A new chart ... and a we-were-wrong

I'm not getting into the debate about global climate change, but you can make your own arguments over the U.S. Department of Agriculture's updated Plant Hardiness Zone Map.

It's the map that shows you what agricultural zone you live in, and it's very handy when you're ordering plants or buying them at a nursery or big-box store. Many growers mark information on the plants, telling you what zones they can grow in.

The news is that the updated Plant Hardiness Zone Map moves the boundaries a bit northward for a number of zones.

That is in response to the milder temperatures of recent years. The zones are based on the lowest winter temperature, and the new map has Charlotte in Zone 7B, which is for areas capable of having winter lows of 0 to 5 degrees above zero.

The northern boundary of 7B in the Carolinas was nudged northward from the old chart, but there really aren't any major changes for our area.

One neat new wrinkle to the USDA's map -- it's interactive, in a way. You can type in your Zip Code and find out what zone you live in.

Here's a link to the map: http://bit.ly/vZ5vuL.

We Were Wrong (or, I Was Wrong) ... Throughout the day on Thursday, we were publishing a story, written by me, that reported on a chance of severe thunderstorms and even tornadoes overnight in the Charlotte area.

Obviously, that didn't happen.

Severe weather that doesn't develop is a sore point with some critics, who blame meteorologists and those who report about the weather with trying to panic people. When severe storms are predicted and don't develop, the criticism grows.

Strangely, I never see comments from those critics when the storms do develop -- such as the tornado outbreak a few weeks ago in Burke, Caldwell and Rutherford counties. But that's another argument for another day.

I like to be open and honest, and I don't run away from what I write. Obviously, my story on Thursday was wrong. If I scared you, I'm sorry.

The combination of warm dewpoint temperatures and a stirred-up atmosphere at the edge of an approaching cold front were expected to be enough for the development of severe weather. But the dewpoint readings -- while well above average for this time of year -- didn't quite get as high as expected. And the atmosphere remained rather stable when the front came through, although the 40 mph gusts we got were evidence of the strong winds a few thousand feet off the ground.

How rare are Carolinas winter twisters?

When tornadoes struck two weeks ago in Burke, Caldwell and Rutherford counties, The Observer and some other sources reported that it was the first time in recent history that a twister struck those counties in January.

Certainly, mid-winter tornadoes are a rarity in the Carolinas, but with the possibility of more severe weather looming tonight, perhaps it's time to take a closer look at the history of "cool weather" twisters and the reason we're seeing them this year.

Pat Moore, who works at the National Weather Service's office in Greer, S.C., and is absolutely addicted to the science of meteorology, has spent the last few days studying records from the past 62 years and compiling a winter tornado history for the Carolinas.

Moore looked at tornadoes that struck in what meteorologists call the "cool season." That's meteorological winter -- Dec. 1 through Feb. 28 (or the 29th, this year).

His findings?

Several counties south of Charlotte, in areas where dew-point temperatures are more likely to rise in advance of approaching low pressure systems, have not recorded a tornado since 1950.

Here's what he found:

0 tornadoes since 1950: Cherokee, Chester, Lancaster and Union counties of South Carolina; Anson, Alexander, Catawba, Lincoln and Union counties of North Carolina.

1: Mecklenburg, Cabarrus and Cleveland. Add to that list, Burke, Caldwell and Rutherford, from the outbreak this month.

2: Iredell.

3: Gaston, Rowan and York.

The reason for the outbreaks of severe weather this month is fairly simple, really. Cold air has not penetrated into the South. For that matter, it really hasn't pushed into much of the United States at all.

Computer models show that most of the truly arctic air has been on the other side of the world -- over Russia, western Asia and eastern Europe -- for much of the winter.

A persistent low pressure system has sat over the Gulf of Alaska, and the counter-clockwise flow of air around that low has prevented arctic air from sliding down from the North Pole and moving into central Canada and the eastern United States.

With no cold air around, the Gulf of Mexico has stayed relatively warm. When low pressure systems move across the South, they are bringing a push of humid, relatively warm and unstable air into the Southeast. It's more of a spring-like pattern than what you'd expect from the middle of winter.

I've been writing since early December about the lack of cold air, and there are no signs of a change in the pattern for at least another 10 days. We might get a few brief (one- or two-day) outbreaks of chilly temperatures, but rapid warming will follow.

It's been a nightmare for snowplow operators and ski resort owners, although the Carolinas resorts have managed to make snow during the brief cold spells, and skiing conditions have been OK in recent weeks.

Official report: 3 tornadoes

I somehow missed passing along the final report from the National Weather Service about the tornadoes last week in the North Carolina foothills.

As we had theorized last week, three counties were affected by the twisters. Burke and Rutherford counties got the headlines, because the twisters destroyed dozens of homes and injured 15 people there. But a third tornado touched down in Caldwell County.

Here is a summary of the storms:

RUTHERFORD COUNTY ... An EF2 tornado, with top winds of 115 mph, injured 10 people and was on the ground for about 2.3 miles.

The storm touched down 2.5 miles northwest of Ellenboro, initially reaching the ground northeast of Bridge Road and Pinehurst Road. A second brief tornado touched down moments later on Tiney Road.

But the major touchdown was near Piney Mountain Church and Piney Mountain roads. The twister was on the ground for more than 2 miles, finally lifting north of Salem Church Road.

About 10 homes were damaged, and several mobile homes were destroyed. Debris from the mobile homes was thrown about 300 yards. The tornado reached peak intensity along Piney Mountain Road, just south of Walls Church Road.

BURKE COUNTY ... The tornado touched down about 5 miles south-southwest of Icard, was on the ground for 3.6 miles, and had top winds of 130 mph. It was a high-end EF2 twister.

The tornado produced brief and intermittent damage south-southwest of George Hildebran School Road before developing more sustained damage on the south side of the road. The tornado stayed on the ground across Paige Street, but the most intense damage was around Johnson Bridge Road.

The eight Burke County injuries happened near Johnson Bridge Road, and on Rock Lane, River Rock Drive and South Fork Avenue. The storm's greatest width, 300 yards, was along George Hildebran School Road and Rock Lane.

CALDWELL COUNTY ... An EF0 tornado (the weakest classification) struck near the Lake Hickory Marina, about 4 miles southeast of Granite Falls. This twister had top winds of 80 mph and was on the ground less than a quarter-mile. It damaged a number of boats and buildings at the lake.

Winter's been put on hold

About a week ago, I wrote about a possible change in the warmer-than-average pattern we've seen so far this winter.

Forget it.

In fact, we might be headed in the opposite direction soon -- to even warmer temperatures.

A series of patterns have conspired to produce what has been a snow- and ice-free winter so far over the Southeast, except for the mountains. We've been locked in a routine in which we have an occasional burst of cold air, followed by slow warming and then several very mild days. Overall, our temperatures are well above average.

The computer models indicate more of the same, at least for the next 10 days and possibly for two weeks out.

A cold front will cross the area at midweek, bringing a slight cool down -- but we're talking about temperatures behind the front being almost at seasonal averages. And then, starting next weekend, a ridge of high pressure will build in the South, and our temperatures will climb.

If the models verify, you can look for at least several days of 60-degree readings, and maybe a bit warmer, between Jan. 21 and the end of the month.

In fact, the models show temperatures climbing well above average in a week or so across central and western Canada, and that eliminates a major source of cold air for our part of the country.

I've seen a lot of conjecture about what this means for February, March and April. Some theorize the law of averages will prevail, and we'll have a chilly late winter and early spring. But all we have in front of us now are La Nina, the lack of a blocking high pressure system in Greenland, and the absence of a strong high pressure over Alaska to send cold air plummeting southward.

This is both good and bad. We don't have to worry about icy streets and sky-high heating bills. But this also could spur plants and trees to bud early, leaving them at risk of a deep freeze in late winter or early spring.

Big pattern change? Maybe not

A significant low pressure system will cross the central and eastern United States at midweek, and some meteorologist speculated a few days ago that the storm might be enough to help change the mild winter pattern we've seen so far.

But the latest evidence indicates that any change won't be a real game-changer ... the kind of change that would leave the Southeast prone to snow next week.

The idea was that as low pressure moves into New England, the counter-clockwise flow around the storm would drag cold air down from Canada. In short, the system might open the flood gates from the north.

Certainly, colder air will follow the storm. High temperatures from Friday into early next week will be held to the upper 40s, although I've seen a few forecasts that take those highs into the 50s over the weekend.

But there is no sign in the next 10 days of a bitterly cold air outbreak, the kind needed for a bout of snow or ice.

Several factors are needed for snow or ice in the Southeast. For starters, cold air is necessary. If high pressure were to build over eastern Alaska, the clockwise flow around the high could send arctic air into the eastern United States. There also would have to be a storm track out of the Southwest, with the center of the storm passing across the Southeast -- not up the Ohio Valley, as has been the case several times this winter (and will be the case with this week's storm).

Clearly, there are signs that a cooling pattern is ticketed for the eastern United States during the latter half of January, but the real question is how far south the really cold air will get. Many of the computer models indicate it won't get cold enough in the Carolinas Piedmont for wintry precipitation in the next 10 to 14 days.

We'll keep an eye on the models over the next few days, to see if that changes.

In the immediate future, we'll have Wednesday's storm system to deal with.

Today's clammy conditions -- light rain and temperatures in the upper 40s -- will be replaced Tuesday by partly sunny skies and highs near 60, as weak high pressure builds into the region. Then showers will move into the Charlotte region before daybreak Wednesday.

At some point Wednesday afternoon or evening, the atmosphere might get unstable enough for thunderstorms. Regardless, a significant rainfall is likely, and we should get another soaker to keep ground water levels from shrinking. It has been quite dry over the last 10 days, and the rain will be appreciated.

Signs that winter is lurking around the corner

Meteorologists and weather weenies have been watching for weeks, looking for what they see as the inevitable -- the arrival of truly cold weather and ice/snow threats for the Carolinas.

For the first time this winter, the computer models are at least hinting of something in the works.

The time frame will be after Jan. 16 or 17, it appears. And as is the case, any time you look at computer models beyond a few days, there's a lot of "what-if" going on.

However, meteorologists seem to be agreeing that a major pattern change is in the offing. The starting point could be next week, with a strong low pressure system that is predicted to cross the country, from the Southwest up to New England. It will be a "warm" storm for the Carolinas, as we'll be on the southeast side. That means the chance of heavy rain and even the rumble of thunder on Wednesday.

But while that storm won't be a winter weather-maker for us, there's a chance it could open the dam for cold air pooling in northern Canada and the arctic. That's the theory, at least.

Several of the computer models show cold air surging into the Midwest and East, sometime after Jan. 16, and staying in place for a few weeks. So far this winter, any outbreaks of cold weather have been short-lived. According to the models, the next one will hang around.

So with cold air in place, any storm systems that happen to move through the area could bring trouble.

Here's the problem ... unlike last year, when high pressure was parked over Greenland and bitterly cold air streamed into the Southeast, there isn't really that much cold air available so far this winter. That could change, if a strong Greenland high develops. But there's no sign of that happening.

The likely scenario, then, would be low pressure systems that cut across the Southeast, and the Carolinas are on the border between frozen and wet precipitation. That is exactly the scenario laid out several months ago by Brad Panovich, chief meteorologist at NewsChannel 36, the Observer's news partner. Panovich theorized that ice storms could be a problem somewhere in the region.

And without a lasting source of cold air, the late-January chill will die out, sometime around the end of the month. That's what the models say, at least.

Regardless, the moral of the story is to enjoy this weekend's mild weather, because changes appear to be in the offing. The middle of next week could be stormy, and then the cold air could follow.

Some trends in our 2011 weather

Weather is loaded with trends, and I came across several when I was looking at what happened last year in Charlotte and across the Carolinas.

Our 2011 weather can be summarized rather neatly ... cold and snowy; then unseasonably warm; then very stormy; then hot and humid; then very wet; and finally warmer than average.

And all the major meteorological events of 2011 fall into one of those trends, except for Hurricane Irene. That's typical, because hurricanes are, by nature, renegade storms that form by themselves and create their own pattern, to some degree.

Overall, the past year was a bit warmer and wetter than average. Charlotte's average temperature for 2011 was about 1 degree above norms, and the precipitation -- 44.52 inches of it -- was 1.51 inches more than average.

Averages can be deceiving, though. Much heavier rainfall fell in some parts of the Charlotte region. During a five-day stretch in late September, about 1.6 inches was measured at Charlotte/Douglas International Airport -- the city's official reporting station. But there were parts of the area that got 5 or 6 inches during that period.

And while we were staying wet, drought conditions were reported in parts of western South Carolina.

So here's a look back at Charlotte's weather in 2011:

Cold and snowy start: December 2010 was the second-coldest in local history, and January picked right up with the trend. The start of the month was cold, and 4.1 inches of snow fell Jan. 9. To make matters worse, a quarter-inch of ice fell atop the snow on Jan. 9 and 10, so the result was really bad road conditions for a few days.

Overall, the temperature was 4.3 degrees below average, but it warmed up by the end of the month (70 degrees on the 30th), and that was a sign of things to come.

February started cold again, too, but there were signs that the Greenland block, which was sending arctic air masses into the eastern United States, would relent by the middle of the month.

Valentine's Day warm-up: It was like someone flicked a switch. On Feb. 14, after seven weeks of bitter cold, the temperature in Charlotte soared to near 70 degrees. And for the most part, it stayed warm for a while. We reached 82 degrees on Feb. 27.

The overall temperature in March was a bit below average, but there were plenty of warm days, including an 85-degree reading March 18. And there was no snow or ice.

A turn to stormy -- very stormy: It could be argued that April and May were among the stormiest months in Carolinas history. And it started early.

A persistent storm track from April through June carried low pressure systems from Texas across Louisiana, western Tennessee, northern Alabama and Mississippi, northern Georgia and Kentucky. That put the Carolinas in the warm and unstable sector of the low pressure systems.

It started April 4-5, with an outbreak of ferocious thunderstorms and 90 mph winds. The storms forced the closure of Interstate 485 for half a day. But that was just the start. On April 9, repeated rounds of hail-producing thunderstorms crossed Gaston, Cherokee, Chester, York and Lancaster counties. The hail damaged thousands of vehicles and houses, and insurance companies say it was one of the worst hail storms in recent years across the country.

Then on April 16, strong low pressure and a powerful cold front crossed the Carolinas. Meteorologists said, 24 hours in advance, that an outbreak of big tornadoes was likely. Charlotte barely missed what turned out to be a swarm of killer twisters. The first tornado formed north of Monroe, and another reached the ground in Rowan County.

As the tornadoes crossed U.S. 1, they grew in intensity. More than 20 people died across the Carolinas, especially in an area from Raleigh and Sanford east to the coast.

Two weeks later, killer tornadoes struck the Deep South, and the last remnants of those storms reached the Carolinas. The second-strongest wind gust of the year at Charlotte's airport, 37 mph, was measured during that series of storms.

There were thunderstorms on eight days in May, although the severity didn't match that of April.

A hot, humid summer: There were only two 100-degree days, and Charlotte got off easy, compared to cities in Tennessee, Louisiana, Arkansas, Oklahoma and Texas. But June, July and early August were unrelentingly hot and humid. There were 20 90-degree days in June and 25 in July. In July, the high reached 95 to 99 degrees a dozen times.

A measurement of the high humidity comes from the morning lows. When lows are warm, it's because the atmosphere is humid. And on 14 days in July, the morning low was 72 degrees or warmer.

Hurricane Irene, and a wet late summer: Irene battered the East Coast and caused misery for millions of residents in the Mid-Atlantic and New England. But the worst of the only hurricane to hit the United States this year was felt in far eastern North Carolina. Severe flooding and damaging winds affected the Outer Banks, Morehead City, Jacksonville, New Bern and Elizabeth City.

Farther inland, it was a very wet period. Rainfall exceeded 5 inches in August and September, and the two-month precipitation total of 10.73 inches was almost 3 1/2 inches above average.

Warm and quiet finish -- with one awful exception: The end of the year was, for the most part, mild. Temperatures were a bit below average in October, but November was warmer than average (1.3 degrees) and December was downright balmy (5.5 degrees above average). Rainfall was a bit above average.

But for the most part, it was a quiet period. The exception came Nov. 16, when killer tornadoes hit York County in South Carolina and Davidson County in North Carolina. In all, five people were killed, and each tornado reached EF3 intensity. A smaller, weaker twister struck near Shelby.