September 2021 – Warm with Near Normal Precipitation Across Delaware

 

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

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

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

 

 

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

 

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

 

 

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

 

 

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

 

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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Drops of water on bright green grass

Temperature and Precipitation Both Above Normal Across Delaware During 2015

 
 
 

Annual Temperatures

Statewide mean annual temperature in 2015 was 56.4°F according to preliminary data from the National Climatic Data Center (NCDC). This was 1.0°F above the 1981-2010 normal of 55.4°F (Figure 1) and was the 11th warmest year in Delaware since 1895.

Monthly temperatures varied greatly throughout the year (Figure 2). The first three months of 2015 saw much below normal temperatures, including the 6th coldest February since 1895. The last nine months of the year saw above normal temperatures, except for October, which was slightly below normal. Tremendous warmth ended the year with December temperatures averaging 12.4°F above the 1981-2010 mean. December 2015 was the warmest December on record, smashing the old record by 6.1°F.

Annual Precipitation

Statewide precipitation in 2015 averaged 46.37 inches, 2.04 inches above the 1981-2010 mean of 44.33 inches (Figure 3).

Monthly precipitation anomalies varied between positive and negative throughout the year, with seven months of below normal and five months of above normal precipitation (Figure 4). June saw the largest precipitation anomaly of 5.30 inches above the 30-year normal, helping to push the annual value above the long-term mean.

Statewide Spatial Averages

According to data from the Delaware Environmental Observing System (DEOS; deos.udel.edu), mean annual temperature anomalies varied across Delaware (Figure 5). Northern New Castle County, much of Sussex County, southern Kent County and Chester County, PA all experienced above normal temperatures for the year. Coastal Sussex County and western portions of News Castle and Kent counties saw below normal mean annual temperatures.

Precipitation across the region varied substantially in 2015, ranging from just under 40 inches to greater than 50 inches at several locations across the State (Figure 6).

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Trees in Autumn

Autumn 2014 Slightly Dry with Near Normal Temperatures Across Delaware

Autumn Temperatures

de_statewideAutumnTemp-1895-2014_0.png
Figure 1. Delaware Statewide mean Autumn Temperature (°F) 1895-2014.

Preliminary data indicates that the statewide mean autumn temperature of 57.8°F was 0.2°F above the

1981-2010 normal of 57.6°F (Figure 1). The near normal autumn temperatures followed four consecutive seasons with below normal temperatures across Delaware. Temperatures

de_monthlyTempAnom_2014.png
Figure 2. Delaware statewide temperature anomalies for January 2014 through November 2014.

have been quite variable across the State during the year (Figure 2), with seven of the first eleven months being below normal.

Autumn Precipitation

Near normal autumn temperatures were accompanied by slightly dry conditions across the state during the autumn season. The statewide

de_statewideAutumnPrecip-1895-2014_0.png
Figure 3. Delaware Statewide mean Autumn Precipitation (°F) 1895-2014.

mean precipitation of 9.52 inches was 1.31 inches below the 1981-2010 normal of 10.83 inches (Figure 3). Monthly precipitation anomalies have varied between positive and negative during the year, but

no month has seen large departures from normal (Figure 4).

de_monthlyPrecipAnom_2014_0.png
Figure 4. Delaware statewide precipitation anomalies for January 2014 through November 2014.

Statewide Spatial Averages

Data from the Delaware Environmental Observing System (DEOS) show that temperatures varied considerably across the State during the autumn season (Figure 5), with generally small positive or negative departures at most stations. The largest departures were found along the coastal areas of Sussex County where cool conditions were dominant.

Precipitation varied from as low as 7.51 inches along the Atlantic Coast to a high of 14.52 inches in western Chester County, PA. Even with this large variation, most stations in the region experienced slightly dry conditions during the season, with the greatest negative anomalies found along the Atlantic Coast and in northern Chester County, PA (Figure 6).

Autumn 2014 average temperature departures
Figure 5. Autumn 2014 average temperature departures from the 1981-2010 mean based upon DEOS station data.
Autumn 2014 precipitation departures
Figure 6. Autumn 2014 precipitation departures from the 1981-2010 mean based upon DEOS station data.