January 18, 2020

Newfoundland Just Endured A Historic Blizzard That Buried People In Their Homes

Residents of eastern Newfoundland spent Saturday conducting an archaeological dig in a valiant attempt to remember what life was like before Friday's historic blizzard. The impressive snowstorm dropped more than two feet of snow on parts of the island in Atlantic Canada, an insult made even worse by 75+ MPH sustained winds that drifted the snow so high that many folks had to tunnel out of their homes.

Friday's snowstorm is widely considered to be one of eastern Newfoundland's worst blizzards in living memory by folks who were in the thick of it. St. John's, Newfoundland, the easternmost major city in both Canada and North America, recorded 30" of snow during the storm and reported blizzard conditions for about 17 consecutive hours between 8:30 AM on Friday and 1:30 AM on Saturday.

The airport's weather station saw a minimum air pressure of 970.5 mb on Friday evening as the center of the winter storm passed just offshore. Some communities around St. John's saw even greater snowfall totals, with Mt. Pearl—the name of a city, not a mountain—reporting just over three feet of snow by the end of the storm.

The pure volume of snow, combined with the immense size of the drifts, quickly transformed this storm from a quirky novelty into a serious situation. The most populated area of the province is at a standstill at the moment while crews attempt to clear away the steep drifts of snow.

Tropical Tidbits

This was the perfect setup for an epic blizzard in Newfoundland. A strong jet stream dipped over eastern Canada at just the right angle to allow a sprawling low-pressure system to rapidly strengthen off the island's southern coast. The storm then underwent bombogenesis, or the process of strengthening 24+ mb over the course of 24 hours...hence all the "bomb snowstorm" and "bomb cyclone" headlines you've seen this weekend. The northwestern side of the storm rode directly over the Avalon Peninsula, exposing St. John's and its suburbs to the storm's heaviest snow and strongest winds.

The St. John's area could see another 5-8 inches of snow on Sunday as another winter storm moves across the region. Temperatures could briefly jump above freezing on Monday before dropping back below freezing through next weekend.

[Top Image: NOAA]

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January 11, 2020

An Inch Of Ice From Freezing Rain (!) Is Possible In Parts New York And Quebec This Weekend

A significant ice storm appears likely across the U.S./Canadian border this weekend as a winter storm moves across the region. Conditions appear favorable for a prolonged period of freezing rain near the border from Michigan to Maine, with some areas potentially seeing as much as 1.00" of ice accretion on exposed surfaces. If the highest totals come to fruition, it will cause significant tree damage and widespread, long-lasting power outages.

The threat for wintry precipitation lies on the northern side of the dynamic low-pressure system that's causing all the severe weather in the southern United States right now. It's cold enough for some areas to see all snow—it's pouring snow in most of Iowa!—but warm air in the lower levels of the atmosphere will make a mess of things in many of the areas expecting wintry precipitation.

Significant Icing Possible

Forecasters expect a prolonged freezing rain event to unfold from Michigan to Maine—including our friends in Ontario and Quebec—as the system moves through the area on Saturday and Sunday. The National Weather Service issued ice storm warnings for eastern Michigan and portions of northern New York ahead of the system, while freezing rain advisories are in effect for parts of southern Ontario and Quebec, including the Montreal metro area.

Precipitation will start as rain early on Saturday, slowly transitioning to freezing rain from west to east on Saturday night as warm air takes over aloft and cold air entrenches at the surface. The storm will likely end with snow on Sunday.

Environment Canada warns of the potential for 15-30 mm of ice accretion from freezing rain in and around Montreal, which translates to about 0.60" to 1.20" of ice. That's a major ice storm anywhere, let alone a heavily populated metropolitan area.

The National Weather Service in Burlington, Vermont, calls for similar ice accretion totals in northern parts of New York and Vermont. The official NWS forecast on Friday night called for 1.00" of ice from freezing rain around Ogdensburg and Massena in New York, with around 0.50" of ice in northwestern Vermont.

It only takes about 0.25" of ice to begin doing damage to trees and power lines. Anything greater than that and the damage increases by a great deal. Significant and widespread damage to trees and power lines is likely once ice accretions exceed 0.50". Areas that see a full inch of ice could see power outages that last for a week or longer and roads made impassable by parts of (or entire) downed trees.

It's also going to be windy in many of the areas expecting freezing rain. Wind will only create additional stress on trees and power lines already struggling under the weight of ice. The additional weight of accumulating snow on the back-end of the system would complicate matters even further.

How Freezing Rain Forms

Freezing rain forms when a layer of subfreezing air hugging the surface is capped by a thick layer of warm air above it. Snowflakes melt as they fall into the layer of warm air. The melted snowflake—now a raindrop—falls into the subfreezing air at the surface, supercooling the liquid and allowing it to freeze on contact when it touches an exposed surface.
Tropical Tidbits

Data collected by weather balloons (or, in this case, simulated by weather models) do a fantastic job showing the temperature profile behind the formation of freezing rain. Take a look at the above sounding from Friday night's run of the GFS model near Montreal, Quebec, showing the atmosphere there just after midnight on Sunday.

The red line traces the temperature of air over Montreal from the surface to the top of the atmosphere. This particular model run shows a surface temperature of -9°C (about 16°F), while temperatures are firmly above freezing between 700 mb and 850 mb, or between about 5,000-10,000 feet above ground level. That's a freezing rain profile if there ever was one.

Freezing rain is finicky. It takes slow and steady freezing rain for ice to build into a thick crust. If it rains too heavily, the water won't be able to freeze on contact, simply running off and freezing into puddles on the ground instead. The worst ice storms are the ones that see hours and days of persistent freezing rain and drizzle. This won't be historic, but it has the potential to be memorable for folks in the hardest-hit areas. 1.00" of ice accretion from freezing rain is enough to fell thousands of trees and damage a power grid for a week or longer. That's no small inconvenience.

[Top Image: Tropical Tidbits]

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January 10, 2020

Dangerous Severe Thunderstorms Are Likely Across The South On Friday And Saturday

A dangerous mid-winter severe weather outbreak will roll across several southern states on Friday and Saturday, bringing the potential for all types of severe weather, including flash flooding. The threat will begin late Friday morning in Texas and slowly shift east through Saturday night.

Severe Weather Risk

The Storm Prediction Center issued a moderate risk for severe weather for parts of the Deep South on Friday, which is a risk more common of mid-April than mid-January. A moderate risk is a 4 out of 5 on the ascending scale used to measure the risk for severe weather.

The moderate risk covers a large portion of Texas, Louisiana, Oklahoma, and Arkansas, including Dallas, Shreveport, and quite a few smaller cities in between. Forecasters pulled the trigger on the moderate category due to the risk for significant, widespread wind gusts in excess of 70 MPH. While the red shading will get all the headlines, it's important to remember that damaging winds, tornadoes, large hail, and flash flooding certainly aren't confined to the moderate risk area. The overall threat for severe storms covers a swath from the U.S./Mexico border to St. Louis.

Damaging winds are the main threat with the storms on both Friday and Saturday, but don't discount the potential for some strong tornadoes. Supercells that develop ahead (or within) the lines of thunderstorms will be able to produce tornadoes, especially if they manage to break away from surrounding storms and take full advantage of the environment around them.

Saturday's storms carry much the same risk as Friday's storms—damaging winds in excess of 70 MPH, tornadoes (some potentially strong), large hail, and flooding rains—just farther east toward the northern Gulf Coast.


Severe thunderstorms are possible across Texas and Oklahoma as early as midday Friday, growing in coverage and intensity as the day wears on. The storms will organize and move into the most favorable environment for severe weather by Friday evening. The line (or line segments) will continue tracking east through Louisiana and Arkansas overnight on Friday into Saturday, reaching Mississippi and Alabama by Saturday morning.

It's helpful to think of this as one long severe weather event. Once the storms develop on Friday afternoon, the threat for severe thunderstorms marches east straight through Saturday night. A broken line of strong storms could even make it to the Carolinas by Sunday morning.

Severe weather taking place after dark makes it even more difficult to get the word out and keep up with rapidly changing conditions. It's tough to deal with nighttime severe weather because 1) people are asleep and 2) people like looking outside before they take cover. Make sure you've got emergency alerts activated on your smartphone so you can hear a tornado warning the moment one is issued for your location. If possible, it's a good idea to hold off going to sleep until the threat for severe weather passes.

The Setup

The GFS model's guidance for winds about 5,000 feet above ground level around 12:00 AM on Saturday, January 11. (Tropical Tidbits)

A low-pressure system will develop over Oklahoma on Friday morning, setting the scene for the severe weather we'll see over the next couple of days. The real story is the wind.

Winds will be ripping in the lower levels of the atmosphere ahead of the cold front, where a "low-level jet"—a localized area of strong winds—could produce winds stronger than 100 MPH just a few thousand feed above the surface. It's dangerous to deal with such strong winds so low in the atmosphere because it wouldn't take much of a downdraft for a thunderstorm to push those damaging winds down to the surface (hence the hullabaloo). A strong low-level jet can also increase the risk for supercells and tornadoes.

Flooding Risk

Damaging winds and tornadoes aren't the only threat over the next couple of days. Showers and thunderstorms will bring a risk for flash flooding for a huge swath of the country from Texas to upstate New York. Several inches of rain are possible even in areas that aren't expecting any severe thunderstorms. This kind of heavy, persistent rain will push natural waterways and drainage systems to their limit, especially if the rain falls quickly. The heaviest totals are likely across areas where severe thunderstorms as possible, where the Weather Prediction Center calls for more than 5 inches of rain in some spots.

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January 8, 2020

Twitter's Proposed "No Replies" Feature Could Be A Nightmare During Weather Emergencies

Twitter announced on Tuesday that they would test a new feature to give users another tool to deal with the site's rampant and often-unchecked harassment problem. Twitter users will be able to limit who can reply to their tweets, even allowing users to shut off replies to their tweets altogether. This feature could have major unintended consequences when it comes to countering false or misleading information. This is especially true during weather emergencies like tornado outbreaks or hurricanes, where every second counts and even a short-lived viral weather hoax can do significant damage to the safety and trust of those in harm's way.

Last year, Twitter rolled out a feature that let users hide individual replies to their tweets, which is great if you get one hateful bonehead yelling at you or saying something completely off-the-wall. In practice, though, it's often used to hide dissenting opinions or replies that attempt to debunk hoaxes and conspiracy theories. Today's proposal goes a step further by allowing users to completely prohibit replies to tweets altogether.

As someone who's been on the receiving end of more hate mail and death threats than anyone should ever see, it's a positive step that Twitter is at least attempting to create tools that help people shake off nasty or harmful replies, even if it's far from enough to address the overall problem. But this new feature fundamentally alters how people interact with each other on Twitter. Limiting or prohibiting replies to certain tweets could have serious unintended consequences when it comes to the spread of fake weather news.

Imagine the scenario I posted on Twitter this morning. We're in the middle of an intense springtime tornado outbreak and a line of supercell thunderstorms is marching across the southern Plains. Amid the flurry of reports comes an ominous tweet: "TAKE SHELTER—MASSIVE TORNADO HEADING TOWARD DOWNTOWN DALLAS!" Attached to the tweet is a picture of the EF-5 tornado that devastated Moore, Oklahoma, on May 3, 1999.

Seasoned meteorologists spot it immediately and try to wave people off of the malicious hoax as it rapidly goes viral in the growing panic, but the person who published the hoax shut off all replies. Meteorologists can't directly reach people seeing the tweet as it crosses their feeds. The only thing most people see is the warning, the old picture, and the fact that it's going viral. Meteorologists have to put the warning on their own feeds and hope that, in the fog of harried warnings about real storms, enough people see the corrections to make a difference.

It's not unrealistic. People pass off old pictures or false information all the time in the midst of severe weather events—tornadoes, hurricanes, floods, blizzards, fires, you name it. Some folks do it for the thrill of going viral, while others just get a sick pleasure out of tricking others in a time of crisis.

That very situation has played out before during tornado outbreaks, but other Twitter users were able to blunt the impact by quickly and forcefully pointing out the hoax. Right now, you have a chance to reach people who are seeing the false information by replying to a tweet. "Hey, this is false. This is an old tornado picture." People do click tweets and look through the replies.

This feature will remove the ability to directly reach those who are taken in by the false information. If there are no replies, that false weather report just hangs out there for thousands of people to see with no indication that it's not true. Under the new system, anyone who tries to refute the incorrect information has to implore their followers to help them spread word that it's bunk. It's a mess, and the corrections don't reach the people who are seeing the viral hoax.

Misinformation and outright hoaxes have plagued the weather community since social media came into widespread use. It's easy for anyone to sound authoritative and go viral. However, unlike politics where stories can take days or weeks to play out, severe weather occurs over a matter of minutes. A major tornado can touch down, destroy neighborhoods, and dissipate in just a couple of minutes. The decision to evacuate ahead of a hurricane needs to be made quickly. False information about the weather isn't just a silly internet thing—it can have a serious, real-world effect on people's safety and well-being.

With the ability to turn off replies to tweets, anyone can craft themselves into an authority figure on any subject without consequential pushback. Folks try to do that anyway, of course, but if you post "this blizzard will hit Washington tomorrow," you're going to get 200 people telling you you're wrong, and anyone who looks at your tweet will see all the people who corrected your misinformation. Eliminating replies will remove that pressure to skew toward truth. In practice, the tweet with the most retweets will become the uncritical truth on the subject, because now who will say otherwise?

After I posted that scenario on Twitter, the company's product lead reached out and said that they were taking this risk into consideration. Using the site's other features to respond to or highlight someone else's tweet simply isn't enough. It's important to be able to pipe up and say "no, this is wrong" when someone posts something that could lead people astray. Without some major tweaks or guards against it, this new feature will make it that much harder to get the word out during bad weather.

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