Signs of some true winter ahead when looking at the computer forecast models over the next couple of weeks. The maps below are from the GFS model & show the upper level 500mb flow & the surface forecast maps. The first map -- at 500mb -- shows the cross polar flow out of Canada down into the Lower 48. The surface maps show waves of low pressure developing along the arctic boundary as the cold front tries to push south & east. Since the 500mb flow is more zonal (east/west) vs. meridional (north/south), the cold front will generally have a difficult time making a lot of progress south & when/if it does, the front will not be able to stay suppressed to the south. Nonetheless, the northern latitudes of the U.S. are in for some true winter weather with a building snowpack while it'll be more of a tease for the First Coast. The upper level ridge over parts of the Gulf of Mexico, SW Atlantic & Caribbean looks like it'll hold strong for a while. So we'll see interludes of colder temps. but with little staying power. With a building snowpack to our north, some pretty cold air could be on the horizon.
From AMS - December night skies:
SkyandTelescope.com for more information.
Easy sky measures: Hold out your arm. Your smallest finger appears about 1° wide, and your clenched fist is 10° wide.
Dec. 12–13 (night): The dark limb of the waxing gibbous Moon “occults” (covers) the bright star Aldebaran for most of the United States and Canada.
Dec. 13–14 (night): The strong and reliable Geminid meteor shower peaks on the evening of December 13th in the Americas, so it should be fairly active on the nights before and after, too. However, the full Moon will hide all but the brightest meteors. Geminid meteors are shed by the “rock comet” 3200 Phaethon.
Dec. 18 (morning): Regulus, the brightest star in Leo, sparkles 5° lower left of the waning gibbous Moon.
Dec. 20-21 (night): Longest night of the year in the Northern Hemisphere (see next entry).
Dec. 21 (night): Winter solstice occurs at 5:44 a.m. EST (2:44 a.m. PST; 10:44 UT). Solstice derives from Latin words for “Sun stoppage” (because in the sky the Sun stops moving southward, turns around, and starts moving northward).
Dec. 22 (morning): Rising in the east by about 3 a.m., the waning crescent Moon, bright Jupiter, and white Spica form a line about 9° long.
First Quarter Dec. 7, 4:03 a.m. EST
Full Moon Dec. 13, 7:05 p.m. EST (Cold Moon)
Last Quarter Dec. 20, 8:56 p.m. EST
New Moon Dec. 29, 1:53 a.m. EST
EARTH GUAGE (NEEF)
Snow & Winter Recreation, Sarah Blount
Did You Know?
- Snowflakes travel one to four miles from their cloud base to the surface of the planet, depending on the positioning of the clouds.
- Snowflakes are typically a half-inch in diameter, but can reach irregular sizes as large as two inches across.
Thinking of heading outside for some winter recreation this season? Whether you’re skiing, snowboarding, hiking, snowshoeing, riding in a snow mobile, or setting up for a snowball fight, the type of snow on the ground can have an impact your winter-weather activities. But, snow is snow, right? It’s all frozen water, so how can there be different “types” of this cold-weather precipitation? Let’s start at the top.
For any precipitation to form, there needs to be enough moisture in the atmosphere that these microscopic particles of water vapor become too heavy to remain suspended in the air. This change in size and weight can occur when the tiny particles bump into each other and join together, or when they freeze around a solid core such as a piece of dust or grain of pollen. In the case of snow, these water vapor particles start their descent at a very low temperature, at or below 32°F, and remain in that temperature range as they travel from the cloud base to the surface of the planet, a distance that can be anywhere from one to four miles depending on the positioning of the clouds. Along that journey, the particles of frozen water vapor, or ice crystals, can still experience a variety of below-freezing temperatures, which can influence the structure and shape of each six-sided crystal. Under certain conditions, these snowflakes can grow beyond their usual half-inch diameter, reaching irregular sizes as large as two inches across.
Snow Ground Cover
Once on the ground, the snow can still change in texture, going through a metamorphosis in response to exposure to sunlight, wind, temperature fluctuations, and more precipitation. For instance, even if the air and ground temperatures remain below freezing, exposure to the elements can cause the top layer of the snow accumulation to melt and re-freeze, creating a crust on top of the snow. In areas that remain cold enough year round, the snowpack, or the total accumulation of ice and snow on the ground, can remain in place for years, developing layers of ice crystals that bear the markers of the weather conditions seen in the area since their deposition, resulting in differences in hardness, cohesion, strength, and even temperature throughout the snow mass. When enough new precipitation accumulates over top of the snow, the weight of this overlaying layer causes the ice crystals to undergo a type of geologic transformation, where hundreds of snowflakes recrystallize into larger and denser ice crystals, which can result in crystals up to one foot long, such as those seen at Alaska’s Mendenhall Glacier.
For some outdoor enthusiasts, powder snow is prized above all else. This is snow that has relatively low moisture levels, and lacks the dense crust that can result from prolonged exposure to the elements. Some skiers argue that the best conditions for skiing come from storms that produce at least a foot of low density, new snow, which allows the skis to “float” through the accumulation with little resistance. This type of snow can be the result of a storm that gets colder over time, causing the driest, lowest-density snow to accumulate at the surface of the pile, with snow that becomes denser with depth. For others, such as those wishing to snowshoe, crusty snowpack might be more desirable—these conditions can occur when there’s a large temperature variation or intense wind or sun applied to the snowpack, causing the surface to melt and refreeze.
Whatever your dream snow conditions, there are many opportunities for winter recreational activities.
- On January 1st, consider taking part in the First Day Hikes put on by your state park system! There are over 400 hikes scheduled this year across all 50 states.
- Check out Recreation.gov’s Winter Sports site to learn more about winter recreation opportunities on a public land site near you, including activities like cross-country skiing, snowshoeing, and snowboarding.
- While some animals might be asleep or away during the cold months, there are other types of wildlife who may be in your area just for the winter season! Check out Recreation.gov’s Wildlife Viewing site to find wildlife-watching opportunities near you.
- National Snow & Ice Data Center. 2015. “All about Snow: How Snow Forms.” Accessed December 7.
- National Snow & Ice Data Center. 2015. “All about Snow: Types of Snow.” Accessed December 7.
- National Weather Service. 2008. “Cloud Classifications.” NOAA. Accessed December 7, 2015.
- NOAA. 2013. “How Do Snowflakes Form?” Accessed December 7, 2015.
- Rocky Mountain National Park Environmental Education Staff. 2013. “Winter Ecology Teacher Guide.” NPS.
- Sobal, Tom. 2004. “The Crust Can Be the Best Part.” Snowshoe Magazine, April 19. Accessed December 7, 2015.
- Steenburgh, W. James, and Trevor I. Alcott. 2008. “Secrets of the “Greatest Snow on Earth.”” Bulletin of the American Meteorological Society 1285-93. doi: 10.1175/2008BAMS2576.1
- University of Illinois at Urbana-Champaign WW2010. 1997. “Precipitation.” Accessed December 7, 2015.
- USGS. 2015. “USGS FAQs: Is Glacier Ice a Type of Rock?” Accessed December 7.
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