Minimum Temperature, January 20, Washington, DC, Reagan National Airport

For more on the January 2025 cold air outbreak see 2024 Cold Snap in the Eastern U.S.

 

January 20, 2025 is Inauguration Day in Washington DC.

The weather forecast was forecast to be very cold.

Here, I explore how cold it will be in a historical context.

When I drafted this, the forecast low was 12°F. That would be 17°F warmer than the record for Washington DC  and 14°F warmer than the coldest Inauguration Day. (measured at Reagan National Airport, which started measurements on 9/1/1936)

For more on the meaning of normal in a warming climate see:

That Arctic blast can feel brutally cold, but how much colder than ‘normal’ is it really?,

which appeared in The Conversation on January 6, 2025. (Republished January 18, 2025)

This entry is mostly graphics with minimal narrative .

Inauguration Day in Washington D.C.

The region

The following two imagines come from observations archived at the National Centers for Environmental Information. They are for Climate Division 4 in Maryland. A climate division is an area, often, the size of several counties. 1 East of the Mississippi River. Further west, they are aligned with watersheds. It is a more representative measurement than a single station, and still locally relevant. This is the division that has Washington DC. 2These charts are from the NOAA National Centers for Environmental information, Climate at a Glance: Divisional Time Series, published January 2025, retrieved on January 18, 2025 from

https://www.ncei.noaa.gov/access/monitoring/climate-at-a-glance/divisional/time-series

 

 

Each chart is a difference from an average. In the first chart, the average is 1991 – 2020. In the second chart, it is 1951 – 1980.

 

Difference from 1991 – 2020 average:


Difference from 1951 – 1980 average:

 

Points on these graphs.

  1. The temperature observations are exactly the same in the two graphs.
  2. There is a line in the top graph that shows the 1991 – 2020 (39.4°F) average and in the bottom graph that shows the 1951 – 1980 (36.8°F) average.  Between these two averaging time spans, there has been an increase of 2.6°F.
  3. From 1900 to 2024 the trend line shows there has been ~  5°F increase in the temperature in this climate division.

 

Reagan National Airport (for DC)

In the next graph, I focus on January 20 minimum temperatures at Washington’s Reagan National Airport. The observations at this location started on September 1, 1936.

Picking a single station and a single day brings focus to the Inauguration event. It, however, is not representative of the winter or the climate.3The data for this graph are from NOAA Climate Data Online. I made the plots.

As of this writing (20250118) the forecast high and low at Reagan National Airport on January 20, 2025 are 25°F and 12°F.

Minimum Temperature, January 20, Washington, DC, Reagan National Airport

Mean:  28.1°F, Standard Deviation 9.0°F

Points on this graph.

  1. The coldest January 20 days are in 1984, 1985, and 1994.
  2. 1985 was Reagan’s second inauguration and is the coldest January 20 in the record.
  3. These 3 cold years are the only years below 15°F and are clear outliers.
  4. If the forecast low of 12*F is realized, then it will join these three outliers and will be between 1 and 2 standard deviations from the average.

How cold is it?

In a historical sense, how cold is it?

Finally, I place January 20 observations in the context of the cold season at Reagan National.

At Reagan National there have been 16 days recorded with a low temperature of 3°F or colder. Of those 16 days, 13 of them have been in January, 3 in December. Only one occurred on a January 20th.

January is, therefore,  the month when the coldest temperatures have been observed. All of those days occurred in 1994 or earlier (before 1995).

1994 was an objectively cold January, and since 1994 there have not been any of the most extreme days of 3°F or less. We will use 1994 as a time for comparison.

At Reagan National, the low forecast for January 20, 2025 is 12°F.

There have been 198 days with a low temperature of 12°F or below observed at Reagan National Airport. Of those, 30 have occurred in 1995 or later. 168 have occurred before 1995.

The 12°F or colder days occur in the ~ 75 days between December 15 and March 1, which I will call the cold period.  We will define 12°F as frigid, and assume that potentially frigid days occur during the 75 day cold period.

From 1995 to present there have been ~ 2250 potentially frigid  days. Prior to 1995 there  are~ 4350 potentially frigid days, in the Reagan National Airport record of observations.

Since 1994, 1.3 % of the potentially frigid days have been frigid.

Prior to 1995 3.9% of the potential frigid days were frigid.

Hence, defining 12°F or colder as frigid in DC, it was 3 times more likely prior to 1995.

In 2025, if it reaches 12°F, it will not approach temperatures close to 3°F, which define the 16 coldest days observed since 1936.  Such temperatures have not occurred since 1994.

The Big Picture

This first image is the forecast temperature for Monday, January 20.  It is from the European Center for Medium Range Weather Forecasts. It is about 12:00 noon in D.C. in this image.

 

The scale is in ° C, so 0°C = 32°F (freezing), -12°C = 10.4°F, and -24°C = -11.2°F.

Points on this figure.

  1. Freezing temperatures in Texas.
  2. It is in the teens °F in the Washington D.C. area.
  3. It is much warmer on the eastern shore of Lake Michigan that the western Shore.

 

This next image is an ensemble of ECMWF forecasts subtracted from a mean (defined as anomaly). The mean is taken from 1991 – 2020.  It is for the week starting on January 20, 2025.

 

 

Points on this figure.

  1. The coldest anomalies, greatest below average, are in Texas and just south of Lake Erie.
  2. The Washington D.C. area is, about, 15° – 20°F below normal.  (Remember chart are in °C)
  3. Where it looked so cold in the first figure in Canada, is close to normal, and north of that temperature minimum is above normal.