Physiographic features

Includes well drained soils under grassland vegetation on slopes in the subalpine zone in the Talkeetna Mountains. Elevation ranges from 1400 to 2500 feet (427 to 762 m); slope ranges from 15 to 35 percent, and occasionally greater.

Table 2. Representative physiographic features

Climatic features

The climate of the Matanuska and Susitna Valleys is transitional maritime-continental, characterized by long cool winters and short warm summers. Long term climatic data for two stations in the area, Palmer and Talkeetna, are provided in Tables 1, 2, 3, and 4 (MatSu Soil Survey). At Palmer, which is near the Knik Arm of the Cook Inlet, maritime influences are more evident and winter temperatures are relatively moderate. At Talkeetna, approximately 100 miles (160 km) inland, continental influences are stronger, and temperatures are more extreme in both winter and summer.
The Chugach Mountains and Cook Inlet have substantial influence on the climate of the Matanuska-Susitna Valley Area. The Chugach Mountains form a partial barrier against moist oceanic air moving in from the Gulf of Alaska and Prince William Sound. Most of the precipitation carried by weather systems originating in the Gulf falls on the windward slopes of the Chugach Mountains. The Matanuska Valley lies in the rain shadow created by the Chugach Mountains. However, the Susitna Valley is directly exposed to moist oceanic air moving up Cook Inlet from the southwest. This air backs up against the Talkeetna Mountains, producing higher precipitation in the Susitna Valley and Talkeetna Mountains compared to the Matanuska Valley.
Long term temperature and precipitation data have been recorded at the Agricultural and Forestry Experiment Station in Palmer (NOAA recording station Palmer AAES, 6870) and at the airport in Talkeetna (Talkeetna WSCMO AP, 8976).
Temperature. Average monthly temperatures during summer are similar for Palmer and Talkeetna (Tables 1 and 2). For July, the average is 57.4 °F (14.1 °C) at Palmer and 58.2 °F (14.6 °C) at Talkeetna. Daily high temperatures in summer occasionally exceed 80 °F (26.7 °C). Daily minimum temperatures in summer are generally between 44 and 47 °F (6.7 and 8.3 °C) at both locations. Freezing temperatures have been recorded as late as June 5 and as early as August 22 at Palmer (Table 3). The frost-free period is usually greater at Talkeetna (Table 4).
Average monthly temperatures during winter are significantly higher at Palmer compared to Talkeetna. For January, the average is 12.8 °F (-10.7 °C) at Palmer and 9.7 °F (-12.4 °C) at Talkeetna. Persistent high pressure may dominate the region for several days or weeks during winter, bringing relatively cold temperatures to the Area. Persistent low temperatures of -20 °F (-28.9 °C) or less at Palmer and -30 °F (-34.4 °C) or less at Talkeetna occur during most winters. In the Susitna Valley, high pressure coupled with the lack of significant air circulation allows heat to radiate to space, further lowering winter temperatures. In the Matanuska Valley, high pressure gradients between the coastal lowlands and Copper River Basin to the east generate strong winter winds along the Matanuska River, which moderate the temperature but escalate the wind chill factor.
Data for the last date in spring and the first date in fall when air temperature drops below certain threshold temperatures are given in Table 3 for Palmer and Table 4 for Talkeetna. The number of continuous days during which the temperature does not drop below the threshold is given in Tables 5 and 6. The threshold temperatures are 32 °F (0 °C), 28 °F (-2.2 °C), and 24 °F (-4.4 °C). The data in these tables are based on records from 1950 through 1993 for both the Palmer and Talkeetna recording stations.
The probability of certain last and first dates, and the number of days, is expressed as the number of years in ten. For example, at Palmer one can expect that the temperature will not drop below 32 °F (0 °C) after May 15 or before September 14 in five years out of ten (Table 3), or for a period of 119 days (Table 5). On the other hand, a frost-free season, above 32 °F (0 °C), of 142 days can be expected in one year out of ten (Table 5).
Precipitation. Average annual precipitation is about 15 inches (38 cm) at Palmer and about 28 inches (71 cm) at Talkeetna (Tables 1 and 2). Precipitation is usually light in spring; average precipitation during May and June is 0.68 and 1.35 inches (1.7 and 3.4 cm) at Palmer and 1.47 and 2.37 inches (3.7 and 6.0 cm) at Talkeetna. Precipitation increases in summer and early autumn to a maximum of 2.47 inches (6.3 cm) during September at Palmer and to 4.6 inches (11.7 cm) during August at Talkeetna. Average annual snowfall is about 45 inches (114 cm) at Palmer and about 115 inches (292 cm) at Talkeetna.
Soil moisture balance, and to a degree ground water recharge and surface water storage, are determined in part by evapotranspiration. Patric and Black (1968) compared annual precipitation and potential evapotranspiration for the Area to determine regional soil water deficits or surpluses. Potential evapotranspiration, which is defined as water losses (to the atmosphere) from fully vegetated land surfaces abundantly supplied with water, was calculated from available temperature and precipitation data from various weather reporting stations. Data indicated that, on the average, an annual moisture deficit exists for the Matanuska and southern Susitna Valleys and a moisture surplus exists for the northern Susitna Valley.
Wind. The proximity of the Gulf of Alaska to the south, and the effects of the rugged terrain surrounding the Matanuska Valley, contribute to strong seasonal winds in the Matanuska-Susitna Valley Area, particularly in the vicinity of Palmer. The "Matanuska" winds blowing down the Matanuska River canyon in winter and "Knik" winds down the Knik River floodplain in spring and summer (and occasionally winter) are well known to local residents and pilots. In spring, when the "Knik" winds, and sometimes "Matanuska" winds, are strong, blowing dust up to 3000 feet (914 m) or higher (Plate 1) darkens the air. The best agricultural soils in the Matanuska Valley are formed in this wind blown dust called loess. The blowing snow and extreme chill factors associated with winter winds impact recreational activities, transportation, and other land use activities throughout the Area.

Table 3. Representative climatic features

Influencing water features

Soil features

Talkeetna soils are formed in a silty mantle of loess and volcanic ash 14 to 25 inches (36 to 64 cm) thick over gravelly and cobbly till.

Cryods component:
This component is on a mountain. The parent material consists of silty volcanic ash and/or silty loess over gravelly glacial drift and/or loamy outwash. The runoff class is medium. The depth to restrictive layer is 20 to 60 inches to bedrock, lithic. It is well drained. The slowest permeability of the soil material is impermeable. Available water capacity is very low and shrink swell potential is low. This soil is not flooded and is not ponded. The water table is deeper than 6 feet. There are no saline horizons within 30 inches of the soil surface. There are no sodic horizons within 30 inches of the soil surface. It is in nonirrigated land capability class 7e.

Talkeetna component:
This component is on a mountain. The parent material consists of silty volcanic ash and/or silty loess over gravelly till. The runoff class is high. The depth to restrictive layer is greater than 80 inches. It is well drained. The slowest permeability of the soil material is slow. Available water capacity is high and shrink swell potential is low. This soil is not flooded and is not ponded. The water table is deeper than 6 feet. There are no saline horizons within 30 inches of the soil surface. There are no sodic horizons within 30 inches of the soil surface. It is in nonirrigated land capability class 6e.

Table 4. Representative soil features

Contributors

Dennis Moore
Dkautz
Michelle Schuman