Atmospheric Struggles to Avoid Snowing in Massachusetts

Even the quiet days in between big storms are producing snowflakes during the amazing siege of winter weather that’s brought parts of eastern New England to a near-standstill. Wednesday brought a whiff of ocean-effect snow, the less-common Atlantic counterpart to the lake-effect snow that often hits cities like Buffalo and Syracuse. Both phenomena are driven by cold air passing over relatively warm water. Lake-effect snow is assisted by bands of converging air that develop when surface winds are aligned with the very linear lakes Erie and Ontario. The New England coast lacks such a geography, so ocean-effect snow is more rare, developing only when the atmospheric structure is highly favorable. Temperatures early Wednesday were in the low 20s along the Massachusetts coast, but as cold as 10°F less than 3000 feet above the surface. This led to enough instability for very shallow clouds and light snow, especially over Cape Cod. A strong inversion above this layer kept the clouds from growing any deeper, putting a lid on more intense snow.

Boston’s Logan Airport recorded eight hours of light snow but only 0.5” of accumulation. Traces of snow were observed as far northwest as suburban Andover--falling under blue sky, according to WSI’s Peter Neilley. “It was snowing lightly despite the fact that two-thirds of the sky was clear, and the southeastern third had just a thin cirrus overcast,” Neilley said. “On the very southeast horizon was some stratocumulus.”



Figure 1. A stripe of ocean-effect snow covered southeast Massachusetts and Rhode Island on Wednesday afternoon, February 11. Image credit: NOAA/College of DuPage.

No rest for the snow-weary
New Englanders continue to grapple with the aftermath of three major snowstorms--Juno, Linus, and Marcus--in less than three weeks. Boston.com writer Charlotte Wilder captured the event’s emotional impact in “A Breakup Letter to Snow from the City of Boston” (right before Valentine’s Day, no less). Today’s ocean-effect snow pushed Boston’s total to 41.3” for the month--just 0.3” short of the February record--and 78.5” for the season. Since the first of the year, the city has set heaviest-snowfall records for intervals of 5, 7, 10, 14, 20, 30, and 40 days. (Thanks go to Michael Palmer and Kathryn Prociv at the Weather Channel for these statistics.)

Upper levels across North America remain locked in a pattern that supports more nor’easters, with the polar jet stream diving southward from Canada across the Midwest, then arcing across New England. The next winter storm will intensify into a powerhouse east of New England on Thursday and Friday, with surface pressure deepening quickly enough (more than 24 mb in 24 hours) to qualify the nor’easter as a “bomb.” It appears the storm will intensify just far enough out to sea to spare the coastline from anything more than continued ocean-effect snow. In its wake, though, the system will pull down another shot of frigid air across the Northeast, setting the stage for a potentially much more serious snow threat late in the weekend with the next nor’easter. Both the ECMWF and GFS models develop this second system near or north of the benchmark location of 40°N and 70°W, a good sign of potential impacts to New England. Temperatures will be cold enough to support another event with high snow-to-liquid ratios, perhaps 20-to-1 or greater, and the most likely focal point once again appears to be from eastern Massachusetts to coastal Maine. If the model trends continue, we could see rapid intensification of the surface low, with blizzard conditions and more than a foot of new snow quite possible over eastern New England (including the Boston area). While this week’s light snows mainly added insult to injury, a storm of the magnitude predicted by some model runs for this weekend could be a daunting blow to already-crippled parts of eastern Massachusetts.

Update (6:00 PM EST]: A blizzard watch has been issued for Saturday evening through Sunday evening for coastal counties of northern Massachusetts, New Hampshire, and Maine, including the cities of Boston and Portland. Widespread accumulations of more than a foot are expected, with wind gusts to 50 - 60 mph, very cold temperatures and wind chills, and extensive blowing snow,




Figure 2. Temperature anomalies (departures from average) of 30°F or more are possible across much of the central and eastern U.S. next week, as depicted in this 168-hour forecast from the GFS model valid at 0000 GMT on Thursday, February 19. Image credit: ClimateReanalyzer.org/University of Maine.


Winter’s coldest week coming up?
The upper-level low that’s plagued New England is projected to sharpen and shift westward next week, tapping extremely cold Arctic air. Several strong surface highs will likely move into the central U.S., much as we saw in early January, but this time bearing even more frigid temperatures. A band of significant snow, sleet, and/or freezing rain could materialize early next week from the mid-South to the mid-Atlantic. The GFS model, which has a cold bias on surface temperature, has pulled back from earlier predictions that would have approached all-time lows in some areas. In our warming winter climate, such records are increasingly hard to come by. Still, we can expect some daily records to be toppled or at least approached across much of the central and eastern U.S. over the next 7 to 10 days (see Figure 2), with some brutal wind chills possible. Already, wind chill advisories for values well below 0°F are in place across the Red River Valley of North Dakota and Minnesota, as well as much of Michigan, Ohio, Pennsylvania, New York, and western New England. Comparable warnings for extreme cold (wind chill) are in effect over much of Ontario and Quebec.


Figure 3. Snow depth at 0600 GMT on Thursday, February 12, averaged more than 20” across most of New England, with small pockets of more than 40” (purple hues) evident in several states. Image credit: NOAA/NWS National Operational Hydrologic Remote Sensing Center.


The best chance for truly historic U.S. cold this weekend or early next week could be over the very deep snowpack of New England, where depths of 10” to 30” or more are now widespread (see Figure 3). On a cold, clear night, snow cover enhances the loss of heat from the ground as radiational cooling predominates (also dubbed nocturnal cooling, as blogger Lee Grenci explains). A deep snowpack also brings the “surface” closer to the height of weather instrument shelters, where thermometers are located 4 - 6 feet above ground level. Since temperatures are coldest just above the top of the snow on nights of strong radiational cooling, deep snow can act to reduce temperatures at thermometer height. Such a setup in Oklahoma brought the nation’s most recent all-time state record low. A major winter storm dropped heavy snow across northeast Oklahoma on February 9, 2011, including a state-record 24-hour accumulation of 27” in the town of Spavinaw. The next morning, an Oklahoma Mesonet station in Nowata dipped to –31°F, breaking Oklahoma’s all-time record of –27°F (which had stood for 64 years). Just a week later, Nowata hit 75°F.

Bob Henson


Figure 4. The Alps of MIT: With more than 40 inches of snow blanketing the Boston area over the past two weeks, snow removal efforts on the campus of the Massachusetts Institute of Technology in Cambridge have engineered this new five-story-high mountain of snow. Image credit: Tom Gearty/MIT.