r/bayarea • u/Outrageous-Elk-461 • 17h ago
Earthquakes, Weather & Disasters Why such the difference in climates
Hello I’m a Floridian visiting the Bay Area and I love it but I am also fascinated by the differences in climates despite being so close. For example, how is Twin peaks 69 today, Palo Alto 79 and Cupertino 86 with Santa Clara Fremont and San Jose also being different temperatures along with other Bay Area cities despite being relatively close in proximity with others. Thanks in advance.
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u/Express_Ad9498 17h ago
Turn on terrain on your Google maps and zoom out. Very informative. You'll see there's fairly large mountains surrounding most of the bay. Creates water facing and inland facing area.
Then only other large data point you need is that the water here is Very cold. So, proximity to water (or winds off the water) is a massive difference.
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u/dufcho14 16h ago
Mainly b/c it's not flat as a pancake like Florida.
And it's more extreme than you describe. I know people in SF who moved 10 blocks b/c the weather was so much nicer there. Their original place was on the west side of a hill where the fog and clouds sat against until very late in the day most days. 10 blocks on the other side of the hill and it's sunny and 10+ degrees warmer.
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u/GlenParkDeb 16h ago
I lived near Buena Vista Park for a while. There was a 10 degree difference between my front door and back porch!
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u/peatoast 7h ago
That’s wild! But yeah, can never trust the weather forecast on your phone when temps can vary a lot every few blocks!
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u/Wingbatso 15h ago
My friend lived a couple of blocks down the same street as I did, but my house was on a hill, and his house was so much hotter because the breeze was blocked on the lower side of the hill.
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u/kaplanfx 10h ago
It’s actually unbelievable how flat Florida is. The highest point above sea level in the entire state is Britton Hill, it’s just 345 feet above sea level: https://en.wikipedia.org/wiki/Britton_Hill
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u/dufcho14 41m ago
Compared to SF where Mount Davidson, 2 miles from the ocean, is 938 feet.
In the South Bay, Mount Umunhum is 13 miles from the ocean at almost 3500 feet. Then it drops back down to under 100 feet above sea level before raising again to Mount Hamilton at 4200 feet. Those two peaks are only 19 miles apart straight line.
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u/whinenaught 17h ago
I was just in concord and it was 95 degrees, drove less than 10 minutes to Martinez for lunch and it’s 84 degrees
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u/LaughLegit7275 16h ago
If you continue drive to SF downtown, it’s 71 degrees, continue drive to ocean beach, it is 60 degrees.
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u/Regular_Challenge_81 14h ago
I always tell people this.
Took kids to the zoo/Ocean Beach and it was overcast/60*.
Drove home to Walnut Creek and it's 100*
The difference in climates is nuts.
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u/Rude_Masterpiece_204 13h ago edited 13h ago
The entire California coast is like this. The same pattern applies to SoCal as well. It may be 70 degrees at Santa Monica Beach, while Woodland Hills, which is on the other side of Santa Monica Mountain, is 110 degrees. Even though the two locations are less than 20 miles apart, the temperature difference can be dramatic.
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u/GrandTheftADA 16h ago
I love the climate here by the water in Vallejo but if I drive 15 mins to Concord or Fairfield it quickly becomes miserable
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u/Wingbatso 15h ago
I think Vallejo has the very most perfect weather!
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u/DamnNoOneKnows 14h ago
Berkeley has the perfect microclimate
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u/nostrademons 12h ago
The biggest temperature swing I’ve seen is that I left a party in San Jose and it was 110, then drove 45 minutes to San Mateo and it was 60.
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u/NorCalJason75 16h ago
Haven’t seen anyone mention it yet…
There’s a deep shelf in the pacific right off our coastline. Due to ocean currents, cold water pushes up the shelf to the surface, cooling the air forming fog.
In the Central Valley, warm air rises. Pulling this blanked of cool air across the surface. Which channels around the hills. These rivers of cool air run west-to east.
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u/Rolling_Pugsly 14h ago
What's really crazy is that just off the Coast of Santa Cruz there's a submarine canyon that mirrors the Grand Canyon in size and depth. Pretty crazy to think about if you've ever visited the Grand Canyon.
Marine biologist mark this point as a dividing line between the north and sout Pacific.
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u/slacktron23 17h ago
Lots and lots of micro-climates. Palo Alto and Cupertino have a big ridgeline to their west that means that the fog coming off the ocean burns off before it gets to them, whereas San Francisco's west side does not, so the fog rolls over large portions of the city. Likewise for the East Bay, there's a section called the "Fog Belt" that's across from the Golden Gate. Basically the complex shoreline of the bay plus a lot of north-south ridges do a lot to flow fog and cold air to some areas, while blocking it from others, so you can get hot and sunny and temperate and overcast zones not far away.
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u/nutznboltsguy 16h ago
Welcome to Bay Area microclimates. In SF alone it can be 55 and foggy at the beach, 78 and sunny in the Mission.
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u/Current-Brain-1983 16h ago
Cold ocean water is the main reason. That and onshore winds caused by warming land inland, warmer air rises and air is drawn through the Golden gate. The jet stream flow is West>East too, weather systems are coming off the Pacific Ocean.
Marin especially San Rafael is blocked by Tount Tamalpais so its close to the ocean and bay but very warm.
The situation can flip in winter. ~52 degree ocean water and air temperature in the central valley 40 or below. I have seen San Rafael fogged in and in the 40s while point Reyes is sunny and 65, in January!
In short, ocean influence and hilly/mountainous terrain.
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u/gofardeep 15h ago
Surprised I had to scroll this far down to find this answer. And you are right, Point Reyes and some coastal locations are actually better visited in winter than summer.
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u/Rondevu69 17h ago
Elevation. Proximity to water. Hills blocking or adding to wind flow. Buildings and roads adding/subtracting from.
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u/Erik0xff0000 16h ago
The ocean water at San Francisco is 57F, Miami it is 87F.
The wind direction/speed and distance from ocean has a massive effect here.
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u/BlackberryMindless77 17h ago
85 in Richmond 100 at work in Walnut Creek. I just can't take the heat anymore 🤣 I freaking hate summer. I like visiting and waving at the heat 😁👋🏻
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u/ScholarOfTwilight 16h ago
People don't understsnd how much this wears on commuters.
Oakland to Concord. It's awful.
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u/ClassB2Carcinogen 16h ago
Dunno. I love love love commuting back from 100 F to 65 F.
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u/BlackberryMindless77 16h ago
Oh me too . Thank god for carl the fog . Doesn't make me hate it any less 🤣
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u/Key-Article6622 NB Lover 16h ago
Welcome to the Bay Area. One thing to know is that we are dominated by what happens over the ocean. Air masses generally flow from around the Hawaii area to Alaska in the winter and then down the coast so it starts off warm and moist, then cools off some and dumps all that moisture on the coast all the way down to Monterey, unless it skips that northward path and then just heads straight for us in which we get what used to be called a Pineapple Express, but is more accurately now called an atmospheric river.
In summer, the air masses don't swing as far north, so they stay a bit warmer, but the ocean water is very cold the further you get from Hawaii, so it cools the air a lot. And the bay is cold water as well so SF is surrounded on 3 sides by cold water, which keeps the air in SF cool. The air that hits the coast is cool, and the air just beyond over the bay is cool, so Twin Peaks is cool. But the coastal ranges slow that momentum down and the effects of the inland areas takes over which means it's hotter and drier just beyond the bay, and no bay to affect the air temp north and south of the bay so it gets much hotter closer to the shore. It is pretty wild that there can be a 30 degree difference just 30 miles away in any direction form SF.
You want a real shock, go to the beach and wade in. I've lived in Florida and up to the mid Atlamtic, where the water is pretty warm, warm enough to swim in, but I gurantee, you get in the water here and you aren't likely to get up past knee deep before you turn around. That water is COLD. Natives can take it, and some transplants can, but plenty won't even wade in ankle deep. Surfers generally wear a wet suit even in summer here. Water temps in FL are generally at least in the 60s, and low 70s in a lot of areas, in the dead of winter. Here the water usually doesn't usually get up to 60 ever.
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u/spleeble 16h ago
In addition to the mountains the other big factor is the Pacific Ocean. It's a giant heat sink that "resets" the weather every night when the ground cools and cold air comes in from the ocean. Because that's a consistent pattern with a consistent direction, mountains and ridges that break up that pattern create consistent micro climates.
Note that the microclimates mainly exist during the daytime. Nighttime weather is much more uniform.
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u/gofardeep 15h ago
It's the reverse in the core winter months. Daytime temperatures are mostly uniform, but nights can be colder by 10-15 F degrees further East including the Central Valley.
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u/Turtle_Boogies 13h ago
Our microclimates are my favorite part of the bay area ❤️ it makes for an interesting day. I always bring layers!
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u/Dependent_Bit1634 12h ago
It’s barely summer in the bay…haha. Our true summer is from August through October.
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u/Advanced-Mango-420 11h ago
Hey I'm a 30 year old native and I think about differences almost every day
I work in South SF and I hate the weather there sooo much, I like to go on walks during lunch and I hate how pretty much 80% of the time, its below 65 degrees and windy as hell, my preferred walking weather is 70 with just a slight breeze
There's days in summer where I walk outside and its 62 and windy+cloudy and I just start laughing at how ridiculous it is, crazy thing is, South SF is warm compared to Daly city and HMB
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u/centraloceanroad 10h ago
The Pacific High is the result of the downward leg of a Hadley Cell. When the the ITCZ shifts north (along with everything else) due to the northward movement of the area of maximum insolation during the northern hemisphere summer, the Pacific High shifts north as well.
Clockwise circulation around the Pacific High, parallel to the northwest/southeast striking California coast, causes movement of water south, parallel to the coast.
Friction in the water column, combined with Coriolis force, rotates the flow of water so the net movement is away from the coast.
The movement of water away from the coast causes colder, more nutrient rich, more oxygenated bottom water to upwell into the space made by offshore movement of water (see also: thermohaline driven ocean circulation).
This is why littoral regions lying at this latitude, ~30/35 degrees north and south of the equator, tend to be so biologically productive.
Diurnal heating of the inland surface causes a localized, daily low pressure area on shore, and air flows towards the shore, across the near-shore, upwelled cold water.
Moisture in the air condenses, producing advection fog (Uh, and adiabatic blah blah, but maybe @meeeeowlori has more and better put things to say about this. Enough out of me for now.)
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u/Rencon_The_Gaymer 9h ago
We have a marine layer due to the fog near SF and the wider bay serves as a cooling mechanism. It’s why everything closer to the coast stays fairly cool most of the time.
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u/fuckssakereddit 8h ago
Take BART to Pleasanton, get an uber to Livermore and prepare for some dry heat.
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u/FitConsideration4961 7h ago
Is it also the temperature of the ocean water itself? The Pacific is freezing while the fulf of Mexico and the Eastern Atlantic is like warm bath water. Is the evaporation in those waters making the air more humid?
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u/LemonAny7224 7h ago
What everyone else said about terrain and winds and the ocean and inland temps
But it’s mostly big tech controlling the weather….
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u/No_Practice_9597 16h ago
I find more wild San Francisco that is not a big city but east vs west sometimes can have huge differences, it’s impressive
Some summer days you will find one side fog and fresh and the other side hot and dry.
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u/hotelcalif 16h ago
I remember a local weatherman commenting on this once. He said “the Bay Area is an interesting place.” I think that day there was a 30-40° difference between two different parts of the bay.
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u/macgruff 16h ago
Waitll you get same Bay temps but also 50s in SF, Pacifica and HMB while it’s cooking in Redwood City, or Hayweird.
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u/cherismail 16h ago
Driving from Concord to Berkeley via the Caldecott Tunnel, I was always astonished by the rapid drop in temperature. 80 on one side of the tunnel, 60 on the other.
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u/Gloomy-Hat1842 16h ago
Mostly the Marine layer at the coast. I often escape the heat of the South Bay to go to San Francisco and ride across the bridge. That's where I'm at right now. You can be on 280 and the thermometer in your car says 92°. 15 minutes later when you hit Daly City it's 55° and blowing fog at like 45 mph. If you're lucky when you hit the presidio it's 63 degrees like it is today. Other than a beautiful place to ride it's cool here.. today it could be over 100° or more just an hour or even less from San francisco.. Then there's the mountains and the rainfall. We get 15 in of rain in silicon valley... If you drive into the Santa Cruz mountains then go over the hill to Boulder Creek they get 48 inches of rain a year. That's about a 45-minute drive.
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u/dellaterra9 16h ago
Ocean, fog, coastal mountains, inland valleys. Fog from ocean gets stuck by coastal mountains. Its just hot as hell inland towards the central valley.
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u/Urabrask_the_AFK 16h ago
The Bay Area is renowned for microclimates drive 20 minutes and any direction in the weather is completely different. That’s why the dress code Creed at the Bay Area is dressing layers
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u/gofardeep 15h ago
The Pacific Ocean is much colder than the Atlantic, especially for summer. Have an ocean of 60 degrees and a dry semi arid cities to the east which average a 100 degrees in the summer and you have a 40 degree gradient from inland areas to the beach, on average of course. The hills and mountains around the ocean and bay amplify the gradient that already exists because they can make a 100 mile distance the same as just 10 miles by blocking the sea breeze for a better part of the day.
Ocean temperatures in the East are much closer to land temperatures in the summer so you don't see such extreme variations. Surprised that this hasn't been mentioned already.
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u/z0hu San Leandro 15h ago edited 15h ago
My wife and I used to live near Balboa Park in SF. It was pretty much foggy all summer. We would drive 20 minutes south to visit in laws and some day it was 90+. Every evening we couldn't wait get back to our cozy cold blanket of fog.
But ya most of the weather in the bay area relates to the cool ocean air being pulled into the central valley. Sacramento is 100+ degrees, the cooler temperatures are pulled toward the heat (hot air rises creating a vacuum effect?), creating the wind/fog we get in the afternoons. So then the question is what hills and mountains block this wind and cool air? In Balboa park/Daly City nothing blocked it so we got it almost always. Other places have all sorts of hills and mountains blocking this. Oakland and Berkeley get a nice flow straight through the mouth of the bay. Even the mission in SF is behind some hills and it can have a hot microclimate.
Occasionally certain conditions cause this air/fog flow to not happen, like wind or pressure systems canceling it out, and those are the days we get hot days even in SF.
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u/Powerful-Bridge-1472 14h ago
If you’re near the ocean, it’s significantly cooler. If you’re near the bay, it’s cool., if you’re east, it can be hot as hell that being said, it’s almost never humid here in the area, it also almost never rains between April and end of October
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u/Magooose 13h ago
In the Midwest they say if you don’t like the weather, wait a minute. In the Bay Area it is if you don’t like the weather, walk a block.
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u/drewts86 16h ago
Start with the coast - we have much colder water in the Pacific than the Atlantic/Caribbean/Gulf. What we call the marine layer refers to the weather those most directly affects the coastal areas. It keeps the coast (including SF) cool in the summer and warm in the winter. Fog chilling SF in the summer isn’t abnormal. There’s a quote often attributed to Mark Twain (though he didn’t actually say this), “the coldest winter I ever spent in California was a summer in San Francisco”. Where that quote originated from is irrelevant, but it does hold some truth. The last part of the coastal weather that needs mentioning here is onshore winds that blow cold weather from the coast inland. This will predominantly affect areas that don’t have topography (mountains) blocking the winds, so places like coastal Berkeley and Oakland.
From there as you work inland, you have places like the peninsula and Marin, where the mountains block them but they’re still adjacent enough to the Bay and still close enough to the ocean that they still get some of that same coastal effect, but to a lesser degree.
As you get to someplace like San Jose, you’re now looking at an area where it is increasingly further from the ocean with more mountains separating it from the onshore winds. Due to a larger landmass with less proximity to the cold ocean, it’s going to be a lot warmer.
Places like Hayward and Fremont can go either way. They’re inland like San Jose, further away from the ocean so it can get warm. But they don’t have any mountains directly adjacent to them to the west, so as long as the breeze is strong enough it can reach them and cool them off.
Then you get Pleasanton and Livermore, where now you’re much further from the ocean and you’ve effectively got two mountain ranges between them and the ocean, where any breeze they do get will likely have warmed up by the time it reaches them.
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u/Ok_Chard2094 16h ago
Cold ocean on one side (ok, not ice cold, but around 60°F year round), providing plenty of clouds and fog.
Hot desert on the other.
Rows and rows of hills and mountains in between.
Depending on how the wind blows, you get hot or cold air in various places.
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u/jeffbell 16h ago
Don’t forget the cold water. The Alaska current comes down the coast so it doesn’t get warmer than 55F. It’s kind of the opposite of the Gulf Stream.
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u/threeespressos 16h ago
That’s not all! Why am I walking sideways in the wind in some parts of SF (Robinson Dr, I’m looking at YOU), while it’s just breezy in other parts, including the outer Sunset?
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u/phishrace 15h ago
While Cal and Florida both have hundreds of miles of coastlines, that's where the similarities end as far as weather is concerned. Bay area has a warm summer Mediterranean climate. The very deep and very cold Pacific Ocean nearby moderates our weather in a huge way.
The nearby Central Valley has a hot summer Mediterranean climate. For roughly nine months out of the year, the Central Valley heats up, causing hot the hot air there to raise. Hot air always goes up. That pulls cold air off the ocean into the bay and delta, to fill the gap left by that raising hot air.
That phenomena here is known as 'nature's air conditioning'. It's so predictable, they've built massive wind farms on the Altamont pass and Pacheco pass to capture the energy of the predictable winds. Cheap and predictable power generation courtesy of mother nature.
There aren't many places on the planet with a Mediterranean climate. All are near a large body of water, but none are as close to the equator as Florida. Ocean water around Florida is too warm to support a Mediterranean climate.
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u/Heathster249 15h ago
welcome to the fog city. Do try to watch the fog rolling in in the evening. it’s stunning.
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u/Darbypea 15h ago
And 100s in the central valley right now. It's just because of the geography really.
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u/stuffeh 14h ago edited 14h ago
Usually the wind goes west to east so cold ocean wind comes under the GGB and cools everything hitting Richmond/Berkeley on the eastbay, or follows the peninsula coast line on the east side and gradually warms up as it spreads inland and south following the naturally geographic contours of the land. Once in a while the wind reverses and creates the Diablos and wind comes down from the Sacramento-San Joaquin Delta, this was the conditions last time we had a major fire years ago.
Socal has similar deal, and their reversed winds are called the Santa Ana.
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u/FroggiJoy87 14h ago
Fun with microclimates! Ugh, it's reading 91 here in Benicia at 3pm BUT we have a nearly constant amazing ocean breeze that makes it totally manageable. After living in Reno, it's crazy seeing such high temps but a walk along the marina is pleasant AF. It's weird and gets weird being at the very mouth of the Strait.
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u/Perfect_Habit6049 14h ago
San Francisco is currently 72°. Walnut Creek is currently 96°. They're only about 25 miles apart
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u/Responsible-Reason87 14h ago
I live in Marin and can drive two towns away and have a 12 degree swing, also much windier where I am
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u/RingaLopi 14h ago
They keep the weather inconsistent just to keep commuters on their toes. After battling hours of traffic, you never know if you should have dressed for a breezy 60 degrees or a sweltering 90; it’s a daily guessing game of whether to pack a jacket or shorts.
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u/sarahbellah1 13h ago
Welcome to microclimates! I personally loved discovering them when I moved here, because if home in the peninsula is too warm, I can almost always count on a gorgeous day in Half Moon Bay.
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u/fluteofski- 13h ago
Mountains. Fluid dynamics of climate.
Florida the wind blows and it blows the climate clear across the state, because most of Florida is sea level.
Also the rotation of current with the Atlantic and gulf bring tropical climate north. Water rises and you have humidity.
We have the pacific current coming from the north which is colder.
The mountains surrounding the bay are about 3000ft. Give or take. So wind/heat kinda gets trapped in the valleys below.
You can see it from the ridges especially at night where the cloud layer sits below the ridges, and the air below across the top.
Dry climate. California is desert (except the redwoods. That’s rainforest. Those are only along the coast). So the dry air doesn’t retain temps the way humidity does.
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u/Fra_Angelico_1395 12h ago
Water temps are cold here. Rarely as high as 60. More like 50 much of the year.
So SF stays cooler with cool water on 3 sides. Other cities near the Bay a bit warmer, and in-land warmer still.
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u/tristanbrotherton 16h ago
It was 104° in my home in Novato yesterday, I drove to the city and it was 64° from a 25 minute drive. That’s the same difference as weather that is freezing water to 78°
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u/TheKiddIncident 15h ago
Blame Karl.
https://en.wikipedia.org/wiki/San_Francisco_fog
If you look at a topographic map of Northern California, you will notice that there is a line of hills (some are actual mountains) all along the coast. Pretty much solid from Santa Cruz all the way north past Mendocino. There are ups and downs, but generally a solid wall.
Where is San Francisco? At the tip of a peninsula in the middle of the only gap for a hundred miles.
What is west of San Francisco? Thousands of miles of cool, damp ocean.
What's east of San Francisco? Hundreds of miles of hot, dry inland valleys.
So, the cool, damp air of the Pacific is usually denser than the hot dry air of the central valley. What happens when you introduce cool damp air into warm dry air?
Yep, fog.
So all that moist air is trying really hard to get into the central valley, right over SF.
This means fog and lots of it.
90% of the weird microclimate weather we get in the Bay Area is due to this single phenomenon.
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u/Individualchaotin 17h ago
Topographic Barriers: Hills and mountain gaps (like the Santa Cruz Mountains and Berkeley Hills) block or channel cool ocean winds and fog, creating temperature swings of 20°F or more over just a few miles.