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