August 2021 – Continued Warm and Wet Across Delaware

August Temperatures

Preliminary data indicates that the statewide average temperature in August was 77.8o F, which is 2.9o F above the 1981-2010 mean value of 74.9o F (Figure 1).  The statewide temperature was the 6th warmest August since observations began in 1895.

August Precipitation

Delaware’s statewide precipitation for August 2021 averaged 5.58 inches, 1.45 inches above the 1981-2010 mean (Figure 2).  This placed this month’s precipitation total in the top one-third 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 largest positive anomalies found across northern New Castle County (Figure 3).  Precipitation anomalies varied across the State with the largest positive anomalies found over Kent and Sussex counties, and the largest negative anomalies in northern New Castle County (Figure 4).

National Anomalies

Temperatures were significantly above normal across much of the northeastern United States and the Great Lakes region.  The Pacific Coast states also recorded above normal temperatures during August (Figure 5).  Some temperature anomalies were greater than 5o F for the month in the Northeast.  Precipitation anomalies varied greatly across the country with dry conditions in much of California and the northwest United States.  Pockets of very wet conditions were found across portions of the Mississippi Valley (Figure 6).  The 500 hPa height pattern for August shows a strong jet stream ridge located over the northeast United States and southeastern Canada (Figure 7), leading to the warm conditions across this region.

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Rain on window

August 2020 – Warm and Very Wet Across Delaware

August Temperatures

Preliminary data indicates that the statewide average temperature in August was 77.6o F, which is 2.7o F above the 1981-2010 mean value of 74.9o F (Figure 1).  August 2020 was the 6th warmest August since observations began in 1895.

August Precipitation

Delaware’s statewide precipitation for August 2020 averaged 7.34 inches, 3.21 inches above the 1981-2010 mean (Figure 2).  The August 2020 precipitation amount was the 17th wettest since 1895, placing this month in the wettest one-third of all Augusts since the start of observations.

Statewide Spatial Anomalies

Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were above normal throughout the State (Figure 3).  Precipitation anomalies were extreme in several locations with many stations reporting positive anomalies of greater than 7 inches, (Figure 4).  These large precipitation anomalies were primarily the result of Tropical Storm Isaias which crossed Delaware on August 4th and severe thunderstorms which impacted northern Delaware just three days later on August 7th.

National Anomalies

Temperatures were above normal across most of the western one-third of the country (up to 10o F) and the Northeast, while below normal temperatures were found across the Great Plains and Midwest (Figure 5).  Precipitation was generally far below normal across the western United States, while much above normal precipitation fell across portions of Arkansas, Louisiana, and the mid-Atlantic Region of the country.   (Figure 6).  The 500 hPa height pattern for August exhibits a ridge dominating the western portion of North America leading to generally warm and dry weather across that region which contributed to the severe wildfire season (Figure 7).

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August 2019 – Warm with Near Normal Precipitation Across Delaware

August Temperatures

Preliminary data indicates that the statewide average temperature in August was 76.8°F, which is 1.9°F above the 1981-2010 mean value of 74.9°F (Figure 1). This places August 2019 as the 13th warmest since records began in 1895, tied with August 2012.

August Precipitation

Delaware’s statewide precipitation for August 2019 averaged 3.78 inches, 0.35 inches below the 1981-2010 mean (Figure 2). Delaware’sAugust precipitation was in the middle 0ne-third of values for the last 125 years, putting it into the “normal” range for this month.

Statewide Spatial Anomalies

Data from the Delaware Environmental Observing System (DEOS) show that temperature departures were above normal throughout most of the State (Figure 3), with the exception of western Kent County. There was a mixture of positive and negative precipitation departures observed across the State (Figure 4). In general, northern New Castle County saw much below normal precipitation, while a few stations in Kent and Sussex Counties actually recorded above normal precipitation amounts. This pattern of precipitation anomalies is a result of the highly localized nature of convective (thunderstorm) rainfall events during the summer months.

National Anomalies

The western United States experienced above normal temperatures during August, with below normal temperatures found mainly across the north-central portion of the country (Figure 5). Precipitation anomalies across the U.S. varied greatly, with above normal rainfall across much of the High Plains and below normal precipitation across California and the southwest (Figure 6). The 500 hPa height pattern for August showed a weak anomalous trough over the north-central portion of the Country (Figure 7), bringing the cool temperatures to that region.

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A bright sun illuminates tall grasses

August 2018: Record Heat Across the First State

 

 

 

August Temperatures

Preliminary data indicates that the statewide average temperature in August was 78.6°F, which is 3.73°F above the 1981-2010 mean value of 74.9°F (Figure 1). August 2018 is tied with August 2016 as the warmest August since records for the State began in 1895. Similar positive temperature anomalies were found across the rest of the northeast United States, and across most of the western and southwestern portions of the country (Figure 2).

August Precipitation

Delaware’s statewide precipitation for August 2018 averaged 4.35inches, 0.22 inches above the 1981-2010 mean (Figure 3). Although statewide totals for August were just above normal, rainfall in southern Delaware was far below normal, while rainfall in the northern portion of the State was far above normal.

Statewide Spatial Averages

Data from the Delaware Environmental Observing System (DEOS) show that temperature (Figure 4) departures were quite large and uniformly positive during August throughout the State. Precipitation departures varied greatly between northern and southern Delaware (Figure 5). Rainfall deficits as large as 4 inches were found in Sussex County, while many locations in northern New Castle County had rainfall surpluses of greater than 5 inches!

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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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Water droplets collect on an autumn leaf

August 2017: Cool, Wet Conditions Across Delaware

 
 

August Temperatures

Preliminary data indicates that the statewide average temperature in August was 74.2°F; this was 0.7°F below the 1981-2010 normal of 74.9°F (Figure 1). August 2017 was the first month of the summer season to register below normal temperatures.

August Precipitation

Delaware’s statewide precipitation for August 2017 averaged 7.25 inches, 3.13 inches above the 1981-2010 mean (Figure 2). August 2017 was the 16th wettest August since records began in 1895.

Statewide Spatial Averages

Data from the Delaware Environmental Observing System (DEOS) show that temperatures were below normal across the entire State with many of the largest negative temperature departures found across the northern portion of the region (Figure 3). The largest precipitation departures were found primarily across southern and central Delaware, where some DEOS stations recorded rainfall that was more than 5 inches above normal for the month (Figure 4).

 

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Warm Sun saturates crops

August 2016 Very Warm and Dry Across Delaware

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August Temperatures

Preliminary data indicates that the statewide average temperature in August was 78.7°F, 3.8°F above the 1981-2010 normal of 74.9°F (Figure 1). August 2016 ranks as the warmest August since records began in 1895. August’s extreme warmth follows the 5th warmest August on record. The Wilmington/New Castle County Airport recorded 15 days with temperatures greater than or equal to 90°F during the month, 10 days more than the long-term mean.

August Precipitation

Delaware’s statewide precipitation for August 2016 averaged 3.21 inches, 0.91 inches below the 1981-2010 mean of 4.12 inches (Figure 2). The combination of low precipitation and high temperatures resulted in dry conditions in many parts of the State by the end of the month.

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 below normal across most of the State, with a few stations showing near normal or above normal precipitation totals due to isolated convective storms (Figure 4).

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Pink flowers

Very Warm Temperatures and Near Normal Precipitation Characterize the 2016 Summer Season Across Delaware

 

Summer Temperatures

Preliminary data indicates that summer 2016 ranked as the 4th warmest summer season since records began in 1895. The statewide mean summer temperature of 76.6°F was 2.1°F above the 1981-2010 mean value of 74.5°F (Figure 1). Delaware’s four warmest summer seasons have all occurred since 2010.

Summer Precipitation

The statewide mean precipitation of 12.4 inches was 0.40 inches above the 1981-2010 normal of 12.0 inches, and was the 4th year in a row with above normal summer precipitation (Figure 2).

Statewide Spatial Averages

Data from the Delaware Environmental Observing System (DEOS) show that summer temperatures were above normal across the majority of the State, with northern New Castle County and Chester County, PA having the largest positive anomalies (Figure 3). The Wilmington/New Castle County Airport recorded 34 days of temperatures greater than or equal to 90°F, twice the normal number. Only two years, 2010 and 1988, had more 90°F summer days than 2016.

Summer precipitation varied significantly across the State depending upon location (Figure 4). The variable pattern of precipitation is due to the small-scale nature of convective storms; dropping heavy precipitation in some areas, while leaving others relatively dry.

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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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Beach in Summer

Seasonable Temperatures and Dry Conditions Characterize August 2015 Delaware Climate

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Figure 1. Delaware statewide mean August temperature (°F) 1895-2015.

 
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Figure 2. Delaware statewide mean August precipitation (inches) 1895-2015.

 

August Temperatures

Preliminary data indicates that the statewide average temperature in August was 74.9°F, equal to the 1981-2010 average for the month (Figure 1). Even with near normal temperatures, August 2015 was the warmest August in the last three years.

August Precipitation

Delaware’s statewide precipitation for August 2015 averaged only 2.81 inches, 1.31 inches below the 1981-2010 mean (Figure 2). August 2015 was the driest August since 2008 across the First State.

DEOS Station Observations

Temperature anomalies varied across the State, with the largest negative departures occurring in Sussex County, and the largest positive departures occurring in the Wilmington area (Figure 3). Precipitation was below normal across nearly the entire State, with deficits of more than two inches found in each County (Figure 4).

August 2015 average temperature departures from the 1981-2010 mean based upon DEOS station data.
Figure 3. August 2015 average temperature departures (°F) from the 1981-2010 mean based upon DEOS station data.

 
August 2015 precipitation departures (inches) from the 1982-2010 mean based upon DEOS station data.
Figure 4. August 2015 precipitation departures (inches) from the 1981-2010 mean based upon DEOS station data.