect.
Ditto, anticyclonic weather system, in summer, with high pressure, in this case you are more likely to experience a cross wind South-> North.
No Coastal Effect.
Link I posted yesterday is meant to explain the weather effect to children.
Little drawing with a sun is... you’ve guessed it....daytime
Darker with a moon, night time.
Depending upon temperature, at dawn and its speed of increase, that narrow widow, where Inland Temp= Offshore temp = no wind either widens or gets narrower.
Clear blue sky, Temp climb fast : narrow window with no wind.
Cloudy sky, slow Temp climb, window with no wind widens.
If all conditions above are met, on a cloudy day, at 6 in Loudéac, per Coastal Effect, night (tailwind) wind starts dying out, that window with no wind starts to open, you could have 1h with no wind.
Same in the evening.
Then, you have a headwind.
That experience of yours, headwind going West and again headwind going East, (without no major weather system change, e.g. Depression with rain) is an all time classic of that pesky Coastal Effect.
You have had a first hand experience of what it does.
IMHO, I insist, all conditions described above met, it’s better to ride a long stretch at night going going West, but not recommended to get up early going East, on your way back, and ride during the day, pushed by that wind coming from the sea (if any).
Hope this helps.