Summer's off to a hot start

Summer doesn't officially begin until this weekend, but meteorological summer started June 1, and it's off to a hot start in the Carolinas.

Wednesday marks the third straight day of 90-degree-plus weather, and it appears as if we're in for at least three to five more days of 90 degrees or hotter before there's a change in the pattern.

By mid-afternoon Wednesday, temperatures were in the low to mid 90s across the Piedmont and Sandhills of the Carolinas. An automated thermometer in Camden, S.C., about 80 miles south of Charlotte was showing 99 degrees at 2:30 p.m.

Technically, a heat wave is a string of three or more days with 90 degrees and above, so this is officially a heat wave.

The National Weather Service forecast a high of 94 Wednesday in Charlotte. That would be the hottest temperature in the city in two years, since a reading of 94 degrees at the end of the Democratic National Convention in Charlotte -- on Sept. 1, 2012.

The hottest temperature in Charlotte last year was 93 degrees. That's a testimony to the frequent and heavy rain we got in the summer of 2013.  The rain and clouds kept the heat under wraps.

Thursday storm threat is wait-and-see for forecasters

Meteorologists in the Carolinas have a very tricky call to make, regarding the possibility of a severe weather outbreak Thursday.

There actually could be a pair of threats, with the first developing in the early-morning hours and the second on Thursday afternoon.

A clusters of strong thunderstorms was moving across the Midwest on Wednesday morning. That mesoscale convective system (MCS), a fancy word for a batch of storms, is forecast to continue moving eastward during the day, crossing Illinois, Indiana and Ohio. Then the MCS is expect to curve southeast, and that's where it starts getting tricky.

Some of the computer models predict the storms will move across Kentucky, West Virginia and Virginia overnight. Other models predict the storms will curve far enough southeast to affect the Carolinas in the early-morning hours Thursday. That MCS could bring damaging wind gusts, so the track of the storms is important.

The path of the storms also could have a big impact on what happens Thursday afternoon, when a weak cold front is predicted to move into the Carolinas.

The atmosphere in areas affected by early-morning storms will become relatively stable afterwards. That would discourage the development of afternoon thunderstorms.

So if the overnight batch of storms curve far enough southeast to affect the Charlotte area, there are questions about whether the atmosphere really will become unstable enough for another round of stormy weather in the afternoon.  If the MCS stays farther north and crosses Virginia tonight, then the Charlotte area's atmosphere will be plenty unstable in the afternoon.

Justin Lane, from the Weather Service's office in Greer, S.C., said it probably won't be until 3 or 4 a.m. Thursday before forecasters have a good idea on what will happen in the afternoon across the Charlotte region.

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.