The capital’s winter forecast calls for higher than normal snowfall and increased chances of major storms

The capital’s winter forecast calls for higher than normal snowfall and increased chances of major storms

Although we’re enjoying unseasonably warm weather, December is only three weeks away, so it’s time for our annual winter forecast.

The past several winters have been exciting for those who prefer mild weather in the Washington area but especially disappointing for snow lovers. Only 0.4 inches of snow fell last winter, the third lowest snowfall on record. It was also the second warmest winter on record. 19 days reached at least 60 degrees in January and February.

We expect a harsher winter ahead, one that will be more satisfying for those who love snow.

Our forecast calls for above-normal snowfall for the first time since the winter of 2018-19, when Reagan National Airport, the official monitoring site in Washington, received 16.9 inches.

The main driver of our snowier future is persistent El Niño, a weather pattern characterized by warmer-than-normal ocean waters in the tropical Pacific. El Niño tends to fuel powerful storms in the southern United States that sometimes reach the East Coast, increasing the potential for rain and snow in the mid-Atlantic. However, every El Niño winter is different; Some produce very little snow, others bring blizzards.

Ultimately, the amount of snow we will see will depend on the strength of the El Niño phenomenon this season and a number of other factors that may be difficult to predict.

How can winter play?

We estimate there will be six or seven accumulating snow events in the immediate area, with two more events in our cold suburbs to the west and north. This does not include dust or ice events; We’ll probably have some of those too.

Some of our winter weather will come from Clippers, fast-moving disturbances from the northwest that typically produce light amounts of snow. We’ll also see more powerful storms pass to the west, often pulling milder air north and turning snow into rain.

What could characterize this winter are coastal or northeasterly storms that carry the possibility of significant snowfall. Because of El Niño, the odds of a large storm dumping a foot or more of snow are higher than average, or about 35%. The typical chance of such a storm occurring is about 10 percent.

We’re seeing winter getting off to a very good start. We haven’t received more than two inches of snow in a December since 2010. Even if we break that streak, we expect monthly snowfall to be modest. Most seasonal snow is supposed to fall between January and March, with an emphasis on February, which we expect to be the snowiest month.

Temperature-wise, we’re leaning toward slightly cooler than normal conditions overall, with February particularly cold after closer to normal temperatures in December and January.

In general, we expect temperatures during December through February to be average to about a degree cooler than normal.

  • December: On average one degree warmer than average
  • January: On average
  • February: 2 to 3 degrees colder than average

Our snowfall forecast covers November through April. Overall, we expect snowfall to be somewhat above average.

  • Reagan National Airport: 16 to 22 inches (compared to average of 13.7 inches)
  • Dulles International Airport: 25 to 30 inches (compared to average of 21 inches)
  • Baltimore-Washington International Marshall Airport: 25 to 30 inches (compared to average of 19.3 inches)
  • Fairfax, Loudoun and Montgomery counties: 22 to 35 inches
  • Alexandria, Arlington, Prince George’s and area counties: 15 to 25 inches
  • Although progress has been made in seasonal forecasting, there remains significant uncertainty and limited skills in developing these forecasts. These remain low confidence forecasts.
  • Note that monthly temperature forecasts are less reliable than whole-season forecasts. Cool or warm pattern lingers A week that is too long or ending a week early can change your monthly average dramatically. Furthermore, it only takes one major snowstorm to reach or exceed our seasonal average.

Why are winter storms so difficult to predict in Washington?

Answers to questions you may have

What are other forecasters forecasting for the Washington area?

We polled five meteorologists who specialize in seasonal forecasting and they are also… Snowfall is expected to be above normal for the winter:

  • Judah Cohen, Verrisk AER: 13.3 inches
  • Todd Crawford, Atmosphere G2: 16 inches
  • Weather Paul Dorian, Arkfield: 20 to 30 inches
  • Paul Pasteluk, AccuWeather: 14 to 18 inches
  • Matt Rogers, Commodity Weather Group: 15 inches

In addition, meteorologists for local TV broadcasters who have issued their forecasts are also calling for higher than normal amounts:

  • Doug Kammerer, NBC4: 22 to 30 inches
  • Mike Thomas, FOX5: 12 to 20 inches

What is your long-term record with these winter forecasts?

We’ve been making winter forecasts since 2005-2006 and evaluated ourselves after they happened over the past 18 winters. We were generally on the ballpark Although we have had notable victories and failuresWe give ourselves an average grade of about a C+.

Since we started this forecast, our best forecast for the winter predates the record-breaking Snowmageddon winter of 2009-10, when we said: “In general, the chances of a major snowstorm of 8 to 12 inches or more are much higher than normal in Next winter.” “.

Our worst forecasts were for the winters of 2011-2012 and 2013-2014. In 2011-2012, we called for near-normal temperatures, which were 5 degrees above average. In 2013-2014, we called for a warm winter with just below average snowfall, and a cold one, with snow totals more than twice average.

Our expectations for last winter were modest. We expected slightly above normal temperatures and less than normal snowfall when in reality the temperatures were much higher than normal and it was almost snow free.

Do you take climate change into account in your winter forecasts?

Since 1970, the average winter temperature has risen between 3 and 5 degrees across the region. Meanwhile, average snowfall over 30 years has fallen from more than 20 inches in the late 1800s to just 13.7 inches today.

Here’s how much snow has fallen during each of the past 10 winters (the full list goes back to 1887-1888):

We take these long-term trends into account in our winter forecasts.

Aren’t weather forecasts only reliable for eight to ten days?

It is true that there is no skill in predicting certain conditions, such as the exact temperature and amount of rain or snow for a given day, more than eight to ten days in the future. However, advances in seasonal forecasting allow us to make educated guesses about the general trend of conditions, such as how temperatures and snowfall compare to the average over a month or multi-month period. Given the uncertainty involved, we give ranges and try to be as transparent as possible in communicating that these forecasts are indeed low confidence.

How could these predictions be wrong?

The main risk to the forecast is that El Niño becomes so strong that it constantly pulls warm air into the region, leading to a very mild winter without much snow. This was the case during the El Niño winter of 1997-98, one of Washington’s snowiest winters on record.

Here are some, but not all, of the factors we took into consideration when determining conditions for next winter.

No single factor tells the whole story, and the connections between past conditions and future conditions—which we used to make forecasts—are not always strong. But we chose factors that have been shown to have at least some predictive value in the past. When we look at them collectively, they help paint a picture of what we think is likely to happen this winter.

Although no two winters are identical, we expect this winter to share some similarities with the winters of 1972-1973, 2002-2003, and 2009-2010. These comparisons helped loosely form the basis of our temperature and snow forecasts, because the weather in those years had some similarities to the factors listed below.

We are currently experiencing a moderate El Niño event that may strengthen further and peak as a strong event. This is the first El Nino since a weaker event in 2018-19, which is the last time we saw above-normal snowfall.

One thing that moderate to strong El Niño events have in common is periods when the subtropical jet stream is active. An active subtropical jet often brings storms ashore in California that cross the southern half of the United States. Sometimes these storms come up the East Coast and produce heavy snow and/or rain.

It is often during the second half of an El Niño event when the subtropical jet stream is most active, and we expect that to be the case this winter.

However, the northern (polar) branch of the jet stream can still assert its dominance at times, especially early in the winter. When the northerly current is dominant, the dominant storm track moves to the west. When storms move toward the west, they tend to pull warm and sometimes dry air over our area. When snow falls in these situations, transitions to sleet or rain are common.

Total snowfall during a moderate to strong El Niño can be feast or famine. They have produced some of the heaviest and snowiest snow winter. While a stronger El Niño can be stormy, it sometimes pulls in so much mild air from the south that it often rains. If the current El Niño event intensifies more than expected, it could lead to reduced snowfall chances, especially under the very warm background conditions associated with human-caused climate change.

The Pacific Decadal Oscillation (PDO) is a measure of the intensity and location of sea surface temperature variations from normal in the North Pacific Ocean. When strongly positive, it is often associated with a cold and stormy pattern for the mid-Atlantic region. When the weather is sharply negative, conditions often, but not always, tend to be warm and dry.

We are in the midst of a very negative period for PDO. El Niño events tend to push the PDO index higher, so we may see some movement in PDO to the positive side. However, we expect the average index to be somewhat negative this winter which could lead to moderate weather in some periods.

Arctic Oscillation (AO) and North Atlantic Oscillation (NAO)

AO is a measure of surface air pressure at high latitudes above and north of Greenland. Pressures lower than normal indicate the positive phase, and pressures higher than normal indicate the negative phase.

During the positive phase of the AO, characteristically cold air over the Arctic is trapped by a strong polar vortex, and the midlatitudes tend to be moderate. In the negative phase of the AO, the polar vortex becomes disturbed, and outbreaks of cold air become more likely over mid-latitudes, including the United States.

The AO’s cousin, the NAO, is technically a measure of differences in air pressure over the North Atlantic Ocean. It is often referred to as either a low pressure (positive phase) or high pressure (negative phase) area over or near Greenland.

A negative AO in the winter months is often associated with the cold pattern in our region, and supports winter storms when other factors align with it, especially when we also have a negative NAO. This was the main factor in our historically snowy winter in 2009-2010.

While the combination of a negative AO and NAO is far from a guarantee of severe winter weather, our chances of a major snow event are much greater without it.

We expect the average AO to be slightly negative and the average NAO to be somewhat negative this winter. There will likely be periods when both indicators become sharply negative. These windows give us the best chance for meaningful snow events.

Ian Livingstone and Dan Stillman contributed to this report.

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