September is a transitional month in many parts of the world, and understanding its temperature patterns is crucial for various activities, from agriculture to tourism. Let's delve into a comprehensive overview of average temperatures and related climate conditions.
Erratic Weather: Why it is cold in September
Global Temperature Overview
To provide context, it's helpful to look at global temperature trends during September. For instance, in a particular year, the average temperature was 67.8°F, which was 2.9°F above the average, ranking it as the seventh warmest in a 129-year record. Some regions experienced record-breaking warmth, while others remained near normal.
Normal September temperatures across the contiguous United States (left). Temperatures in September 2023 (center). Temperature in September 2023 compared to the 1991-2020 average (right), showing places that were warmer than average in red and places that were cooler than average in blue.
Regional Temperature Variations
Temperatures can vary significantly by region. For example, temperatures were above average from parts of the Southwest to the East Coast and along parts of the Northern Tier, with near- to below-average temperatures from parts of the northern Plains to the West Coast.
Precipitation Patterns
In addition to temperature, precipitation is a key climate factor. Precipitation patterns can vary greatly. Precipitation was below average across much of the Mississippi Valley, Great Lakes and Ohio and Tennessee valleys as well as in parts of the Southwest, southern Plains and Southeast. Conversely, precipitation was above average across much of the West and northern Plains and along parts of the East Coast.
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Normal September precipitation (rain and snow) across the contiguous United States (left). Precipitation in September 2023 (center). Precipitation in September 2023 as a percent of the 1991-2020 average (right), showing places that were wetter than average in green and places that were drier than average in brown.
Local Weather Conditions: San Francisco and Baton Rouge in September
To get a more granular understanding of September weather, let’s look at specific locations. San Francisco and Baton Rouge offer interesting contrasts.
San Francisco, California
In San Francisco, daily high temperatures are around 72°F, rarely falling below 64°F or exceeding 83°F. Daily low temperatures are around 58°F, rarely falling below 54°F or exceeding 62°F. The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 89% of the time. The average sliding 31-day rainfall during September in San Francisco is gradually increasing, starting the month at 0.1 inches and ending the month at 0.4 inches.
Baton Rouge, Louisiana
In Baton Rouge, daily high temperatures decrease from 90°F to 84°F, rarely falling below 77°F or exceeding 94°F. Daily low temperatures decrease from 72°F to 65°F, rarely falling below 54°F or exceeding 76°F. The clearest day of the month is September 30, with clear, mostly clear, or partly cloudy conditions 64% of the time. The average sliding 31-day rainfall during September in Baton Rouge is decreasing, starting the month at 4.6 inches and ending the month at 3.6 inches.
Climate Normals and Their Significance
Understanding climate normals is essential for assessing long-term weather patterns. A "normal" is the 30-year average of a particular variable’s measurements, calculated for a uniform time period. These normals are derived from weather and climate observations captured by weather stations. NOAA produces Climate Normals in accordance with the World Meteorological Organization (WMO), which requires member nations to compute 30-year meteorological quantity averages at least every 30 years.
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Climate Normals were not developed to track or document climate change, but instead to characterize the current climate. However, the differences between each installment do provide some evidence of climate change.
Additional Factors Influencing Temperature
Several factors can influence temperature in a region. In Colorado Springs, the altitude and proximity to the mountains provide for a year-round, mild climate. The low humidity keeps out the bone-chilling cold found in other destinations.
The topography within 2 miles of San Francisco contains significant variations in elevation, with a maximum elevation change of 597 feet and an average elevation above sea level of 128 feet.
Conclusion
Understanding average temperatures in September requires a multifaceted approach, considering global trends, regional variations, and local weather conditions. By analyzing climate normals and additional influencing factors, we can gain a more complete picture of September's climate patterns.