Climate Overview:
The Southwest is actually comprised of two distinct regions: the coastal plains and inland high deserts. While the high deserts encompass a much bigger geographical footprint, the coastal areas contain the major population centers. One thing both areas have in common is abundant sunshine. The coastal regions enjoy moderate temperatures year-round. Rain averages 15 to 20 inches per year and falls primarily in the winter months of February and March. The farther inland you travel, the warmer the temperatures get, with summer highs reaching 100 F. The larger high desert area is characterized by little rainfall and blazing-hot summer temperatures. Most desert regions average 10 to 12 inches of rainfall annually. Precipitation occurs during winter storms that occur from November to February, and "monsoon" season during July and August.

Winter

Climate (December - February): Winters are mild. Most precipitation will fall in this region during these few months. Higher elevations will see snow, while most areas see rain. Day time temperatures are mild and range from 50 F to 70 F. The higher elevation areas of Northern Arizona and New Mexico can see periods of cold weather, but typically they do not last for more than a week, with abundant sun shine right behind. Moderate temperatures and midrange humidity make the winter months a great time for exterior concrete placement in most of these regions.

Mix Designs: With the exception of the high deserts, this region does not see much in the way of harsh weather. Most exterior concrete mix designs have compressive strengths of 3000 psi concrete and need little in the way of additional chemical set accelerators. In colder regions, 4000-psi concrete is often specified and set accelerators and air entrainment may be used if necessary.

Placement and Curing Practices: Moderate temperatures and mid-level winter humidity allow for relatively easy placement and curing of concrete during the winter. For high elevation regions (above 3000 feet), cold-weather concreting practices and the use of curing blankets may be needed when temperatures fall below 40 F at night. The use of water- or solvent-based curing compounds is always recommended to achieve quality concrete. During dry Santa Ana wind conditions, make sure to follow proper curing practices to avoid rapid hydration and shrinkage cracking of the concrete surface.

Special Equipment: Since this region does not see the ground freeze or significant snowfall, there are no special equipment requirements when placing concrete in the winter, with the exception of curing blankets in the colder regions, if needed.

Spring

Climate (March – April): For the coastal regions, spring ushers in warmer temperatures but is still mild and pleasant. The high deserts start to experience the first hot weather in late spring, but overall conditions are still favorable for exterior concrete pours. Spring rains may occur for prolonged periods in early spring, but are rare after March.

Mix Designs: Standard mix designs are the norm. Eliminating set accelerators and adding fly ash into mixes is normal as the temperatures start to increase. Air entrainment may be needed in high-elevation areas.

Placement and Curing Practices: Transitional placement and curing practices are the norm, as temperatures will dictate cold- or warm-weather practices.

Special Equipment: Sprayers to apply curing compounds and curing blankets for the rare late snow at higher elevations.

Summer

Climate (May – September): Sunny and hot! Mild temperatures are limited to within 10 miles of the coast, with all other regions experiencing hot to extremely hot conditions. Coastal areas will see fog in early summer, but this ends by July. Along with the warmer weather comes blazing sunshine, dry winds, and low humidity. In most areas, summer can be the most demanding time of year to pour exterior concrete.

Mix Designs: When hot conditions exist, hydration stabilizers, fly ash, and water reducers are common admixtures used to extend working life without affecting performance. The use of ice in mix water is also common to cool the concrete during transport. Air entrainment may be needed in high-elevation areas.

Placement and Curing Practices: Hot-weather concreting practices are the norm in the summer months. With some of the highest temperatures in the country, placement and curing of concrete in the summer may require extreme measures. In the hottest desert regions, most concrete placements take place before 10 a.m. On many larger projects, concrete is placed at night or during the early morning hours to avoid the extreme sun and heat of the day. Rapid surface hydration is always a threat, so surface evaporative control agents and curing compounds are common on exterior concrete placements.

Special Equipment: Sprayers to apply curing compounds and surface evaporative control agents.

Fall

Climate (October – November): Fall temperatures can still be quite hot. Coastal regions will see temperatures moderate earlier, while the deserts remain very warm. Early winter storms can begin to erupt in the late fall.

Mix Designs: Standard mix designs are the norm. Eliminating fly ash and retarders from mixes is normal as the temperatures start to decrease.

Placement and Curing Practices: Hot-weather concreting practices are in effect well into the fall in most areas of the region.

Special Equipment: Sprayers to apply curing compounds and surface evaporative control agents; plastic sheeting.

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