I’m a cyclist, so I pay a lot of attention to the weather, especially during times I’m interested in riding. Based just on that, it seems to me that it rains somewhat less during the afternoon than during the morning or evening. Is this observation borne out by actual statistics?
You clearly don’t live where afternoon thundershowers are common.
This depends on your location … I made a quick search but came up empty for a map showing when the most likely time of day for a thunderstorm … but I seem to remember that afternoon was the most likely, on average.
Depends totally on where you live and why it’s raining there. Give us more & we’ll give you more.
All the jokes about New England weather are based in fact. In Northern California, weather was rarely a surprise - it fell into a pattern by day, by month, by season and annually. It was newsworthy-rare not to get what you expected in any given time frame.
Here, you can get almost any bizarre mix of weather in the course of one day, with little or not predictability. We have, in recent days, gone from hot/sticky/humid through a morning, rapid temperature drops leading to snow by noon, and hard warmer rain washing it away by nightfall… only to be warm and humid again the next day.
So it all depends on whether you live in a stable weather zone or, well, New England. 
Check the Doppler radar before you start out … that should give you a good hour’s forecast … anything past three hours is going to come with a probability attached to it … “should be but maybe not”
Where I live (western Oregon) we actually rarely get thunderstorms. So I forgot about the fact that some places get them in the afternoon. Although it’s usually late in the afternoon, no?
We just get weather systems that come off the Pacific. I wouldn’t expect there to be any pattern for time of day that they do. So I don’t know if my impression that there’s less rain in the afternoon (and when I say afternoon, I mean 12 to 4, not later) is correct.
BTW, I don’t need no stinkin’ Doppler radar to get a short period forecast. I can look at the sky to the west and get a very good idea of what the weather’s going to be for the next couple hours.
I use the crest of the Coast Mountains … if I can see them, I’ve a good thirty minutes dry weather … but if they’re obscured, I’m packing things in so they don’t get wet …
I live in the Willamette Valley of Oregon and ride my scooters a lot, so weather is important for me too. It’s pretty easy here because most of our rain and storms come off the Pacific and roll over the coast range. I monitor the weather forecasts, but will often check radar right before I leave to see where and how big the coming rains are. I am something of a fair weather rider.
As a general rule, excluding approaching fronts, showers are more common in the afternoon because of convection. Mornings are generally cooler (excluding weather systems in play) and as the air heats up it rises. (This is convection.) When it reaches the saturation point clouds form and it may rain depending upon other factors.
OK, I can see how that works in most of the country. But in Oregon here, virtually all our rain comes from fronts. Summers are usually dry with low humidity, so any convection will not result in rain.
My observation is that we often get rain in the morning but then it slackens off in the afternoon but may resume in the evening. So I guess my real question is, do the mountains in this region affect weather fronts such that we get this pattern? Or is it not the mountains but some other factor, such as convection?
Depending on how close to the coast “Western Oregon” is you may be affected by Marine layer - Wikipedia. That tends to maximize low-level moisture in early morning and late afternoon to evening, with minimum moisture during midday.
If you are close to the coast you also enjoy Orographic lift - Wikipedia. In simple terms when the wind from offshore pushes the moist air up against the coastal foothills and mountains the air has to go someplace. It goes up, cools, condenses, and, if there’s enough water, rains.
Those two things working together will explain most of the very high rain amounts within 0-20 miles of the Oregon coast. Farther inland you’re probably looking at more local effects or a false correlation as to time of day.
barbitu8 is describing continental climates … places with large areas of land upstream with places of uneven heating …
Oregon is a maritime climate … with large areas of open ocean upstream where the heating is much more the same …
We do occasionally build up a thermal ridge along the coast and this will slow down any weak fronts approaching … and this would cause a bit of difference for the afternoon rains … I honestly have never noticed this effect …
If it’s raining in the morning, that’s because the front is passing through … by afternoon it’s move on and it will dry up a bit … only to have the next front pass over in the evening … it’s just as likely that it’s dryish in the morning … wet in the afternoon … and then dryish in the evening … this is all driven by the Pacific Westerlies and her 10,000 mile fetch …
I’ve recorded 14 inches of rainfall in the past 17 days here … and my catchments are still empty … still, seems a bit early in the season to forget what the sun looks like, but there it is …
I’m in the Portland area. That’s further inland than 20 miles, more like 80, with some mountains (the Coast Range) in between.
Fronts don’t come in that quickly, that is, one in the morning and the next the same evening. At least I can’t recall ever seeing that. Even if there’s a dozen lined up in the Pacific ready to come in, it’s usually a day or two between successive fronts.
This is the fog layer associated with a high pressure area over the Eastern Pacific … the warmer ocean water evaporates into the cold air and condenses … we can get a few hundredth’s of inch of water in our rain gauges but this isn’t really a rain event … even the wimpy Coast Range blocks most of this from reaching the Willamette Valley … except up the Columbia River into Portland.
Indeed, it is in these Coast Mountains we find our 12 to 14 foot annual rainfall averages … and we do see a rain shadow effect on the eastern slopes … however the Valley is only 30 to 40 miles wide and then the air flow hits the Cascades … which are much taller and once again we get considerable orthographic lift … here is where annual rainfall rates drop down to 8 to 10 feet a year … beyond the Cascades is where we see the rain shadow effect in all it’s glory … Eastern Oregon is something of a desert … think Nevada dry … and for the same reasons …
The main driving force here is the Westerlies … any little disturbance coming off of the Asian mainland has days and days to build up energy … remnants of tropical storms paint a bull-eye on the Pacific Northwest coast … polar vortices pealing off slamming into the headlands … about the only rain maker we don’t see is thunderstorms … at least not very often …
With all this sloppy wet air flowing in off the Pacific … the first thing it hits is a short mountain range … dumps a load of rain … then it hits a big mountain range … dumps another load of rain … rain rain rain … rains every day all day long … orthographic in shovels …
In the Southern Hemisphere, these latitudes are called the furious forties … really powerful storms there
Excellent explanation. Maybe the OP will tell us where he lives or name a nearby town with similar topography so we explain for sure what’s driving his weather.
Micro-nit: you might have been a spellcheck victim. Mechanical airmass lift from terrain is “orographic” lift, not “orthographic”.
You may be thinking of the long wave fronts … those are a few days apart … but we still get short wave fronts spinning through off these long waves … and those can get to be every few hours apart …
Should’ve refreshed before I posted. :smack: Thanks.
Spelting is overratted and grammering is art, not science [adorable grin] … but yes I did mean orographic … thank you for the correction …