|Above: Rayford Allen, an employee of the Tampa Bay Rays, takes some pictures of the snow at Yankee Stadium before the scheduled New York Yankees' home opener game against the Rays, Monday, April 2, 2018, in New York. The game was postponed until Tuesday due to weather. Image credit: AP Photo/Seth Wenig.|
Even as most of the U.S. West deals with another lackluster winter of snowfall, quick shots of snow continue to taunt the calendar across the Midwest and Northeast. New Yorkers returned from their holiday weekend to a winter-like Monday morning of wet snow and messy commuting.
With 5.5” as of 10 am EDT, New York’s Central Park got its heaviest April snow in 36 years. In records going back to 1869, the city has seen only ten other April snows of at least 4”:
1 10.2" 1915-04-03/04
2 10.0" 1875-04-14
3 9.6" 1982-04-06
4 8.5" 1924-04-01
5 6.5" 1944-04-05
6 6.4" 1917-04-09
-- 6.4" 1938-04-07
8 5.0" 1907-04-09
9 4.2" 1956-04-08
10 4.0" 2003-04-07
New York’s snow was deposited by a fast-moving upper-level impulse that dropped a narrow swath of up to 6” from southern Nebraska across parts of the Corn Belt. Kansas City picked up 1.1” on Sunday, its heaviest April snow since 2.6” on April 5, 1994.
In the wake of the snow, there were some impressively cold temperatures on Sunday night where clear skies and calm winds allowed for ample radiation to space from atop the snowpack. Kirksville, MO, set an all-time low for April with 5°F early Monday. The previous record of 8°F was set on Apr. 1, 1899, and Apr. 5, 1920. There were at least three readings below 0°F in Illinois, including -1°F at Macomb. The state had seen only two other cases of sub-zero cold in any previous April, according to climatologist Brian Brettschneider.
The -1°F temperature at Lincoln, IL, is the most southerly sub-zero reading in the month of April for any station between western Kansas and eastern W. Virginia in the climate record. @NWSLincolnIL pic.twitter.com/24LGwN2nw6— Brian Brettschneider (@Climatologist49) April 2, 2018
The latest in a seemingly endless stream of Midwest/Northeast snow-droppers will race from the northern Rockies on Monday across the Great Lakes on Tuesday. As much as 6-12" could fall across parts of Minnesota, Wisconsin, and Michigan from this storm, dubbed Wilbur by the Weather Channel. See the weather.com feature for regular updates. Models are suggesting yet another quick-hitting round of mostly light snow could sweep across parts of the Northeast and New England toward the coming weekend.
|Figure 1. Except for 2016-17, each of the last seven snow seasons has produced below-average snow water equivalent (the amount of water held in snowpack) across the U.S. West. Above are the percentages of the 1981-2010 average for each year since 1981. Image credit: Climate Central, with data from the USDA/NRCS SNOTEL network. Data shown for 2017-18 is through March 27.|
A long-term drop in snowfall across the U.S. West
Six of the last seven snow seasons—including the one now drawing to a close (see Figure 1)—have ended up below average for the amount of water held in snowpack across the West.
This year’s shortfall was coupled with a classic La Niña pattern: heavier-than-usual snows to the north and lighter-than-usual to the south (see Figure 2). Across the Upper Yellowstone River Basin, content in snowpack is running at more than 150% of the season-to-date median—with yet another winter-like storm hitting the area on Monday—whereas snowfall has been abysmal over New Mexico and Arizona. As of mid-March, the U.S. Bureau of Reclamation was predicting that the Upper Colorado River will most likely be providing less than half of the normal long-term inflow into Lake Powell from April through July.
California’s Sierra Nevada played an impressive game of moisture catch-up in March after one of the driest October-to-February periods on record. South Lake Tahoe had its wettest March in records going back to 1968, with 6.78” of liquid. Some of the month’s storms were on the warm side, though, and snow water equivalent remains 15-30% or more below the seasonal norm across most of California’s high country. A manual snow report on Monday conducted near Echo Summit by the state's Department of Water Resources found less than half of the average for season-to-date snow water equivalent.
Late this week, a powerful atmospheric river is on track to bring high-end precipitation amounts for April to central and northern California and the Sierra Nevada.
The potential for an #atmosphericriver is increasing, bringing wet and relatively warm weather for late this week! This animation shows a strong plume of Pacific subtropical moisture aimed at California. #CAwx pic.twitter.com/9G2KGYWW80— NWS Sacramento (@NWSSacramento) April 1, 2018
|Figure 2. Snow water equivalent across the U.S. West as of Thursday, March 29, 2018, as a percentage of the 1981-2010 average for the date at each location. Image credit: USDA/NRCS SNOTEL.|
A grim prognosis for U.S. West’s snowfall
Snowfall is a crucial lever for water supplies across the largely arid U.S. West. A healthy snowpack enables water to be stored during the winter and then released in the form of snowmelt during the subsequent spring and summer, when the water is needed most.
The annual maximum of snow water equivalent dropped by 10% to 20% across the western U.S. from the 1980s to the 2000s, according to a 2017 study in Nature Communications last year led by John Fyfe (Canadian Centre for Climate Modelling and Analysis). The drop was consistent with a large group of climate model simulations that included both natural factors (such as volcanoes and changes in solar input) and human-induced factors (such as greenhouse gases, aerosols, and land use). Models that omitted the human-produced factors tended to hold snowfall steady rather than producing the observed decline.
Looking forward, the model ensemble projected that a continued drop in Western snow water equivalent was very likely. From 2011-2015 to 2036-2040, individual model runs varied from a gain of 3% to a loss of 60%; the average result was a drop of about 30%. “The projected losses have serious implications for the hydropower, municipal and agricultural sectors in the region,” noted the authors.
East of the Rockies, there’s also been a general trend toward less snowfall over the past several decades, although there is much point-to-point variation (this is common with precipitation, which can vary greatly over small distances). Changes in snow measurement practice may have given an artificial boost to snow totals at some locations since the 1990s. An analysis by Climate Central found that 27% of U.S. stations have seen upward trends in snowfall since 1970, whereas 73% have seen a decreasing trend.