DC Summer Weather Forecast: Expect Generally Sweltering Conditions

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Given our recent battle with temperatures in the mid-90s, we’re not easing into summer. But at least we can enjoy some relief over the weekend.

Last week’s weather may well be a microcosm of what lies ahead this summer – periods of high heat and humidity, but also pleasant respites.

Overall, we expect near-normal summer temperatures and a reasonably strong chance of avoiding the historic heat.

If this idea works, it would be a welcome change. For the past twelve years, our summers have been extremely hot and humid. Eight of our 10 hottest summers on record have occurred since 2010. Last year was our eighth hottest summer on record, with 48 days reaching at least 90 degrees (normal is 40).

But we think this summer has a 50-50 chance of being the coolest summer since 2014. Admittedly, what we consider cool is relative since temperatures are rising due to climate change.

Our outlook requires interpretation in the context of the past 30 years of very warm weather data. Our latest climate normals, based on the period between 1991 and 2020, are 1.2 degrees warmer than the normals between 1981 and 2010.

Washington’s new climate ‘normals’ are warmer and wetter

While each of the past 10 summers has been warmer than the 1981 to 2010 normals (77.7 degrees), three of them would be cooler than the 1991 to 2020 normals (78.9 degrees). Our forecast for the average temperature this summer is slightly warmer than the old normals and a little colder than the new normals.

In other words, we don’t expect this summer to be unusually hot or memorably cool. On the contrary, we expect this summer to be hot and humid, like almost all DC summers.

Compared to the perspectives put forward by other groups, ours is a bit aberrant. The National Weather Service, AccuWeather and The Weather Company are all leaning towards warmer than normal conditions. However, we agree with the Weather Service and The Weather Company that June will be slightly warmer than normal.

Computer models also generally predict a somewhat warmer than normal June and are mixed as to what to expect in July and August.

The weather pattern, alternating between stuffy uncomfortable and tolerable, will likely endure a fair share of storm. We are leaning towards above average summer rainfall – continuing the pattern we saw in May – our 14th wettest on record.

Our outlook for this summer is similar to what we issued for last summer. This forecast turned out to be a little too cold as we had forecast slightly lower than normal temperatures and they were slightly higher than normal.

When developing a summer outlook, we are less likely to see the signals of warmer or cooler than normal (compared to average) weather that we sometimes see before winter. As such, our outlook is low confidence. This type of seasonal forecast is experimental and errors are possible.

Summer outlook in numbers

Average summer temperature: We expect the average temperature to range from near normal to one degree below normal.

Temperatures compared to normal month by month:

  • June: 1 degree above normal
  • July: 1 to 2 degrees below normal
  • August: 1 degree below normal

Number of days at 90 degrees for June, July and August: 28-35, compared to the normal 34. Note that six more 90-degree days occur on average outside of June through August. So far this year, we have three.

Longest sequence of days at 90 degrees: five to seven days

Number of days at 100 degrees: None

Precipitation: Slightly above average rainfall

We considered several factors, described below, in preparing this outlook. It should be noted that any one factor is not necessarily related to a particular type of summer (eg hot, cool, dry or wet).

We are currently experiencing the La Niña phase of the El Niño Southern Oscillation, and we expect it to persist through the summer, although it continues to weaken a bit from its winter peak.

The presence of El Niño or La Niña in the tropical Pacific Ocean sometimes makes it easier to predict summer conditions, as El Niños can promote cooler summers, while La Niña often promotes hotter summers. However, we do not expect this La Niña event to be a dominant factor in our weather as it is weakening.

In addition to La Niña, we considered the current phase of the Pacific Decadal Oscillation (persistent negative) and previous spring weather patterns. This data informed the identification of analogues, or years with similar weather patterns, which we used to develop our outlook.

In this case, the summers of 1950, 1956, 1971 and 2000 emerged as the best analogues. The weather for these summers has been taken into consideration in our projections for the one starting now.

May was a confusing month as we closed out spring.

Temperatures were cold at times, with the coldest lows in the 40s, then quite warm, such as Tuesday’s high of 96, the highest for the month in more than a decade. Overall the month ended 0.6 degrees warmer than normal with an average temperature of 67.8 degrees. It was the hottest May 31 on record, matching 2007 and 2000.

The fluctuating temperatures reflected a stormy pattern, with measurable rain on 14 of the 31 days. The monthly total was 6.36 inches (2.42 inches above normal), marking the second wettest May in the past decade and helping 2022 to be wetter than normal overall.

As temperatures warmed in the last third of the month, Dulles Airport set several temperature records:

  • May 21: Record low of 73 and record high of 92, tied with 1996
  • May 22: a record of 91
  • May 31: A record 94, tied with 2011

Dulles also set a rainfall record on May 7, picking up 1.18 inches. Only one record was set in Washington: on May 21, the low of 73 was the hottest observed for the date. No record was set in Baltimore.

At the end of April, we correctly predicted near-normal temperatures in May, projecting a range between 65 and 69 degrees. Our rainfall forecasts were less good. We asked for slightly larger quantities than normal between 3.8 and 4.5 inches, which was about two inches too low. We’d give our April outlook a B.

Temperature and precipitation since the beginning of the year

Year-to-date temperature and precipitation tracking shows that 2022 is slightly warmer and wetter than normal and last year, but not at extreme levels:

Outlook and evaluations of the past summer

CWG Summer 2021 Outlook (We haven’t rated this outlook, but the results are summarized above)

CWG Summer 2020 Outlook (Post-Summer Assessment)

CWG Summer 2019 Outlook (Post-Summer Assessment)

CWG Summer 2018 Outlook (We haven’t rated this outlook, but we did well to call summer an average of one degree above normal, and it ended two degrees above normal. (above normal. Also, we forecast 35 days at or above 90 between June and August, which was the exact number.)

CWG Summer 2017 Outlook (Post-Summer Assessment)

CWG Summer 2016 Outlook (Post-Summer Review)

CWG Summer 2015 Outlook (Post-Summer Assessment)

CWG Summer 2014 Outlook (Post-Summer Assessment)

CWG Summer 2013 Outlook (Post-Summer Review)

CWG Summer 2012 Outlook (Post-Summer Assessment)

CWG Summer 2011 Outlook (Post-Summer Assessment)

CWG Summer 2010 Outlook (Post-Summer Review)

CWG Summer 2009 Outlook (Post-Summer Review)

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