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