Tornado watch extended until 4 a.m., more areas included

A tornado watch has been extended for the Charlotte region until 4 a.m. Wednesday. The weather system that could produce tornadoes swept into the region slower than expected.

The watch includes all counties in the Charlotte region except Anson, Stanly and Richmond. Basically, the watch covers the area from Union County westward.

Once we get past the stormy weather, chilly temperatures are coming.

Much of the explanation about this system is in my blog post from earlier today (see below).

We'll keep tabs on developments throughout the evening.

Tough night could be ahead

Conditions appear primed for an outbreak of severe weather this evening and overnight in the Carolinas and southern Virginia.

Meteorologists locally and at the Storm Prediction Center in Norman, Okla., are predicting severe thunderstorms and possible tornadoes in that area. On top of that, flooding is likely in the mountains, and some flooding already was taking place early Tuesday afternoon.

The scenario has developed pretty much the way we outlined it yesterday, with strong low pressure moving eastward across the South, a warm front pushing northward through the Charlotte area, and a cold front advancing from the west.

Charlotte moved into the warm and unstable area about 11 a.m. The temperature at Charlotte/Douglas International Airport rose from 54 degrees at 9 a.m. to 65 degrees two hours later. Dewpoint temperatures soared from the upper 30s early this morning to near 60 degrees.

The temperature actually might approach 70 degrees in Charlotte this evening.

In contrast, Hickory, which remains in the cool and more stable air, was at 45 degrees at 1 p.m. Heavy rain is falling in the cool area, however, but temperatures probably won't ever climb out of the 50s in the foothills, so that area is expected to escape the severe weather. Flooding will be more of a concern there.

A flash flood warning was issued at midday for the Hendersonville area, with flooding reported near the airport. More flood warnings are likely later today.

But the severe weather situation probably will develop in the Charlotte area sometime this evening.

By early Tuesday afternoon, a tornado watch was in effect for much of Georgia, and you can expect that watch pushed into the Carolinas in a few hours. Tornadoes and severe thunderstorms were pounding western Georgia.

Jonathan Garner, a meteorologist at the Storm Prediction Center in Oklahoma, said the corridor of damaging winds this evening probably will stretch from the Piedmont to the coastal plain in the Carolinas. He also said strong tornadoes are a possibility.

Once the cold front crosses the area, sometime early Wednesday, the stormy weather will come to an abrupt end. And temperatures will take an abrupt tumble, too. Look for temperatures to fall from near 70 at midnight to the lower 50s by daybreak, and they won't climb much Wednesday.

Frozen Precipitation? Yesterday, I wrote about the GFS computer models indicating a chance of wintry storms around Dec. 8 and Dec. 13. I plan to follow that prediction every day until those dates arrive -- so we can get an idea of how the computer-generated forecasts often change dramatically.

But so far, there's nothing new to report. A strong storm system is still forecast to cross the area Dec. 8, and another storm system is predicted to move up the Carolinas coast five days later. In both cases, especially the Dec. 13 storm, temperatures could be cold enough to present some problems.

We'll keep an eye on this.

By the way ... one reader reminded me yesterday that some weather followers refer to the GFS as Good For ****. Officially, it's an acronym for Global Forecasting System and is among several models used by the National Weather Service.

Trouble late Tuesday ... and beyond

Another round of stormy weather is headed for the Carolinas later Tuesday, and the computers hint at more trouble -- possibly of the frozen variety -- late next week and about two weeks from now.

Some rapid and major changes in our weather will take place over the next 24 hours.

A flash flood watch already is in effect for Tuesday and Tuesday night for Burke, Caldwell, McDowell, Rutherford, Watauga and Wilkes counties in the Charlotte region. Additional watches and warnings are likely Tuesday.

Today, we're locked in a chilly pattern, governed by high pressure off the East Coast. But the seeds of change are visible. The cloud cover that thickened overnight is a telltale sign of the moisture surging into the Carolinas from the Gulf of Mexico.

By later today, low pressure will move eastward from the Arkansas-Texas area. Rain gradually will spread into the Carolinas, falling mostly in the mountains initially but reaching the foothills and Piedmont by later this afternoon.

It will be a chilly rain at first, with temperatures staying in the 40s today and dewpoint readings also in the 40s.

But a warm front on the east side of the low pressure system will move northward Tuesday, crossing the Charlotte area sometime in the morning. That will push our temperatures into the 60s, and the dewpoint temperatures will follow suit.

The Carolinas will be in the warm, unstable southeast side of the low pressure system by Tuesday afternoon and night, and that's where severe weather takes place.

Chris Horne, of the National Weather Service's office in Greer, S.C., says strong thunderstorms and heavy rain are forecast across the Carolinas, with the most likely area for severe weather being in the Piedmont.

"Some degree of thunderstorm wind damage threat -- perhaps even a tornado -- should exist into the night," Horne said.

These likely will be those sneaky severe storms -- the kind we experience in the Southeast during the winter. They move extremely fast, sometimes at 50 mph, and often have little or no lightning to herald their arrival.

And looking ahead? This part of the discussion is based on some GFS computer model projections for Dec. 8-9 and again Dec. 13. The GFS is one of several computer models used by meteorologists for long-range forecasts.

First, an important caveat ... long-range computer model forecasts often don't pan out. The science of meteorology has a tough enough time predicting 24 or 48 hours ahead. Forecasts such as these -- 192 to 264 hours in advance -- are iffy.

But the computers show a pattern of low pressure systems forming over the Southwest and moving across the Southeast and up the East Coast. This is exactly the pattern predicted by a number of long-range forecasters for the winter.

The big questions are: 1. Which path will the storms follow? 2. How much cold air will be in place in the Carolinas?

The storm path is important. If the Charlotte region remains on the north and west side of the storm's center, we're more likely to see cold rain or frozen precipitation. The GFS model has been waffling on the storm expected to affect our area Dec. 8-9, predicting a chance of frozen precipitation one time, then making it a rainy forecast the next. These models are updated a couple times each day.

However, the Dec. 13 storm system has been predicted consistently to remain east of the Charlotte area, putting us at a risk of something frozen.

I mention these GFS forecasts not to sound an alert about an upcoming ice storm. I think the computer models will change a bunch of times between now and then. In fact, the storm might never develop.

But I introduce the topic now, because we'll be dealing with it a lot this winter. Let's see how these long-range forecasts fare.

Attention, holiday shoppers. It's getting colder!

Timing can be everything in weather.

The folks who stood in line outside stores early this morning for those Black Friday specials caught a break. A strong cold front didn't cross the Charlotte area until about 7 a.m., several hours after the stores opened.

By that time, shoppers were inside. If the front had been earlier, the people in line would've gotten a drenching, as the front was accompanied by a band of heavy showers.

The early shoppers caught another break. Temperatures were near 65 degrees at 4 a.m., but the front dropped those readings 10 degrees in an hour, and we can look for the thermometer to keep falling during the day.

The heaviest of the rain has moved to the east, but we can expect a few showers until late afternoon. Meanwhile, temperatures probably will stay in the mid 50s for a few more hours but will fall into the upper 40s by late afternoon.

So if you have shopping plans later today, take an umbrella and a jacket.

And if you're heading out to a high school football playoff game tonight, count on a cold night, with a northwest breeze that will be strong enough to make conditions seem even chillier.

This cold front is a serious character. Nashville was basking in 70-degree weather at 5 p.m. Thursday. Nine hours later, at 2 a.m., it was 35 degrees, with light snow falling.

We won't see snow in the Carolinas today, but temperatures will be in the lower 30s Saturday morning and in the upper 20s Sunday morning.

After a brief warm-up Tuesday, another strong front is forecast to move through the area, bringing even colder air. Despite sunshine, our high temperatures next Thursday and Friday might not get out of the upper 40s.

By the way, a deep storm system over southern Canada and the colder air will produce the first significant lake-effect snow outbreak of the season in the Great Lakes. A west-northwest wind off lakes Superior, Michigan, Huron, Erie and Ontario will dump 1 to 2 feet of snow in parts of Michigan's Upper Peninsula (from Lake Superior); western lower Michigan (from Lake Michigan); southwest Ontario (from Lake Huron); the Buffalo area and northwest Pennsylvania (from Lake Erie); and upstate New York (from Lake Ontario).

Snow won't be a problem for the Panthers' game at the Cleveland Browns on Sunday. It will be cold (near 40 degrees) but sunny.

Thanksgiving travel could be iffy

Thanksgiving travelers have been lucky the last two or three years.

There has been little inclement weather in the East, and even the trip home for travelers has been good, for the most part. That's unusual, considering it's late November, a stormy time of year in much of the United States.

It looks like the good luck has run out.

A strong low pressure system and a couple of associated fronts will bring an assortment of bad weather to a number of popular travel destinations for Carolinas residents. That will include rainy weather and thunderstorms in the Southeast and up the East Coast, a blizzard in the Upper Midwest, possible severe weather late Wednesday in the lower Great Lakes, and utterly nasty wintry conditions in the Northwest.

Seattle and Portland, where snow rarely falls, could get some of the white stuff this week.

It's a fairly complex and fluid situation, which means the forecast likely will change a lot as we get closer to Thanksgiving and the days after, but anyone planning to travel this week should be aware that there could be a few bumps along the way.

And the bad weather will mean delays at the airports ... as if the TSA's new security measures aren't enough of a potential headache.

In the Carolinas, the bad weather probably will hold off until late Thursday and Friday.

By late Monday or early Tuesday, we should have a better idea on the timing of all this messy weather.

A winter of close calls?

Nearly every forecast I've seen for this winter paints roughly the same picture for the Carolinas and the rest of the Southeast:

1. Generally, a mild and fairly dry pattern (due to La Nina).
2. A storm track that takes most systems up the Appalachians and then through the Northeast either along the coast or slightly inland.
3. An occasional burst of arctic air southward -- with the boundary of the cold air stopping somewhere in the region of the Carolinas. Most of the time, it'll stall to the north of our region. But occasionally, it'll reach the Charlotte area.

That's why meteorologists like WCNC-TV's Brad Panovich have forecast a better-than-average chance of ice storms in our area this year. With both the cold air and the storm track nearby, we'll be on the edge between rain and frozen precipitation.

Incidentally, another common theme has been the idea that March could be a chilly and wet month in the East.

But I've seen another interesting aspect to this winter's forecast ... something to keep in mind in the weeks to come.

A couple of long-range forecasters have mentioned that they expect the computer models to produce several bogus predictions of cold air outbreaks in the East. This winter's pattern is set up for cold air and heavy precipitation in the Northwest, but some meteorologists think the computers will erroneously forecast the dip in the jet stream to progress into the East.

Most recently, I saw that comment from Dave Tolleris, who runs a private meteorological firm called wxrisk.com.

In early to mid October, some of the computer models began predicting an outbreak of cold and wet weather in the East. It never happened. We had a cold snap for a few days in the first weekend of November, but the latter half of October was mild. The prediction of stormy weather verified (remember the tornado outbreak on Oct. 25).

But the storm systems were working with mild temperatures.

Now it seems to have happened again. Some of the models earlier this week were predicting a surge of arctic air into the Southeast on Thanksgiving weekend. Now those forecasts are being scaled back.

We're looking for above-average temperatures early next week, with highs possibly reaching 70 degrees on one or two days. The cooldown will come late Thanksgiving Day, but the "arctic surge" now is predicted to be only slightly-below-normal temperatures. We're talking about highs in the middle 50s next Saturday and Sunday.

A Reminder, Folks: I saw a series of comments under one of my blog entries earlier this week, in which sometime questioned my credentials to write a weather blog.

Let me repeat what I wrote in my first blog entry ... I am not a meteorologist. I have been covering weather for almost a decade at The Observer, and I've attended a number of workshops and seminars. I've asked hundreds of questions of meteorologists, and when I don't have the answer to a question, I'll go back to them again.

This blog is not aimed at professional meteorologists. It's for people who are interested in weather, especially in the Carolinas. Basically, it's for weather geeks like myself.

I'll try to mix forecasts, weather stories, and some scientific discussion.

I am not writing this blog from a scientific standpoint. Instead, I'm trying to translate the science of meteorology into words that every-day people can understand. If I mention the North Atlantic Oscillation, I'll explain it -- rather than simply throwing the acronym NAO into this column. The same goes for a myriad other meteorological terms.

I hope that helps.

Atmosphere primed for trouble today

It won't take much to set off severe weather later Tuesday afternoon and early evening across the Charlotte region.

A low pressure system is moving northeast, on a track just west of the Appalachians. As the system moved into eastern Tennessee and Kentucky, it dragged a warm front northward across North Carolina. That put the Charlotte area in an area known as the "warm sector."

Being in the "warm sector" can mean trouble.

In today's case, it means strong winds are blowing from different directions at different levels of the atmosphere. That is known to meteorologists as shear. High levels of shear often are associated with severe thunderstorms and tornadoes.

"Shear is through the roof today," National Weather Service meteorologist Neil Dixon said early Tuesday afternoon.

But it takes another factor -- instability -- to combine with high levels of shear and create severe weather.

In the summer, daytime heating often causes air currents to rise in the atmosphere. There's your instability.

But there's not much daytime heating at this time of year, so the instability has to come from another source.

That source might be a cold front crossing the Southeast today. That front is expected to move across the Charlotte area early this evening and might produce small lines of showers and thunderstorms. If storms develop, they could become tornadic.

Severe storms and tornadoes at this time of year are especially dangerous because they can arrive with little warning.

"In this type of situation, it's possible to get a tornado without any lightning," Dixon said.

By later this evening, the cold front should have passed east of the Charlotte area. That will put an end to the severe weather threat.

My guess is the most likely place for severe weather will be in eastern North Carolina, where the instability levels probably will be higher than in the Charlotte area. But this is a situation worth watching today.

The Witch of November

I've been away from writing for about 10 days but didn't want to miss the opportunity to mark last week's 70th anniversary of one of the most deadly winter storms in U.S. history.

The Great Lakes and Upper Midwest frequently are recipients of vicious autumn storms, which are known in that area as the Witches of November.

Typically, a deep trough (low pressure system) over the Upper Midwest or in Canada causes a buckling in the jet stream, and strong storm systems ride that current of air. Frequently, these storms move inland off the West Coast, dive southward in the Great Plains, and then surge northeastward across the Midwest or Great Lakes.

As was the case with such a storm system Oct. 26 and 27, these low pressure systems can have amazingly low barometric pressures -- equal to those of Category 2 hurricanes. Normally, the result is a wind machine and sometimes a blizzard.

While the Oct. 26-27 storm set records for low barometric pressure, meteorologists usually point to the Armistice Day Storm of 1940 as the most memorable in weather history.

For some reason, many of these storms seem to form on Nov. 10 or 11, and the Armistice Day Storm was, of course, a Nov. 11 event.

It killed more than 150 people, including more than 60 sailors on ships that sank in Lake Michigan and dozens of duck hunters in Minnesota and Iowa.

The storm came with little warning, as the U.S. Weather Bureau of that time was still developing its forecasting methods. Temperatures were in the low 40s as the low pressure system swept into Iowa, Wisconsin and Minnesota, but those readings plummeted to single digits in some parts of Minnesota.

Stories of the time tell of duck hunters who were on small islands in the Mississippi River when the storm arrived. They tried to take shelter, but many drowned when the 50 mph sustained winds (with gusts around 80 mph) created waves of 4 and 5 feet on the river and inundated the hunting camps. Others died of exposure to the cold.

Nearly 17 inches of snow accumulated in Minneapolis-St. Paul, and drifts of up to 20 feet were reported in the region.

With much more sophisticated forecasting tools and better communication systems today, an Armistice Day Storm still could cause plenty of problems but almost certainly wouldn't leave such a death toll.

The Carolinas aren't immune to such a powerful cold-season storm system. A similar storm swept across the Southeast and the East Coast in March 1993, you might remember. That storm produced record snowfall in parts of Alabama, Georgia, Tennessee, the Carolinas, Virginia, Pennsylvania, West Virginia, Maryland and New York.

The immediate Charlotte area escaped with only a few inches of snow, but Carolinas mountain residents measured the snow in feet.

Autumn arrives ... at its worst

You know those beautiful crisp autumn days, when the color of the leaves contrasts against the clear blue sky?

Well, forget about it for a while.

We're facing two days of autumn at its worst, courtesy of a Carolinas specialty -- cold air damming.

And when that event ends, it'll be replaced by an invasion of the coldest air we've experienced since last spring.

After weeks in which it seemed as if daytime temperatures in the 70s and 80s would stay with us forever, some really chilly air is filtering into the Carolinas. Highs today will reach the 60s, thanks to sunshine.

But low pressure will form in the Gulf of Mexico later today and then move up the East Coast later Wednesday and Thursday. At the same time, high pressure over the Northeast will send a flow of chilly air into the Carolinas.

Cold air, being heavy, sinks. This cold air will pile up against the mountains, and clouds will form. High temperatures Wednesday and Thursday won't escape the 50s, and there'll be a chilly northeast breeze to make things worse. This situation is called cold air damming, because the cold air is dammed up against the mountains.

In such an event, sunshine and temperatures 10 to 15 degrees warmer often can be found on the western side of the mountains.

The low pressure system moving up the Carolinas coast won't be strong enough to produce much rain, and the Charlotte area won't get much more than 1/10 to 1/4 of an inch, mostly from noon Thursday to early Friday. But with the gloomy skies, it'll be rather ugly around here for a few days.

On Friday, a cold front will wash out the chilly, damp air. But it also will bring winter-like temperatures, with Saturday's highs only reaching the low to mid 50s. Morning lows Saturday probably will be around freezing, and that will put an end to the growing season for much of the area.