Southern California Weather FAQ

[weatherlover427]

In this topic, I will try to answer some of the most commonly asked questions about southern California weather. Please note that this is not a comprehensive or exhaustive summary; and that for official information you should consult your local National Weather Service Office.

~-~-~-~-~-~-~-~-~-~-

Table Of Contents

1. What is the marine layer?
2. What are Santa Ana Winds?
3. What is the average rainfall for Los Angeles / San Diego / John Wayne Airport?
4. In what month does southern California see its hottest and coldest weather, and the most and least rainfall?
5. How often does this area see thunderstorms?
6. Has it ever snowed in southern California? (not counting mountainous terrain)
7. Has there ever been a tornado in southern California? What about a violent (F3 or more) tornado?

Personal Questions

8. What is your favorite type of weather?
9. What kind of weather do you hate the most?
10. Have you ever gone storm chasing? If so, tell us what you saw.
11. What's the average weather like where you live?
12. What do you think of Hurricane Season 2005?

~-~-~-~-~-~-~-~-~-~-

Question 1. What is the marine layer?

The marine layer is a low-lying bank of stratus clouds that sometimes actually touch the ground; at which point they are defined as fog. Otherwise; the correct terminology for the marine layer is low clouds. Sometimes; if the marine layer deepens rapidly enough; it creates just enough lift in the atmosphere to produce some drizzle / mist or even some very light rain in the most prone areas, such as areas right along the coast and also in foothill and mountain areas.

Question 2. What are Santa Ana winds?

The Santa Ana winds are a seasonal event in southern California; mainly occurring from late September or early October through the end of winter. Sometimes they can last into April. These winds always bring very dry, desert-like air with them; however the air mass that is associated with the Samta Anas varies between cold and hot depending on how much cold air advection comes down from the Great Basin (aka the Four Corners).

These winds are usually strongest in the mountains and foothills; and also in the passes and canyons of the mountains. Usually a Santa Ana wind event will bring with it wind speeds of 20-30MPH with gusts to 45-50MPH along the coast; with speeds about 20MPH higher in the mountains. But the most extreme events can send wind speeds to 110MPH plus in the most prone areas, such as Fremont Canyon (which is in the Santa Ana mountains, where the winds get their name from) and also the Cajon Pass, where Interstate 15 leads to Las Vegas.

During such events, residents of southern California must drive very carefully. Semi trucks are prone to tipping over on freeways, roof shingles and tiles can blow off of homes and businesses, trees can blow down, and on trash days; well; you know. The Pacific Ocean; as well as Irvine Lake and other area lakes; become very choppy and small craft advisories or even gale warnings go up for the inner waters.

Also; people who live in hilly terrain must be careful to clear any and all brush within at least 200 feet from all around their home. This helps in case a brush fire gets near; such as was the case many times in October of 2003; when numerous brush fires affected almost all areas of southern California.

Question 3. What is the average rainfall for Los Angeles / John Wayne Airport / San Diego?

(to be answered soon)

Question 4. In what month does southern California see its hottest and coldest weather, and the most and least rainfall?

Typically, Southern California follows most other locales in that its coldest month is January for almost everywhere within the confines of the area that is known to be southern California. Howeverl; due to the cooling effects of the Pacific Ocean andf the resultant marine layer, the hottest month (or months) are usually reserved for this area until August and September; and sometimes even October. Highs of 100°+ have been known to cocur in southern California in almost all months except December and January, though.

As for rainfall; this area follows that of most other western climates in that its driest months are the summer months - that is, June - September. The exception to this rule is the summer monsoon, which is a seasonal shift in the airflow pattern; which brings in moisture from the Gulf of California and sometimes even the Gulf of Mexico. Daytime heating will combine to create showers and thunderstorms over the mountains and deserst; and if the upper airflow is strong enoug; some of the storms may drift all the way to the coast.

Question 5. How often does this area see thunderstorms?

Usually, southern California does not see that many thunderstorms compared to other areas of the country; except for the mountains and deserts due to reasons described in question 4 above in paragraph #2. However, the most common trigger of thunderstorms in southern California outside of the summer months is the passage of cold fronts and their associated cold air masses and instability.

The conditions are not always met with such passages for thunderstorms; as several things must come together for them to happen. Some of them include:

* 700mb VV;
* -16°C or lower 500mb temps;
* A strong enough 500mb vort;
* and more.

Question 6. Has it ever snowed in southern California? (not counting mountainous terrain)

The answer to this question is YES! There are instances of this happening; but the occurrences of it are very rare. The reasoning for this is our proximity to the Pacific Ocean. Being that it is only a few miles to our west; its moderating influence on our local weather usually keeps our air more marine-ish instead of the continental air mass that places such as Topeka, KS or Minneapolis, MN have; where it obviously snows a lot more in the winter than it does here (and hence their weather is a lot different than ours is).

Question 7. Has there ever been a tornado in southern California? What about a violent (F3 or more) tornado?

We do get tornadoes here; but not like places in the Midwest and South. Most of ours are either wathespouts that come in off of the ocean and travel for up to a mile inland before dissipating; or else they form in more inland areas due to turbulence in the atmosphere. Our highest Fujita scale rating locally is F2, recorded 4 times during the 1982-1983 major El Niño season (source: http://www.spc.noaa.gov/climo/online/rda/SOX_data.txt. Therefore; no violent (F3 or higher) tornadoes have been recorded in southern California.

Personal Questions

Question 8. What is your favorite type of weather?

I personally like a lot of different types of weather. I like the Santa Ana winds, I like it when it rains, I like it when it's foggy, I like the hot weather, I like sunny weather, etc etc etc.

Question 9. What kind of weather do you hate the most?

I HATE COLD AND ICY AND SNOWY AND BLIZZARDRY WEATHER!!!!!!!!!! ARGGGGGGGGGGGHHHHHHH!!!

Question 10. Have you ever gone storm chasing? If so, tell us what you saw.

I have gone / been storm chasing 3 times (May 2003, April 2004, and August 2005). We have seen some interesting weather (and done some interesting things ) but we personally (on our trips at least) haven't run into anything like 3 mile wide tornadoes, 4 inch hail, 100mph derechos, etc.

Probably some of our most exciting weather was the New Mexico trip last year. That storm blew up to a giant flipping mushroom cloud. The thing was huge, you would have to have been there to believe how big the cloud was. It took up almost the whole southern horizon (at least I think it was south). Hundreds of lightning flashes each minute, winds went from 0 to 50 in a matter of minutes, and very torrential downpours. Quite a storm.

Not to mention the freeway chase on the way back home, or driving across the center divider and breaking the transmission, or passing the guy we were chasing, or doing 110MPH in a 65 zone, etc...

Question 11. What's the average weather like where you live?

Here, since I live close to the coast; the weather is comparatively cool when you compare it to areas just a few miles inland. We don't get as much rain as inland areas either. But that could be a good thing since we don't have air conditioning here, I guess. Only bad thing is it gets hot as heck when we have the Santa Ana winds (and by that I mean 100+ with no humidity, it sucks).

Question 12. What do you think of Hurricane Season 2005?

It blows. We have had WAY too much destruction, loss of life, etc. Too many storms as well. Way too many vulnerable areas (Nawlins, Mahmi, Pensacola, etc.) have been hit this year. That's one of the main reasons for there being so much damage. Hopefully nexct year will be a LOT better.

[wxmann_91]

Thanks for posting these weatherlover. I'm not a California native, so I was just wondering, you say that measurable snowfall has occurred, when was the last time measurable snowfall was recorded?

[weatherlover427]

I should have included that in my original post, so sorry for the omission. The last time a major widespread snowfall in the lowlands of so Cal happened was IIRC in January of 1949 or thereabouts; when LA proper picked up 1-2" of snow and even the beaches got a light coating. Temperatures never dipped below the mid 20's (butt cold for us) throughout the netire event.

[wxmann_91]

I should have included that in my original post, so sorry for the omission. The last time a major widespread snowfall in the lowlands of so Cal happened was IIRC in January of 1949 or thereabouts; when LA proper picked up 1-2" of snow and even the beaches got a light coating. Temperatures never dipped below the mid 20's (butt cold for us) throughout the netire event.

Thanks for the info. I never thought snow could occur here, imagine if it happened today!

[Aslkahuna]

January 1949 remains the coldest Winter month on record in the Western US. Besides snow in coastal SoCA (with San Diego getting a Trace of snow-its only known instance of snow), Las Vegas had 17 inches of snow that month.

The Marine layer is basically the boundary layer which has been chilled by contact with cold ocean water. The low stratus and fog is due to the air being cooled to the dewpoint. In the SFO Bay Area, the Marine Layer is normally some 2500' thicj with bone dry warm air above it. This subsidence inversion is due to the presence of the Pacific cell of the Subtropical High. While in SoCA the water temperatures are in the 60's, in July and August when the upwelling due to the strong persistent NW flow out of the ST High is strongest, the SST's near Pt. Reyes can fall as low as the upper 40's. It is a point of fact that the water temperatures off the WA coast near the Strait of Juan de Fuca are higher than they are just north of SFO some 600 miles to the south. Marine Air Meteorology is an important field of study in CA, For us in AZ, we are concerned about the Marine Layer in the Winter for it is when the dynamics of of a trough digging off SoCA deepens the Marine Layer enough to allow Pacific moisture to cross the Mountains of Baja that we get a chance for Winter rain in SE AZ.

Steve

[weatherlover427]

I should have included that in my original post, so sorry for the omission. The last time a major widespread snowfall in the lowlands of so Cal happened was IIRC in January of 1949 or thereabouts; when LA proper picked up 1-2" of snow and even the beaches got a light coating. Temperatures never dipped below the mid 20's (butt cold for us) throughout the netire event.

Thanks for the info. I never thought snow could occur here, imagine if it happened today!

Yeah, I camn just see all the drivers here going "eh wth, snow?" and start looking around, not paying attention to the road in front of them - then CRASH BOOM BANG - accidents all over the place.

@Steve's reply - There are occasional times here in far SW California when the surface ocean temps get to the low 70s during our warmer summer months; but as you stated they usually remain in the 60s. It's far different from when I lived in Orlando, FL; when it felt like you were stepping into a bath when you went into the waters there.

[TT-SEA]

After spending many years in SoCal... I can say that the weather down there can be exciting at times.

I saw many thunderstorms, hail covering the ground, flooding, incredible winds, and mountain snow.

The thing that bothered me the most though is the persistent stagnant weather that often produces haze and smog.

It just happened way too often for us.