DC’s worsening drought conditions

 

NOAA's precipitation outlook

Severe drought conditions now cover the entire DC Metro Area and the record heat this week has only made conditions worse. The rain and showers in the forecast over the coming days are beneficial despite the bad timing ahead of the Memorial Day holiday weekend.

Chronic drought conditions of varying intensity have been an ongoing issue for much of the DMV (DC, Maryland and Virginia) the last ten years. That’s because 21 of the last 32 months have been drier than average in the nation’s capital dating back to September 2023, including nine of the last 12 months with below average rainfall. This drier than average 32-month period has led to an accrued rainfall deficit of 12.71” in the nation’s capital as of April 30.

Although today will be the third and final day of record heat across the DMV, this May has been cooler than average, overall, in the nation’s capital. Cooler than average temperatures starting tomorrow combined with increased rainfall chances over the next several days are a positive development. While not enough rain will occur the next few days to make up DC’s entire deficit, it will help May finish with near average monthly rainfall.

The current 32-month stretch of drier than average weather is similar to another such period of even drier conditions. The nation’s capital had 25 drier than average months in the 32-month period from August 2015 – March 2018. That produced a rainfall deficit of 16.42”. Widespread moderate to severe drought conditions enveloped much of the DMV as of mid-February 2018. A hard pivot in the weather pattern then occurred and 2018 ended up being DC’s wettest year on record.

A similar degree of hope also exists now. Not for record rainfall, but a recent outlook issued by NOAA’s Climate Prediction Center shows an expectation for above average rainfall potential through mid-July across the DMV. That would be great news after such a prolonged stretch of drier than average weather.

Hurricanes in May?

 

Tropical Storm Arlene, April 2017 (Source: NOAA)

Hurricane season runs from June 1 through November 30 with the busiest months being August and September. June is typically a quiet month in the tropics, but tropical storms and hurricanes do occur sometimes. Every so often tropical storms also develop before the season officially gets underway.

Although unusual, having a named storm develop before June 1 has occurred more often in recent years. At least one named storm has developed early in the Atlantic a total of nine times since 2012. A system becomes a “tropical storm” and is given a name when the sustained winds around its center reach 39 mph. If sustained winds reach 74 mph, then the tropical storm becomes a hurricane.

On occasion, a named storm has characteristics of both a tropical system and a non-tropical area of low pressure. Under such circumstances, the system is classified as a “subtropical storm.”  That’s what happened with Tropical Storm Alberto in May 2018. It began as a subtropical storm in the Gulf of Mexico. However, it eventually became a fully tropical storm before it made landfall in the Florida panhandle on May 29.

Alberto was also significant for making 2018 one of seven consecutive years at least one named storm formed prior to the official start of the hurricane season. That broke the previous record for most consecutive years that a tropical storm developed prior to June 1 (1951 – 1954).

In January 2016, Hurricane Alex developed south of the Azores and was the first Atlantic hurricane during the month of January since 1955. Some may wonder if having a named storm prior to the official start of hurricane season is a reliable indicator of whether or not a given season will be an active one. Quite simply, it isn’t. If conditions are favorable for a tropical storm to develop prior to June 1, it isn’t a guarantee that conditions will remain favorable for an active hurricane season as a whole.

If a tropical storm or hurricane develops before this June 1, it would be the first season since 2023 that’s occurred in the Atlantic Ocean. The first named storm of 2026 will be given the name “Arthur.”

Summer-like heat in the DMV?

 

NOAA's 6 to 10 day temperature outlook

Washingtonians typically see the first 90-degree temperature of the year on or around May 18. The nation’s capital averages 36 days per year with high temperatures of at least 90° with the majority coming in June, July, and August. Over the last 30 years, the nation’s capital has averaged between one and two 90-degree May days.

Interestingly, Washingtonians haven’t experienced any 90-degree May heat in two of the last three years. However, that has little bearing on how hot the corresponding summer will be. For example, May 2016 was cooler than average in the nation’s capital. No 90-degree heat occurred in 2016 until June 11. However, the summer of 2016 went on to become the third hottest on record (at the time). 

More recently, DC’s first 90-degree day in 2024 was a record-tying high of 91° on May 2. No more 90-degree heat occurred, thereafter, until June 13. Nevertheless, the summer of 2024 finished as DC’s third hottest on record despite the lack of extreme heat in May and the first half of June.

DC’s earliest 90-degree day on record was March 22, 1907 (90°). The latest first 90-degree temperature in the nation’s capital occurred on July 12, 1979 (93°). Both of those summers were significantly cooler than average. This illustrates that no correlation exists between when the first 90-degree temperatures occur and whether a summer is warmer than average.

Washingtonians sometimes experience 90-degree heat before May begins. Such was the case last month when the nation’s capital sweated through its first 90-degree April heat since 2017. Highs reached 90° at National Airport on April 15 and April 16. That was also the first time the nation’s capital experienced two 90-degree April days since 2010.

A “heat wave” is loosely defined as three or more consecutive days in the 90s. The nation’s capital has experienced three of those in May over the last 30 years, with the most recent being in 2019. No triple-digit heat has occurred in the nation’s capital in May, but highs reach 95° roughly once every five years with the most recent on May 31, 2022 (96°).

NOAA’s Climate Prediction Center expects a hard pivot to more summer-like weather in the nation’s capital next week, following a near to cooler than average week.