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bubba

Question about Western Micro-Climates

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bubba

I was reviewing temperatures in several areas of California and Arizona this morning and observed the following temperatures in relatively close areas:

35F at LA Civic Center/50F at Rolling Hills; 33F at Bonita/46 at Coronado; 36F at Rancho Mirage/47F at La Quinta; 
 

In Arizona in Phoenix, 30F at Green Gables/50F at Palm Verde Foothills 

These are large temperature fluctuations in relatively nearby locations. Can you explain the variables that cause these large temperature differences in relatively short distances?

Also, is this a cold front or standard December temperatures? In Florida currently where I am located, it is 73F headed to 80F plus. If we experienced the simple cool down that may be standard December for the west, we would be receiving national attention. It has been far too hot this winter in South Florida and I am aching for some of that wonderful cool California weather!

 

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bubba

I am seeing a station on Wilshire, extremely close to Santa Monica, reporting 30°F. at the same time numerous locations nearby are reporting low 40°F temperatures and even as high as 50°F. Would this be considered a cold front or standard winter based upon micro-climates?

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chinandega81

In Socal it's all about elevation. The desert and valley floor are always where cool air pools. The foothills, a mere few hundred feet up, are always much warmer on calm, cool to cold nights.

Urban LA sees light scattered frost most winters on rooftops or car surfaces out in the open. Usually, the civic center in DTLA is the warmest spot so the 35 number you saw there shocked me...usually downtown LA gets to the upper 30s at the colded, same for LAX. The surrounding neighborhoods cool off to the mid or low 30s in times like this. 

It is similar to SoFlo, they get in a warm dry or cool and wet pattern, while the other half of the country sees the opposite. Trust me, people in Socal are complaining about the cool weather. Usually Santa Ana winds kick in and warm the area up dramatically. But on average, there are several day stretches in the 60s/40s in LA, moreso than in SoFlo.

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ahosey01
On 12/18/2021 at 6:10 AM, bubba said:

I was reviewing temperatures in several areas of California and Arizona this morning and observed the following temperatures in relatively close areas:

35F at LA Civic Center/50F at Rolling Hills; 33F at Bonita/46 at Coronado; 36F at Rancho Mirage/47F at La Quinta; 
 

In Arizona in Phoenix, 30F at Green Gables/50F at Palm Verde Foothills 

These are large temperature fluctuations in relatively nearby locations. Can you explain the variables that cause these large temperature differences in relatively short distances?

Also, is this a cold front or standard December temperatures? In Florida currently where I am located, it is 73F headed to 80F plus. If we experienced the simple cool down that may be standard December for the west, we would be receiving national attention. It has been far too hot this winter in South Florida and I am aching for some of that wonderful cool California weather!

 

It has to do with cold drains.  Basically anywhere that water flows off a mountain, cold air will flow down that same path.  If the weather station is reading from inside a cold drain - it will read colder than the surrounding areas.  If it is reading from above one - it will read warmer.

Interestingly, the historic data from the Boyd deep canyon research station above Palm Desert, CA, actually points to a 10b/11a microclimate, although nobody lives up in that canyon.  The point is that these cold drains really change the way the temps work.

I have read some pretty convincing work by permaculture types that indicates that careful placement of windbreaks can actually stop this phenomenon from occurring if it effects your garden.  As an example, say your house sits midway down a cold drain.  There are different schools do thought on this, but some say planting a windbreak “upstream” from your house in the cold drain works, while others say planting it close to your home - but “downstream” is the key. Both of those arguments contend you can actually increase your lows by up to a zone (I.e. 8b becomes 9a).  Don’t know how true that is - but I’ll be finding out in the next few years.  My house is in a cold drain and I’m planting a windscreen beneath it - not for zone pushing (I don’t do that), but just to block my view of the highway.  If I incidentally acquire a warmer microclimate as a result, I won’t be upset.  LOL

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Tracy
On 12/19/2021 at 8:13 AM, chinandega81 said:

Usually Santa Ana winds kick in and warm the area up dramatically.

It really depends on time of year and where one is located.  Some Santa Ana winds later in Autumn and in Winter actually blow cold air from higher elevations inland down to the coastal zones, pushing the moderating effects of the ocean warmed onshore wind further out to sea.  Close to the coast, both of our most extreme weather events are associated with Santa Ana's.  The late Summer (September) Santa Ana's that cause temps to reach their peak without the moderating blanket of cooler onshore winds, as well as the later Autumn (Thanksgiving and later) events that give us our clear cold nights without our moderating marine layer.  So when this post was started, we were in the midst of a few days of clear cold offshore winds.  As soon as the clouds returned overnight low temps on the coast warmed by 10 to as much as 15 degrees.  

It is accurate to say that the large driver of different temps is elevation though.  Topology of the land on the west coast is so much more dramatic than anywhere on the east coast, it isn't a  wonder that one would see more variation in close proximity here than on the east coast.

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mnorell

Bubba--

Tracy is right that the winds have a good deal to do with temps (in addition to elevation and aforementioned other factors). And sometimes the coast will be warmer than inland, and that can be caused by Santa Ana-type compression winds, but also when the marine layer that blankets the chilly eastern Pacific gets pushed in over the coastal plain (or sucked in from inland, i.e. in Spring when the deserts heat up, creating a sort of a vacuum), preventing radiational heat-loss for several miles inland.  The south-facing Santa Monica Mountains/Hollywood Hills are a pretty reliably mild-to-warm microclimate even on still, clear winter nights due to their orientation (and of course the UHI effect of the entire L.A. basin). But the many canyons in that mountain range that drain down into the L.A. Basin create formidable cold-drains. After a cold event, one can drive up Laurel Canyon or Coldwater Canyon and see the crispy Ficus, Strelitzia nicolai, et al., and that damage can extend down into the open areas of Hollywood until the surrounding warmer air mitigates the damage. Likewise any river-bed, such as the Ballona Creek, which runs alongside and to the south of the I-10 through Culver City and Playa del Rey, is a cold-basin. the same goes for the many coastal creek-beds that run perpendicular to the coast throughout northern San Diego County, notably in the Oceanside, Carlsbad and Del Mar areas, sometimes 20 degrees colder than immediately adjacent terrain! San Diego is very different from L.A. in its topography and climate, being largely flat mesas interrupted by canyons, and without the uniformly encircling hills that make the gently sloping plain of L.A. a "basin" that catches the warmth...San Diego being a much breezier/windier area (and historically with much better air quality, since the air can be dispersed much farther inland).

The old UC climate map (for many years now updated in concert with Sunset Magazine) calls the chilly coastal air-drainage areas "zone 22" while the air-drained foothills are classified as the "sweet spot" Zone 23. But things do reverse at times, I noticed a station on Coronado (mild marine Zone 24) was just above freezing one morning in the last couple of weeks while other areas inland were ten degrees warmer...completely counter-intuitive since Coronado should be one of the warmest spots (and usually is very mild indeed). In the Coachella Valley (Palm Springs to La Quinta, etc.) elevation is a general indicator but with many caveats...and on otherwise calm nights the fierce and nearly ever-blowing winds spinning the windmill farms through the San Gorgonio Pass usually keep the whole I-10 corridor as much as 15-20 degrees warmer than the more sheltered west side of the valley due to the mixing of air-layers. Our house in Rancho Mirage is elevated in comparison with the valley floor, at 300 feet ASL, but we are in a wind-sheltered alluvial "cove" and very cold air drains past us, down from the 10,000' mountains to our west, through the Magnesia Falls Canyon area, and off of Larry Ellison's "Porcupine Creek" fairways, emptying into two flood-control channels that drain down to the Whitewater River basin. When walking through our neighborhood, the temperature at sunset drops 10-15 degrees when you reach the vicinity of these drainage canyons. And just as surprisingly, much of La Quinta, at sea level, is warmer than the higher areas draining into it (though most of La Quinta Cove is generally a bit colder, usually on par with our neighborhood in Rancho Mirage). I still don't understand why that should be. The warmest areas (inversion layer) around Palm Springs-Rancho Mirage-Palm Desert are between 600-1000 feet, but during very cold storms that situation can reverse and (rarely) snow may fall at those levels. There are many more examples of this strange behavior throughout California, it is not cut and dried, and it demands serious study when one is trying to locate for optimized temperature, and can really trip you up if you don't carefully monitor the many personal weather stations on Wunderground before reaching a decision. Florida is a much, much easier animal to tame in the study of climate variation!

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bubba

Truly great explanations of a phenomenon that I have observed and never fully understood. Michaels explanation is absolutely stunning and substantial in detail.

As a Florida flatlander, where the very few microclimates that we have are generally related to proximity to warm water, this gives understanding on a number of levels. One example, the “Corona Coconut”. Thank you and marvelous!

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