January 17, 2019

Thunderstorms Roll Across Central California as Potent System Drenches West Coast

A strong low-pressure system rolling through the northeastern Pacific Ocean is responsible for the latest wave of precipitation washing over the West Coast. The storm system is so potent that thunder (gasp!) was reported across central California on Wednesday night as clusters of storms moved ashore between San Francisco and San Luis Obispo. The heavy rain will continue through Thursday before a brief break ahead of the next storm system this weekend.

PowerOutage.US tracked more than 100,000 power outages in California late Wednesday night, mostly situated in the central part of the state where strong winds accompanied heavy rain and thunderstorms. The radar was pretty interesting to watch during the height of the storms. A squall line that developed in the Central Valley around 11:00 PM PDT—pictured at the top of this post—would be impressive anywhere else in the country, let alone in California. There were still about 60,000 power outages across California by noon on Thursday.

Much of the West Coast will continue to see heavy rain on and off for the next week. The heaviest of the rain set to fall over the next week will cover most coastal areas from British Columbia through northern California. The higher terrain of southwestern Oregon could see up to seven inches of rain over the next week. The I-5 corridor between Portland and Seattle should see lower rainfall totals, but they're still on track for a couple of inches of rain by the end of the next procession of storms.

It's not just rain the west is dealing with. Higher elevations are seeing snow from this storm—and lots of it. Blizzard warnings are in effect for the Sierras in California as ripping winds blow around the many feet of snow that will fall through Thursday night. Local NWS offices warn that the ridgetops could see wind gusts in excess of 100 MPH with five to six feet of snow possible in some spots. Heavy snow will continue through the Rockies as the latest storm—as well as the next storms behind it—make the trek across the country. (PS: Yes, that's a lot of snow back east. Yes, I will cover that in another post.)

Source: U.S. Drought Monitor

The drought situation across the West Coast—and most of the rest of the country, as well—has actually improved slightly over the past couple of months. Above is an animation showing the difference in drought conditions between the beginning of last November and today's update for January 15. The drought has worsened a bit in central and northern California where they haven't gotten as much precipitation as they historically do by this point in the rainy season. Elsewhere, though, it's improved a bit. It hasn't improved all that much, but any improvement is a step in the right direction.

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January 10, 2019

Here's What We Do (And Don't) Know About This Weekend's Snowstorm

A winter storm will move across the Midwest and Mid-Atlantic this weekend, bringing a blanket of snow to the center of the country and a mix of rain, snow, and ice to the Mid-Atlantic. A significant chunk of Missouri stands to see more than half a foot of snow from this storm. Exact totals—and even what kind of precipitation will fall—is still uncertain farther to the east.

What We Know

A low-pressure system will develop in the southern Plains on Friday.

This storm system will likely track farther north than the one we saw a month ago that produced epic snowfall totals in North Carolina and Virginia. My little town north of Greensboro, N.C., saw an entire season's worth of snow in one day back on December 9. What does that mean in practical terms? A track farther to the north will also force the warm air farther to the north. This storm also isn't as juicy or intense as the storm we saw last month, either. That will help to cut down on snowfall amounts in many places.

The best chance for snow exists in the Midwest.

If you're looking for a good snowstorm, your best bet is probably to stake out in central or eastern Missouri on Friday and Saturday. The latest forecast from the Weather Prediction Center, which I've mapped out above, calls for a widespread area of 6"+ across a huge chunk of Missouri and central Illinois. The bullseye for the heaviest snow will very likely shift around and change over the next couple of days as forecasters get a better idea of what the storm will do, but if you're looking for snow, it's probably a safe bet to meet it in St. Louis. (Booo. Sorry.)

Aside from specific amounts, the storm's life in the Midwest is a fairly straightforward event. From here on, I'll mostly talk about the effects of the storm once it crosses the Appalachian Mountains.

Something's gonna happen back east.

That's the best non-answer I can give for what is likely to unfold overnight Saturday and into Sunday. The storm will run into too much cold air for everyone in Virginia and North Carolina to wind up seeing plain old rain. Some folks will have a decent, shovelable thumping of snow. Others may see a prolonged period of freezing rain or sleet. Many communities—likely to the south of I-85—will just deal with a cold, annoying rain.

Cold air damming will determine the rain/ice/snow line.

This point is in a similar vein to the big storm back on December 9. That storm was able to produce prolific snowfall totals across N.C. and Virginia in part due to the resilient wedge of cold air that dammed up against the eastern slopes of the Appalachian Mountains. This allowed precipitation to almost entirely fall as snow, plopping a foot or more of snow across dozens of counties.

The cold air damming ahead of this storm likely won't be as intense or resilient as what we saw the last time around. There's going to be a layer of warm air forcing its way above the cold air during the storm, causing at least some of the snow to turn into freezing rain or sleet before it reaches the surface. It looks like the best chances for an ice storm exist in the Piedmont Triad, the border region between Winston-Salem, Greensboro, and Burlington in North Carolina and Danville and Martinsville up in Virginia.

What We Don't Know

What kind of precipitation will fall.

Snow is more likely closer to the Appalachian Mountains in the Mid-Atlantic and along a relatively narrow path between the mountains and the Atlantic Ocean. Delightfully vague, right? That's because it depends on how much precipitation is able to coincide with the best profile of cold air through the atmosphere.

Since Saturday night and Sunday are too far out right now for me to post any WPC/NWS forecasts, here's a look at (forgive me, Weather Twitter, for I am about to sin) what the last ten runs of the GFS weather model have shown in terms of precipitation types. Each image shows what the model thinks will happen at 7:00 AM EST on Sunday. The first image starts with the Monday afternoon run of the GFS model and shows 7:00 AM Sunday according to each successive run of the model through Wednesday evening. This shows us the trends from run to run.

Source: Tropical Tidbits
Don't take it literally—it's just a weather model and there's a bunch of caveats to what it's showing above. But you can see how the rain/mix/snow line shimmies with each update of the model. That's due to changes in the track of the storm and temperature profile through the atmosphere near that transition point. Folks close to that transition zone will likely see multiple precipitation types during this storm, complicating predictions of how much will fall and making conditions exceptionally dangerous for travel by car or foot.

How much will fall.

We can't quantify snow/ice that may or may not exist. Not yet, anyway. The best chance for an all-snow storm will lie well to the north of the low-pressure system's track. The folks who manage to stay all snow will see the greatest snowfall totals, since freezing rain and sleet pack significantly pack down accumulated snow.

Right now, it looks like the higher elevations of the Appalachians and central Virginia stand the best chance of seeing all (or mostly) snow from this storm, which would give them a shot at the best snowfall totals. Farther south, enough ice is possible that it could damage to trees and power lines. Again, it'll depend on how much precipitation falls as freezing rain and how long it lasts.

We'll know a lot more about this storm on Thursday evening and Friday.

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January 2, 2019

AccuWeather CEO's Nomination to Run NOAA Expires as 115th Congress Adjourns

Donald Trump's nomination of AccuWeather CEO Barry Myers to run NOAA will expire without action on Thursday with the adjournment of the 115th Congress. Myers' nomination faced pointed opposition from ethics watchdogs and groups within the weather industry due to the nominee's conflicts of interest, including his company's past support for legislation that would have severely curtailed the National Weather Service's ability to provide weather forecasts and data to the public.

The New York Times reported last month that the Senate will not take up Myers' nomination by the end of the session on January 3, and it was unclear whether Trump would re-nominate Myers to the position once the new Congress begins. 

For the foreseeable future, NOAA—and, by extension, the National Weather Service—will remain under the charge of Acting Administrator Tim Gallaudet, who holds a doctorate in oceanography. Myers, who holds a business degree, would have been a rare NOAA Administrator without an academic background in science. Gallaudet's leadership of the agency has so far been uncontroversial.

Myers is one of hundreds of presidential nominees who didn't receive a final confirmation vote before the Republican-controlled Senate. A whopping 47 percent of executive branch positions that require presidential nomination and Senate confirmation remained unfilled during the first half of Donald Trump's term in office, either for lack of a nominee or through Senate inaction. These positions are currently filled by acting officials or simply remain vacant.

Unlike the protracted battles over other controversial nominees to the executive and judicial branches, the kerfuffle surrounding the AccuWeather CEO's nomination to run NOAA came and went fairly abruptly in the days after the White House announcement in October 2017.

The greatest single point of opposition to Barry Myers leading NOAA is the many conflicts of interest that would follow Myers into office. The greatest example of these potential conflicts was his company's support for S.786—the National Weather Service Duties Act of 2005. The bill, introduced and unilaterally supported by former Sen. Rick Santorum (R-PA), would have effectively privatized the NWS and used the agency to subsidize private weather companies.

Santorum's legislation would have required the National Weather Service to stop issuing public forecasts except for "severe weather forecasts and warnings designed for the protection of life and property of the general public"—in other words, it limited the agency's public portfolio to emergencies like tornado warnings. All of their other forecasts, products, and data had to be provided "through a set of data portals designed for volume access by commercial providers of products or services," turning private weather companies into middlemen between the NWS and the public.

Why would the bill go to such great lengths to dismantle the National Weather Service as we know it? First, some right-leaning meteorologists and weather industry executives routinely criticize the National Weather Service's efforts to directly interact with the public, arguing that the federal government is unfairly competing with private companies like AccuWeather. (Sidenote: this is also the main reason you'll never get an official NWS smartphone app, in case you've ever wondered.)  

The second factor is just pure politics. Joel Myers, the nominee's brother and founder of Pennsylvania-based AccuWeather, donated $2,000 to a political action committee supporting Santorum's failed 2006 reelection bid just days before Santorum introduced the doomed legislation on the floor. It's not exactly breaking news when a company's executives appear to have a cozy relationship with their home state's congressional delegation, but the bill was awful enough—and AccuWeather's tremendous potential benefit from the bill obvious enough—that the donation sent up red flags in the weeks and months after its introduction.

A failed piece of legislation from a decade-and-a-half ago isn't the entire reason for opposition to Myers' nomination. But it typifies the potential that exists for Myers to act in ways that benefit companies like AccuWeather. The nominee would enter office with enormous conflicts of interest in tow. If Myers became the NOAA Administrator, he would control the agency that directly competes with his company. Even if Myers divested from AccuWeather, his brothers still control the company and he has a vested interest in seeing his family's company thrive against the direct competitor he would control. 

Donald Trump can easily re-nominate Myers once the 116th Congress is sworn-in on Thursday. The president could also nominate someone else or simply opt to let Gallaudet continue serving as Acting Administrator for the remainder of the administration. Republicans gain two additional seats in the midterm elections, expanding their majority to 53-47. However, the president's party could easily confirm nominees on a simple majority vote—a luxury they had in the previous Congress, as well, indicating a lack of will to expend the political capital necessary to push Myers into the job.

[Top Image: Pierre cb via Wikimedia Commons]

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December 31, 2018

2018 Is Set To End With The Fewest Tornado-Related Fatalities On Record

A relative lull in tornado activity in 2018 allowed the year to finish with the fewest number of tornado-related fatalities since reliable records began in 1940. Assuming we get through today’s severe thunderstorms without any significant tornadoes, the United States will end the year with 10 deaths attributable to tornadoes.

2018 will end with a little more than 1,100 reports of tornadoes submitted to the Storm Prediction Center. A decent number of those reports were sent in for the same tornado—adjusted for inflation, the agency received reports of just shy of 1,000 tornadoes across the country in 2018. An official count of all confirmed tornadoes will be released sometime in the new year.

Fewest Tornado Deaths

Ten people died as a direct result of injuries inflicted by a tornado according to the latest count from the Storm Prediction Center. This would be the lowest number of tornado fatalities in a year since the National Weather Service’s database of weather-related fatalities began in 1940. The previous record low occurred in 1986 when 15 people died in tornadoes.

Half of this year’s tornado deaths occurred in November or December. Four people died in a permanent building, including two Amazon employees who were killed when a tornado struck the company’s distribution facility near Baltimore, Maryland. Four people died at home, and two others were killed in vehicles.

The record-low number of tornado-related fatalities this year is attributable both to the overall downtick in tornadoes this year, the lack of violent tornadoes, and likely an overall trend of better warnings and tornado safety education.

Below-Average Tornado Activity

Source: Storm Prediction Center

The Storm Prediction Center’s inflation-adjusted tornado count for 2018 shows this year’s tornado activity well below average and near an all-time minimum. Tornado activity was fairly steady through 2018, steadily building up through the year rather than coming in big bursts like we’ve seen in years past.

The biggest single day for tornadoes reports in the U.S. was Halloween, when the SPC received 61 tornado reports, followed by April 13 (46 reports), December 1 (38), July 19 (31), and April 3 and November 11 tied at 28 tornado reports. It’s notable that only two of the six biggest tornado days this year occurred in the springtime, which is typically the peak of tornado activity across the country.

We also made it through the year without recording any EF-4 or EF-5 tornadoes anywhere in the United States, the first such year on record. The last EF-4 tornado in the U.S. touched down in Texas in April 2017, and the last EF-5 struck Moore, Oklahoma, in May 2013.

Where Tornadoes Happened

It’s no surprise that an unusually quiet year populated by off-season tornado outbreaks would see the bulk of tornadoes touch down outside of what is traditionally considered Tornado Alley. The stretch of the Plains from Texas to the Dakotas saw fewer tornadoes than usual. Nobody died in an Oklahoma tornado this year for the first time since 2006.

Most of the tornadoes we saw this year touched down in the southeast or Upper Midwest. There’s a strong argument to be made that the United States’ “tornado alley” is actually shifting (or at least expanding) east toward the Deep South—covering states like Louisiana, Mississippi, and Alabama.

Noteworthy tornadoes occurred in central North Carolina—where an EF-2 tornado cut through the city of Greensboro and very close to where I live—as well as Maryland (hitting the aforementioned Amazon warehouse) and a photogenic tornado that hit central Iowa at the same time a severe thunderstorm capsized a duck boat in Missouri, killing 17 people.

Some Still Strike Without Warning

Tornadoes striking without warning is a popular narrative news organizations use to cover devastating tornadoes. But the fact of the matter is that most tornadoes that injure or kill people are warned in advance—it’s just that some people in the path of the storm don’t hear the warning in time.

However, some tornadoes really can (and do!) strike without warning. I combed through the tornado reports and tornado warnings issued between January 1 and December 30 and found more than 100 tornado reports that didn’t coincide with any tornado warning polygons at any point during the year.

Now, not all of these tornado reports were confirmed tornadoes. Some likely wound up being damaging straight-line wind events once crews took a better look on the ground. But it’s a stark reminder that warningless tornadoes can happen anywhere in the country—from coast to coast—and that it’s more important than ever to take strong thunderstorms seriously even if they lack a tornado warning.

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December 20, 2018

Look At This Entire Trough

An ambitious butterfly could make it from Orlando to Buffalo in a couple of minutes if it flew high enough on Friday. An incredibly amplified trough entering the eastern United States will bring this week to the same dreary close we saw last week. In addition to lots of heavy rain and dangerous thunderstorms in Florida, the resulting surface low could bring some of the lowest air pressures ever recorded during the month of December in the Mid-Atlantic.

A line of severe thunderstorms was ongoing in Florida at the time of this post. It's a classic wintertime severe weather setup for this part of the country. Warm, moist air ahead of an advancing cold front allowed a line of strong thunderstorms to sweep across the Florida Peninsula. Cooler, drier air will follow soon after the rain stops, bringing comfortable conditions as far south as Cuba and Mexico's Yucatan Peninsula through the weekend.

A slog of steady, heavy rain will coat just about every square inch of the East Coast between now and Saturday. Most areas can expect an inch or two of rain with heavier totals likely in areas that experience thunderstorms. Some of the storms in the Carolinas could be severe on Thursday night, packing the risk for damaging winds and possibly an isolated tornado.

That trough is something else. I mean, look at this thing:
An animated model image of the jet stream. Source: Tropical Tidbits

A sharp trough like that is impressive enough on its own, but the combination of the amplified trough and strong winds of the jet stream within will strengthen the surface low moving over the Carolinas tonight and Friday. The latest forecast from the Weather Prediction Center shows the minimum surface pressure at the center of the low potentially reaching 987 mb on Friday as it moves over western North Carolina and Virginia.
December record low air pressures (adjusted for sea level). Add a 9 to the front of every number for the value, which is rounded to the nearest tenth ("888" in Greensboro is 988.8 mb). Source: WPC

A surface pressure of 987 mb is extremely unusual for this part of the country during this time of the year. Surface pressure records compiled by David Roth at the WPC show the lowest air pressure recorded during the month of December in Greensboro, N.C., was 988.8 mb, and 986.5 mb up the road in Roanoke, VA. It'll be a close one.

The lower air pressure itself won't really have much of a direct effect other than kicking up a stiff breeze and possibly making your joints achier than usual. Other than that, it's just a novelty.

[Top Image: Tropical Tidbits]

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December 19, 2018

A Rare Tornado Touched Down Near Seattle on Tuesday

A strong tornado touched down in Port Orchard, Washington, on Tuesday, damaging several homes and businesses along its path. Meteorologists will conduct storm surveys on Wednesday to assign the tornado an EF-Scale rating, but pictures from local news organizations and social media seem to show that this was a formidable tornado in a part of the country that doesn't typically see this kind of weather.

Today's tornado in Port Orchard—which is next to Bremerton and about 30 miles west of Seattle—is a stark reminder that A) tornadoes can happen anywhere in the United States, and B) a significant number of tornadoes in the United States truly occur without warning.

The nasty weather today in the Pacific Northwest is directly tied to the same low-pressure system that generated all of the epic waves that hit the West Coast a couple of days ago. A long fetch across the northeastern Pacific Ocean allowed wave heights to reach 50 feet, posing significant risk to anyone ill-advised enough (to put it nicely) to go swimming or even just wander to the ocean's edge.

Each dot represents a lightning strike on December 18, 2018. Source: LightningMaps.org
Bursts of showers and thunderstorms moved across western Washington during the day on Tuesday, producing dozens of lightning strikes along the way. (That's nothing east of the Rockies, of course, but even one rumble of thunder out west is a talking point for days.) At least one of the thunderstorms was strong enough to tap into enough low-level wind shear to begin rotating.

The thunderstorm that produced today's tornado had a fairly pronounced signature on it as it crossed the Kitsap Peninsula. The storm's rotation grew strong enough to produce a short-lived tornado once it reached Port Orchard. Social media lit up as onlookers recorded a funnel that was mostly obscured by heavy rain but clearly present due to the immense amount of debris kicking up into the air. The thunderstorm quickly fell apart after the tornado touched down as more stable air wrapped in and choked off the instability feeding the storm.

We only had five-minute radar scans of the storms in northwestern Washington today—we're spoiled by rapid-scan radar imagery these days—but we did get a radar sweep at a critical moment: 1:51 PM PST, during or immediately after the tornado touched down and caused the most damage. That sweep took place at just the right moment to allow us to see debris in the air.

Dual polarization technology allows us to see the size and shape of the objects showing up on radar. Correlation coefficient (CC) tells us how similar or dissimilar airborne particles are to one another. Raindrops have a high CC value because they're all pretty much the same size and shape. Tornado debris, on the other hand, has a low CC because you're seeing everything from branches to vehicles being lofted into the air by the tornado.

Here's a two-pane radar image from Port Orchard around the time of the tornado. The left pane shows CC values while the right shows precipitation.

The debris on the CC imagery stands out as the dark blue circle near the center of the pane on the left. The radar beam is about 3,100 feet above ground level when it reaches the location of the tornado. Even if we didn't have videos of the tornado in progress, a quick look at that kind of a debris signature that high above the ground is a sign of a strong and sizable tornado.

It's common to see this somewhere like Alabama or Kansas, but not Washington. The Storm Prediction Center has more than 62,500 tornadoes in its database since reliable records began in 1950. Since then, only about 100 of those tornadoes occurred in Washington.

Heck, there are so few tornado tracks in Washington that you can barely make them out on a map of the whole country. You have to zoom in on the state to see them.

Most of the tornadoes reported in Washington over the past seven decades occurred along the coast, in valleys, and in the eastern part of the state where thunderstorms aren't as hampered by terrain and a stable marine layer as out west. The majority of Washington's tornadoes were relatively weak and short-lived.

The Storm Prediction Center's tornado database shows 121 tornadoes recorded in Washington between 1950 and 2017. More than half of those tornadoes—69 of them—were an F0 or EF-0 on the Fujita and Enhanced Fujita scales. (The Fujita scale was updated as the Enhanced Fujita Scale in 2007.) Only three tornadoes in Washington have produced F3/EF-3 damage. Based on pictures of the damage, today's tornado is likely to get at least an EF-1 rating, if not higher.

Tornadoes are rare in Washington, and strong tornadoes are even rarer yet. They're so rare, in fact, that the National Weather Service office in Seattle hasn't issued a tornado warning in more than four years—including today. Residents of Port Orchard had no tornado warning or severe thunderstorm warning before the tornado touched down. They only knew there was a tornado if it hit them, they saw it, or they heard about it afterwards.

For all the talk of false alarms when it comes to tornado warnings, an uncomfortable fact we have to live with is that quite a few tornadoes actually wind up going unwarned. The National Weather Service fails to issue a tornado warning for 30-50% of all tornadoes that form each year. The agency does better warning for tornadoes that occur during organized outbreaks than in one-off situations like we saw today.

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December 14, 2018

Heavy Rain Brings a Flood Threat to the East Coast This Weekend

Several inches of heavy rain on Friday and Saturday could lead to flooding to parts of the southeast and Mid-Atlantic. Some of the heavy rain will fall over areas that saw more than a foot of snow just a couple of days ago. The abundant snow deposited by last weekend's historic snowstorm could lead to significant flooding in some areas.

The upper-level low responsible for the upcoming rain made a mess of things in Texas this week—including intense winds and even some heavy snow—and it'll continue to swoop across the southeast over the next two days, creating a large shield of precipitation that should bring substantial rains to most of the southeast and Mid-Atlantic on Friday and Saturday.

The latest precipitation forecast from NOAA's Weather Prediction Center shows a couple of inches of rain stretching from Florida through the Mid-Atlantic. This kind of rain would lead to some flooding concerns under normal circumstances, especially if it falls in a short period of time, but the risk for flooding is enhanced due to the epic amounts of snow that still blanket the ground in interior parts of North Carolina and Virginia.

We saw a historic snowstorm on Sunday that dumped enormous amounts of snow, with totals exceeding a foot across most communities between Interstate 85 in N.C. and Interstate 64 in Virginia. The resulting snowpack is thick and wet and it's hung in there pretty resiliently over the past couple of days.

That's bad news when it comes to this much rain. Drains are clogged, which could lead to street and parking lot flooding. Snowmelt will add extra water on top of the rain, having a greater effect than just a couple of inches of rain straight-up.The rain will pool on the snow. The snow and wet soil beneath it will both prevent the rain from soaking into the earth effectively. In addition to the risk for urban street flooding, all that excess water could push local streams and creeks to flood stage.

All those typical flood tips apply—be careful where you drive, have a secondary route, don't drive through a flooded roadway—but pay attention to where you park, as well. I'm sure my apartment complex's parking lot will flood in spots because of the clogged drains, possibly endangering vehicles parked in those end spots. That could be a problem in large parking lots with poorly-placed snow mounds.

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December 7, 2018

A Significant, Disruptive Winter Storm Will Hit North Carolina This Weekend

The winter storm we've been watching for the past week is almost a certainty at this point. North Carolina stores are quickly running out of the staples as residents collectively realize that we'll be sitting around the house for a couple of days. A disruptive winter storm will trek across the southern United States this weekend, and the brunt of the snow and ice is expected to unfold across western and central North Carolina. Some locations could see more than a foot of snow, which is on the high-end of winter storms for this part of the country.

What We Know

Heavy snow is almost a certainty across much of North CarolinaJust about everyone west of Interstate 95 in North Carolina will see some amount of wintry precipitation from this storm. The heaviest snow will occur in the western and central parts of the state—think Asheville, Charlotte, and Greensboro—while areas east of there are more likely to see sleet, freezing rain, and plain ol' rain than anything else.

It won't just be North Carolina. The major focus is on North Carolina, but the surrounding states will also see a thump of winter weather. The mountains of southwestern Virginia stand the best chance to see disruptive snowfall totals as well as sleet and freezing rain that could make it impossible to walk or drive and could expose residents to power outages. Snow and ice is also possible in parts of upstate South Carolina and the mountains of eastern Tennessee.

Sunday will be the worst day. The low-pressure system will approach the state from the west on Saturday night. Snow will begin to overspread western and central North Carolina on Sunday morning and continue to grow in coverage and intensity through the day. The snow will be so heavy in spots that snow plows will have a hard time keeping up even on the major highways.

Snow and ice may linger through Monday. The bulk of the heavy snow and ice should subside during the early hours of Monday, but some precipitation may linger through Monday morning. It's going to be incredibly difficult to travel in western and central N.C. on Monday anyway, so it won't make too much of a difference.

Beware the wobbles. You've been warned. The effects of a storm like this are wholly dependent on the track of the low-pressure system. If the storm deviates even a dozen or two miles to the north or south of its current predicted track, that shift will mean all the difference for the location of the rain/ice/snow line and the axis of the heaviest snows. Likewise, if temperature profiles shift by a few miles, the sleet and freezing rain will follow. I guarantee you that some towns bracing for epic snows will see a decent snow followed by lots sleet or freezing rain, which will compress the snow into a dangerous sheet of ice. Lots of independent variables have to come together perfectly for a major snowstorm in this part of the country. It's hard to do.

Some areas will flirt with records. North Carolina sees snow pretty reliably every year, but these annual snowstorms usually aren't blockbusters. They clip the state, drop something like 2-6" of snow, snarl traffic for a day or two and then everything gets back to normal. A big-time snowstorm with forecasts freely bouncing around figures like 12"+ is...not typical for this area!

This state isn't great at handling snow. Drivers aren't used to driving in snow. Crews don't have enough equipment to keep the roads clear like they do up north. Heck, even many apartment complexes (mine included) don't plow or shovel, leaving residents stranded in their parking spots if they don't have a vehicle that can traverse a foot of snow.

Sorry folks, state's closed. When we get lots of snow like what's forecast for this weekend, it shuts everything down until the snow can melt. I guarantee you that there's some county in this state that will have no school all week. Before you scoff, think about what happened a few weeks ago when road crews in the New York City metro were caught unprepared for snow that was heavier than forecast. Plows couldn't keep up with the snow, grinding traffic in the NYC metro to a halt. Remember how easily things fall apart the next time you see the infamous flaming snow car.

What We Sorta Know

We're close enough to know some snowfall totals now. The latest forecast from the National Weather Service and the Weather Prediction Center (whose forecast is shown in my map above) is pretty settled into a significant, disruptive snowstorm across the western half of North Carolina. These snowfall totals are subject to change over the next day or two as forecasters refine their thinking on the track of the storm and location of the freezing line above the surface.

Western North Carolina: The mountains of western North Carolina stand the best chance to stay all-snow during this storm. It's likely that many areas here will easily see more than a foot of snow by the end of the storm. Some lower elevations may start to mix with sleet or freezing rain by the end of the storm on Sunday night—compressing and glaciating the blanket of snow—but many areas will escape this fate.

North-Central North Carolina: Communities (like mine!) in the middle of the state near the Virginia border could see hefty snowfall totals, but they also run a decent risk of seeing ice mix in with the snow. We could push double-digit totals in places like Winston-Salem, Greensboro, Burlington, and Reidsville if we manage to stay mostly snow. Totals will drop precipitously (sorry) if sleet or freezing rain begins to mix in. The deepest snows should occur north of Interstate 40/85.

South-Central North Carolina: Locations along and south of I-85 stand the best chance to see ice during this storm, which could significantly limit snowfall totals and make the storm even more dangerous than if it were pure snow. That sharp cutoff is readily apparent on the Weather Prediction Center's snowfall forecast, shown above.

Virginia: Most of the snow in Virginia will fall across the southern part of the state near the North Carolina border. The cities with the best chance for significant snowfall totals are Roanoke, Blacksburg, Martinsville, and Danville. Accumulating snow is possible as far north as I-64. The storm should stay far enough south that Virginia shouldn't have to deal with much ice at all—precipitation here should remain all snow.

South Carolina: There will be a sharp cutoff between snow, ice, and rain close to the low's track as it moves across Georgia and South Carolina. The most snow will fall in far upstate South Carolina, with the heaviest totals likely right along the NC/SC border.

Tennessee: Given the complex setup of cold air that's allowing it to snow and sleet and freezing rain in the first place, much of Tennessee should be spared from the wintry effects of this storm. The mountains right along the NC/TN border will see heavy snow, but there will be a sharp cutoff in snowfall to the west.

Who's going to get iceFreezing rain is most likely across northern Arkansas, parts of Tennessee, and some parts of central North Carolina that wind up right on the line between snow and rain. All of the areas that experience freezing rain will have impassable roads until the ice starts to melt. You can't drive on a sheet of ice no matter how good you think your vehicle is.

Get ready for power outagesThe combination of heavy, wet snow, gusty winds, and freezing rain will lead to power outages in some areas. They shouldn't be as widespread as you'd see after a severe thunderstorm outbreak or a horrific ice storm, but some areas will lose power during this storm and they may not get it back right away. That's no good when it's cold and wet. Make sure you're prepared for a power outage with food you don't have to cook, batteries to power things like flashlights and radios (remember those?), and a way to charge your cell phone in a vehicle or with a portable power pack.

There's going to be lots of heavy rainAreas that don't get to see wintry precipitation will still see rain—and lots of it. Some parts of the deep south will see flooding rains from this storm. The latest forecast from the Weather Prediction Center shows a widespread area of heavy rain stretching from central Texas to the coast of the Carolinas. Widespread parts of Texas and Louisiana could see more than 5" of rain. This kind of rain in such a short period of time will lead to flooding issues.

Some severe thunderstorms are also possibleAs if everything else isn't enough, some severe thunderstorms are possible along the northern Gulf Coast on Friday and Saturday. The main threats will be damaging winds and quick tornadoes. The threat warrants paying close attention to watches and warnings as they're issues. Some of the storms will occur at night, so it's a good idea to make sure your cell phone has the ability to receiving warnings and audibly warn you when it receives an alert.

The Dam Setup

Source: Tropical Tidbits

This storm is a classic setup for snow and ice across the southeastern United States. The overall setup behind this snowstorm involves a low-pressure system moving across Georgia and South Carolina and a high-pressure system over the Mid-Atlantic. 

The low to the south is responsible for the precipitation and the high to the north is responsible for the cold air. Winds flowing clockwise around the high will place a pool of subfreezing air against the Appalachian Mountains in North Carolina, a scenario known as cold air damming. It's very hard for warm air to scour away the cold air at the surface, so any precipitation that falls into this pool of cold air falls in the form of snow, sleet, or freezing rain.

A situation like this can lead to prolonged ice storms in central and western North Carolina, but if temperatures are cold enough and the layer of cold air is deep enough, it can also lead to a significant snowstorm. Many communities in the path of this storm will be right on the line between snow and ice, which is why the snowfall forecast is so uncertain.

Many of the high-end totals you're hearing will only happen if no sleet or freezing rain mixes in with the snow. Ice will compress a blanket of snow in a flash, turning the snow into a slushy, soon-to-be-glacial sheet of misery that can quite literally strand people where they are if they don't have the equipment or vehicles to remove or traverse a thick coating of ice.

History Repeats

Snowfall totals from the storm of December 7-9, 2017.

This snowstorm is happening one year to the day that another early-season snowstorm rolled across the southeastern United States and dropped significant amounts of snow. The former storm produced more than half a foot of snow near Corpus Christi, Texas, one of the biggest snowstorms ever recorded in that part of the country. 

The storm we'll see this weekend isn't anything like the storm a year ago. The previous storm followed a path that took it from Texas to New England, dumping heavy snow along a path that stretched from the Mexican border to the Canadian border. This weekend's storm is on a more west-to-east track, bringing it straight across from Texas and Oklahoma to the Carolinas before it hooks out to sea in the western Atlantic.

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