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Plant Heat Zone Map


chris78

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In 1997 the American Horticultural Society came out with the "AHS PLANT HEAT ZONE MAP".... It has 12 zones, and are based on the Average number of days per year that the temperature were 86F or above. It was developed because plants have heat requirements to grow, flower and fruit successfully.

As we all know, zone 10 in Florida is a different animal than zone 10 in California. Many of the zone 10 palms that grow like weeds in Florida, struggle in zone 10 in California if they live at all. Lets face it, there are more zone 10 plants growing in zone 9 in Florida than than there are growing in zone 10 or 11 in California.

The map places South Florida in zone 11 or 12.... zone 11 has 180 to 210 days at 86F or above, zone 12 has 210 day or more. While the coast of Southern California is a zone 4....which ave about 14 to 30 days at 86F or above. Which is about the same as some parts of Vermont.

We Palm people spend lots of time talking how much frost or freezing weather a palm will take, but we don't always look at how much heat a palm requires to grow at its best.  I seen other gardeners use the heat map to better pin point a climate that a plant will do its best.

Could we use this for palms? Like the coconut....hardy in zone 10 or above...and in heat zone 9 to 12.... So a person in south Florida will see that a coconut will do find in that climate, but a person in zone 10 in the Bay area of California which has an heat zone of 2 will see that a coconut will not do well at all in that climate.

Also on the other hand some cool loving palms do not do well in S. Florida because of the heat.  Another example...Hedyscepe canterburyana hardy in zone 9 and 10 and best in heat zone 1 to 5. Someone in the Bay area might want to try one but  someone in Miami may not.

What do you think?? Do you think this could help us palm people?

Phoenix Area, Arizona USA

Low Desert...... Zone 9b

Jan ave 66 high and 40 low

July ave 105 high and 80 low

About 4 to 8 frost a year...ave yearly min temp about 27F

About 8 inches of rain a year.

Low Desert

Phoenix.gif

Cool Mtn climate at 7,000'

Parks.gif

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It does sound like it could prove useful, but most of us just seem to spend our time trying to prove the zone ratings for palms wrong.

I assume my place would be a zone 1 with 0-10 days of 30°C/86°F or above.

]

Corey Lucas-Divers

Dorset, UK

Ave Jul High 72F/22C (91F/33C Max)

Ave Jul Low 52F/11C (45F/7C Min)

Ave Jan High 46F/8C (59F/15C Max)

Ave Jan Low 34F/1C (21F/-6C Min)

Ave Rain 736mm pa

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Is there a map that shows the opposite - ie cold? Sometimes I wonder if what I want to get can survive. Granada Hills which is a small community has more than one micro climate and elevation. It can be beautiful in the rest of the city, yet a cold wind storm right where I am.

Scott

San Fernando Valley, California

Sunset Climate Zone 18

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South Texas is zone 9 and 10 and heat zone 11 and 12.  The only think keeping deep south Texas from being the equivalent of south Florida is those stupid pesky artic fronts that roll through once every blue moon.

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(syersj @ Oct. 03 2006,13:15)

QUOTE
The only think keeping deep south Texas from being the equivalent of south Florida is those stupid pesky artic fronts that roll through once every blue moon.

Not to be too picky, but perhaps south TX might be closer to central FL with regard to normal wintertime temps?

Larry 

Palm Harbor, FL 10a / Ft Myers, FL 10b

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AAAAARRRGGHHHHHH!!!!  You mean our little corner of the central Floridian arctic tundra right Larry?

Tampa, Interbay Peninsula, Florida, USA

subtropical USDA Zone 10A

Bokeelia, Pine Island, Florida, USA

subtropical USDA Zone 10B

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(Ray, Tampa @ Oct. 03 2006,14:01)

QUOTE
AAAAARRRGGHHHHHH!!!!  You mean our little corner of the central Floridian arctic tundra right Larry?

Yeah.....thatd be it :D

But, when I see some of the temps logged at other areas further inland, Im happy to be at least where we are :;):

That being said, I wouldnt mind living...oh...an extra 1.5 miles west :D

Or...perhaps about 20 miles SE to that little corner of Tampa Bay in the Old North East!

Larry 

Palm Harbor, FL 10a / Ft Myers, FL 10b

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Tampa is USDA zone 11+ and AHS heat zone 12+ and Shobert Zone #1

Rest of Earth does not fit the Shobert Model thus: Earth Shobert Zone #not Tampa,  unless it is Tampa, then #1

Shobert the Way

I ran out of pills

Also, I propose a ban on cold-talk till Spock puts on his socks.

Alan

Tampa, Florida

Zone - 10a

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(spockvr6 @ Oct. 03 2006,13:24)

QUOTE

(syersj @ Oct. 03 2006,13:15)

QUOTE
The only think keeping deep south Texas from being the equivalent of south Florida is those stupid pesky artic fronts that roll through once every blue moon.

Not to be too picky, but perhaps south TX might be closer to central FL with regard to normal wintertime temps?

That's true Larry.  Deep S. TX is identical to Central Florida temperature wise in winter.  Averaging in the 70s for highs, 50s for lows in winter.  In Jan it bottoms out at about 70/50, same as Tampa, Orlando, etc.  San Antonio is within a degree or 2 of Jacksonville during the winter.  I guess it's wishful thinking to be like S. FL., although they can grow some cocos and such in very deep S. TX.

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(syersj @ Oct. 03 2006,21:47)

QUOTE
That's true Larry.  Deep S. TX is identical to Central Florida temperature wise in winter.  Averaging in the 70s for highs, 50s for lows in winter.  In Jan it bottoms out at about 70/50, same as Tampa, Orlando, etc.  San Antonio is within a degree or 2 of Jacksonville during the winter.  I guess it's wishful thinking to be like S. FL., although they can grow some cocos and such in very deep S. TX.

Dont short me my 2 degrees!  Its 72F in Jan for the average high in Tarpon Springs!  

I need every degree I can get around here :D

Larry 

Palm Harbor, FL 10a / Ft Myers, FL 10b

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(Alan_Tampa @ Oct. 03 2006,16:44)

QUOTE
Also, I propose a ban on cold-talk till Spock puts on his socks.

Alan

I am assuming this year will be a no palm sock year Alan!

Larry 

Palm Harbor, FL 10a / Ft Myers, FL 10b

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Cold? What cold?  It was 91F at the airport today.

Tampa, Interbay Peninsula, Florida, USA

subtropical USDA Zone 10A

Bokeelia, Pine Island, Florida, USA

subtropical USDA Zone 10B

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(Ray, Tampa @ Oct. 03 2006,22:32)

QUOTE
Cold? What cold?  It was 91F at the airport today.

My little plot only managed to eek out an 89.2F high today before the winds shifted to the NW, which almost invariably raises the dewpoint and holds the temperature steady.

See a pattern in the below?

temps.jpg

winds.jpg

Larry 

Palm Harbor, FL 10a / Ft Myers, FL 10b

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(spockvr6 @ Oct. 03 2006,22:28)

QUOTE

(syersj @ Oct. 03 2006,21:47)

QUOTE
That's true Larry.  Deep S. TX is identical to Central Florida temperature wise in winter.  Averaging in the 70s for highs, 50s for lows in winter.  In Jan it bottoms out at about 70/50, same as Tampa, Orlando, etc.  San Antonio is within a degree or 2 of Jacksonville during the winter.  I guess it's wishful thinking to be like S. FL., although they can grow some cocos and such in very deep S. TX.

Dont short me my 2 degrees!  Its 72F in Jan for the average high in Tarpon Springs!  

I need every degree I can get around here :D

Tampa Airport bottoms out at 70F during Jan, you must be 2 degrees warmer than the airport.

http://www.weather.com/weather....Month=1

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(syersj @ Oct. 03 2006,22:48)

QUOTE
Tampa Airport bottoms out at 70F during Jan, you must be 2 degrees warmer than the airport.

http://www.weather.com/weather....Month=1

Well...I will tell you exactly what my yard does in Jan in a few more months :D

The Tarpon Springs station for the South East regional Climate Center shows the average high as 72F for Jan.  I believe weather.com gets their data from there as well, so it should also show the same.

However, all this is academic as the data one sees depends on which station is used.  The University of South FL has a couple of stations in town and both are in coastal areas (one is near a large river and the other is smack dab on the Gulf).   If you want to make Tarpon Springs look like its 10b, one can use this data :D  But, these numbers are not valid for 90% of the area.  See my sig :P

Larry 

Palm Harbor, FL 10a / Ft Myers, FL 10b

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Yeah, I lived in inland Hillsborough during the 90s and there was a big difference between there and Pinellas Co (from what I remember) on the coldest nights.  So taking one station doesn't really get the whole picture.

I remember watching the news and it seemed Brooksville, north of Tampa, got waaay colder than any where else in the Bay area.

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Yay, I'm zone 2, that's better than expected and better than some parts of Hawaii.  I think I'll try some C.renda outside this year.

]

Corey Lucas-Divers

Dorset, UK

Ave Jul High 72F/22C (91F/33C Max)

Ave Jul Low 52F/11C (45F/7C Min)

Ave Jan High 46F/8C (59F/15C Max)

Ave Jan Low 34F/1C (21F/-6C Min)

Ave Rain 736mm pa

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Hi all

Interesting map, but I dont think it is useful unless you are planning to open a date farm. We fall withing zone 7 or maybe 8 on some years but we never get below 3c and dont get frost.

Cheers

Dennis

Sub-tropical

Summer rainfall 1200mm

Annual average temp 21c

30 South

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  • 3 weeks later...

According to this map  where I live  ... inside that little dot of zone 8 in central Virgina  and on the boarder of  the  7a/ 7b   plant  zone.  Am I  realy pushing the limits on my windmill palms?  If not,  what else would be worth giving a shot?

thanks

Jim

will try to do the things that they say can't be done

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(spockvr6 @ Oct. 03 2006,11:29)

QUOTE
Heres a link to the map.

As can be seen, the Zone 12 areas are pretty much confined to an area in the extreme SW partof FL and the southern tip of TX.

http://www.ahs.org/pdfs/05_heat_map.pdf

Thanks for the link.  Embarrassed to admit it was my first study of plant heat zones.

Anybody see the tiny red dot in SoCal? Looks to be Palm Springs.   ???

Noticed the lack of heat along the Cali coastline. Map doesn't quite capture the numerous micro-climates.  High resolution would be great.

Los Angeles/Pasadena

34° 10' N   118° 18' W

Elevation: 910'/278m

January Average Hi/Lo: 69F/50F

July Average Hi/Lo: 88F/66F

Average Rainfall: 19"/48cm

USDA 11/Sunset 23

http://cdec.water.ca.gov/cgi-progs/queryF?MTW

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I don't know about this!! Is there a way to enlarge part of the map? Difficult to see the details for the Big Island, but we have VERY few days above 86F, and as a result we have more or less the same color as Pennsylvania! :D  Hmm... Anyone in Pennsylvania growing Cyrtostachys or Pigafettas??

Leilani Estates, 25 mls/40 km south of Hilo, Big Island of Hawai'i. Elevation 880 ft/270 m. Average rainfall 140 inches/3550 mm

 

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The heat zone has nothing to do with winter cold....Most of Pennsylvania is in plant zone 5 to 7, so while it may get the same # of 86F days as some parts of Hawaii, most of Hawaii is in plant zone 11 or better....You use both to get a better picture of the climate.

For example in Flagstaff AZ it's ave lows in winter are about -5 or a little lower, about plant zone 6a.....but heat zone wise its more like a climate in Vermont. Now red delicious apples or concord grapes are cold hardy for the winter lows in the area and the trees do ok but don't fruit often if at all... well the trees does not get enough heat for fruit producton....

So I tell friends up there they need to grow apples and grapes breed for plant zone 3 or 4. Mostly because Flagstaff zone 6a get as much heat as places in zone 3 or 4, not like most places in other zone 6a areas.

I hope I explained this in a non confusing matter :P

Phoenix Area, Arizona USA

Low Desert...... Zone 9b

Jan ave 66 high and 40 low

July ave 105 high and 80 low

About 4 to 8 frost a year...ave yearly min temp about 27F

About 8 inches of rain a year.

Low Desert

Phoenix.gif

Cool Mtn climate at 7,000'

Parks.gif

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There is only one flaw with using this data, and that is that Hawaii would be in zones 2-4 along with most other areas in the tropics.  I agree that some palms may need more heat than others but that is not the only deciding factor.  That would also mean that where I live 30-35 miles from the coast where the summer months average 95f with 15 to 20 days over 100 would be better place for growing palms than say San Diego where over 400 species of palms can be grown.  On top of that Virginia would then be better for palms than here in so cal which it isn't.  So although the info can be usefull, nothing speaks more than what has been tried and tested an any given area.  As palm growers though were always trying to push the limits and this is a good thing.  One only has to look at what Bobby in Ny has done with a little extra work and he has done what most people would have said isn't possible.  But thats what makes palm growing so much fun.

Don_L    Rancho CUCAMONGA (yes it does exist) 40 min due east of Los Angeles

             USDA Zone 10a

July Averages: Hi 95F, Low 62F

Jan Averages: Hi 68F, Low 45F

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The heat map along with GDD figures explain why my area of the country, though a solid zone 6 can grow what it can. So, while it may not be very useful for determining what palm might have a better chance of succeeding in your locale, it is a useful tool for my area to explain why crape myrtles thrive, southern magnolias grow twice as large here than 25 miles away, why albizia julibrissin is a weed tree sustaining very little if any dieback most winters (almost non-existant just 25 miles to the north) and so on.

Cincinnati, Ohio USA & Mindo, Ecuador

 

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(Don_L @ Oct. 21 2006,18:35)

QUOTE
On top of that Virginia would then be better for palms than here in so cal which it isn't.

True, but its not about using the heat map as an stand alone method. Virginia is plant hardiness zone 7 (mostly) and southern Calif is mostly zone 10.... It does not matter if Virginia gets more yearly heat then San Deigo. Because zone 10 does not freeze like zone 7....

On the other hand, zone 10 in Florida is different than zone 10 in California, by using the heat map you can tell that Florida zone 10 has more yearly heat then zone 10 in California. Coconuts have a higher heat requirement to grow well.....That why you see coconuts all over zone 10 in Florida and NOT IN ZONE 10 IN CALIFORNIA!!!!

By using the heat map, you can better guess what palm might grow better in zone 10 Florida than zone 10 California... If the palm has high heat requirements, it will grow faster and better in Florida zone 10..... If the palm has low heat requirements then it might do better in California zone 10 than Florida zone 10....

Phoenix Area, Arizona USA

Low Desert...... Zone 9b

Jan ave 66 high and 40 low

July ave 105 high and 80 low

About 4 to 8 frost a year...ave yearly min temp about 27F

About 8 inches of rain a year.

Low Desert

Phoenix.gif

Cool Mtn climate at 7,000'

Parks.gif

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It's true the information is helpful but my point is simply that other factors come into play.  As I mentioned here where I am at we have 6 months out of the year with temps over 80 and 3 of those are over 90.  But  there are two other factors that come in to play.  1. Here in so Cal we lack the humidity which many palms prefer and want for maximum growth rate. 2. Winter night time temps, although seldom freezes are generaly cooler than Hawaii and Florida and so slows down growth of most palms here because lack of soil warmth.  With few exeptions we don't get much growth from palms during winter months even though we may occasionaly have daytime temps in the eighties.  The heat zone for my area of so cal is listed as 8 and for most of Hawaii it is 2-4 but palms grow much faster and nicer there in part due to the reasons listed above.

Don_L    Rancho CUCAMONGA (yes it does exist) 40 min due east of Los Angeles

             USDA Zone 10a

July Averages: Hi 95F, Low 62F

Jan Averages: Hi 68F, Low 45F

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(Don_L @ Oct. 22 2006,02:50)

QUOTE
1. Here in so Cal we lack the humidity which many palms prefer and want for maximum growth rate.

I have read that, but climate reports does not really support that, at least for the coast of S. Calif..

Relative humidity

   

                 Jan    hr  02        08       14        20

SD calif                      70%    55%    56%     70%

Miami                         81%    84%    59%     69%

Honolulu                    81%    81%    62%     74%      

                  July

SD                              82%    69%    66%      80%

Miami                          82%    84%    63%      73%

Honolulu                     73%    67%    52%      68%

              year ave

SD                              76%    62%     62%       75%

Miami                          81%    84%     60%       70%

Honolulu                     76%    72%     56%       70%

Not a whole lot of differance

Now it may feel different in each city

a ave summer day in SD lets say @ 75F and RH @ 65% would feel like 76F

but ave summer day in Miami say @ 90F and RH @ 65%

would feel like 102F

You feel the heat and humidity more in Maimi than in SD, but the RH is much the same.

I always been a climate nerd :laugh:

As far as soil temperatures, well yeh the cooler and cloudier the climate the cooler the soil... But I think palms need both warm soil and air... The bud of the palm is in the air (the growing point) and would not be effected by soil temperature. But nutritent uptake is by the roots which is effected by soil temperature. So a palm need both to really grow the way it should.

And the warmer the climate the warmer the soil temperature, it goes hand in hand. Even if you warm the soil, which would help, the palm bud still has to deal with the cold air.

So if you did warm the soil, I don't think a coconut would grow as well or as fast in Calif as it would in Florida which has both warm soil and air.  

Many factors go into play when growing plants, that why I am alway looking for someway of using and understanding these factors when choosing plant to try for a given climate.  

Palms grow better in Hawaii because the year round warm day and night temperatures, warm soil and humidity. It has it all...

Phoenix Area, Arizona USA

Low Desert...... Zone 9b

Jan ave 66 high and 40 low

July ave 105 high and 80 low

About 4 to 8 frost a year...ave yearly min temp about 27F

About 8 inches of rain a year.

Low Desert

Phoenix.gif

Cool Mtn climate at 7,000'

Parks.gif

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I agree Hawaii does have it all now if we can just find a way to bring their climate over this way.

Don_L    Rancho CUCAMONGA (yes it does exist) 40 min due east of Los Angeles

             USDA Zone 10a

July Averages: Hi 95F, Low 62F

Jan Averages: Hi 68F, Low 45F

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(chris78 @ Oct. 22 2006,07:05)

QUOTE
Not a whole lot of differance

Now it may feel different in each city

a ave summer day in SD lets say @ 75F and RH @ 65% would feel like 76F

but ave summer day in Miami say @ 90F and RH @ 65%

would feel like 102F

You feel the heat and humidity more in Maimi than in SD, but the RH is much the same.

I always been a climate nerd :laugh:

Wouldnt comparing dewpoints be a more telling?

I believe plants care about the temperature of the air and the actual amount of moisture in the air.  Short of discussing absolute humidity levels, dewpoint seems applicable.

Larry 

Palm Harbor, FL 10a / Ft Myers, FL 10b

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Astute discussion, Don, Chris & Larry

Case in point. Today : continued inland heat courtesy of 'santa ana'  Hi: 80's/90's Lo: 50's/60's.  Beaches are foggy at times and barely break 75F.  Typical pattern of ebbing offshore winds that don't quite reach Santa Monica bay.

Elevation/topography is the major player.  Check out overnight readings at the Getty Center.  Some of the warmest minimums in the area and within 2 miles of the Pacific.

The south-facing foothills from Santa Barbara to San Bernardino are the most favored for tropical gardens.   :cool:

At an elevation of 900' I am located at the top of a somewhat steep hill between downtownLA & Pasadena.  The rim of mts that defines the LA basin from Santa Monica mts/Malibu thru the Hollywood hills/SilverLake, San Rafael hills/MtWashington/El Sereno and down to Montebello/Whittier hills is USDA 11.  In California!    :P   At 33/34N latitude.  No simularity to KeyWest & higher elevation Hawaii except being frost-free.

Average minimums : 50-52 Dec-Feb / 63-67 Jun-August

Average maximums : 69-72 Dec-Feb / 84-90 Jun-August

Generally record several winter minimums above 70F during 'santa ana' events.  Last freeze 1990.  It's coming!  :o

Los Angeles/Pasadena

34° 10' N   118° 18' W

Elevation: 910'/278m

January Average Hi/Lo: 69F/50F

July Average Hi/Lo: 88F/66F

Average Rainfall: 19"/48cm

USDA 11/Sunset 23

http://cdec.water.ca.gov/cgi-progs/queryF?MTW

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Good point Happ, I'll have to check the dew points.  Like you we're on the south facing slopes of the foothills just below the 210 fwy which is why we're considered 10A here but weather here is much different than Hawaii or Florida.  Inland a few miles the daytime temps are much  higher but the relative humidity tends to be higher along the coast case in point the numbers that Chris showed but inland the humidity is lower.  I never gave dew points much consideration but something for me to become familiar with.

Don

Don_L    Rancho CUCAMONGA (yes it does exist) 40 min due east of Los Angeles

             USDA Zone 10a

July Averages: Hi 95F, Low 62F

Jan Averages: Hi 68F, Low 45F

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(spockvr6 @ Oct. 22 2006,14:11)

QUOTE
[

Wouldnt comparing dewpoints be a more telling?

I believe plants care about the temperature of the air and the actual amount of moisture in the air.  Short of discussing absolute humidity levels, dewpoint seems applicable.

Larry

I am not sure? more telling in what way? When I studied weather, dew point was mostly used to tell at what temperature dew, frost or fog was going to be formed. and is used to tell when fog is most likely to form.

.

This is out of one of my weather books....."Dew point is the temperature to which air must be cooled to become saturated by the water vapor already present in the air....The difference between air temperature and dew point temperature is popularly called the spread. As spread becomes less, relative humidity increases, and it is 100% when temperature and dew point are the same. Surface temperature dew point spread is important in anticipating fog."

This happens more on the California coast      Mean # days with heavy fog  San Deigo is 23 a year...Miami is 6 days a year and Honolulu its zero days a year. So SD gets more days a year that the air is saturated to the point to from fog. (When the air temperature is right) Other than that I not sure how dew point will help you.

Out of interested I will include what its says about dew and frost:

"During clear nights with little or no wind, vegetation often cools by radiation to a temperature at or below the dew point of the adjacent air. Moisture then collects on the leaves just as it does on a pitcher of ice water in a warm room. Heavy dew often collects on grass and plants when none collects on pavements or large solid objects. These more massive objects absord adundant heat during the day, lose it slowly during the night and cool below the dew point only in rather extreme cases."

Frost forms in much the same way as dew. The difference is that the dew point of surrounding air must be colder than freezing. Water vapor then sublimates directly as ice crystals or frost rather than condensing as dew. Sometimes dew forms and later freezes, however, frozon dew is easily distinguished from frost. Frozon dew is hard and transparent while frost is white and opaque"  

I only use dew point with my plants is when the spread is great ( between the dew point and air temperature) because the greater the spread the faster the night time temperature will drop. and on frost forming nights this will let you know what temperature you need to worry about before frost is formed.

Phoenix Area, Arizona USA

Low Desert...... Zone 9b

Jan ave 66 high and 40 low

July ave 105 high and 80 low

About 4 to 8 frost a year...ave yearly min temp about 27F

About 8 inches of rain a year.

Low Desert

Phoenix.gif

Cool Mtn climate at 7,000'

Parks.gif

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Don

You live in a warmer climate.  Both regions average above 80F half the year but summer maximums are hotter in Rancho Cucamonga than Los Angeles.  Isn't Rancho Santa Ana botanical gardens near you?

SoCal dew point temps are relatively low even during summer.  Humidity levels can soar like last July.    :o  Floridians would consider our highest dew points as normal.  But maximums above 100F for several weeks on end drove California into unbearable comfort zones & loss of life.

Current : 4PM

Humidity : 21%  Dew point : 19

Temp : 89F

Wind : E 5MPH

Los Angeles/Pasadena

34° 10' N   118° 18' W

Elevation: 910'/278m

January Average Hi/Lo: 69F/50F

July Average Hi/Lo: 88F/66F

Average Rainfall: 19"/48cm

USDA 11/Sunset 23

http://cdec.water.ca.gov/cgi-progs/queryF?MTW

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Someone mentioned it to me before but never had been there.  I just found out it's about 7 miles from where I live, I'll have to make it a point to get over there and see it.  Usually My wife and I like to go to the Huntington and since I have membership there we visit there usually even if it's to just to get a nice walk and dinner in Pasadena.

Don_L    Rancho CUCAMONGA (yes it does exist) 40 min due east of Los Angeles

             USDA Zone 10a

July Averages: Hi 95F, Low 62F

Jan Averages: Hi 68F, Low 45F

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(chris78 @ Oct. 22 2006,18:35)

QUOTE

(spockvr6 @ Oct. 22 2006,14:11)

QUOTE
[

Wouldnt comparing dewpoints be a more telling?

I believe plants care about the temperature of the air and the actual amount of moisture in the air.  Short of discussing absolute humidity levels, dewpoint seems applicable.

Larry

I am not sure? more telling in what way?

Dewpoint is directly proportional to the absolute humidity in the air (i.e. lb water in the air per lb of dry air) and is not a function of temperature.  Thus, this measure tells one how much actual water is in the air.  This unit of measure is convenient as measuring the dewpoint is alot easier than measuring the lb of water vapor per lb of dry air!

When the dewpoint and air temperature (the dry bulb) are the same, the RH is 100%.  

Unlike dewpoint, relative humidity is a function of temperature, and thus muddies the waters (as can be seen in the examples you gave).

For example, if the dewpoint is noted as 75F (typical of Miami), then there is about 0.019 lb of water vapor in the air per lb of dry air.  If the air temperaure is 75F or 95F, there is still 0.019 lb of water vapor in the air per lb of dry air.

Using your sample data points for Miami and San Diego--

Miami - 90F and 65% RH.....This would equate to a dewpoint of about 76F and about 0.0195 lb of water vapor per lb of dry air.

San Diego - 75F and 65% RH....This would equate to a dewpoint of about 63F and about 0.0125 lb of water vapor per lb of dry air.

So, the air in Miami, at the same RH, actually has 56% more water vapor in it than San Diego!  That, combined with the higher temperature, is what makes it feel so nasty.  

 

If you have access to psychrometric charts (a search online will allow you to see some free ones), youll see what I am talking about.

Heres an example---

http://www.truetex.com/psychrometric_chart.htm

Larry 

Palm Harbor, FL 10a / Ft Myers, FL 10b

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Larry you got me on this one, I have to study this for a while. I have not really took much time trying to understand wet/ dry bulb and what it all means.

I looked at the chart, is it a method to find RH by using dry and wet bulb temperature? That what it says!!!

"The psychrometric chart gives the relative humidity for a given wet-bulb and dry-bulb temperature. To use, find the vertical line for the dry bulb temperature at the bottom of the chart, and the slanted line for the wet-bulb temperature at the curved top-left edge. Find the intersection point of these two lines, and read the percent relative humidity from the curved lines nearest that point."

So I looked at Phoenix climate data  ave daily max is 105F, ave daily min is 80F  mean dry bulb is 93F the mean wet bulb is 70 and the mean dew point is 57.

All the weather charts list wet bulb and dew point as two different readings. And your chart put it as one in the same. It calls it "Wet bulb-dew point-saturation temperature"

here are some of weather data for some cities....

                                       

                 July mean     dry bulb       wet bulb       dew point      normal % RH

Phoenix                              93                 70                 57                   32

SD Calif                               70                 65                 61                  75

Miami                                  83                 76                 73                   75

Honolulu                             80                 72                 67                    65

These are the reading I get for these cities...

Like I said, I have to read up on this to see what it all means...give me your input and we all can learn...

Phoenix Area, Arizona USA

Low Desert...... Zone 9b

Jan ave 66 high and 40 low

July ave 105 high and 80 low

About 4 to 8 frost a year...ave yearly min temp about 27F

About 8 inches of rain a year.

Low Desert

Phoenix.gif

Cool Mtn climate at 7,000'

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You guys have some very interesting information.  I guess I understand now why the fog forms around here in the country on nights where the temperature is in the 70's F.  Just as the sun goes down patches of fog form over the forest.  This makes driving the few roads we have out of town a real pain sometimes.  I have had to stop the car sometimes as I could not see a thing.  

dk

Don Kittelson

 

LIFE ON THE RIO NEGRO

03° 06' 07'' South 60° 01' 30'' West

Altitude 92 Meters / 308 feet above sea level

1,500 kms / 932 miles to the mouth of the Amazon River

 

Manaus, Amazonas, Brazil - A Cidade da Floresta

Where the world´s largest Tropical Rainforest embraces the Greatest Rivers in the World. .

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Click here to visit Amazonas

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Really enjoy this site   :P  

Larry

Your graphics/data are a definite plus.  It will be great receiving your reports this winter.  Always spend a few days in Miami in Feb.  I know Fairchild is best visited in spring/summer but even in winter it's a thrill.   :cool:

Chris

Meet another "nerd".   :P    I have daily records going back to 1980.   Discovered that climate provides fun gardening.  Either looking up into the sky or gazing on palm trees, I'm an easily distracted driver   :laugh:      

High humidity/dew points offers the necessary moisture for vegetation.  Ironic that winter is Cali rain season   :(

Los Angeles/Pasadena

34° 10' N   118° 18' W

Elevation: 910'/278m

January Average Hi/Lo: 69F/50F

July Average Hi/Lo: 88F/66F

Average Rainfall: 19"/48cm

USDA 11/Sunset 23

http://cdec.water.ca.gov/cgi-progs/queryF?MTW

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(happ @ Oct. 23 2006,21:03)

QUOTE
 

Larry

Your graphics/data are a definite plus.  It will be great receiving your reports this winter.  

Winter reports may start tonight Happ!

At 915PM its 67F with a dewpoint way down at 45F.....lots of room to cool off tonight before that moisture can start to fall out and hold temps steady :D

However, earlier this evening the dewpoints were in the upper 30's!

Larry 

Palm Harbor, FL 10a / Ft Myers, FL 10b

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