Spatial Synoptic Classification (SSC) A method of synoptic weather-typing; the classification of ambient weather conditions into categories Surface weather types 4x Daily surface obs at individual stations  Temp, dp, wind, pressure, cloud cover

SSC History Kalkstein and Greene (Kalkstein et al. 1996) Stations east of Rockies winter and summer Sheridan 2000 (Sheridan 2002) Expanded to 300+ stations U.S. and Canada All seasons Bower, McGregor (mid 2000’s) Expanded into Europe Slightly different methodology

Methods Hybrid scheme Weather types first identified manually Seasonal typical seed days were then picked for each weather type for every station Algorithms then use hypothetical seed days 365 days a year Actual daily conditions then compared to seed day conditions Day is classified into a weather type that most closely resembles the seed day

Weather Types DP (dry polar) is synonymous with the traditional cP air mass classification. This air mass is generally advected from polar regions around a cold-core anticyclone, and is usually associated with the lowest temperatures observed in a region for a particular time of year, as well as clear, dry conditions.

Dry Moderate DM air is mild and dry. It has no traditional analog, but is often found with zonal flow in the middle latitudes, especially in the lee of mountain ranges. It also arises when a traditional air mass such as cP or mT has been advected far from its source region and has thus modified considerably.

Dry Tropical DT (dry tropical) weather type is similar to the cT air mass; it represents the hottest and driest conditions found at any location. There are two primary sources of DT: either it is advected from the desert regions, such as the Sonoran or Sahara Desert, or it is produced by rapidly descending air, whether via orography (such as the chinook) or strong subsidence.

Moist Polar MP air is a large subset of the mP air mass; weather conditions are typically cloudy, humid, and cool. MP air appears either by inland transport from a cool ocean, or as a result of frontal overrunning well to the south of the region. In can also arise as a modified cP air mass, especially downwind of the Great Lakes.

Moist Moderate MM is considerably warmer and more humid than MP. The MM air mass typically appears in a zone south of MP air, still in an area of overrunning but with the responsible front much nearer. It can also arise within an mT air mass on days when high cloud cover suppresses the temperature.

Moist Tropical MT analogous to the traditional mT air mass, is warm and very humid. It is typically found in warm sectors of mid-latitude cyclones or in a return flow on the western side of an anticyclone; as one approaches the tropics this weather type dominates. MT+ is a subset of MT that was derived after the initial classification, to account for the lack of utility of a weather-type scheme in the warm subtropics when one weather type dominates most of the year. It is defined as an MT day where both morning and afternoon temperatures are above seed day means, and thus captures the most "oppressive" subset of MT days.

Transitional TR days are defined as days in which one weather type yields to another, based on large shifts in pressure, dew point, and wind over the course of the day.

Weather Type Considerations Within the SSC scheme, weather-type characteristics change from station to station and day to day. Moist Tropical weather type is hotter and more humid in the southeastern US, nearer its source region, than in the northeastern US, after it has modified somewhat. MT is warmer at all locations in July than in January.

Experimental SSC Climate Zones

Southeastern Zone Southeast 60 stations Capital: Jackson, MS distinct seasonality variable winter calendar During the summer, the subtropical Bermuda High controls the weather Moist Tropical (and Moist Moderate on cloudier days) account for nearly 3/4ths of all days.

Basin and Range Basin and range 34 stations Capital: Amarillo, TX elevated arid areas second-most affected by dry weather types nearly half of all days DM.

Laurentian Laurentian 58 stations Captial: Alpena, MI considerable difference between winter and summer presence of all weather types throughout the summer limited tropical influence in the winter.

Northern Rockies Northern Rockies 33 stations Capital: Glasgow, MT limited MT-penetration high terrain nearby some incidence of DT year-round greater MP occurrence than in other temperate zones

Mid-Latitude True mid-latitude 54 stations Capital: Washington, DC summer significant MT occurrence, and more limited polar-weather type influcence than 3a or 3b only climate zone that is influenced by all weather types year- round.

Arctic Arctic 37 stations Captial: Schefferville, QC abundance of polar weather types DP peaking in late winter MP peaking at the autumn ice minimum.

Tropical Tropical 13 stations Capital: Key West, FL MT monopoly in the summer limited variability in the winter only zone with the same weather type making up more than 50% of the calendar in every month of the year.

Boreal Coast Boreal coast 15 stations Capital: Yakutat, AK adjacent cold ocean waters dominated by MP Dry Polar is common in the winter months MM occurrence varies from station to station, based on proximity to a milder oceanic fetch on occasion.

Sonoran Sonoran 5 stations Capital: Phoenix, AZ dominated by DT five stations in this zone have two distinct summer patterns Phoenix and Yuma heavily affected by the (MT) monsoon, and Las Vegas, Tucson, and Daggett not. Resulting climograph is midway between the two.

Marine Marine 16 stations Capital: Halfiax, NS similar to Boreal warmer waters bring MM days more frequently MT occurring on occasion in summer has the highest TR frequency

European European 58 stations Capitals: Seattle, WA and Stuttgart, Germany western Europe, with a few Pacific US stations included Similar to zones 3a and 3c, all weather types have a presence MM is more prominent here than in any other zone.

Polar Air Mass Frequency (Jan) DPMP

Polar Air Mass Frequency (July) DPMP

Moderate Air Mass Frequency (Jan) DMMM

Moderate Air Mass Frequency (July) DMMM

Tropical Air Mass Frequency (Jan) DTMT

Tropical Air Mass Frequency (July) DTMT

Transition JanJuly Oct April

SSC Applications Bioclimate Human Human Health/Mortality Air pollution/Aerosols Behavior/suicide/crime Agriculture and Forest Urban Heat Islands Temp and Precip modification Cryosphere/Snow Heat Waves/Drought Synoptic Climatology Atmospheric circulation