Data Date: September

Rain drops collect on brownish red wood

September 2023 – Warm with Above Normal Precipitation Across Delaware

Posted on | by Dan Leathers

September Temperatures
Preliminary data indicates that the statewide average temperature in September was 70.4°F, which was 1.3°F above the 1991-2020 mean value of 69.1°F (Figure 1). This September’s temperature was the 21st warmest since observations began in 1895.

September Precipitation
Delaware’s statewide precipitation for September 2023 averaged 5.97 inches, 1.75 inches above the 1991-2020 mean of 4.22 inches (Figure 2). This month’s statewide precipitation total was the 14th wettest September since observations began in 1895.

Statewide Spatial Anomalies
Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were primarily positive across the state, but generally small except in the Wilmington area (Figure 3). Precipitation was above normal across most of the state, with some locations seeing positive anomalies of greater than five inches (Figure 4).

National Anomalies
Temperatures were generally above normal across the central portion of the country, and New England. Positive temperature anomalies were up to 6°F across portions of Texas. The far western U.S. experienced below normal temperatures (Figure 5). Negative precipitation departures covered most of the eastern U.S. except for the Mid-Atlantic region and southern New England where precipitation was above normal (Figure 6). The 500 hPa height pattern for September shows a jet stream trough covering the Pacific Coast of the U.S. and a jet stream ridge covering much of the central portion of the country. These two features were responsible for the temperature anomalies in both locations. (Figure 7).

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September 2022 – Near Normal Temperatures and Dry Conditions Across Delaware

Posted on | by Dan Leathers

September Temperatures

Preliminary data indicates that the statewide average temperature in September was 69.6o F, which is 0.5o F above the 1991-2020 mean value of 69.1o F (Figure 1).  September 2022 was in the top one-third of all September temperatures since observations began in 1895. 

September Precipitation

Delaware’s statewide precipitation for September 2022 averaged 3.50 inches, 0.72 inches below the 1991-2020 mean (Figure 2).  This month’s precipitation value placed it in the normal category when compared to September values since 1895.

Statewide Spatial Anomalies

Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were varied across the state (Figure 3) and generally small.  Precipitation observations were below normal at all but two stations across the State, with some negative precipitation anomalies topping two inches (Figure 4).   

National Anomalies

Temperatures were above normal across most of the conterminous United States west of the Mississippi River, and across much of the mid-Atlantic.  Only the Appalachians and parts of the southeast U.S. saw temperatures below normal.  In general, dry conditions prevailed across much of the eastern half of the United States, except for northern Pennsylvania, New York, and New England.  The 500 hPa height pattern for September shows a jet stream ridge over the western United States contributing to the positive temperature anomalies across that region  (Figure 7).

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September 2021 – Warm with Near Normal Precipitation Across Delaware

Posted on | by Dan Leathers

 

September Temperatures

Preliminary data indicates that the statewide average temperature in September was 71.0o F, which is 3.0o F above the 1981-2010 mean value of 68.0o F (Figure 1).  This month’s statewide temperature was tied with 1925 as the 13th warmest September since observations began in 1895.

September Precipitation

Delaware’s statewide precipitation for September 2021 averaged 4.04 inches, 0.07 inches above the 1981-2010 mean (Figure 2).  This placed this month’s precipitation total in the normal range of all years since 1895.

Statewide Spatial Anomalies

Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were above normal across the entire State, with the exception of southwestern Sussex County (Figure 3).  Precipitation anomalies varied across the State with large positive precipitation anomalies found in northern New Castle County.  The largest negative anomalies were found along coastal areas of Sussex County (Figure 4).

National Anomalies

Temperatures were above normal across most of the United States, with the largest temperature anomalies found across the Great Plains and New England.  Precipitation anomalies varied greatly across the country with dry conditions across much of the western United States except for Oregon and Washington and portions of the Desert Southwest (Figure 6).  Wet conditions were found across much of eastern Pennsylvania and southern New England.  The 500 hPa height pattern for September shows a weak jet stream ridge located over the western United States except for the Pacific northwest.  This jet stream pattern contributed to the generally warm and dry pattern found across that region (Figure 7).

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Colorful autumn leaves

September 2020 – Near Normal Temperature and Precipitation Across Delaware

Posted on | by Dan Leathers

September Temperatures

Preliminary data indicates that the statewide average temperature in September was 69.0o F, which is 1.0o F above the 1981-2010 mean value of 68.0o F (Figure 1).  September 2020 was the 35th warmest September since observations began in 1895.

September Precipitation

Delaware’s statewide precipitation for September 2020 averaged 3.99 inches, 0.02 inches above the 1981-2010 mean (Figure 2), placing this month in the “normal” category for all months since 1895. 

Statewide Spatial Anomalies

Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were generally small, and varied in sign, throughout the entire state (Figure 3).  Precipitation anomalies differed greatly depending upon location.  Kent and northern Sussex counties showed large positive precipitation anomalies while northern New Castle County saw substantial negative anomalies (Figure 4). 

National Anomalies

Temperatures were above normal across most of the western one-third of the country (5 – 10o F), while below normal temperatures were found across the Great Plains.  Most of the eastern United States saw near normal temperatures during the month (Figure 5).  Precipitation was generally below normal across the majority of the United States, while above normal precipitation fell across the southeastern portions of the country (Figure 6).  The 500 hPa height pattern for September exhibits a ridge dominating the western portion of North America leading to generally warm and dry weather across that region which continues to contribute to the severe wildfire season (Figure 7).

 

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Low water level in a wet pond.

September 2019 – Warm and Very Dry Across Delaware

Posted on | by Dan Leathers

September Temperatures

Preliminary data indicates that the statewide average temperature in September was 71.1°F, which is 3.7°F above the 1981-2010 mean value of 68.0°F (Figure 1). This places September 2019 as the 9th warmest since records began in 1895.

September Precipitation

Delaware’s statewide precipitation for September 2019 averaged 1.15 inches, 2.82 inches below the 1981-2010 mean (Figure 2). September 2019 was the 9th driest on record since 1895.

Statewide Spatial Anomalies

Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were above normal throughout the State (Figure 3), with the largest positive anomalies found across northern New Castle County. Precipitation was below normal at every station (Figure 4), with the largest negative anomalies found across New Castle County, where some stations recorded precipitation totals more than 4 inches below the September normal.

National Anomalies

Temperatures were far above normal throughout most of the eastern two-thirds of the U.S, where some positive anomalies reached greater than 7°F (Figure 5). In general, precipitation was below normal across the eastern U.S. and much of the country’s southern tier. Only the northern Great Plains and Pacific Northwest saw significantly above normal precipitation (Figure 6). The 500 hPa height pattern for September showed an anomalous ridge over the eastern U.S. (Figure 7), bringing the warm temperatures to that region.

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Autumn leaves submerged in water

September 2018: Extreme Warmth and Very Wet Across Delaware

Posted on | by Dan Leathers

 

 

September Temperatures

Preliminary data indicates that the statewide average temperature in September was 74.0°F, which is 6.0°F above the 1981-2010 mean value of 68.0°F (Figure 1). September 2018 was the warmest September since records for the State began in 1895. The eastern one-third of the United States shared in the extreme warmth, with many cities breaking September temperature records (Figure 2).

September Precipitation

Delaware’s statewide precipitation for September 2018 averaged 6.42 inches, 2.45 inches above the 1981-2010 mean (Figure 3). This placed September 2018 as the 11th wettest September on record since 1895.

Statewide Spatial Averages

Data from the Delaware Environmental Observing System (DEOS)show that temperature (Figure 4) departures were positive and large throughout the State. Temperature departures were greater than 5.0°F at many stations across Sussex County. Precipitation departures were positive throughout the State. Departures were as high as 8.6 inches above normal at Stokley.

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Autumn leaves shine in the bright Sun

Warm and Dry Conditions Characterize the 2017 Autumn Season Across Delaware

Posted on | by Dan Leathers
 

Autumn Temperatures

Preliminary data indicates that autumn 2017 ranked as the 3rd warmest autumn season since records began in 1895 (tied with three other autumn seasons). The statewide mean autumn temperature of 60.2°F was 2.6°F above the 1981-2010 mean value of 57.6°F (Figure 1).

Autumn Precipitation

The statewide mean precipitation of 8.23 inches was 2.60 inches below the 1981-2010 normal of 10.83 inches, and was in the driest one-third of autumns since 1895 (Figure 2). Precipitation during the autumn of 2017 was the lowest since the 2013 season.

Statewide Spatial Averages

Data from the Delaware Environmental Observing System (DEOS) show that autumn temperature anomalies were generally positive across the State, with a few locations experiencing near normal temperatures for the season (Figure 3).

Autumn precipitation was much below normal across the entire State, with the exception of extreme southeastern Sussex County (Figure 4). However, the size of the negative anomalies varied greatly from one location to another. Several stations in northern New Castle County and Chester County, PA saw negative anomalies of between four and six inches during the autumn months.

 

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Dried leaves scatter the autumn forest

September 2017 Climate Conditions – Warm and Dry Across Delaware

Posted on | by Dan Leathers

 

 

September Temperatures

Preliminary data indicates that the statewide average temperature in September was 70.2°F, which was 2.2°F above the 1981-2010 normal of 68.0°F (Figure 1). September 2017 was the 19th warmest September since 1895.

September Precipitation

Delaware’s statewide precipitation for September 2017 averaged 2.17 inches, 1.43 inches below the 1981-2010 mean (Figure 2), placing it in the driest one-third of Septembers since records began in 1895.

Statewide Spatial Averages

Data from the Delaware Environmental Observing System (DEOS) show that temperatures were above normal across the majority of the State with the largest positive temperature departures found across Chester County, PA and northern New Castle County, DE. (Figure 3). All stations in the DEOS network recorded below normal precipitation except for extreme southeastern Delaware (Figure 4). In the northern portions of the region, negative precipitation departures reached over 3 inches at several stations.

 

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Golden sky, dark clouds, and rain

Very Warm, and Moist Conditions Characterize the 2016 Autumn Season Across Delaware

Posted on | by Dan Leathers

 

 

Autumn Temperatures

Preliminary data indicates that temperatures were significantly above the 30-year normal during the autumn season. The statewide mean autumn temperature of 60.3°F was 2.7°F above the 1981-2010 mean value of 57.6°F (Figure 1). Autumn 2016 was tied with the 2005 season as the 2nd warmest autumn since records began in 1895.

Autumn Precipitation

The statewide mean precipitation of 13.23 inches was 2.40 inches above the 1981-2010 normal of 10.83 inches (Figure 2). However, much of the autumn total fell during September, when 9.43 inches of precipitation fell across the State, the 3rd wettest September total on record.

Statewide Spatial Averages

Data from the Delaware Environmental Observing System (DEOS) show that autumn temperatures were much above normal across northern New Castle County and Chester County, PA, along with southern portions of Kent and northern Sussex counties (Figure 3).

Autumn precipitation varied appreciably across the State depending upon location. Very dry conditions were especially apparent across extreme northern Delaware and Chester County, PA (Figure 4), while southern Delaware saw much above normal precipitation during the autumn Season.

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Rain drops collect on brownish red wood

September 2016 Brings Very Warm and Very Wet Conditions to Delaware

Posted on | by Dan Leathers

 

September Temperatures

Preliminary data indicates that the statewide average temperature in September was 72.3°F, 4.3°F above the 1981-2010 normal of 68.0°F (Figure 1). September 2016 ranks as the 3rd warmest September since records began in 1895. September’s extreme warmth follows the warmest August, and the 5th warmest July on record. The Wilmington/New Castle County Airport recorded 6 days with temperatures greater than or equal to 90°F during the month, 4 days more than the long-term mean.

September Precipitation

Delaware’s statewide precipitation for September 2016 averaged 8.18 inches, 4.21 inches above the 1981-2010 mean of 3.97 inches (Figure 2). The large September total for the State was primarily a result of extreme rainfall that fell on September 29th, especially in the southern portions of the State. During this event, portions of eastern Sussex County received more than 12” of precipitation, with over 4” falling in a one-hour period in Harbeson, DE.

Statewide Spatial Averages

Data from the Delaware Environmental Observing System (DEOS) show that temperatures were above normal at nearly every station across the State, with the largest temperature anomalies found across northern New Castle County, and Chester County, PA (Figure 3). Precipitation was far above average across most of Sussex and Kent counties, with several stations posting anomalies of greater than 10 inches for the month (Figure 4).

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