5/19/2023 0 Comments Aeroweather downThe other cool thing (pun totally intended) about the inversion is that it made the thunder really – REALLY! – loud. South Mississippi had all of those things So the mid-levels have to be pretty moist. If too much dry air gets into the mid-levels the storm will start to produce hailstones that are too big to melt before they hit the ground. Lucky number seventhly! The mid-levels of the atmosphere have to be very moist. Without this, there can’t be the build-up of an electrical charge, and there won’t be any lightning. But sixthly!There has to be enough wind shear within the atmosphere to organize the storm and differentiate the rain droplets. Honestly, I don’t even know if ‘sixthly’ is a word. And that difference between the inversion and, say, 500mb, needs to be equal to the difference you would see between 850mb and 500mb on a day with the threat for regular storms. That is to say, the inversion has to have a warm-enough layer of air, underneath cold-enough air above it. Fifthly! There has to be instability above the inversion. And if the ground temperature is 33-degrees, you can’t move up very high before you get to a point where you are below freezing. That is about 5-degrees Celsius per kilometer.Įither way, your shallow cold-air-layer can’t be very deep, because you start to naturally cool down as you gain elevation. When the air is saturated, it is known as the moist adiabatic lapse rate. The atmosphere naturally cools at about 9.8-degrees Celsius per kilometer if the air is not saturated, it is known as the dry adiabatic lapse rate. A lapse rate is the rate at which the atmosphere cools as you move up. And also close enough to the ground so that as you move up from the surface you reach the inversion before the temperature falls below freezing.Īlong the same lines, the shallow layer of cold air can’t be more than half a kilometer deep due to what is known as the lapse rate. One that is warm enough to melt any frozen precipitation that forms aloft. Since the surface temperature is near freezing, this also has to be a deep inversion above a shallow layer of cold air. There has to be an inversion that is particularly stout – greater than 8 degrees Celsius. As the rain began to fall, it evaporatively cooled the air temperature to at or below freezing and rain turned to freezing rain, and water started to stick as ice. Places were at 33 and 34 degrees… but drier with lower humidity. This is something we saw earlier in the day along the I-20 corridor. The surface humidity has to be above 90-percent, or else evaporative cooling is likely going to cool the temperature down as the rain falls. So the temperature needs to be above 32, but below 36. It takes cold air at the surface, but cold air that is not below freezing, because then it would be “Freezing rain” and not just rain. But everyone in South Mississippi probably saw something he will never experience.īecause to get a thunderstorm with just rain – and nothing frozen – at temperatures that cold takes a very unique – and very particular – set of events in order to occur. Jim Cantore can get excited about the rarity of thundersnow. Sure does! And I recently broke down Thundersleet, too! But that is frozen precipitation. ![]() What’s so special, Nick? It thundersnows! I was about two miles down the road and it was all rain. That may say “light snow” at KPIB but I can assure you that no snow was falling.
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