They tell me that my trip to SF in early August will be "cold" by summer standards. How can that be?
I assume if we travel towards Napa and inland it will be consideraby warmer?
It sounds like a packing nighmare!

Dorgal,
When my family visited SF two August's ago it was downright cold. We went to a baseball game and the people there were wearing winter coats and gloves and we were freezing because we did not dress warm enough. They told us that a couple weeks earlier it had been in the upper 80's which was highly unusual for that time of year. The highs for us were low 60's. We drove down the coast and it was warmer but never got "hot". Make sure that you bring jackets and sweatshirts and dress in layers and then you will be warm enough.

Much of SF's "cold" climate is due to the fog that is so prevalent in the summer (particularly in the morning). The guidebook we used on our SF trip last summer says the average temps in August are between 54 and 65F. We went in June, and the very first thing we did after arriving was walk to the Wharf and buy a thick hooded sweatshirt for my son, who didn't really expect it to be that "cold", and he wore it practically the whole week. The important thing for SF is to dress in layers. If it warms up, you can "strip down" a bit. And yes, it does get warmer if you go a ways outside of the city.

Fog is a symptom of factors that cause the weather in SF, but not the cause itself.

San Francisco is cold because of its location in the mid-Pacific latitudes, where the water tends to be cooler, and the impact of the wind and tidal patterns in the Pacific Northwest. Those patterns cause a constant "upswelling" where the much colder water from the ocean depths rises towards the top and replaces warmer "tidal" waters. The fog is a function of the colder water and higher ambiant tempatures and that fact is exacerbated by SF's location on a Peninsula, where it is surrounded on three sides by cool water.

In addition, the prevailing winds and tempature differential between the ocean
and the inland valley's cause dramatic movements in weather fronts which is further impacted by the coastal mountain range and one major break in that range - the entrance to SF Bay.

BTW, the SF Bay area has one of the most diverse weather patterns in the world. Variances in tempatures between relatively close geographic areas can be substantial.

The cold and the fog are both related to the very cold ocean waters that surround SF, even in the summer. Mark Twain once said that the coldest winter he ever spent was a summer in San Francisco. It can be 10 or 20 degrees warmer just across the bay, and another 10 or 20 degrees warmer than that further inland. Napa will in general be warmer, but the Carneros area of southern Napa can still be quite cool due to the influence of the waters of San Pablo Bay.

Yikes, this is good to know ahead of time.

I knew it would be cool,but not that much. Is it usually a heavy fog in the morning - say one that restricts views and makes you plan around it?

While looking for housing in the late 70's my husband and I had on light summer clothing which we gave no thought to in August. Wow, were we caught by surprise and yes, the natives were bundled up in parkas and wool caps! I found the most delightful weather to be around Christmas.

ChatNoir: We never had a visibility problem with the fog, but we were always walking -- not driving. The only time it interfered with our plans was the morning we had book a hot-air balloon ride over the Napa Valley. The driver who picked us up in SF ended up having to drive nearly 100 miles to an alternate launch site, due to the fog.

By the way, I felt really foolish that I had booked TWO hotels in SF with swimming pools. There was NEVER any time while we were there in June that it was warm enough for a swim (outdoors).

The "fog season" in San Francisco and other coastal Northern California locales is a dependable, yearly occurrence. Personally, I love it. After a long day of driving in hot temps and glaring sun, it is incredibly refreshing to be heading across the Bay Bridge or Golden Gate towards the City and see that fog bank rolling in.

In general, in San Francisco proper, the fog comes in at around 5 or 6 p.m., lingers overnight and in the morning, then lifts by 10 a.m. or so. The further west in the city you go, the more likely you will be in a neighborhood where the fog just does not go away at all during the day. You can board the underground at Castro Station, where people will be walking around in tank tops and shorts, and then emerge at West Portal Station 10 minutes later, where the denizens will be wearing sweaters and windbreakers. That's our famous "microclimates" thing!

One year, we left a foggy and cold Monterey for the Garlic Festival in Gilroy, dressed in jeans and t-shirts and shivering, but figuring we'd be set once we got further inland. Well, Gilroy hit 105F that day--our jeans felt like lead weights! I believe that was in June or July. We also took in a ball game on July 5 one year and had the same experience as luvstotravel--they sold out of hot chocolate! So bring layers! I rely on a high-grade, windproof and water repellant fleece jacket; it goes everywhere with me, because even in Napa, evenings can be cool. Enjoy your trip!

I think that parkas and wool caps are a bit of an overkill for SF in August. It's chilly, but not THAT cold. I would take a windbreaker and a sweater and just layer up. Then, if you travel inland - or just to a different part of the city where it's warmer - you just take off a layer or 2. I generally wander around SF with a day pack to carry the layers I take off.

Coastal fog isn't the same as valley fog which obsures visability. Coastal fog is generally higher, obscuring the sky and sometimes the tops of tall buildings, but not the ground. It also generally has a wispy quality to it and you can see it drifting around above you. One of the coolest sights is to watch the fog roll in through the Golden Gate.

It simply is.That being said the advice to pack with layers in mind is a good one. For evenings, I'd bring a pashima shawl. A sweater or similar lighter outerwear should be enough. As you drive to Napa or inland it will definitely get hotter. I'd bring everything you usually do for warm temps. I live in the East Bay(at the Bay) and wear linen all summer long.

dorgal...i was in san francisco 4 years in ago in august and it was one of the coldest i've ever been!! i mean it's sunny, but the temp. just doesn't get high. a sweatshirt/sweater at night should be fine, and i wouldn't bring just shorts. maybe one pair or something, but pants at night...i loved san francisco!

While August may be one of the hottest and sunniest months of the year elsewhere, for future reference it is not the best month to visit San Francisco. September and even October usually offer glorious weather.

OK, I need to add my two cents worth.

First of all, most scholars believe that the Mark Twain quote about "The coldest winter" is misattributed to him. See:

http://www.boondocksnet.com/twainwww...le_mt0002.html

for more information.

Secondly, as Ryan stated, the reason San Francisco is so cool in July and August is not anything that's happening on the Pacific but is due to the fact that the great Central Valley (from Redding to Bakersfield) is so darn hot. The often 100+ temperatures of inland California draws in the cooler air from the Pacific which results in the coastline being covered by a huge fog bank and making the area in between quite windy.

On a typical day in July and August, daytime highs on the coast will be around 60 degrees. Around the Bay, it will be in the low 70's. Inland a little, it will be around 80 in places like Napa, Sonoma, San Jose, and Novato. Up around St. Helena or Healdsburg or down around Morgan Hill it could be 90. And in Calistoga, Gilroy, or Livermore the temperature might be around 100.

Because of this summer weather pattern, July and August are perhaps the two least desirable months to visit San Francisco. That said, even in July and August you will find days that are quite beautiful and warm. Just be prepared for changeable weather. At least it doesn't rain.

Otis (and others too) explained it very well. Normally - the hotter it is inland the colder it is in SF. And August is the hottest month inland -- so you can figure it out.

BUT, sometimes there can be a heat wave even in SF (but more likely in June than in August) when it is HOTTER than Hades inland and merely hot in SF. High 80's low 90's in SF are comparable to 110F in the Sacramento Valley.

You can always tell at a glance the summer tourist in SF - blue legs and a brand new souvenir sweatshirt.

Last year I went down to the Garlic Festival - HOT as usual - and then stayed the next 2 nights in Pacifica and took BART into the city. 105F in Gilroy and 58F in Pacifica on the same day.

I have no idea how it can be so cold - 2 years ago we spent time in Seattle and drove to SF. It was much warmer in Seattle than SF. Watching 7/4 fireworks we wore every article of clothing we had with us. And we thought we knew about possible cooler summer weather since we live in New England.

J. Correa--I agree that heavy winter clothing was a bit much, but that's what most people were wearing that night.

We live in the Petaluma Valley-
western Sonoma county and here's a typical summer day. Shorts and tees after 10AM until 4PM when the fog begins wisping in at which time you grab a sweatshirt which is good until around 7PM. This is the same hour you trade your shorts for jeans or such.
Our yearly treck on July 4 to board the Tiburon ferry for a sail and to watch the fireworks has us sweating in line wearing jeans & tees. Out on the water the closer we get to the Embarcadero the cooler it gets and mid-bay gloves, hats and parkas are a must! I have a great photo of us bundled like eskimos
with the fireworks going off over the water. (You probaly only need the wooly caps if you're out on the Bay
I think my fellow Bay area residents
will grin when I say we carry jackets, socks,gloves,& sweatshirts in the trunk April-Sept. You just never know...
R5
wearing shorts or capri's

We live in the Petaluma Valley-
western Sonoma county and here's a typical summer day of attirehorts and tees after 10AM until 4PM when the fog begins wisping in at which time you grab a sweatshirt which is good until around 7PM. This is the same hour you trade your shorts for jeans or such.
Our yearly treck on July 4 to board the Tiburon ferry for a sail and to watch the fireworks has us sweating in line wearing jeans & tees. Out on the water the closer we get to the Embarcadero the cooler it gets and mid-bay gloves, hats and parkas are a must! I have a great photo of us bundled like eskimos
with the fireworks going off over the water. (You probably only need the wooly caps if you're out on the Bay
I think my fellow Bay area residents
will grin when I say we carry jackets, socks,gloves,& sweatshirts in the trunk April-Sept. You just never know...
R5
wearing shorts or capri's