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.