This page is a work in progress on the development of SSC climate zones, based on PCA decomposition of seasonal normals, and a k-means cluster analysis. All North American and European available stations were included. Nine zones were originally defined, and since zone 3 had nearly half of the stations, I ran a second cluster analysis to furhter divide the zone into 3 subzones. Jim Detwiler has produced the maps below depicting these zones.
Stations in this zone experience a distinct seasonality, with a very
variable winter calendar, during which time nearly all weather types are
present. During the summer, the subtropical Bermuda High controls the
weather, and Moist Tropical (and Moist Moderate on cloudier days) account
for nearly 3/4ths of all days.
Basin and range
This climate zone is found in elevated arid areas. Following Zone 7, it
is the second-most affected by dry weather types, with nearly half of all
Of the three mid-latitude subzones, this zone features the most variability, with considerable
difference between winter and summer, and the presence of all weather types throughout the summer,
with limited tropical influence in the winter.
Farther west of Zone 3a, this zone features much more limited MT-penetration.
With high terrain nearby, there is some incidence of DT year-round, but also greater MP occurrence
than in other temperate zones.
Farther south of Zone 3a, this zone which borders Zone 1 contains a longer
summer of significant MT occurrence, and more limited polar-weather type influcence than 3a or 3b.
Its name derives from the fact that it's the only climate zone that is influenced by all weather types year-round.
Dominated by adjacent cold ocean waters, this climate zone is dominated by the MP weather type, which makes up over
half of the average calendar. Dry Polar is common in the winter months,
and MM occurence varies from station to station, based on proximity to a milder oceanic fetch on occasion.
The most distinct of the climate zones, this is the only climate zone
dominated by DT. The five stations in this zone actually have two distinct
summer patterns; Phoenix and Yuma heavily affected by the (MT) monsoon, and
Las Vegas, Tucson, and Daggett not. The resulting climograph is midway
between the two.
This climate zone is quite similar to Zone 6, although with the
stations farther south, warmer waters bring MM days more frequently, with
MT occurring on occasion in summer. This climate zone also has the highest
TR frequency of the lot.
Most of the stations within this climate type are in western Europe,
with a few Pacific US stations included. Similar to zones 3a and 3c, all
weather types have a presence, although due to Zone 9's maritime location,
MM is more prominent here than in any other zone.