 Photo: 24-Hour Accumulated snowfall map showing lake effect snows bringing accumulation to lake adjacent areas. Map generated from pivotalweather.com on December 28, 2017. As December has come and gone and we are knee deep in Meteorological Winter, the discussion of winter weather in the Midwest usually starts with strong cyclones passing through the continental United States bringing anything from blizzards to the north and strong thunderstorms to the south. We can steer our focus into something on a smaller scale (or mesoscale) and focus on the Great Lakes region, specifically on lake effect snow. The importance of understanding lake effect snow lies in the fact that it is convectively induced (similar to thunderstorms in the summer), thus is often very intense compared to other systems. The snow-to-liquid ratio for lake effect snow can range from 15 to up to 30 inches of snow per one inch of liquid, compared to 10:1 for other systems as a general ratio. Bands of lake effect snow can fall at intense rates of 2-3 inches in the matter of one hour and can be very localized in nature based on the size of the snow band. Snowfall forecasts can often be misleading if we are unaware of the ratio during a given system. The general rule of thumb with these snows is when cold air passes over a generally warmer lake, the temperature differential causes rising motions over the lake producing a cloud and eventual strong snow. When forecasting lake effect snow, there are multiple aspects to consider besides cold air over a warm lake:
Lake effect snow bands are different from most other snows that there are usually more intense snowfalls in a short time period. These storms can also occur during large scale high pressure, which can be deceiving for a storm to pass in a moment’s notice, only to have the sun reappear. Observing temperatures at 850mb is a common forecast tool because the convective cloud tops for these systems usually is between 700 and 850mb. Convection refers to the ability of motion in warmer air to rise and cooler air to sink which in the atmosphere can create varied forms of severe weather. Warm waters in contact with cold air allow for CAPE (Convective Available Potential Energy) to be generated (usually around 300-400 J/KG) in a shorter layer called the boundary layer (roughly a mile above the surface) that allows for quick rising motions to create these systems. This can be compared to summertime convection which can reach and exceed 200mb (6-7 miles) into the atmosphere where CAPE values have values in the thousands and allow for higher and faster updrafts (rising motion).  Photo: 850mb Temperature, Height and Wind map showing cold air over the Great Lakes Region ideal for producing lake effect snows. Image generated from pivotalweather.com on December 29, 2017. Based on the forecasting factors, travelers will need to be aware of changing conditions based on their proximity to lakes. Short term forecasts and nowcasting is crucial to understanding where these bands could hit and who can be affected. Snows like these can mean significant accumulation to nothing in as little as 40 miles distance. Ultimately, preparation will be important as these storms can be deceiving since they can occur during high pressure systems, meaning that a strong winter storm can pass by with high pressure behind it, but still bring more accumulation near a lake. Awareness of the situation is important along with staying up to date with changes throughout the day. To learn more about other interesting winter weather topics from around the world, click here! © 2019 Meteorologist Jason Maska
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 Photo: Satellite image of Lake-Effect Snow over the Great Lakes region on January 5, 2015. (Image courtesy of The Weather channel) Lake-effect snow primarily affects the Great Lakes region of the Midwestern United States but can have an impact on any region near a lake, capable of the ideal temperature differential to form these snows. The difference of 13 degrees Celsius in lake water temperature and air one mile above the surface is the ideal and primary ingredient necessary to form lake-effect snow. While there are other bodies of water that can have this effect (rivers, oceans, etc.), the focus of this discussion will be on lakes. The intensity of these storms can create snowfall rates of 2-3 inches in an hour and have liquid rain to snow equivalent (in inches) ratios anywhere from 1:15 to 1:30. Due to stronger updrafts (faster rising air) from the temperature differential over the lake, this leads to a higher ratio, higher snowfall rates and greater impacts to travel. The Great Lakes is the most common region where this phenomenon occurs, impacting the surrounding coasts based on the wind direction steering the snow bands. Typical lake-effect snow events are steered by a variety of north winds that brings in cold air needed to generate this phenomenon. Other locations with bodies can experience lake-effect snow like the Great Salt Lake in Utah and the finger lakes in New York. Regions can also experience ocean, river or sea-effect snow if the conditions are right. There are multiple types of lake-effect snow bands that can occur based on wind direction and can have various impacts. Short lake axis parallel (SLAP) bands are often multiple small bands that follow the short axis of the lake and impact multiple smaller areas. Long lake axis parallel bands are often single bands following the long axis, usually creating a larger band with impacts over a single greater area. Other types of lake-effect snow are those that make multiple lake interaction, form and remain mainly over the lake, and form a vortex (or a small scale low pressure system, often called a meso-low) that can bring snows onshore. Due to shifting wind directions and weak synoptic (large scale) winds, vorticies can form within the snow band or over the lake. If stronger winds were present, a vortex will generally break up, but with cold air present and weak wind directional changes they can form and bring snow inland.  Photo: Map of Lake Michigan with red line indicating the Short Axis of the lake and the black line indicating the long axis of the lake. Image courtesy of the University of Michigan. Terminology can often be confused when discussing lake induced snow events and how they impact a region. Since there is a difference between lake-effect and lake-enhanced snows, the distinction is necessary to discuss. Lake-effect produces snowfall as an effect of the presence of the lake, thus if the lake were not present, then the temperature differential needed to form the band would not exist. On the other hand, lake enhancement will enhance the snow production of a lake-passing system because of cold air aiding the development of clouds while passing over the warmer waters. Understanding the nature of different types of lake-effect snow will help determine the impacts to a specific region based on the size of the bands. Forecasting is difficult for lake-effect snow because of the mesoscale nature of the event, but there are multiple processes that we can use to better that prediction. Nowcasting becomes necessary to concentrate on the changing structure of the bands and pinpoint the direct impacts to a town. Overall, lake-based snow systems are location dependent on proximity to a lake and how far inland these systems can impact. The best practice during winter storms would be to be aware of and prepared for rapidly changing conditions in real-time to determine the impacts to your specific location. To learn more about other interesting winter weather topics from around the world, click here! © 2018 Meteorologist Jason Maska  Of all the media attention the polar vortex has received in recent years, the majority of people just know it as “a system that brings cold air to my city every winter.” Although this is a true statement, let’s discover together what exactly the polar vortex is. After all, the term “polar vortex” has been in use even before the Civil War.
The polar vortex is a low-pressure system that resides over the poles with its strongest extent during the winter months. It is strongest in the winter because of the vast temperature contrast between the Polar regions and the mid-latitude regions. People often associate the polar vortex with cold fronts that produce snow. Although this vortex does bring a punch of cold air, the association of it with snow is simply not the case. The polar vortex primarily occurs in the stratosphere, a layer of the atmosphere about 6-30 miles above the troposphere where most of the weather occurs. Although it is 30 miles above the ground, it still has a profound impact on day-to-day weather. Changes in the stratospheric polar vortex can effect jet-stream patterns by forcing them southward which in turn can influence the location and persistence of cold air masses across North America and Europe. Here’s the kicker: when the polar vortex is strongest, we are less likely to see a deep cold air mass plunge into North America or Europe. It’s actually when the vortex is at its weakest, when we typically will see the cold air punch. An easy analogy to remember this would be when it is strongest (like in the left picture above) with no waves, it keeps the cold air at bay, kind of like a barrier. When it is at its weakest (like in the picture on the right) with multiple waves, the cold air rushes through the barrier and into North America and Europe. Like North America and Europe is currently seeing, the polar vortex occasionally weakens. This is due to energy being brought upward from the lower atmosphere. This happens when the stratosphere suddenly warms, an event referred to as sudden stratospheric warming (SSW). This event raises temperatures to about 50 degrees Fahrenheit, or more, in just a few days in the stratosphere. Although this event sounds rare, it occurs at least once every other winter season. This sudden warming disrupts and weakens the polar vortex which shifts the location of it southward and can physically split the vortex up. When this happens, the weakened vortex forces the jet-stream to become more prone to “blocking.” This blocking usually happens in colder months and can easily break down the “cold air barrier” as stated earlier. This leads to a more persistent cold weather pattern for weeks. A lot goes into fully understanding the polar vortex. Even more goes into forecasting it and knowing exactly when or if it will impact weather patterns across North American and Europe. As we travel through colder weather months, the ever-impending polar vortex may soon make an appearance but before that happens, much more forecasting is needed. For more winter weather topics, click here. ©2018 Weather Forecaster Alec Kownacki    DISCUSSION: An early December winter storm made its way across the southern United States with past week. The storm initially impacted southern California on Dec. 5th, 2018. It brought heavy snowfall to the mountain regions, with some areas recording over a foot of snow. In the lower elevations and closer to the coastline, extreme rainfall lead to flash flooding from Los Angeles to San Diego. According to the NWS San Diego, rainfall totals from the storm were greater than 4.5 inches in some places. John Wayne Airport received 3.5 inches while the San Diego International Airport received 2.6 inches. In addition to causing flash flooding, the extreme rainfall triggered mudslides, resulting in road closures, including the Pacific Coast Highway, and evacuations in areas that recently evacuated due to the November wildfires. However, a silver lining does exist for California, the early season snow has resulted in a higher than average snowpack in the Sierra Nevada Mountains. California relies on the melting of this snowpack in the spring to recharge its reservoirs to support their water demand during their dry season in summer and early fall.
After impacting southern California, the storm traversed across Arizona and New Mexico before moving into Texas, with heavy snow and rainfall impacting the state. In northern portions of Texas heavy snowfall occurred and places like Lubbock saw as much as 10 inches of snow from the storm. Meanwhile, rain was dumped across the Houston region, resulting in major flooding. Some places saw over six inches of rainfall, while College Station broke its daily maximum rainfall record with 4.01 inches of rain on Dec 07, 2018. According to the NWS Houston/Galveston the previous record was 1.70 inches in 1931. Moving out of Texas the storm traversed across southern Louisiana, the Florida Panhandle, and into southern South Carolina. As it tracked eastward, snowfall continued to fall within the northern portion of the system, bringing snow from southern Oklahoma to the Mid-Atlantic Mountains. The heaviest of this snow occurred in the Blue Ridge Mountains in North Carolina and Virginia, with some areas in recording over two feet of snow. One place in North Carolina, the small town of Busick, which is located in the mountains of the state, saw 34 inches of snow. Meanwhile areas not in the mountains saw record breaking snowfall. The Raleigh/Durham international airport North Carolina recorded 7 inches, which is a record for Dec 10. Additionally, the city of Raleigh saw the most snowfall in a single day in the month of December since 1958. Furthermore, this event resulted in the city already exceeding their yearly average snowfall of 7 inches. Another record was set, the second highest single-day snowfall total, at the Richmond International airport in Virginia, which recorded 11.5 inches of snow on Dec 9, 2018. When all was said and done, this early winter storm brought snowfall across the southern US, from CA to VA and heavy rainfall to many locations. It resulted in road and school closures, thousands of cancelled flights and car accidents, hundreds of thousands without power, mudslides, flash floods, and, unfortunately, some deaths. The system is now off the eastern coast, over the Atlantic Ocean but it is still driving freezing temperatures and gusty winds across the south, resulting in freeze warnings extending into Florida. To learn more about other interesting winter weather topics from around the world, click here! © 2018 Meteorologist Sarah Trojniak, Ph.D. How can snow be on Doppler radar but not reach the ground? (Imagery credit: WSI Radar Imagery)12/7/2018   DISCUSSION: Have you ever been impacted by a classic mid-Winter snowstorm and found that there was snow falling over your region according to Doppler radar imagery, but there was nothing falling at the ground? Most people get confused about when this situation unfolds with an approaching snowstorm. However, there is a relatively simple explanation for why this type of situation can be realized in association with any given snowstorm. That simple explanation comes with the meteorological term which is known as virga. Virga is simply snowfall or any other type of precipitation which is unable to reach the ground.
As a classic inland or coastal winter storm is approaching a given region, there is often a particularly cold air mass in place. The exceptionally cold air which happens to be in place across the specific region will typically have the characteristics of being a drier air mass. As a result of there being a drier air mass present over the given region, this will consequently lead to there being a larger dew point depression. A larger dew point depression is simply the measurement which is defined by the difference between the air temperature and the dew point temperature at a given location. The larger the dew point depression happens to be at a given location, the longer it will take snowfall to evaporate the respective layers of the atmosphere from cloud level and on down to the surface of the Earth. As the snowfall continues to evaporate through the depth of the drier low levels of the troposphere, this consequently leads to a decrease in the regional dew point depression values which ultimately leads to an increasingly moister near-surface layer. Thus, as the near-surface to sub-cloud layers become increasingly moister with time, this will gradually allow snowfall to finally reach the ground and accumulate on the ground if the surface is sufficiently cold. Hence, if you ever find yourself looking at a news station’s regional radar imagery or your local National Weather Service forecast office radar imagery and see snowfall over your region (but not quite reaching the surface yet), you will now have more insights as to why this is happening. To learn more about other interesting winter weather topics from around the world, click here! © 2018 Meteorologist Jordan Rabinowitz   DISCUSSION: Even though the month of November just ended, and the month of December is underway, there are still things to remember and learn about Mother Nature. One major thing is that Mother Nature most certainly does not hardly ever follow a set clock. More specifically, most people most often associate the heart of Winter with the occurrence of coastal or inland low-pressure systems which induce regional and/or multi-regional snowstorms. Thus, if someone ever is completely shocked by heavy, accumulating snowfall occurring across the central of eastern United States during late October or throughout any part of November, this should not be nearly as shocking as one would think. That is a result of the fact that under the right combination of larger-scale and smaller-scale atmospheric and environmental conditions, a snowstorm can occur well before the start of December. The upper-most image is taken during the evolution of the third Nor'easter which occurred off the coastline from the northeastern United States in March of 2018.
In looking at the lower graphic attached above (as provided by Meteorologist Tom Niziol from The Weather Channel), the above information is clearly reflected by the corresponding graphical context. To be precise, the context of graphic above reflects the reality that between 1959 and 2000 (i.e., the 41-year period ending at the start of the 21st century) there was a substantial prevalence of blizzard occurrence during the month of November across a good portion of the central and the north-central Plains states. It is important to acknowledge the fact that this graphic came from the journal article published by Schwartz and Schmidlin (2002) which was a research project that involved studying blizzard events across the contiguous United States and was entitled “Climatology of Blizzards in the Conterminous United States, 1959-2000.” As you can see from the lower image above, there have been a solid distribution of November blizzards across the northern tier of the United States with the heart of the November blizzard event concentration being across North Dakota and South Dakota. It just goes to show that as the atmosphere is transitioning from Fall to Winter, the southern shifting of the Polar jet stream likely has a role in the presence of the greater snowstorm frequency across the north-central Plains region of the United States. To learn more about other winter weather topics, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz  DISCUSSION: When it comes to anticipating rounds of cold air intrusions during a given Winter season, there is no doubt that one of the more interesting non-precipitative atmospheric phenomena which occurs is cold air damming. Cold air damming occurs most often during the early to middle parts of Winter when high-pressure systems sink southward out of eastern and/or southeastern Canada and deliver colder air masses to the greater part of the northeastern United States. As this process unfolds, there is a plethora of cold air which will often get “stuck” within valleys or any other regional areas of lower elevation. This phenomenon most often is famous for occurring along the East Coast of the United States in the vicinity of the Appalachian Mountains.
The premiere reason for why cold air damming is so impactful during any part of a Winter season has to do with several different factors which play a key role in association with cold air damming. Cold air damming typically occurs in the mid-latitudes as this part of planet Earth lies within the prevailing westerlies which is an area where frontal intrusions are more common during a typical calendar year. When the Arctic oscillation is in its negative phase and the regional atmospheric pressure is found to be higher over the polar regions, the flow is more meridional (i.e., more curvy flow with respect to the east-west plane), blowing from the direction of the pole towards the equator, which brings colder air into the mid-latitudes. It is worth noting that cold air damming is observed in the Southern Hemisphere just to the east of the Andes Mountains, with cool incursions sometimes observed as far equator-ward as the 10 degrees south. In the Northern Hemisphere, common situations occur along the east side of ranges within the Rocky Mountains system over the western portions of the Great Plains, as well as various other mountain ranges along the West Coast of the United States. The initial is caused by the poleward portion of a split upper level trough, with the damming preceding the arrival of the more equator-ward portion of the approaching upper level trough feature. Furthermore, it is also important to acknowledge that some of the cold air damming events which occur east of the Rockies will go on to continue southward to the east of the Sierra Madre Oriental through the coastal plain of Mexico and down through the Isthmus of Tehuantepec. Further funneling of such cool air occurs within the Isthmus of Tehuantepec, which can occasionally lead to winds of gale and hurricane-force. Other common instances of cold air damming take place on the coastal plain of east-central North America, between the Appalachian Mountains and Atlantic Ocean which are the most common trigger mechanisms for coastal ice storms and heavier snowfall during Winter-time along the East Coast of the United States (and this is also reflected by the idealized graphic which is attached above courtesy of the National Weather Service network). In Europe, areas south of the Alps can also be quite prone to cold air damming which can help to support quite impressive snowfall events in the higher elevation regions spread across the span of the Alps. Lastly, in parts of central and eastern Asia, cold air damming has been documented near Taiwan and the Korean Peninsula which will often have similar consequences to cold air damming events which occur in other parts of the world. To learn more about other high-impact winter weather topics from around the world, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz  While the term "lake effect snow" may have little meaning for people who live a good distance away from the Great Lakes, people who live near the Great Lakes are very familiar with the extreme impacts it has on daily routines. The formation of lake effect snow first starts when cold air, that normally originates from Canada, drifts across the relatively warm waters of the Great Lakes. As the cold air travels across the lakes, warm moist air will begin rise into the lowest section of the atmosphere. This warm moist air will then cool and condense into lake effect clouds. These clouds will then congeal into these narrow bands of heavy snow or also known as "streamers" that could produce intense snowfall rates of 2 to 3 inches per hour. And depending on how cold the air is at the surface, the snowfall rates could be even higher. The graphic below is a brief description by the National Weather Service (NWS) showing how lake-effect snow forms.  Wind direction plays a key role in not only the formation of lake-effect snow, but what areas receive the most snow from a lake-effect event. For example, after a low pressure system moves through the Great Lakes region, flow will be mostly dominate from the Northwest. Wherever that northwest flow is the strongest is where you will find lake-effect streamers with the most intense snowfall rates. Underneath these streamers, it may be snowing heavily or whiteout conditions could be present. And just a few miles down the road, the sun could be shining with no snow accumulation on the ground. This goes to show how narrow a lake-effect streamer may be. Though streamers are very narrow, they could stretch for more than 100 miles from their original starting point. Sometimes, they could stretch as far east as the Appalachian mountains.  Another key element that aid in the formation of lake-effect snow is the amount of instability or energy there is in the atmosphere. For lake-effect clouds to form, there needs to be a temperature difference of at least 13 degrees Celsius or 26 degrees Fahrenheit between the temperature of the lake and the temperature about 5,000 feet up in the atmosphere. This temperature difference provides the necessary ingredients for instability to build over the lakes which will allow the warm moist air to rise vertically. Sometimes, the amount of energy that forms from the instability could be enough to produce another fascinating and somewhat rare weather phenomenon called thundersnow. In other words, lightning that accompanies an intense snow band. And depending on your location, you may even be able to observe the actual lightning bolt. Other key factors for lake-effect snow include wind shear (change in wind speed and direction with height), fetch, the amount of moisture, synoptic forcing, and topography. But one factor that definitely takes a toll on the duration of lake-effect events is the percentage of ice cover over the lakes. As we head further into the winter season, the air will get colder and the lakes will gradually begin to freeze over. The more ice there is covering the lakes, the chances for a lake-effect event become very slim. And the lake doesn't need to be completely frozen to stop the formation of lake-effect precipitation. That is why late fall and early winter is the time of the year where lake-effect events make there appearance the most. One of the most known historical lake-effect events happened near Buffalo, NY just prior to Thanksgiving in 2014. This was a multi-day event that pummeled the Buffalo area with an astonishing 88 inches of lake-effect snow. Provided below are some of the mind-blowing snowfall totals and radar imagery by the NWS office in Buffalo from that multi-day event. - Cowlesville: 88 inches - Orchard Park: 71 inches - Lancaster: 74 inches - Wales Center: 69.3 inches - West Seneca: 52.5 inches - Buffalo Int'l Airport: 16.9 inches - Tonawanda: 7.9 inches To learn more about other interesting and/or high-impact winter weather events occurring around the world, be sure to click here!
© 2018 Meteorologist Joseph Marino 
DISCUSSION: As many people living across southern and western Alaska look to the skies tonight, things are likely pretty typical across most of Alaska. However, in southern Alaska (i.e., not too far from the city of Juneau), there was an interesting and complex situation on the regional radar screens as of earlier Tuesday evening. This interesting site came in the form of a reasonably well-wrapped low-pressure system which was moving to the northwest and was on a collision course with the coastline of western Alaska. More specifically, this low-pressure system was taking aim close to the city of Sitka, Alaska.
What was somewhat peculiar about this low-pressure system is the fact that it tremendously resembled a tropical cyclone even though it is a system which is occurring in mid-November here in 2018. The reason for the mention of this specific tropical cyclone similarity is the fact that this low-pressure system had features which included the following: spiral rain-bands, deeper convection near the center of the low-pressure circulation, the almost perfectly symmetric rotation throughout the periphery of the low-pressure system, and a feature which closely resembles the eye and broken eye-wall of a typical tropical cyclone. What is even more interesting is the fact that such an event is occurring at this unusually far northern latitudinal position and is occurring in colder waters during November which is unfavorable for an event with such uniquely dynamic characteristics to occur in both regards. As noted in the Tweet attached above (courtesy of the National Weather Service office in Juneau, Alaska), this system will have more than likely delivered sustained winds in excess of 50 to 60 knots by earlier on Tuesday evening. Thus, despite not quite being a true tropical cyclone in all facets of the typical tropical cyclone scenario, this is still going to be regarded as an interesting event which more than likely will deliver substantial impacts to the western parts of southern Alaska. This situation just goes to prove that interesting and compelling weather events can occur at any time of the year and without much notice even with the best numerical forecast models at the ready. To learn more about other interesting and/or high-impact winter weather events occurring around the world, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz How To Correctly Prepare Yourself for Winter Weather. (Credit: National Weather Service, FEMA)11/5/2018  DISCUSSION: As we get closer and closer to the Winter season of 2018-2019, it is critical to remember that preparation is everything when it comes to being ready for whatever may come your way. For example, one such way of getting ready for the heart of a cold, snowy Winter season, is to get a safety and emergency preparedness kit for your automotive vehicle which contains all the critical essential components for you and anyone you live with to be ready when the time comes.
First off, when it comes to travelling during the Winter, you should always be sure to have items such as automotive vehicle jumper cables, a spare tire, emergency flares, a full tank of fuel, sand or kitty litter, tow rope, a snow shovel, water and snacks, a flashlight, and a cell phone charger. Thus, it is important to always be ready for any situations during a given winter storm or winter weather event you run across in which you happen to run off the road or get into an automotive accident. Moreover, it is critical to always have enough power in your cell phone so that if you do run into trouble, you will have a means of communicating to friends, family, and/or emergency services. Thus, whenever you start to get ready for Winter, always be sure to have these items on hand well before you must travel out and about around the time at which winter weather is predicted to hit. This information is all courtesy of the National Weather Service and the Federal Emergency Management Agency. To learn more about how you can prepare and be ready in many other aspects for what winter weather can bring, be sure to click here! To learn more about other winter weather topics and/or issues from around the world, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz |
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