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Fall is fast approaching which opens the door for winter forecasts in the US based on various atmospheric and oceanic phenomena. One such parameter is ENSO, (weak El Nino this year?), another major contributor is the atmospheric pattern around Greenland.  This article is not a winter forecast at all, rather a look at the current to near future weather in Greenland. A low-pressure system is currently in far northeaster Canada moving northeast and will be intensifying throughout Wednesday. Moisture is being advected originally from the Gulf of Mexico through portions of eastern Canada up into this low pressure system fueling a heavy precipitation event in southern Greenland. With temperatures cold enough to support snow, or mostly snow across the region (possibly excluding the far southern immediate coast), a pretty impressive snow storm will develop dropping anywhere from half an inch of liquid precipitation further inland to close to 2 inches near the coast, especially on the southeastern side of the country (refer to the image above from Tropical Tidbits). As this low-pressure system drops close to the 970 mb range, strong winds will impact the coastal regions as well.  Above, the storm system deepening to the east of the southern tip of Greenland. Notice the Precipitable Water being drawn north from portions of the US, which originated in the Gulf of Mexico, as well as the Atlantic to create anomalously high moisture streaming into Greenland leading to this hefty snowfall (Image from Pivotal Weather).  GFS interpretation of the snowfall across Greenland, notice heavier amounts closer to the coastal regions, especially on the eastern side where the low pressure is expected to intensify near and track just to the east and northeast (Image from Tropical Tidbits).  The upper level pattern near Greenland is associated with the North Atlantic Oscillation. At this time, a positive NAO has developed, leading to anomalous low-pressure systems in the upper atmosphere around the region, in a direct cause and effect relation to this surface system development as discussed before. Shown above (Image from CPC), the NAO has been neutral to positive throughout the entire summer, but recent ensemble guidance shows a possible dip to neutral to possibly slightly negative values near mid-September. By the fall and early winter, East Coast snow lovers want the NAO to trend, or continue to trend in the negative which blocks up the atmosphere and allows for colder air to spill in from the far north. If the southern jet stream can provide moisture (as it is looking like an El Nino winter, this tends to happen along the southern US), while this negative NAO develops injecting bouts of colder air, a potential big snowstorm can develop.  Above, upper level low pressure near and around Greenland symbolic to the positive NAO being forecast around this time. Whether all or some of these factors pan out to produce an eventful winter will not be known for several months, however, Greenland may become an important factor within the coming weeks/months and may hint at some possible patterns for the upcoming winter season. Until then, GWCC will continue to monitor these ever-changing conditions with future articles. Stay tuned to the latest winter weather right here!
©2018 Meteorologist Joe DeLizio
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 DISCUSSION: The jet stream marks the boundary between cold polar air and warmer air to the south. In addition, it serves as the storm track along which low pressure centers (i.e., mid-latitude cyclones) tend to move. Currently, the jet stream is dipping down across the center of the U.S. allowing especially cold air to filter farther south than it normally would this time of year. When you combine unusually cold temperatures with mid-latitude cyclones, there is the potential to get snow/ice in places that normally don't see such weather in April. In particular, there are three mid-latitude cyclones that are expected to impact the northern half of the U.S. over the next four days, bringing the potential for snow as far south at Springfield, MO and Washington D.C. as indicated in the graphic above. Many local-scale factors influence snow totals. For example, if the ground is or was recently above freezing, that could contribute to melting and a smaller snow total. If more precipitation falls as sleet or freezing rain, that also would reduce the snow totals. Outside of higher elevations out west, there could be just a dusting of snow up to several inches. The key point is that if you live in the northern half of the country, your might want to keep your winter coats and other winter gear out for a bit longer this season.
To learn more about other high impact winter weather events occurring around the world, be sure to click here! © 2018 Meteorologist Dr. Ken Leppert II  DISCUSSION: Now that spring has officially begun, many in the northeast corridor of the United States are recuperating from the major snow storms to have battered the area. These storms are referred to as “nor’easters”. If you live anywhere else in the United States, or anywhere in the world for that matter, you may ask yourself, “what exactly is a nor’easter?” A nor'easter is a strong area of low pressure that often progresses along the Eastern Seaboard of the United States. As the storm system rotates counterclockwise in the storm, the winds tend to blow northeast to southwest over the region covered by the northwest quadrant of the cyclone. They are usually accompanied by heavy rain or snow, and can cause severe coastal flooding, erosion, hurricane-force winds, and/or blizzard conditions. These storms thrive on the convergence of the polar air masses and warmer air over the gulf stream off the East Coast of the United States. Due to the significant difference in temperature of these air masses colliding in the winter months, with the Gulf stream current often pushing near 70 degrees Fahrenheit (21 degrees Celsius), the low pressure that forms tends to be more severe during the predominantly winter months.
So, what has caused all the storms recently in the northeastern United States? It’s fairly uncommon for this area to receive four separate nor’easters of this magnitude in a span of three weeks during March, much alone any winter months. Many local meteorologists in the Boston area such as Danielle Nyles of WBZ-TV as well as Kevin Lemanowicz of Fox-25 have referred to this event as a “four-easter”. This unusual occurrence is caused by the North Atlantic Oscillation, which are fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high in the Atlantic Ocean. Over the past several weeks, there has been a significantly stronger-than-normal oscillation with high pressure stalling over Greenland. When this happens, it is commonly referred to as the “Greenland Block.” With this setup, the jet stream is able to pull warmer air up over Greenland, forcing the cooler air from Canada to push southwards towards the northeastern section of the United States. As the cooler air from Canada is being pushed southwards, this also brings areas of low pressure down towards the same areas. This will create an active storm pattern with the several areas of low pressure. These storms then often tend to regroup over the warm Gulf Stream current off the East Coast of the United States. The blocking high pressure system over Greenland often prevents such winter-time low-pressure systems from moving westward, hence the origin of the name, “nor’easter”. As spring has begun full swing, please keep everyone in the Northeast in your thoughts, as that seems like a pipe dream for them! To learn more about other high impact winter weather events occurring around the world, be sure to click here! © 2018 Weather Forecaster Michael Ames While February was quite mild and wet across much of the eastern U.S. (except south Florida which was warm and dry), March has taken a turn for the colder [thanks to three “nor’easters” (so-called due to their location, strength, and impact)] and associated strong cold fronts that reach well to the south (thanks to northwest winds in the wake of the nor’easters). Don’t look now, but another East Coast storm (and associated Florida cold frontal passage) are underway… To read the full story, click here - http://www.weatherworks.com/lifelong-learning-blog/?p=1466  A Deeper Look Into the Workings of Thundersnow in Nor'easters (credit: Dr. Marshall Shepherd)3/9/2018   DISCUSSION: During a given Winter season, it is quite rare for a given region to experience the apex of all Winter-time atmospheric phenomena which is most commonly referred to as thundersnow. It is a fairly rare Winter-time atmospheric phenomena due to the fact that there are a number of factors which have to come together just right in order for it to occur during a given winter storm. Attached below are exact excerpts from the article written by Dr. Marshall Shepherd from the University of Georgia which gives absolutely perfect insights into the science behind thundersnow.
"The basic ingredients required for cumulonimbus clouds (with lightning and thunder) are not often associated with winter precipitation events. According to a recent paper in the journal Weather Analysis and Forecasting, there are certain necessary ingredients for thundersnow, and they are not very different than what you expect in warmer season thunderstorms: lift, moisture, and instability. The study of thundersnow in the central United States found that lightning (and thus thunder) happens when convective instability (explained later) is found in the comma-head. In a SUNY-Albany Master's thesis by Kyle Meier, it was found that thundersnow is also common in regions of intense snowfall banding. Thundersnow storms are often found with lower convective available potential energy (CAPE), which also means weaker vertical motion in the cloud and more shallow cloud tops. CAPE is basically a measure of how potentially buoyant rising air "volumes" might be. For example, the concept of a hot air balloon is that you try to get the balloon warmer (more buoyant) than the air it is rising into. Larger CAPE values mean there is greater potential for the air to rise (and stronger updrafts). Other conditions associated with thundersnow include surface temperatures at or just below 32 deg F and a sub-freezing air layer from the cloud base to the surface. Typical thunderstorm electrification usually involves collisions between ice crystals and lumps of ice called graupel. These collisions in the presence of supercooled water (liquid phase though temperature may be below freezing) are the basis for what is called noninductive charging. While this may also be possible in thundersnow, there is likely less supercooled water and possibly more graupel. An analysis of dual-polarization radar (a new type of weather radar that improves identification of the types of particles in a cloud) in the Weather Analysis and Forecasting finds "the sudden appearance and expansion of radar gates classified as graupel preceded most of the flashes in these cells. Thus, such a signature in the operational HCA (classification system) should warrant more attention for the possibility of lightning production." Interestingly, some of this graupel (a seedling hailstone) may have fallen out of this Nor'easter storm. Folks, that is rare: thundersnow and hail. Professor Bob Rauber at the University of Illinois emailed me shortly after my original post with a series of papers that explain the instability and cloud ice aspects of thundersnow in greater detail." To learn more about other neat winter weather stories from around the world, be sure to click on the following link: https://www.globalweatherclimatecenter.com/winter! © 2018 Meteorologist Jordan Rabinowitz Understanding the Dynamics of Precipitation in Nor'easters (credit: Meteorologist Jordan Rabinowitz)3/7/2018 
DISCUSSION: Earlier in the day on Wednesday (March 7th, 2018), both the United States (U.S.) and the world watched as the Northeastern U.S. got struck by yet another potent Nor'easter (i.e., a Winter-time coastal extra-tropical low-pressure system). During the course of its lifetime, this particular Nor'easter put on quite the show for many people living across the Tri-state area of New York, New Jersey, and Connecticut. Despite many locations across these respective states and beyond not seeing quite as high as a storm snowfall total as anticipated by NWS forecasts, there was still a lot to be admired and respected from this second March snowstorm in March of 2018.
First off, even though this storm under-performed in terms of many locations receiving substantially less snowfall than was projected, the snowfall which did fall across much of central/eastern Long Island, central/northern New Jersey, and western/central Connecticut was rather convective in nature. More specifically, as the actual coastal low-pressure system deepened rather quickly just offshore from southeastern New Jersey, there were particularly convective banding features which quickly developed just as the storm began to deepen just offshore the New Jersey coastline. As shown above in the Radarscope tweet sent out by Weather Channel Meteorologist Jim Cantore earlier in the day on Wednesday, a good portion of southern and central New Jersey was experiencing rainfall during a good portion of the period between 1:00 PM and 2:00 PM EST. However, in the last 10 to 15 minutes leading up to 2:00 PM EST, a very neat and fascinating atmospheric phenomena unfolded quite rapidly. This atmospheric phenomena in question was intense diabatic cooling. Diabatic cooling is the process wherein when a Nor'easter is deepening and producing pockets of both rain and snow, it is important to note that nearly all precipitation associated with Nor'easters begins as snow. Thus, the difference between precipitation at the surface being observed as rain or snow has to with what happens with said precipitation during the last few thousand feet above the surface. If there happens to be a warmer layer in these critical last few hundred to few thousand feet above the ground (as there was one for a brief time in the radar animation from Mount Holly, New Jersey as shown above), then the precipitation is often either a mix of rain or snow, or just a very cold rain. However, in situations when there is incredibly convective precipitation falling through a near-surface warm layer, it is not uncommon to see a rapid change-over to all snow. This occurs as a result of the heavily falling snow above the near-surface warm layer quickly melting and consequently extracting all of the ambient heat energy. Thus, the temperature subsequently falls rather swiftly and facilitates a complete changeover to all snow as observed at the surface. Thus, diabatic cooling was perfectly displayed in the convective precipitation with this early March Nor'easter here in 2018 along with all of the incredible thundersnow produced by this storm as well. To learn more about other high-impact winter weather events occurring around the world, be sure to click on the following link: https://www.globalweatherclimatecenter.com/winter! © 2018 Meteorologist Jordan Rabinowitz  DISCUSSION: In lieu of the impactful nor’easter that produced rain, snow, wind, coastal flooding, the whole atmospheric sink essentially, let’s take a look at this storm system now and in the near future on a global perspective. Attached below is an animated global surface wind map, (courtesy to weatherTap for providing these mesmerizing world-view products). What is incredible about this product is how expansive it shows the wind field of our nor’easter. This nor’easter easily has the largest wind field of any storm on the planet at this time with winds 30 – 50 knots from east and north of Nova Scotia stretching down across much of the western Atlantic and to around 25 degrees North. Of course, we see tropical storm Dumazile churning just east of Madagascar as well in this imagery. Watch as Dumazile intensifies as the loop progresses through tonight and into the afternoon on Sunday March 4th (see the loop below as well). Shifting to another feature of this world view is the predictive radar. This is exactly what it sounds like, a radar that animates into the future on a global scale. There are a bunch of features that can be examined with this radar. The big Alaskan Low is shown beautifully, with a nice comma head look in the precipitation, (also evident in the surface wind animation above!) Our nor’easter is shown as a large band of precipitation originating just off the North Carolina coast arching just off the New England coast and south of Nova Scotia and stretching back south and east across the central Atlantic. Another amazing simulation of the incredible size of this system. Farther east, the active pattern in Europe continues with rounds of precipitation accompanied with some wind impacting much of western Europe in both animations.
Another interesting feature shown is the strong cyclone across far southeastern Russia with a trailing cold front potentially producing heavy rain and snow across much of Japan over the next 24 hours. Watch both loops and check out the similarities to the cold fronts experienced on the U.S East coast! This is just a minor look at the features weatherTap Global has to offer and how it can be used to study the global weather. Be sure to stay tuned to more global winter analysis here! ©2018 Meteorologist Joe DeLizio Europe Braces for Extreme Cold Snap (credit: Met Office UK, Washington Post, Climate Reanalyzer)2/28/2018  DISCUSSION: Between February 26th and March 4th, Europe will experience an extremely cold snap with temperatures falling way below freezing. This could bring some of the most extreme temperatures since the cold snap back in 2013.
A negative phase of the North Atlantic Oscillation is an atmospheric pattern where the stratosphere above the North Pole warms, resulting in polar vortex over mid-latitude areas. This pattern is known to create cold temperatures and bring along stormy weather for the affected regions. These patterns are also known to bring strong snowstorms to the East Coast of America as well. The cold air that will flow into Europe allows air to evacuate the Arctic, making temperatures there warmer than normal. This pattern creates a high-pressure system, drawing air clockwise and bringing in cold air from Siberia. Average temperatures during this time in Europe average from 3 - 16 degrees Celsius, but temperatures are expected to be 10 degrees Celsius below normal. The highs in London are projected to stay around 0 - 4 degrees Celsius, with wind gusts making it feel a lot colder. While most of Europe is already under a yellow warning for snow, places in southeast England are under an Amber warning. A yellow warning just means to be aware that severe weather is coming and an amber warning means to be prepared for the increased likelihood of extreme weather. Furthermore, with this accumulating snow, transportation is expected to be affected during this cold snap. Europe isn’t the only place experiencing these cold temperatures either. Areas as far south as France are enduring below normal temperatures for this time of year. The increase in internal heating resulted in France’s natural gas levels spiking within the last few days to its highest level since 2008.Temperatures in France haven’t dropped this low since the cold snap back in 2005. On the other hand, places in the Arctic are experiencing record warmth. In Cape Morris Jesup, the northernmost point of mainland Greenland, temperatures have been above freezing between February 16th- February 25th. The warmth in this area over the Arctic have resulted from the same pattern that is bringing the brutally cold air into Europe. (Citied: Met Office UK, Washington Post, Climate Reanalyzer) To learn more about other winter weather stories from around the world, be sure to click here! © 2018 Weather Forecaster Allison Finch Forecast Discussion: Wet Winter Weather for Isles (Credit: National Weather Service Honolulu)2/18/2018  Image Courtesy: NOAA NESDIS DISCUSSION: Climatologically there are seemingly only two seasons in Hawaii, these being summer and winter. While there are over 10 climate zones experienced in Hawaii, it can be apparent that summer is often May through October with Winter from November to April. Much like the Eastern Pacific portion of the United States the winter is often the wet season for Hawaii, diminishing the coveted trade wind weather and bringing a slew of cold fronts and/or troughs of poor weather with increased precipitation, often posing major hazards to the area. President’s Day and its week are expected to see some of this wet and typical weather for mid- winter season. The island chain is under a rather slow trough located at the surface with an upper-level disturbance bringing in round after round of thunderstorms to the islands. These unstable conditions are bringing widespread lightning, thunderstorms, and flash flooding to the island especially in windward location of the islands. With some winds out of the south, the chain has been experiencing unsettled weather associated with this moisture plume bringing increased possibilities for water spouts, thunderstorms, and lightning. The National Weather Service Honolulu (NWS) has issued a flash flood watch for the entire state, as moderate to heavy rain falls. In addition, the NWS has issued a winter weather advisory for the Big Island summits (Mauna Loa and Mauna Kea) as snow is expected to fall with this system. Due to the precarious nature of this forecast, moisture will remain in the area as this unstable weather will be supported by a trough, and a developing upper level low. As the trough evolves into a closed low over the next day or so, heavy precipitation will persist, the atmosphere will become increasingly unstable and the NWS has indicated, “updraft strength becomes sufficiently strong to support the development of small hail and funnel clouds.” Diagram 2, current analysis for the Skew-T diagram has indicated K-index of 33 a moderate potential for convection, total totals at 53 indicating widely scattered severe storms, as verified by radar, however Lifted index only -4 indicating marginal instability. Overall there’s increased potential for convective action and flash flooding but no determination for extreme instability regarding the slow-moving trough. This wet pattern is expected to stick throughout the week, with at least some marginal chance for precipitation each day. For more forecast discussions or information about weather in your locale, visit the Global Weather and Climate Center! © 2018 Meteorologist Jessica Olsen  DISCUSSION: It is important for the National Weather Service to issue weather-related warnings to the public for their safety. A new type of snow warning called a “snow squall warning” can be issued, as of January 3rd, 2018, by the National Weather Service. A snow squall is a sudden, short period of heavy snowfall accompanied by strong winds and occasionally lightning. During this time, snow accumulation may be substantial.
Snowstorms and snow squalls are much different. A snowstorm can be predicted days in advance. They are typically larger in scale and affect more area than snow squalls. Also, the likelihood of an accumulation is always greater with snowstorms than with snow squalls. Although accumulation is less with a snow squall, the sudden reduced visibility from sudden heavy snowfall causes danger to travelers. Snow accumulation is typically around 1 to 2 inches of snow with visibility that can be less than one quarter of a mile and is expected to last less than an hour. According to the National Oceanic and Atmospheric Administration (NOAA), the new warning can be issued in the following NWS offices: Buffalo, NY; Detroit, MI; Cheyenne, WY; Pittsburg, PA; State College, PA; Binghamton, NY; and Burlington, VT. These warnings are first sent from the Advanced Weather Interactive Processing System (AWIPS) to the National Weather Service (NWS) as a code. For example, “SQWBUF” is the Buffalo, NY snow squall warning code. If the weather forecast office in Buffalo, NY was to receive that code, the NWS would then issue a snow squall warning to the public for that area. The NWS has given advice if a snow squall warning is issued in your area: 1. Consider avoiding or delaying travel until the snow squall passes your location. 2. If you must travel, use extra caution and allow for extra time. 3. Rapid changes in visibility and slick road conditions may lead to accidents. It is crucial that the public is notified as soon as possible. According to The Weather Channel, research indicates many highway pileups are attributed to snow squalls each winter season. For example, on March 20, 2017, there was a 30-car pileup on Interstate 81 in Schuylkill County, PA that killed one person. Similarly, there was a 50-car pileup on February 13, 2016, in Lebanon County, PA that killed three people. These are just a couple examples of some of the highway accidents associated with snow squalls. They create low visibility and slippery road conditions that cause tires to lose traction on the road. Most of the time, snow squalls create minor snow accumulations as opposed to greater totals dropped by snowstorms. NOAA states that they can now better predict short-term weather events with the new GOES-16 satellite as well as, recent improvements in Doppler-radar, and more accurate and detailed weather models. Some of the short-term weather events which can now be detected quickly include snow squalls, thunderstorms, and tornadoes. With this new technology, the NWS can alert the public in a timely manner and reduce snow squall related accidents. (Credit: NOAA, The Weather Channel) To learn more about other winter weather stories from around the world, be sure to click here! ©2018 Weather Forecaster Brittany Connelly |
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