Analysis of the 1+ snow events at BWI and DCA

[PrinceFrederickWx]

Since this topic came up in various threads, I wasn’t sure where to post it, so I just made a new topic altogether. I looked up all the snow events that were 1” or more over the last 40 years at BWI and DCA (1980-2019) and charted them. An event was defined as 1” or more within a 3-day period. In some cases there was accumulating snow on four consecutive days- those were treated as two events, since NWS does not recognize 4-day snow events.

Surprisingly for BWI, the trend line was slightly positive. On average, there are about 4-5 snow events of 1” or more during the season at BWI.

For DCA, the trend was slightly negative. On average, there are about 3-4 snow events of 1” or more during the season at DCA.

The year-to-year volatility for both locations started to increase from the mid-90’s onward. One other thing is that the number of events does not always correlate to whether the overall season was above or below average in total snowfall. For example, 2001 had below average snow and 2016 had above average snow; however, 2001 had more events than 2016.

1” was just an arbitrary line in the sand- perhaps if I raised or lowered the threshold, the story would be completely different. But the main topic on the forum recently has been (for example) that a 2” event would now be 0.2”. This chart should capture a decrease in those situations.

@psuhoffman @North Balti Zen and @RevWarReenactor may be interested in this. Feel free to discuss or poke holes in it. It was a cursory look, but I can dig deeper if there's something more that anyone is interested in. Although I would ask that anyone please ask my permission first if they want to copy the charts to another site, thanks!

[George BM]

@PrinceFrederickWx Lovin' it!

I'd be very curious to see these same graphs over the past 100+ years... or since record keeping began at the local airports.

[North Balti Zen]

Fascinating - thanks for the work on that, PFW.

[North Balti Zen]

@PrinceFrederickWx@psuhoffman  @George BMtoday's CWG with an article rather on point for this discussion as it has carried over through several threads:

https://www.washingtonpost.com/weather/2020/02/05/study-reveals-climate-change-is-shrinking-snow-south-fall-spring-over-much-nation/

 

Quote

 

During the 1970s, Nashville averaged just under a foot of snowfall each winter. Nowadays, Music City is lucky to see half that in a season.

The same is true in Knoxville, El Paso and Albuquerque; all have seen their typical wintertime snowfalls slashed by half in the past 50 years. And they’re not alone. A broad swath of the United States is seeing changing snowfall patterns, many of which are commensurate with those expected as a result of climate change.

In much of the South, the Plains and the interior Mid-Atlantic, seasonal snow totals are dwindling. That’s according to Climate Central, a nonprofit group specializing in climate change research and communication. A report released Wednesday reveals where snow hopes are beginning to melt away, while a select few locations may actually be seeing more snow thanks to climate change.

Where seasonal snowfall is diminishing

Snowfall was seen to be decreasing especially rapidly in the South. These are largely areas that pick up their snow in marginal environments anyway, so any subtle warming can tip the scales and favor temperatures above freezing. That can cut back on snowfall.

This was also prevalent in parts of the Rockies and interior Appalachians, as well as the central and southern Plains in between. Springfield, Mo.; Evansville, Ind.; and Lubbock, Tex., all saw a greater than 40 percent decline in annual snowfall between in the 2010s compared with the 1970s. Even State College, Pa., saw about 20 inches per year less during the 2010s.

Perhaps the most telling aspect of the report wasn’t necessarily where snowfall is decreasing, but rather when.

“In the shoulder seasons, when we look at the nationwide average, in the fall and the spring, we’re starting to see a tendency for the amount of snow to decrease,” Climate Central meteorologist Sean Sublette said.

That’s because the “shoulder seasons” on either side of winter — spring and fall — are warmer than winter. By nature of being transitional seasons, their snowfall events typically occur at warmer temperatures closer to the freezing mark. Any climate warming would nudge spring and fall snow events above freezing first, before affecting any trends in the wintertime.

In the South, 13 out of 14 cities saw a decrease in fall snowfall, while 71 percent experienced a drop in spring snowfall. Each of the five stations in the Southwest recorded a drop in fall and spring snowfall. And in central regions, three-quarters of stations witnessed a decline in fall and spring snowfall.

And in the Northeast, 71 percent saw a decline in the fall, but less than half did in springtime.

In the dead of winter, Sublette says the trends “are much more piecemeal.”

Snowfall increasing in some areas

In a few spots, snowfall is actually increasing — particularly in the wintertime. According to the report, this occurred in some Northeast cities as well as several communities in the Upper Midwest. Why?

For every degree Fahrenheit the air temperature increases, the atmosphere can hold 4 percent more water. That means that, as long as temperatures stay below freezing, an increase in temperature could lead to a juicier storm and actually produce more snow. For areas that are already plenty cold, such as the Upper Midwest and Interior Northeast, that could be a trend going forward — until, down the road, rising temperatures push some storms over the freezing line.

With a greater atmospheric moisture content, Sublette said, we would expect to see “more snow when the temperature is sufficiently low.”

The report also mentioned that lake-effect snow off the Great Lakes will probably increase because of climate change. With warming temperatures, ice cover is dropping. That leaves comparatively warmer waters exposed, which are source for lake-effect snow bands.

“With open lakes, you get much more heat and moisture flux off the lake, and again if it stays below freezing, you have more snow in that time frame” Sublette said.

Bigger storms for the Northeast

In recent years, there has been a demonstrable trend in many East Coast cities, during which some winters will feature booming blockbuster storms while others pass with hardly a flake. The “feast or famine” nature of the snowfall may have a climate explanation behind it.

“It gets back to the fundamentals of the physics of these systems,” said Dave Robinson, a professor of atmospheric sciences at Rutgers, who runs the university’s Global Snow Lab. “You can develop stronger storms over warmer seas. And with more moisture in the air and a greater temperature contrast.”

As long as you can still be “dynamically cold enough to snow … they’re powerful systems. We’re seeing some suggestion of more large storms, more impactful storms, up in the north,” Robinson said.