Like it or not, winter is officially here. For the next three months or so Midwesterners will endure cold temperatures and, of course, the dreaded “S” word—snow. But did you know that snow is favored in some areas more than others? These areas are called snow belts and lake-effect snow bands amplify these areas. Let’s dive in and take a look.
The official definition of a snow belt is rather simple; it is any area where heavy snowfall is particularly common with the help of lake-effect snow. Also, wind direction helps position these snow belts in the Great Lakes region. As you can see in the image above, most of the snow belts are on the leeward side of the Great Lakes. Cold winds in the winter usually prevail from the northwest. This wind direction produces substantial lake-effect snowfall across the Great Lakes region. The wind direction influences the amount of time cold air is over the lakes, which aids lake-effect snow. Lake-effect snow results from cold air passing over relatively warm waters of lakes. This causes lake water to be evaporated into the air, thus warming it. This warmer, wetter air rises and cools as it moves away from the lake. Once cooled, this causes the moisture to be released in the forms of snow. The greater the temperature difference between the air and water, the greater the potential of a more intense lake-effect snow event.
The Upper Peninsula Snow Belt experiences probably the vastest effect of lake-effect snow in terms of area, with the exception of the Lake Michigan snow belt. Stretching from the Porcupine Mountains (Western U.P.) to Canada, anywhere in this region can experience upwards of 250 inches (20.8 feet) of snowfall per year. For comparison, Duluth, Minnesota which is located on the southwestern tip of Lake Superior, only experiences 78 inches (6.5 feet) of snowfall per year.
Another snow belt in the Great Lakes region that experiences dramatic snow fall is the Lake Ontario and Lake Erie snow belts. These two belts can clearly be seen from the first image above. These two regions see daily snowfall totals that are higher than anywhere in the United States. This is due to intense lake-effect snow bands blasting the region with whiteout conditions. The average snowfall for these regions is roughly around 116 inches (9.6 feet) of snowfall. Due to Lake Erie’s relatively shallow depth, this lake is the only lake that is capable of completely freezing over. If this happens, the moisture source for lake-effect snow bands is cut-off, thus ceasing lake-effect snow events. This is why early in the season lake-effect snow is favored for snow accumulation.
The Lake Michigan and Lake Huron snow belts are similar in terms of intensity. The Lake Michigan side, however, can be rather unique. Under the right conditions, northerly winds can form a single band of lake-effect snow stretching along the Lake Michigan coast. This produces intense and localized snow fall. Lake Huron can experience this same intensity for the Bruce Peninsula and Georgian Bay regions. Lake-effect snow is almost a given during any winter precipitation event. It is only when small bays in this area freeze over that lake-effect snow is cut-off, other than that, localized, heavy snowfall blankets the region.
Are you in a Great Lakes region snow belt? If so, make sure proper plans are in place in case heavy snowfall impacts your area. Even if you are not in a snow belt, the winter months in any area in the Great Lakes region has their fair share of heavy snowfall.
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©2019 Weather Forecaster Alec Kownacki
Winter weather can have a major impact on all aspects of life. From school closings to travel delays and cancellations, snow and ice cause a wide range of difficulties during the winter months. Additionally, snowflakes are present in almost all clouds (as most clouds exist at altitudes that experience below freezing temperatures) and as such, it is important to learn about the processes by which they grow. Whether falling to the ground as a melted summer rain or a frozen mid-winter snowstorm, ice crystals play a major role in our weather and the hazards it can sometimes produce.
Once an initial snowflake has formed, there are three primary mechanisms by which it may grow: deposition, accretion and aggregation. In the deposition process, ice crystals grow as a result of the difference in saturation vapor pressure between liquid water and ice at a given temperature. Saturation vapor pressure is the pressure exerted outward by a vapor (in this case water vapor) when the surrounding air is saturated. Since liquid water has a much higher saturation vapor pressure than ice, and molecules in the atmosphere move from high pressure toward low pressure, water vapor travels from liquid droplets toward the lower-pressure crystals. This flow of water vapor aids the growth of ice crystals and development of snowflakes. It is important to note that deposition relies heavily on the presence of both ice and liquid water and is thus temperature dependent. Maximum rates of growth by deposition occur around -15℃.
When ice crystals collide with supercooled water droplets, the crystals grow by a process known as accretion. Supercooled water simply refers to liquid water molecules that exist in liquid form at a temperature below freezing (0℃). As an ice crystal falls through a cloud, any supercooled water it comes in contact with will freeze to the crystal surface, quickly increasing the crystals size. This mechanism is most efficient between 0℃ and -10℃, where supercooled water droplets are commonly present.
Lastly, snowflakes can grow in size by aggregation, a process by which ice crystals collide with one another to form larger ice crystals. The probability that two random snowflakes collide and combine depends strongly on the shape of each crystal and the presence of liquid water on each molecule. This liquid water helps ice crystals bond together molecularly, creating larger and larger ice crystals over time. In fact, snowflakes formed by aggregation can reach 3 to 4 inches in diameter. It is important to keep in mind that all of these mechanisms for snowflake growth refer to the ice crystals within a cloud, not near the surface. However, if the temperature is consistently below freezing between the cloud and surface, these crystals can fall toward the ground and create dangerous winter weather conditions!
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©2019 Weather Forecaster Dennis Weaver
FORECAST DISCUSSION: The start of winter for the United States has already proved to be an impressive one, and despite Hawai’i’s mild weather year-round, it does not disappoint to bring an intriguing forecast to the island chain. The islands have seen unsettled weather patterns in recent days, and it isn’t expected to improve within the immediate forecast period.
Winter often brings slightly cooler temperatures, with a wet pattern, and it has not failed to show itself. West of the island chain an area of low pressure, which is expected to propagate northeastward, will pump in winds from the south. In recent days, high wind advisories have been issued and this forecast period proves no different. Beginning Tuesday afternoon through Wednesday a High Wind Watch is in effect for Kauai Windward-Kauai Mountains-Oahu North Shore-Oahu Koolau-Olomana-Central Oahu-Waianae Mountains. In fact, there is a High Surf Advisory until 6 AM HST Tuesday for Kauai Windward-Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward Haleakala-South Big Island-Big Island North and East. These winds have the potential to cause damage and power outages of note in downslope mountainous areas of Oahu and Kauai. As the front moves eastward, its strength will decrease significantly towards the Big Island and will generate a more typical trade wind pattern as high pressure moves in behind the front.
In addition to concerns with the immediate weather pattern the National Weather Service (NWS) has issued a special weather statement regarding coastal flooding coupled with strong southerly winds. With high water levels being apparent around the Hawaiian Islands, coastal flooding is possible over the next few days, but chances for coastal flooding reduce in the latter part of the week when the high-pressure system with trade wind pattern are expected to return.
For more on various forecasts and winter weather visit the Global Weather and Climate Center!
© 2019 Meteorologist Jessica Olsen