This time, the cold air wedge does Charlotte a favor

The cold air wedge has done it again -- but this time, we should be thankful.

The wedge -- a pocket of cool, damp but relatively stable air that is pushed into the Carolinas Piedmont by high pressure systems over New England -- usually causes us plenty of problems. In winter, areas inside the wedge are prone to ice storms and snow.

In spring, the wedge often contributes to those chilly, rainy days. Does anyone remember the day before Easter?

A wedge of cool air was locked in place Monday across the northern half of North Carolina. While Charlotte was in the lower 80s on Monday afternoon, temperatures were 20 degrees cooler in Raleigh and Greensboro. Computer models, as they usually do, vastly underestimated the strength of the wedge. The models predicted the cool air would remain north of Charlotte.

It didn't. About 11 p.m. Monday, the wedge front pushed south of Charlotte. Dew point temperatures, which measure the level of humidity and instability in the atmosphere, dropped sharply. The wind shifted from south to northeast.

And at that moment, Charlotte was protected from the severe weather to the west.

As is often the case, the wedge of cool air was pushed up against the mountains. Cooler air sinks, and so it often is lodged against the mountains. That is why strong storms dumped several inches of rain overnight in Burke, Caldwell, McDowell and Catawba counties -- areas that were along, or just outside of, the cool air pocket.

So the big question is how long the cool air will remain in place?

Once again, the compute models predict the cooler and more stable air will retreat northward Tuesday. I enjoyed the comment from Justin Lane, a meteorologist at the National Weather Service's office in Greer, S.C. Talking about the predicted northward movement of the cooler air, he said, :"I don't have a lot of faith in that."

More likely, it will be late Tuesday night or early Wednesday before that happens.

Eventually, the severe thunderstorms probably will reach the Charlotte region. But the presence of the cool air wedge in Charlotte has prevented a couple inches of rain from falling overnight. That will decrease the overall storm total for the area and lessen the threat of flash flooding from whatever rain falls Tuesday night and Wednesday.

Is storm threat for real? And what about Quail Hollow?

Since late last week, meteorologists have been beating the drum -- increasingly louder every day -- about the threat of severe weather and flash flooding this week in the Carolinas.

There is a group of people that complains about weather stories that forecast doom and gloom, and I understand all that.  The critics are tired of having their fears built about bad storms (or their hopes built over winter snow) ... only to have the bad weather not develop. 

This time around, the threat seems legit.  This isn't a localized situation of a few severe storms developing on a hot summer afternoon.

Radar image from Monday morning.

A very big low pressure system that has been cut off from the main jet stream flow is slowly meandering eastward across the United States. There's enough heat and humidity in the South, and enough of a spin in the atmosphere, for severe thunderstorms to break out.

There also will be a warm front in the Carolinas later Monday, and those fronts tend to serve as triggers for severe storms.

If nothing else, look at what happened Sunday in Arkansas, Oklahoma, Nebraska and Missouri. And then watch developments Monday, especially in northern Mississippi and southern Tennessee.

Flash flooding might wind up being the biggest problem from the next three days' bad weather. Regardless of whether there are severe storms, we'll see repeated rounds of heavy showers and thunderstorms. The Carolinas have received well-above-average rainfall since December, and it won't take much to trigger flooding.

So, yes ... this appears to be a legitimate threat.

Now, will it have an impact on the Wells Fargo Championship out at the Quail Hollow Club this week?

It looks as if the four competitive rounds, Thursday through Sunday, have a reasonable chance of being played without a lot of interruptions. There still might be a shower or two in the area around daybreak Thursday, but the chances seem good of everyone getting in their first rounds. The next problem would be Saturday, with a chance of showers again. But that looks like a scattered shower situation.

Temperatures won't be summer-like.  We'll be looking at daily highs around 70 degrees and morning lows around 50. It'll feel more like early April.

As for the pro-am tournaments and practice rounds early this week ... Monday's pro-am should make it through without big problems. But any activity scheduled for Tuesday and Wednesday looks mighty unlikely.

Tornado, flood threat looms this week

A slow-moving and massive low pressure system is expected to cause a wide variety of stormy weather across the Carolinas from Monday evening into Wednesday night.

Severe thunderstorms, tornadoes and flash flooding will be threats for the Charlotte region this week, and National Weather Service forecasters say it's a foregone conclusion that the area will be under various severe weather watches and warnings over the next few days.

"This will be a very active weather week," said Scott Krentz, of the National Weather Service office in Greer, S.C.

The severe thunderstorm and tornado threat began Sunday in the Midwest and is expected to shift eastward Monday into the Tennessee Valley and Mid-South. By later Monday, that threat will reach the western Carolinas.

"I think most of the day Monday will be OK, with a few showers around," Krentz said. "But things will start to degenerate around sunset Monday.'
The severe thunderstorm and tornado threat will be at its greatest in the Charlotte region from Monday evening through Tuesday. Forecasters say a warm front that will stretch east to west along the Carolinas border Monday morning will push slowly north during the day and evening. That front will be the focal point for trouble.

"The wind shear will really increase after dark and continue to be high during the night," Krentz said, referring to a weather condition in which winds blow from different directions at various levels of the atmosphere.

Often, especially during the warm season, thunderstorm activity dissipates in the evening, with the loss of daytime heating. That will not be the situation Monday night and early Tuesday, due to the advance of low pressure and the presence of the warm front. Krentz said areas north of Interstate 40 probably will escape the severe threat Monday night, but the warm front is forecast to push northward into Virginia on Tuesday, so all parts of the Carolinas will be at risk then.

The nature of the threat changes as we go through Tuesday, Krentz said. He said severe storm will remain a possibility, but repeated episodes of heavy showers and storms will cause a flooding threat.

"I think that we'll probably be under a flood watch by then," he said, referring to Tuesday and Wednesday.

Krentz said computer models indicate about 3.5 inches of rain will fall in Charlotte from Monday night until precipitation tapers off later Wednesday. About 4.5 inches is expected in the South Carolina Upstate.

1st major severe storm threat begins this weekend

The same slow-moving low pressure system that is expected to bring several rounds of heavy rain and thunderstorms to the Carolinas next week is forecast to produce the nation's first major outbreak of severe weather this weekend.

One round of showers and storms is predicted to affect the South on Thursday evening. That area of precipitation also might trigger some severe storms Friday afternoon and evening in eastern North Carolina.

But the big event will take shape Saturday and Sunday.

A deep low pressure system is forecast to move very slowly across the Midwest both days. The center of that low is predicted to move -- at a snail's pace -- along a stationary front that will be struck in an east-west line across Maryland, Virginia, West Virginia, Kentucky, Missouri and Kansas.

Areas to the north of that front are in store for a lot of rain and chilly temperatures through the middle of next week. Areas to the south, like the Charlotte area, figure to get milder temperatures but several clusters of showers and potentially heavy thunderstorms.

Evan Myers, an Accu-Weather meteorologist, said Thursday that the first major tornado outbreak of the year is expected to develop Saturday in northern Texas, Oklahoma, Arkansas, Missouri, Kansas and southwest Illinois. By Tuesday and Wednesday, that area will reach the Southeast.

"Indications are it will move slowly," Myers said.

NOAA's Storm Prediction Center in Oklahoma also is warning about severe weather caused by the slow-moving low. It is mentioning the chance of strong tornadoes this weekend in the Deep South and the Mississippi Valley.

By the time that precipitation area reaches the Southeast later next week (Tuesday and Wednesday, most likely), the nature of the threat is expected to change from tornadoes to a pattern of damaging wind gusts, hail and flash flooding.

Next week figures to be very interesting for the Carolinas.

Incidentally, meteorologists agree that once the low pressure system eventually wobbles off the East Coast late next week, a pattern of summer-like weather will take hold in the South. The week of May 5-11 could produce a lot of 80s in the Carolinas.

What to wear at the Wells Fargo: How about a rain coat?

The feature story on the Charlotte Observer's website Wednesday afternoon is a piece by Cristina Bolling on what fans should wear at next week's Wells Fargo Championship golf tournament.

Cristina's story focuses on what a well-dressed golf fan will wear to Charlotte's PGA tournament.

My suggestion: Rain gear.

By nearly every prediction, it looks as if we're in for a very wet week -- with the emphasis on "very."

The computer models insist on creating a blocking pattern over Greenland and northeast Canada. That will stall the west-to-east movement of weather systems across the United States. And considering that a slow-moving low pressure system is expected to be in the eastern half of the country next week, it's a recipe for days of rainfall.

The good news is that it apparently won't be a cold rain -- at least not in the Carolinas. Chilly temperatures and the rain could be confined to areas north of the Mason-Dixon line. High temperatures each day look to be from the upper 60s to the mid 70s.

But the upper-level low pressure system will barely move during the week, becoming a cut-off low pressure system that is left outside the jet stream and becomes stuck over the eastern United States. In those kinds of situations, we tend to get frequent periods of showers and thunderstorms. Severe thunderstorms usually don't develop in those patterns, but storms with heavy rainfall are more likely.

The exact timing is a bit uncertain, but it appears as if showers will begin to move into the Carolinas on Monday, with the amount of rainfall increasing Tuesday and Wednesday. It could be the end of the week before the cut-off low finally meanders off the East Coast.

Charlotte's rainfall since early December is several inches above average, and it appears as if we'll add to the surplus next week.

An update on this Easter weekend washout

It's late Saturday afternoon, and an update on what to expect for Easter might be in order -- especially many people will be attending sunrise services in the morning.

Obviously, the weekend so far has been a miserable washout. In fact, the spring break week for children in the area has been largely a bust.  That also goes for the original forecast for this weekend. If you'll remember, we were talking as late as Wednesday about 70 degrees (with clouds) for Saturday and sunshine and 70s for Sunday.

A low pressure system that was stronger than expected and slower than expected has ruined all that -- just like a cold high pressure system over New England ruined most of the outdoor plans for students last week.

We're approaching 2 inches of rain from this weekend's storm, and we've passed 4.5 inches for the month. That means April will make five of the last six months with above-average rainfall for Charlotte. Let's remember that the first time we have five straight dry, warm days, and someone starts talking about "drought."

So what about the rest of the weekend?

Easter Sunday will not start great.

Since the left-over moisture from the very slow-moving low pressure system will still be around in the morning, and we'll still have a cool northeast flow, I think daybreak will be cloudy, misty and cool (upper 40s).

Figure on the clouds hanging around all morning, then slowly breaking in the afternoon. It won't be a warm day, either. Those morning clouds and the northeast breeze will limit highs to the mid 60s, and that might be a stretch.

Temperatures today were more than 20 degrees below average, and they'll be 10 degrees below average Sunday, too.

In short, it'll be a great indoor Easter.

It looks like conditions turn warmer next week, and since the students will be back in school and most of us back at work, that figures.

Back in March, we said spring would be slow to arrive this year in the eastern United States. And it has played out that way. Cold air has been persistently lodged in the northeastern part of the country since January. Here in the Southeast, we've had brief warm spells over the past few weeks, but cold high pressure repeatedly has wedged its way into the Carolinas, and we've been visited by these cold rainy systems.

Until the pattern breaks, expect more of the same.

The good news is that the pattern has kept storm systems from moving up the Tennessee and Ohio valleys, for the most part, and that has saved us from severe weather outbreaks.

Are we safe from frost? What about Easter weather?

The two questions I've been hearing a lot in recent days concern frost and the advance outlook for Easter weekend.

As you well know, there are dangers in giving definitive answers in either case.  The date of the last frost is an average, with wide variations. And predicting the weather for Easter, which is 10 days away, taxes the limits of meteorology.

But let's talk about it.

The average date of the last frost in Charlotte is April 2, according to numbers I found, although I also discovered a listing that said "somewhere between April 1 and 10." By either of those averages, we are safe.

But you'll be taking a chance, as you know, by planting anything tender vegetation now.  It's a small chance, but we've had freezing temperatures as late as April 25 in recent years (31 degrees on April 25, 2005). And it doesn't take freezing temperatures at Charlotte Douglas International Airport for frost to develop. If it's in the mid 30s at the airport, there easily could be frost nearby.

Looking at the last several years, here are the last dates of chilly temperatures:

2013 ... April 20 (39 degrees)

2012 ... April 24 (39 degrees); also April 13 (34 degrees)

2011 ... May 5 (36 degrees)

2010 ... April 29 (38 degrees)

Computer models show some chilly air infiltrating the Carolinas next week after the current warm spell is broken. If skies are clear at night, we easily could see some mid and upper 30s in the region. However, there are signs that the period from Wednesday through Good Friday, the three-day period of the coolest weather, could be cloudy. That would keep overnight readings warmer than they otherwise might be.

About Easter ...

Several long-range forecasts show the same thing next week -- cloudy and rather cool temperatures from Wednesday through Saturday, the day before Easter.  Predicted highs are in the mid and upper 60s, and there could be some rain around Good Friday.

But the good news is that most of those forecasts show clearing skies and much warmer temperatures for Easter Sunday, with highs around 80 degrees.

The amazing power of the cold air wedge

We talked for several days about the revved-up weather that we were expecting today. It was to be a one-two punch of heavy rain in the morning and then severe storms in the afternoon and evening.

The first part developed pretty much as expected.  But the severe storms apparently will be a no-show for the Charlotte region.

And it's all because of the amazing power of the cold air wedge.

A quick review ... the cold air wedge is the name given a condition in which cool air becomes trapped in the Piedmont and foothills of the Carolinas and Virginia.  Typically, an onshore wind brings the cool air into the Carolinas. Since cold air is heavier than warm air, it sinks -- and becomes trapped against the mountains.

Sometimes we get what's called an in-situational cold air wedge.  The air is relatively cool and quite dry. Then precipitation from a low pressure system arrives. As it falls into the dry air, it cools temperatures even more.

Often in these situations, a warm air mass is lurking somewhere to the south or southeast. Occasionally, a warm front plows into the cold air wedge and erodes it.  Usually, the cold air wedge holds on. When that happens, Charlotte is stuck in the soup, with chilly, damp conditions.

Weather computer models frequently err in predicting the erosion of the wedge. They tend to forecast the wedge will break down, but that often doesn't happen. Today is the latest case in point. The warm air that several of the models predicted would reach the I-85 corridor by Monday afternoon hasn't even pushed west of I-95.

The cold air wedge is a real pain for meteorologists, whose forecasts are busted when the warmer air never arrives.  Charlotte was supposed to have reached the middle 60s by late Monday afternoon. Barring something unexpected, temperatures will remain stuck in the lower 50s.

At 3 p.m. Monday, it was in the upper 70s along the coast and about 40 miles inland. Temperatures were 30 degrees colder along the I-85 corridor. And to the west of the mountains, temperatures were in the low and mid 60s, on the other side of the trapped air.

Monday could be a wild, wacky weather day

Rainy days and Mondays are not a big hit with most people, especially when they're one and the same.

But Monday could be a very interesting day for weather geeks, especially if you live in the southern portion of the Charlotte region.

A big storm system that covers hundreds of miles and much of the South will affect the Carolinas on Monday, bringing plenty of rain and a chance of severe weather in some places.

If you live to the northwest of Interstate 85, chances are Monday will be a chilly, wet day -- and not a whole lot more. Places like Hickory and Statesville probably will stay in the lower 50s for much of the day, with a steady, soaking rain falling.

To the southeast of I-85 ... that's another story.

First, for the basics.  The center of low pressure will move northeastward Monday, crossing Tennessee and into Kentucky. A cold front that pushed south of Charlotte on Friday evening is moving back to the north as a warm front. Forecasters say any severe weather that develops Monday will be in the warmer, more unstable air.

The question is how far north that front will get. Cool high pressure to our north and falling rain have created a cold air wedge over the Carolinas, and severe weather won't develop in that cool pocket. But the northward-moving warm front on Monday will trim back the cold air pocket. Computer-generated forecasts show the warm front pushing as far north as I-85.

Typically in these situations, the cold air wedge is very difficult to dislodge. If Charlotte, Monroe, Rock Hill and Lancaster get into the warmer air, it probably won't happen until mid or late afternoon.

So here are some things to look for Monday:

1. A lot of rain across the entire area. The National Weather Service is predicting about 1.6 inches in Charlotte, Concord, Monroe, Rock Hill and Salisbury. The forecast is closer to 1.8 or 1.9 inches in Gastonia, Lincolnton, Hickory, Statesville and Shelby. Heavier amounts are possible, however.

2. Most of South Carolina will get into the warm, unstable air.

3. As the warm front moves into North Carolina, it will push inland toward the foothills. Areas east of U.S. 1 are likely to get into the warm, unstable air. How much of the area between U.S. 1 and I-85 gets into the warmer air? That's the question mark.

4. Winds in the atmosphere -- south of the warm front, at least -- will be set up to create rotating thunderstorms.

5. There will be remarkable contrasts in temperatures Monday. Don't be surprised to see some afternoon temperatures in the foothills in the upper 40s, while it's 75 degrees in Columbia or Florence, S.C.  And especially in the early afternoon, don't be surprised to see readings around 70 degrees near Wadesboro or Pageland, S.C., while it's 15 to 20 degrees colder in Gastonia or Lincolnton.

6. If fog develops, it could be a sign that you're near the warm front. Warmer air will pile into the area from upper levels of the atmosphere, squashing the cooler air toward the surface. That's when fog develops. If it's foggy in your area, and the ceiling suddenly lifts (and the temperature climbs), it's an almost certain sign that you're south of the warm front.

Monday could be a stormy and very wet day

We've been spared the typical springtime weather woes of heavy rain events and severe thunderstorms, largely because of that persistent block of cold air to our north that pushed its way into the Carolinas frequently in February and March.

But things are shaping up for a potentially wild day on Monday.

Our string of 80-degree days will come to an end when a cold front pushes across the region later Friday night. Behind the front on Saturday, we'll have a very nice day, with partly sunny skies and temperatures somewhere around 70 degrees.

But then things go downhill.

Low pressure is expected to form in the lower Mississippi Valley on Sunday and push northeast. The track of the system is important, because the center of the low is predicted to push across Louisiana and Mississippi through Tennessee and then Kentucky.

Clouds will increase in the Carolinas on Sunday, and it probably will be a chilly day, with temperatures not getting much above the lower 60s. And rain from the low pressure system is expected to arrive by Sunday evening.

Andrew Kimball of the National Weather Service's office in Greer, S.C., said computer models indicate "copious amounts" of moisture will be spread northward from the Gulf of Mexico into the Carolinas.

How much is "copious"?  Some of the computer-generated forecasts show up to 3 inches of rain falling from the system.  That would be enough to cause some flooding problems in areas where the heaviest rain falls.

But that's not all.  Remember the cold front that passes through our area tonight. It will stall somewhere to the south of us this weekend, then be dragged northward by the low pressure system pushing up through Tennessee and Kentucky. All the ingredients will be there for severe weather sometime Monday.

Areas to the south of that front will be at risk of severe thunderstorms with damaging winds and hail. And tornadoes will be possible, too.

It's nearly a sure thing that much of South Carolina will be in the warm sector south of the front. Kimball said computer models predict the front will move far enough north to put the I-77 / I-85 area in the warm sector, too. And there even is a possibility of the front pushing up to the foothills.

Rain, some of it heavy, is a very strong possibility from Sunday evening through late Monday. And severe weather will be in the mix, too.

We'll watch how this develops over the next few days.

Snowfall totals, and more Grandfather Mountain

I saw a list of North Carolina snowfall totals for the 2013-14 season, while I was looking around on various weather bulletin boards the other day. I don't recall exactly where I saw it, but I think it was at the American Wx page (www.americanwex.com).

Anyways, I was struck at the lack of uniformity in snowfall in various parts of the state. Some reporting stations within a few miles of each other had very different totals.

I think these totals came from CoCoRaHS observers, so they might not be the same numbers you get from the official National Weather Service reporting stations.

By the way ... I wrote a story online last week about the recruiting drive for more CoCoRaHS observers. Sometime in the next few days, I'll devote one day of this blog to some of the interviews I conducted with those observers. They are really neat people -- true weather geeks.

But back to the snow ...

In our part of the state, most of the snow fell Feb. 10-13. We had some light snow on the night of Monday, Feb. 10, then about an inch on grassy surfaces on Tuesday, Feb. 11. The major snow fell on Feb. 12 and 13.

Anyways, here are some of the numbers I culled:

Mount Mitchell ... 35.5 inches

Boone ... 33.8

Winston-Salem ... 16.3

Greensboro ... 15.3

New Bern ... 14 (kind of strange for a coastal area to be among the state leaders, but that's the way it works sometimes)

Rockingham ... 10.3

Salisbury ... 10.1

Concord ... 9.6

Asheville ... 9.4

Charlotte ... 9.3

Hickory ... 8.7

Greenville ... 7.2

Raleigh ... 5.8 (that number seems low)

Wilmington ... 0.6

Snow-lovers are never satisfied, but it seems as if they had a good year.  It always kind of intrigues me how people in the Carolinas cheer for snow, while their counterparts in the North would be happy to have snow-less winters.

More on Grandfather Mountain ,,, Yesterday, I wrote about the iconic Grandfather Mountain sign being crushed by wind gusts Sunday. The sign had stood for more than 50 years in Linville, but the impact of rough weather over those five decades finally claimed the sign.

Today, I heard from Sherry Fletcher, who says she and a group of people are lobbying officials to replace the sign -- with something resembling the original Grandfather Mountain sign. She says they have a Facebook page with 600 members. Here's a link, if you're interested -- https://www.facebook.com/groups/498965223547384/

And I have a correction to make. Yesterday, I wrote that the 13 inches of snow in February at Grandfather Mountain set a record for the month. I should have known better, because that total is far too low for a record.

Anyways, Kellen Short of Grandfather Mountain sent me a note today, reminding me that the February total was the most for this season.  He says they believe the February record is 36.81 inches of snow, in 1971.  And the record for any one month is 64.05 inches in March 1960.  That, of course, is the month when it snowed every Wednesday over much of the state.

Sunday's wind claims an iconic victim

Those gusty winds that left tree limbs cluttered across your yards and knocked out power to some Carolinas residents on Sunday also did a number to one of North Carolina's well-known tourist attractions.

The large wooden sign that advertised Grandfather Mountain for the past half-century was flattened by wind gusts early Sunday in Linville. Officials at Grandfather Mountain say the sign, at U.S. 221 and N.C. 105, had been designed by architect Charles Hartman, the same person who designed the famous Mile High Swinging Bridge.

"The sign was an icon in North Carolina's travel industry," said Harris Prevost, vice president of Grandfather Mountain Stewardship Foundation. "It was pure Americana -- 1950s, all the way. We're sorry to see this piece of history lost forever."

Grandfather Mountain officials say the sign was painted in bright yellow and green when it was built in the late 1950s, and then repainted in tan and brown in 2006. (The photo of the damaged sign above was shot by Kellen Short of the Grandfather Mountain Stewardship Foundation.)

The weather station at the Mile High Swinging Bridge recorded winds of up to 92.5 mph early Sunday. That is a lot stronger than elsewhere in North Carolina, but Grandfather Mountain is noted for having some extreme winds.

Wind speeds recorded atop the mountain came into question from some scientists, especially after the anemometer measured a 200 mph gust in 2006. Critics said the measuring device was mounted atop a building, allowing wind to funnel up the side of the building to the top -- producing an inaccurate measurement.

Grandfather Mountain officials responded by positioning the anemometer atop the Swinging Bridge, free of any interference.

Record Snow ... By the way, Grandfather Mountain set a record in February for the snowiest month ever up there.  More than 13 inches fell during the month, including 10 inches on Feb. 13. That was the same storm that brought about 8 inches to Charlotte.

Sometime over the next few days, I'll publish a list of snowfall totals across the Carolinas for the winter of 2013-14.

But Mount Mitchell led the way with about 35 inches, a few inches more than Grandfather Mountain.
This is the iconic Grandfather Mountain sign that was felled by Sunday's strong winds.