The 2000 US National Arboretum "Web Version" of the 1990 USDA Plant Hardiness Zone Map

Zones 3a through 9b represented here.
   
North-West region Hardiness Zone MapZones Color Key

As shown in the map above and blowup below, a distinct salmon colored area denotes Powell River as climate zone 9a.  That's the same climate zone as Houston, Texas and St. Augustine, Florida.  Also note that the Powell River area is surrounded by an dark olive color code which is labeled climate zone 8b, the same as Austin, Texas and Gainesville, Florida. The dark olive area is also surrounded by the light olive color code for climate zone 8a, the same as Tifton, Georgia; and Dallas, Texas. Although winters can bring snow to the area, this data shows you can grow the same plants as in California, Texas, Forida and other southern states.  The reason for such a warm spot in Powell River is because of a shallow inland sea and the rain shadow effects of the 6,000 foot high mountains on Vancouver Island.  This unique topography protects Powell River and creates a simi-tropical oasis.  In addition, summer days are quite long this far north and provide ideal conditions for growing high THC cannabis.  Powell River is the home of Texada Timewarp, which was named after  nearby Texada Island, but is mostly grown in Powell River, along with many other potent strains.
 

USDA Hardiness Zones and Average Annual Minimum Temperature Range

  Zone  
  Fahrenheit  
    Celsius    
  Example Cities  
1
 Below -50 F  
Below -45.6 C
Fairbanks, Alaska;   Resolute, Northwest Territories (Canada) 
2a
-50 to -45 F  
-42.8 to -45.5 C
Prudhoe Bay, Alaska;   Flin Flon, Manitoba (Canada) 
2b
-45 to -40 F
-40.0 to -42.7 C
Unalakleet, Alaska;   Pinecreek, Minnesota 
3a
-40 to -35 F
-37.3 to -39.9 C
International Falls, Minnesota;   St. Michael, Alaska
3b
-35 to -30 F
-34.5 to -37.2 C
Tomahawk, Wisconsin;   Sidney, Montana
4a
-30 to -25 F
-31.7 to -34.4 C
Minneapolis/St.Paul, Minnesota;   Lewistown, Montana
4b
-25 to -20 F
-28.9 to -31.6 C
Northwood, Iowa; Nebraska
5a
-20 to -15 F
-26.2 to -28.8 C
Des Moines, Iowa;   Illinois
5b
-15 to -10 F
-23.4 to -26.1 C
Columbia, Missouri;   Mansfield, Pennsylvania
6a
-10 to -5 F
-20.6 to -23.3 C
St. Louis, Missouri; Lebanon, Pennsylvania
6b
-5 to 0 F  
-17.8 to -20.5 C
McMinnville, Tennessee;   Branson, Missouri 
7a
0 to 5 F
-15.0 to -17.7 C
Oklahoma City, Oklahoma;   South Boston, Virginia
7b
5 to 10 F
-12.3 to -14.9 C
Little Rock, Arkansas;   Griffin, Georgia
8a 
10 to 15 F
-9.5 to -12.2 C
Tifton, Georgia;   Dallas, Texas 
8b
15 to 20 F
-6.7 to -9.4 C
Austin, Texas;   Gainesville, Florida
9a
20 to 25 F
-3.9 to -6.6 C
Houston, Texas;   St. Augustine, Florida
9b
25 to 30 F
-1.2 to -3.8 C
Brownsville, Texas;   Fort Pierce, Florida
10a
30 to 35 F
1.6 to -1.1 C
Naples, Florida;   Victorville, California
10b
35 to 40 F
4.4 to 1.7 C
Miami, Florida;   Coral Gables, Florida
11
above 40 F
above 4.5 C
Honolulu, Hawaii;   Mazatlan, Mexico