February 28, 2021

A Flash Freeze Will Chill New England on Monday Night And Tuesday

A brief but deep freeze will descend over New England on Monday night and bring the region a downright impressive temperature drop for this late in the season. Temperatures will swing more than 40°F between Monday afternoon's high and Monday night's low across parts of interior New England, with communities near the international border waking up to subzero lows on Tuesday morning.

A low-pressure system moving toward the Great Lakes today—part of the same pattern responsible for all the rain and thunderstorms down south this weekend—will strengthen as it heads into Ontario and Quebec on Sunday night and Monday. Winds wrapping around the low will pull bitterly cold Arctic air over New England as the cold front passes through on Monday evening. Temperatures will quickly fall behind the cold front, plunging into the teens and single digits across interior New England.

The greatest threat from this cold weather is a flash freeze, which occurs when standing water quickly freezes as temperatures drop. It's already raining, or will rain soon, across many of the areas expecting subfreezing temperatures on Monday night and Tuesday. The rapid temperature drop will set in before water on roadways and sidewalks has a chance to evaporate in the wind. 

The Weather Prediction Center's new-ish Winter Storm Severity Index highlights that parts of the region are at risk for minor to moderate impacts from a flash freeze. Travel on Monday night and Tuesday morning will be very dangerous in these areas due to the widespread potential for black ice. There are probably going to be a few accidents across the region as a result of the slick roads.

The sudden freeze on Monday night is the most pressing concern in the region from this week's weather. Tuesday should be the coldest day of the week. Temperatures will rebound a bit on Wednesday before falling back into "chilly for this time of year" territory through next weekend. 

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February 14, 2021

Snow, Ice, And Bitter Cold: This Is A Storm The South Will Talk About For Decades

The winter storm moving over the southern United States has all the hallmarks of one of those storms that people talk about for decades. The system will bring significant amounts of snow and ice to areas that don't typically see this kind of wintry weather, and the cold air that follows the storm is on a level the region hasn't seen in more than 30 years.

Meteorologists spent Sunday ogling at the National Weather Service's map of watches, advisories, and warnings across the country:
Source: NWS

That huge swath of pink is a winter storm warning. It covers the entire states of Texas, Oklahoma, and Arkansas, along with most of Louisiana and Mississippi, and continues on into the Northeast. The criteria for a winter storm warning changes from one office to the next based on what a region is used to during a typical winter. Any amount of snow and ice warrants a winter storm warning in parts of Texas, while it takes many inches of snow to trigger the same alert up north. 

It takes lots of things going juuust right for such an intense winter weather event to stretch so far south. The cold air is rooted in the infamous polar vortex. I explained the process more in-depth last week, but a disruption in the polar vortex circulation over the Arctic allowed a piece of the vortex to break off and sit over the Upper Midwest. This disruption allowed cold air to flow straight out of the Arctic and park itself over the central United States for a couple of weeks.

Meanwhile, an upper-level trough moving out of the Rockies led to the development of a low-pressure system over the southern Plains. Conditions are deteriorating across Texas tonight as the low organizes and snow, sleet, and freezing rain fill in. The low will strengthen and move northeast over the next 48 hours, bringing plenty of wintry precipitation from the Gulf Coast to interior New England.

Here's the National Weather Service's snowfall forecast through Wednesday evening. Widespread totals of 6-12" are possible from northern Texas to northern Maine and just about everywhere in between. Forecasters expect the greatest totals in central Oklahoma and central Arkansas, where some communities could wind up with more than a foot of snow by the end of the storm.

Freezing rain will fall closer to the track of the low. A significant ice storm is possible in Louisiana, Mississippi, Tennessee, and along the Appalachians. Down south, this could be the worst ice storm in memory for many folks.
Source: NWS

Everywhere shaded red on the map above could see more than one-quarter of an inch of ice accretion. Some areas could see one-half to three-quarters of an inch of ice, which will cause significant damage.

One thing to keep in mind is that there really isn't much infrastructure in this part of the country to deal with significant amounts of snow and ice. This isn't a situation like North Carolina falling apart when it snows. We see snow and ice frequently enough that it's a shame we can't handle it better than we do.

This is all the way down south. They don't have many snow plows or salt/sand/brine trucks to go around. Most people don't have snow shovels at home or ice scrapers in their cars. You're lucky if you just happen to have sand or rock salt on hand. The region doesn't see winter weather enough to justify spending the money to have an infrastructure in place to deal with it. 

As if the snow and the ice isn't bad enough, tonight's cold is only going to get colder. This winter storm will drag the Midwest's frigid air all the way to the Gulf of Mexico, allowing temperatures to plummet on Monday and Tuesday.

Here are the National Weather Service's high and low temperature forecasts for Monday, Tuesday, and Wednesday:

Bitterly cold air will surge as far as northern Mexico, with low temperatures in the single digits approaching the suburbs of San Antonio. It hasn't been this cold across these regions since December 23, 1989, when it hit -2°F in Fort Worth, 0°F in Waco, 8°F in San Antonio, and a comfy 14°F in Houston. 

Between the snow, the freezing rain, and the surge in demand due to the frigid temperatures, the region will probably experience a tremendous number of power outages this week. Some communities will probably go without power for a week or longer in extreme cases. Trees in places like Louisiana and Mississippi aren't accustomed to the weight of ice on their branches and limbs. It won't take much ice—maybe not even one-quarter of an inch—to bring down limbs and cause trees to snap in half. 
I took this photo just a few minutes after a tree snapped and knocked out the power for 28 hours.

Don't take the threat for prolonged power outages lightly. If you follow me on Twitter, you probably saw that we were without power for 28 hours in my town near Greensboro, North Carolina, after about a third of an inch of ice overnight Friday into Saturday. I try to stay as prepared as I preach when it comes to having the supplies needed to get through an extended outage and it was still tough to get enough battery power and warmth to make it through more than 24 hours in the dark.

It's probably a little too late to get ready now, but if you're in a position where you still have time to prepare, make sure you've got enough batteries, flashlights, water, and non-perishable, ready-to-eat food to get through several days without power. Bottled water (or containers filled with water) are a mainstay on preparedness lists because municipal water treatment plants can lose power as well, potentially hampering their ability to treat or pump water out to you. (It's no joke. My town is under a boil water advisory for two days!)

Oh, and one more thing—if you live in an area expecting ice, stay away from parts of the house where trees and limbs could fall into the roof or walls. It's something people don't really think about until it's too late. Trees are heavy and houses are comparatively weak. Lots of injuries and deaths during ice storms are caused by trees falling into homes.

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February 11, 2021

We're Coming Up On This Winter's Roughest Stretch Of Cold And Snow

The next five days will see the roughest stretch of winter weather the United States has seen in quite a few years. Bitter cold will grip the center of the country while snow and ice fall on the Pacific Northwest, the southern Plains, and the Mid-Atlantic. The southern Plains could see some hefty snowfall next week if the forecasts pan out.

First thing's first, though, since I've seen (and experienced) some confusion about this. Winter storms aren't named in the United States. There's no such thing as Winter Storm Quavo/Boppo/Filbert or whatever you've hear on television or social media. The Weather Channel unilaterally names winter storms for the purposes of its coverage. The system is deeply flawed for many reasons, not the least of which is the fact that it doesn't work when hardly anyone else recognizes the names. Since the names are arbitrary, the DAMWeather Winter Storm Naming And Hot Wing Quality Assurance Committee voted 1-0 to name all of this year's winter storms Skittlebip.

There are plenty of Winters Storm Skittlebip rolling across the country this week. So many areas are at risk of disruptive snow and ice (and bitter cold) that it's best to break the threat down into three sectors: Pacific Northwest, the southern Plains, and the Mid-Atlantic. 

Since my computer has a case of the Mondays on this rainy Thursday afternoon, I'm not able to make a map of the National Weather Service's snowfall forecasts today. The snowfall graphic I usually compile and upload (like this) combines all 100+ snow forecasts issued by individual NWS forecast offices.

Given the issues I've had today, above is a hastily thrown together and ridiculously busy map highlighting the threats over the next couple of days.

This map combines the Weather Prediction Center's 50th percentile forecasts for snow and ice through Sunday evening. Some areas will see higher or lower snow and freezing rain totals than what's shown above, but this gives you a good rough idea of who could see significant snows or ice accretion from freezing rain over the next three days.

Pacific Northwest

Source: NWS Seattle

There's a pretty good chance of snow and ice along the I-5 corridor in Washington and Oregon through Saturday. If everything stays on track according to the forecast, the region is looking at a disruptive snowstorm over the next couple of days.

Seattle averages about 5 inches of snow in a normal winter, while Portland typically sees about 7 inches of snow each year. But those snowstorms aren't a sure thing each year—Seattle received hardly any snow last season, but saw 20 inches of snow the previous winter.

Through this weekend, Seattle could wind up with up to half a foot of snow by the time the storm is over, with higher amounts at higher elevations. Covered roads, cancelled flights, and delayed trains will make it difficult to get around the region for a couple of days. 

Farther south along the interstate, southwestern Washington and northwestern Oregon will see a mixture of both snow and freezing rain. It's going to be a mess. Here's NWS Portland's helpful graphics highlighting the threat for wintry precipitation over the next couple of days.


Source: NWS Portland

And the threat for ice from freezing rain:

Source: NWS Portland

The greatest ice accretion is possible in the mountains between Tillamook and Portland, where one-quarter of an inch of ice or more could bring down tree limbs and power lines. Freezing rain is possible in the Portland metro area as well, which is expected to see a couple of inches of snow right now. Any ice mixed in with snow makes it even more difficult to deal with.

Freezing rain is an ugly threat. It only takes a tiny amount of freezing rain to leave a glaze of ice on exposed surfaces, making it nearly impossible to drive safely—or even walk down the driveway. The threat of heavy snow and freezing rain in such heavily forested areas heightens the concern. If you live in an area expecting freezing rain, make sure you stay away from rooms in your house where large trees or tree limbs could fall through the roof or walls if they snap under the weight of the snow or ice.

Extreme Cold & Southern Plains Snow

Last week's cold didn't just stick around—it's getting worse. The heart of the much-maligned polar vortex will dip over the Upper Midwest early next week, sending subfreezing temperatures dipping as far south as the Gulf of Mexico. Tuesday looks like it's going to be the coldest day for the most people.

Low temperatures on Tuesday morning will dip below zero in northern Texas, with single digits likely in the Dallas-Fort Worth area. Lows in the teens are possible as far south as Houston and San Antonio. Temperatures this cold diving this deep into the southern Plains will easily break daily record lows. Some areas could come within a few degrees of their all-time record low temperatures.

The all-time lowest temperature on record in Dallas is -1°F at KDFW in December 1989 and 0°F at KDAL in January 1940. The all-time record low in Houston was 5°F at KHOU and 7°F at KIAH, both also set during those two cold snaps in 1940 and 1989. While it seems unlikely these two cities will see all-time lows, one of their top-ten coldest mornings on record is certainly possible.

It's going to be even colder up north, with subzero temperatures firmly gripping Oklahoma and temperatures in the double-digits below zero the norm from Kansas northward. Folks on the northern Plains and Upper Midwest just can't catch a break from this stretch of cold weather. Minneapolis has recorded highs in the single digits and lows below zero every day since last Saturday. It'll get even worse, with forecasts showing the city dipping below zero this evening and likely not seeing readings above zero again until early next week. 

Wind chill values will come in even colder than the actual air temperature. The wind chill is what it feels like to exposed skin when you factor in the cold air and gusty winds. Higher winds efficiently presses cold air right up against exposed skin, which allows frostbite and hypothermia to set in faster when it's windy than when it's calm. It doesn't take very long for the cold air to take its toll when wind chills fall below zero.

If everything goes according to forecast, a developing winter storm will meet that cold air over the southern Plains and bring the region a hefty dose of snow and ice. It's still too early to talk about specifics, but the potential is there for a high-end and disruptive amount of snow and ice from freezing rain beginning on Sunday and lasting through Monday. Winter storm watches are already in effect in central Oklahoma and northern Texas to make people well aware of the event. 


Source: NWS EDD

The ongoing slog of rain moving across the Mid-Atlantic will pose problems in the overnight hours on Friday morning and Saturday morning as temperatures close in on the freezing mark. Lots of areas will hover right around 32°F, leaving some areas with ice-glazed roads and other areas just wet. This kind of borderline setup can lead to serious traffic accidents.

Greater ice accumulations are possible from the Piedmont Triad to the southern D.C. suburbs during a steady period of freezing rain on Saturday. Winter storm watches are in effect for parts of northern Virginia, with more alerts possible farther southwest as we get closer to the event. Some areas could see one-quarter of an inch of ice or more, which makes tree damage and power outages possible.

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February 7, 2021

This Weekend's Brutal Cold Snap Isn't Going Away Anytime Soon

Just stay home. It's a mantra we've lived by for almost a year now (oh good grief), but it'll take courage to even go check the mail for the next week. The coldest air of the season—the coldest air in the last several seasons—will make itself right at home over the central United States this week, sending low temperatures into the double digits below zero. Wind chills will dip even lower, posing a threat for serious injury if you're outdoors with exposed skin for any length of time.

After a few frigid days, lows sank like a rock on Sunday morning. Folks from eastern North Dakota to northern Wisconsin woke up to temperatures below -20°F, with the zero-degree line dipping into central Illinois and single digits approaching southern Missouri. That's pretty darn cold even for regions used to cold winters. Fargo's average low for February 7th is 2°F. This morning's low of -21°F is a full 23°F below normal there. 

Things are even colder across the border in Canada. Sunday morning's temperature analysis revealed lows below -40°F in south-central Canada. Saskatoon managed to reach -40°, which is the same misery in both °F and °C.

It's going to remain frigid across the north-central United States through next week. The animation above shows the National Weather Service's forecast low temperatures from Monday morning (2/8) through Saturday morning (2/13). When you factor in the winds, conditions in the coldest areas will allow frostbite to develop on exposed skin in as little as 15-30 minutes. The wind chill hit -34°F in Minneapolis around 2:00 AM on Sunday.

If current trends hold, towns on the Northern Plains and the Upper Midwest will struggle to climb much above 0°F the entire week. The deepest reserve of Arctic air should remain confined to the central United States. The Rockies will do a good job holding off the cold air for a while, but it's possible that even Seattle could see lows in the low 20s by the end of the week.

It's worth pointing out that:

1) the bitter cold could last beyond next weekend and into the following week, and 

2) there's some uncertainty right now about just how far south and east the cold air will slide this week. Don't be too surprised if forecasts shift over the next few days and that Arctic chill seeps farther than predicted right now.

P***r V****x

Why is it so cold? This is a part of the polar vortex. Yes, that polar vortex.

Any talk of the polar vortex sounds ominous because it's usually devoid of any meaningful context.

I intended to use this graphic back on The Vane a few centuries ago but never had the chance, so I recycled it for this Very Instructive And Useful Purpose.

The term "polar vortex" itself, though it predates us all, seems tailored to our modern attention spans. It's fodder for overly dramatic nightly news graphics and the perfect hook to tap into some of that sweet, sweet algorithm juice and help posts get around on social media. It's tough out there right now. I've been up against a traffic quota before. I don't really blame them. (Though it's annoying, and I totally blame them.)

But the polar vortex isn't scary. The skies don't fill with the hum of chanting aliens. The stratosphere doesn't crash down on Dennis Quaid while he hides in a cargo ship (or a hospital? a mall? I can't remember, I haven't watched that movie in forever). 

The polar vortex is a large upper-level circulation that sits over the Arctic. This circulation sort of acts like a moat that keeps winter's coldest air confined to the polar regions. As long as that upper-level circulation remains relatively smooth, conditions will remain stable and the coldest of the cold will stay far to the north.

Source: TropicalTidbits.com

It doesn't take much for a low-pressure system or a ridge of high pressure to destabilize that circulation. This instability results in troughs that swoop over lower latitudes and bring fleeting bursts of cold weather. Some of these troughs can break off and become cutoff lows that linger for days at a time. Frigid Arctic air follows these troughs and cutoff lows to the lower latitudes, which is what they're talking about when you hear "the polar vortex is coming" ahead of a cold spell.

Sometimes, like this week, the entire circulation is displaced by an upper-level ridge over the Arctic, which is what you can see in the model image above. This graphic depicts the height of the 500 millibar layer of the atmosphere on Tuesday.

The dark red over northern Canada shows areas where unusually strong upper-level ridging will bring abnormally warm weather to the Arctic. That ridge displaced the polar vortex circulation and sent it diving south toward us.

Source: TropicalTidbits.com

It's even easier to visualize this displacement when you look at surface temperature anomalies. The model graphic shows temperatures surging above normal in the Arctic while frigid air floods south toward lower latitudes over the United States and Russia. 

As long as that anomalous ridge lingers over the Arctic, the cold air will have no choice but to relocate itself, and the United States is in prime location to feel the chill. Bundle up.

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