DISCUSSION: As we head deeper into Fall and towards the beginning of Winter 2018-2019, there are several curious things which people wonder about day-to-day weather on even the calmest of days. More specifically, om days when there is little to no active weather occurring in a given region, there are still many curious things which will often occur even on the clearest of days. One such example of an unusual phenomena to the minds of most average people is when there is a random, light breeze on a calm, clear day with no clouds or precipitation in sight. However, there happens to be a clear and concise explanation for why such breezes occur on the calmest of days.
First off, it is important to understand that when infrared radiation enters the Earth’s atmosphere and reaches all the way to the surface of the Earth, this process acts to heat the immediate surface and surface layer. Thus, this incoming infrared radiation which reaches the surface of the Earth acts to increase the Earth’s skin temperature and gradually will partially be re-emitted back from the immediate surface and surface-based layer of the Earth in the form of weak low-level thermals. Thermals are effectively small-scale perturbations (i.e., smaller-scale changes) which transfer infrared radiation-based heat energy just above the surface. As a result of this infrared radiation being re-emitted from the surface of the Earth, these low-level thermals act to induce very small-scale pressure changes. These very small-scale pressure changes ultimately lead to light breezes which will occasionally reach the surface of the Earth.
Therefore, the next time that you go outside on a calm Fall or Winter day, you can now understand how and why you will sometimes experience an occasional light breeze even on the calmest of days. Of course, it is worth noting that such light breezes occur even more often on Summer days since there is even more intense infrared radiation reaching the surface of the Earth due to a higher Sun angle during the Summer-time months.
To learn more about other winter weather topics from around the world, be sure to click here!
© 2018 Meteorologist Jordan Rabinowitz
Discussion: It’s that time of year again. The months of September through April are very familiar with Nor’easter storms. Nor’easters can occur throughout any point of the year, but they are oftentimes shown in the media dumping feet of snow in the wintertime. For example, a series of Nor’easterspummeled the Northeast towards the end of the last winter. Other historic Nor’easter events include the Blizzard of 1888, the “Ash Wednesday” storm of March 1962, the New England Blizzard of February 1978, the March 1993 “Superstorm”, and the Boston snowstorms of January and February 2015.
Image: Visible satellite image of the Nor’easter in March 2014. Credit: NWS
You may be wondering, “just what is a Nor’easter?” It is simply a mid-latitude cyclone, or a storm rotating counter-clockwise in the mid-latitudes along the U.S. East Coast. These storms usually develop between Georgia and New Jersey within 100 miles east or west of the East Coast. In a Nor’easter, the winds typically come from the northeast and typically become most intense near New England and the Maritime Provinces of Canada.
The National Weather Service explained that Nor’easters are most common in the winter because the polar jet stream transports cold Arctic air southward across the plains of Canada and the U.S. before heading eastward toward the Atlantic Ocean where warm air from the Gulf of Mexico and the Atlantic tries to move northward. These storms are fueled by the difference in temperature between warm air over the ocean and colder Arctic air over the land. When the warm waters of Gulf Stream keep coastal waters relatively mild during the winter, that helps heat up the cold winter air over the warmer ocean water.
Image: Sand covering cars in Winthrop, Massachusetts on Saturday, October 27, 2018. Credit: The Weather Channel
Image: Coastal flooding in New Jersey on Saturday, October 27, 2018. Credit nj.com
The winds associated with Nor’easters can be quite powerful, oftentimes reaching gale force and causing extreme damage. The Nor’easter that recently passed through New Jerseyon October 27th, brought 60 mph winds and heavy rain to the area leaving more than 22,000 homes without power. The same storm eventually made its way up to Massachusetts and covered cars in coastal Massachusetts with a blanket of sand. Depending on the time of year, Nor’easters bring heavy rain or snow. Other impacts include heavy surf and high tide yielding rough seas and coastal flooding, downed power lines and trees, and damage to infrastructure.
As we head into November and later the winter months, keep your eye on the U.S. East Coast looking for Nor’easter conditions. If you live along the east coast, especially the I-95 Corridor between Washington D.C. and Boston, always be prepared with a kit of extra materials in case you lose power or are stuck in your home for multiple days as a result of the storm. Some essential items to always have at a stone’s throw include blankets, flash lights, non-perishable food, water, medications (if necessary), and extra clothes.
For more winter weather information, click here.
© 2018 Meteorologist Amber Liggett
Long Range Model Comparison (Photo Credit: Tropical Tidbits, S-J Lin, NOAA Geophysical Fluid Dynamics Laboratory)
As fall has begun and the leaves begin to change, so does the weather pattern on a large scale. This is a very volatile time for weather models. This article will look at the upper air pattern the ECMWF, GFS, and FV3-GFS (updated version) all develop along with the similarities and differences.
It is known from verification scores that the ECMWF more often than not scores higher than the GFS (a big part of this resides in the superior data assimilation, but this is a topic for another article). This was made clear as the ECMWF predicted the track of hurricane Florence days in advance while the GFS stuck with the idea that Florence would progress farther north and stall along the coast. However, the FV3-GFS had Florence near the southern North Carolina coast well before the GFS caved to this narrative. Is this sign of a significant improvement?
Let’s compare the 500 mb height anomaly maps for North America via the 18Z GFS, FV3-GFS, and the 12Z ECMWF all valid the morning of Saturday October 6th. These model runs at this point initiated early to midday September 26th. Just glancing over the three maps below, there is one clear outlier within the three models, the GFS. Right away the overall pattern from the FV3-GFS and the ECMWF is rather similar, ridge over portions of the central US, western Canada, and into Alaska. A trough is shown in portions of southern Canada stretching into the northern US, as well as a possible tropical system to the southwest of Baja California. The locations of the ridge in the west are different, as well as the depth of the trough with the FV3-GFS showing a deeper more amplified solution. These differences are in relation to the pattern in the Pacific stretching into coastal portions of the West coast. Both models want to advertise an upper level low pressure system (possibly more than one of the FV3) somewhere in the CA/NV region.
The GFS on the other hand shows a completely different pattern with a ridge in the east, and troughiness over the Northern Rockies stretching into Canada, along with a different Pacific pattern.
In retrospect, this is clearly a very complex pattern developing and these are only one run of each model (10 days in the future mind you) so although there are similarities in the two models, all three of these solutions are likely wrong on certain levels.
As winter approaches, it certainly will be interesting to see how the FV3-GFS handles the state of the atmosphere along with the tracks of these winter storms compared to the ECMWF. Something to keep an eye on and possibly become excited for depending on the verification of this model.
Be sure to stay tuned to GWCC for the latest on weather, climate, and winter weather here!
©2018 Meteorologist Joe DeLizio
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
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
If Three Florida Cold Fronts Are A Charm, Then Four Must Be Delightful! (H. Michael Mogil, CCM, CBM, NWA-DS*)
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
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)
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