Sunday, January 16, 2022

Massive South Pacific volcanic eruption sends shockwaves around the globe that were measured in Memphis

Many of you may have seen the news that an undersea volcano very near the island kingdom of Tonga in the South Pacific erupted with violent force early on Friday morning (January 15) Memphis time. The force of the explosion sent ash some 100,000 feet into the air and generated a shockwave that traveled around the world, in both directions (eastbound and westbound), from the epicenter. Satellite views of the colossal eruption are mesmerizing:

In the top two loops, you can see the "waves" emanating outward from the blast. That is the "shockwaves" that circumnavigated the globe. 

Later in the day I started seeing some tweets about changes in barometric pressure in the United States that could be traced directly to those waves propagating around the world through the upper atmosphere. 

Using timestamps from a few of those other pieces of information, I then turned to the data from my Davis Vantage Pro2 weather station, which archives all weather elements every five minutes around-the-clock. Below is that data plotted on a line graph. You can see that graph below.

The timing of the first (eastbound) wave that traveled across the Pacific Ocean and then the United States would have likely been unnoticed had I not known what time to look. But there it is, between 7:40-8:00am Friday (first red box below), represented by a slight rise in pressure, then a return to the slow fall that was in progress ahead of the winter storm that arrived Friday night.

The second wave, coming from the east, and which had traveled almost three-fourths of the way around the globe, was much more pronounced about 16 hours later. Notice the second red box below. The pressure was naturally falling towards a low around 5am as surface low pressure was passing by to our south during the winter storm. However, there was a large rise in pressure that started just after midnight and lasted about 20 minutes, followed by a major drop of nearly 0.10" of mercury in 10 minutes between 12:20-12:30am. Pressure values then returned to "normal" about 30 minutes later. So the wave that passed overhead unnoticed to all of us I am sure, lasted about an hour and included a sudden rise and then precipitous drop in pressure.


A trace of the raw barometric pressure from MWN's weather station in Bartlett recorded two pressure changes that were the result of the shockwaves emitted by the explosion of Volcano Hunga-Tonga, some 6800 miles away. The first, around 8am Friday, was relatively minor. The second, some 16 hours later or just after midnight Saturday morning, was much more noticeable to the instrumentation, if not the general public. 

Of course our prayers are with the 100,000 inhabitants of the island of Tonga in the south Pacific northeast of New Zealand, who are cut off from the world and likely dealing with significant issues from one of the largest volcanic eruptions in the modern satellite era, which allowed the rest of the world to see it in stunning detail.

Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Wrapping up the January 16, 2022 snow event

Well, that was fun! 

That is one way to describe about 3 days on non-stop hand-wringing over one of the most challenging winter weather forecasts this meteorologist has encountered in 25 years of forecasting the Memphis area. Friday's blog described the scenario - one in which a rare atmospheric setup resulted in an upper level low taking a giant hook over the southern Plains towards the area and merging with surface low pressure over the Deep South. Even our most reliable medium-range global models and short-term high-resolution models struggled with consistency and output, with wild swings in potential snow amounts for the area. Add in the potential for "banding" of snow in small areas due to the power of the upper low, and you end up with a very challenging event.

In the end, on Friday I decided on rain changing to snow near or after midnight, potential heavy in the early morning hours, tapering in the hours after sunrise, and "generally 1-4 inches with the greatest probability of the higher amounts east of Memphis." I also said in the blog "localized bands could produce up to 4-6" of snow." And with a little bit of luck, that verified pretty well if I do say so myself. 

How it started: How it ended:
 
A preliminary listing of snowfall totals from across the Mid-South can be found here.

Overall, 1-2" is what the immediate metro received with lower amounts closer to the river and higher amounts in eastern rural areas. Going further east, areas near the TN/MS state line east of the metro saw isolated amounts of up to 5-9"! The amounts in the city were slightly reduced by the "wetness" of the snow that fell. Typically, snow in the Mid-South has about an 8:1 to 10:1 snow ratio, meaning that for each 0.10" of liquid water that falls, about 3/4"-1" of snow can be expected. Because temperatures were just above freezing, relative humidity was above 90% and the amount of moisture above us was high, the snow ratio for this system ended up being closer to 5:1. That reduces potential snow totals by up to one-half of what would fall with snow that isn't so wet. We knew it would be a wet snow, but not quite THAT wet! 

In addition we also saw that where snow came down hard (like in the video above where snow-globs were more than an inch in diameter as they fell), even with temperatures above freezing, the roads can coat pretty quickly. The fact that temperatures didn't get below freezing by much, or for long, meant that they also melted fairly quickly once the sun rose and snow ended.

There were scattered power outages in the Memphis area and, tragically, one woman lost her life while driving a vehicle when a snow and ice laden tree fell over and landed on her car in southeast Memphis. But overall, it ended up being a manageable event for most.

Hopefully you were pleased with what you ended up getting today! Given the MLK Day holiday tomorrow, I expect no issues at all when work and school start back on Tuesday. If you are out early tomorrow though, you will want to keep an eye out for a little black ice in spots where melting occurred and left water on the roads tonight. Hopefully we don't have any more of those types of events again for a long while!actio

Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder