DC's summer preview

 

A fine spring day in suburban Washington, D.C.

This month is finishing on a very warm note in the nation's capital. Today could become the first 90° April day in seven years since a record-tying high of 91° on this date in 2017. DC averages only one 90° April day every three to four years, based on NOAA data over the last 30 years.

April 2024 will finish as a warmer than average month in the nation's capital. Depending on how warm it gets today and tomorrow, this month could rank among DC's Top 10 warmest April's on record. That's notable since four of DC's 10 warmest April's have occurred in the last 14 years. 

What makes this month different is how streaky temperatures and rainfall have been. April got off to an unusually chilly start with below average temperatures on six of the first seven days of the month. That was followed by 11 consecutive warmer than average days, including April 15 that featured a high/low of 83°/63°. Seven of the following nine days, through April 27, were cooler than average in the nation's capital.

That's brought us to this June-like weather pattern to finish the month with several days in the 80s or higher. Unlike June, however, this week's temperatures will lack the muggy conditions that often accompany DC's summertime heat.

While it could reach 90° in the nation's capital this afternoon, it isn't a sure thing given National Airport's proximity to the Potomac River. If the wind direction is blowing from the south off the chilly water, then temperatures at the airport, DC's official weather reporting site, remain a few degrees cooler than downtown areas. While a south wind pumps more humid air into the nation's capital during the spring and summer, DC's hottest days occur when a more westerly wind occurs.

April 2024 will also finish as a drier than average month in the nation's capital. That's despite 1.68" of rain, more than half of DC's April rainfall average of 3.21", during the first week of the month.  Only 0.38" of rain has fallen since then, for a monthly rainfall total of 2.06". Despite the below average rainfall this month, no drought conditions exist in the DMV given how wet 2024 has been so far. The nation's capital has a yearly rainfall surplus of 2.29" since January 1.

Warmest April’s in Washington, DC (Source: NOAA)

1. 63.8° (2017)
2. 62.4° (2019)
3. 62.1° (2023, 1981)
5. 62.0° (1994)
6. 61.6° (1985)
7. 61.2° (1960)
8. 60.9° (2010)
9. 60.6° (1941)
10. 60.1° (1980, 1977)

DC's changeable April weather

 

Signs of spring abound around the DMV

Although it isn’t typically as cold in the nation’s capital in April as it is in March, it can still get chilly. Moreover, while April doesn’t often see weather as hot as in May, it can also be quite hot.

2021: Washingtonians experienced very streaky weather during April with above average temperatures on eight of the first 11 days of the month. However, there were only five warmer than average days the rest of the month. This led to DC's temperature for the month to finish at 58.2°, which is spot on average. Finishing with merely "average" temperatures for the month hides how streaky this month's weather was. DC's low temperature of 31° was the first at or below average April temperature since 2016.

2020: DC’s high temperature on April 13 was 81°, which was still significantly warmer than DC's average high temperature for the date of 66°. That was soon followed by four consecutive days with highs in the 50s through April 18, which is more characteristic of early March.

2017:  This was DC’s warmest April on record with an average temperature seven degrees above the average. Monthly average temperatures are comprised of daily high and low temperatures. All but seven days this April were warmer than average. April 29 was also the last time Washingtonians experienced 90° heat during April, with a record-tying high temperature of 91°. Four of DC’s 10 warmest April’s have occurred just since 2010. 

2007:  DC had three consecutive days of low temperatures at or below 32° from April 7 – April 9. The month finished 3.2° cooler than average, with an average temperature of 53.6°. This was also the last time Washingtonians experienced a record low temperature during the month of April, as the low fell to 29° on April 8.

2002:  April finished as DC’s 12^th warmest on record and featured a rare stretch of three consecutive 90-degree days from April 16 – 18. There was a record high of 95° on April 17 that also tied DC’s record high for the entire month of April.

Warmest April’s in Washington, DC (Source: NOAA)

1. 63.8° (2017)
2. 62.4° (2019)
3. 62.1° (2023, 1981)
5. 62.0° (1994)
6. 61.6° (1985)
7. 61.2° (1960)
8. 60.9° (2010)
9. 60.6° (1941)
10. 60.1° (1980, 1977)
12. 60.0° (2002)

Getting ready for the 2024 hurricane season

 

The 2024 Atlantic hurricane season gets underway on June 1. If recent seasons are any indication, it will be another active one. There are some important trends to look for as hurricane season gets closer.

Hurricane Lee was the strongest hurricane of the 2023 Atlantic season, reaching its peak intensity on September 8 as a Category 5 storm over the open Atlantic with sustained winds of 165 mph. Fortunately, it didn’t impact any land masses at that potentially catastrophic intensity. Lee was the eighth Atlantic Category 5 hurricane just since 2016. Also, last season became the ninth season over the last decade with at least one storm prior to June 1.

A system gets a name when it reaches tropical storm intensity with sustained winds around the center of circulation of at least 39 mph. A tropical storm becomes a hurricane when sustained winds reach 74 mph. A hurricane becomes “major” when sustained winds reach 111 mph or greater, making it a Category 3 on the Saffir-Simpson Hurricane Wind Scale.

Hurricane researchers at Colorado State University (CSU) recently issued their April forecast for the upcoming Atlantic hurricane season. Once again, they're calling for an unusually active season with 23 named tropical storms, of which 11 become hurricanes and 5 of those become "major" hurricanes. 

The key factors cited in their forecast are: (1) The presence of unusually warm sea surface temperatures in the tropical Atlantic (warm ocean water is the fuel for tropical storms and hurricanes); and (2) The expectation La Nina conditions will develop over the summer.  The presence of La Nina (the opposite of El Nino) helps create more favorable environmental conditions for hurricane development and intensification in the Atlantic. This is because La Nina is associated with a reduced amount of wind shear (i.e., winds of different speeds in different directions), which allows for tropical systems to develop as well as warmer sea surface temperatures.

An “average” Atlantic hurricane season has 14 tropical storms, of which 7 intensify into hurricanes with 3 becoming “major” hurricanes. NOAA’s average is based on the 30-year period from 1991-2020.