Wednesday, August 27, 2014

Has this been a cool summer?

Several times this week, someone mentioned to me that this has been an unusual summer. When I asked what was unusual, the other person mentioned "cool weather."

Without checking the statistics, I agreed.  I remember a large number of mornings since mid-July when temperatures were in the lower 60s -- and, in a few cases, even the upper 50s. The low temperature Wednesday morning at Charlotte Douglas International Airport was 57, just 2 degrees off the record for the date.

Temperatures are a few degrees below average in August and were a bit below average in July.

But the numbers tell a different story. I defined "cool mornings" as days when the low was less than 65 degrees. In mid-summer, Charlotte's average daily low is almost 70 degrees.

By that measure, August 2014 has been pretty much the same as the last three years. July 2014 was definitely cooler, though.

Here's a look at the numbers in Charlotte, through Wednesday:

AUGUST

Cooler than 65 degrees in 2014: 5 days (4 more had a low of 65).

2013: 6 days (2 more were 65)

2012: 9 days (3 more were 65)

2011: 7 days (3 more were 65)

2010: 2 days

JULY

2014: 6 days (2 more were 65)

2013: 0

2012: 0

2011: 2 days (1 more was 65)

2010: 4 days, including 2 in the 50s (1 more was 65)

Weather records show that Charlotte usually gets a stretch of several days in August, usually near the end of the month, when cooler temperatures seep southward and lows are in the low 60s. That doesn't usually happen in July, however.

All things considered, this has been an ordinary summer in the Carolinas, with a stretch of wet and rather unpleasant weekends in late July and early August.

Saturday, August 23, 2014

Will Cristobal be a fish storm, or another Arthur?

A tropical depression developed Saturday evening in the southeast Bahamas, and the National Hurricane Center expects the system to become a tropical storm on Sunday and a Category 1 hurricane by late Tuesday or Wednesday.

It will be the third named storm of the Atlantic season, Cristobal.

Now comes the fun part ... figuring out what impact, if any, Cristobal will have on the Southeast coast, and the Carolinas in particular.

The official National Hurricane Center forecast map calls for Cristobal to remain a few hundred miles off the coast, sort of splitting the difference between Arthur, which made landfall on the North Carolina coast July 3, and Bertha, which passed about halfway between the United States and Bermuda.

Cristobal's sustained winds are forecast to be 80 mph by Thursday.

If you look at the computer models, they mostly forecast Cristobal to move northerly from the Bahamas and remain off the Florida coast, then curve a bit northeast and miss the Carolinas comfortably.

But if you remember correctly, the official forecast for Arthur also called for a miss. That didn't happen.

It appears as if a trough over the Northeast would grab Cristobal and steer it away from the mainland, but there is enough uncertainty over what will happen later this week to make National Hurricane Center meteorologists a bit nervous.

As forecaster Michael Brennan said Saturday evening, it's a low-confidence forecast right now.

Thursday, August 21, 2014

Heat wave won't last long for us

Strong high pressure is building over the lower Mississippi Valley, and it's pumping the hottest air of the summer into the Carolinas on Thursday and Friday, but the Charlotte region won't have to endure the heat as long as our neighbors to the west.

Slightly cooler weather is likely Saturday, and a pronounced cooldown will arrive Sunday and last through the middle of next week.

That's because another high pressure system is forecast to build this weekend in the New England area. If that sounds familiar, it's because New England highs have been the dominant pattern in the eastern United States since mid-July.

The New England high will push its influence down the East Coast, driving a "back-door" cold front southward across the Carolinas on Saturday night. Behind that front, we'll be in a cooler air mass that also will be stable enough to prevent thunderstorm activity.

That cold front won't push much farther west than the eastern part of Georgia, so much of the South -- except the Carolinas and Virginia -- will continue to deal with temperatures in the mid and upper 90s into early next week.

For us, it'll be low to mid 80s for highs from Sunday through next Wednesday.

Before that, it will be hot. Temperatures climbed into the mid 90s Thursday afternoon across the area, and National Weather Service meteorologist Harry Gerapetritis said we could add a degree or two Friday. "Southern Piedmont heat index values could surpass 100 degrees Friday afternoon," Gerapetritis said, referring to the combined impact of temperature and humidity.

By Saturday, that New England high will be pushing its influence into Virginia. That, in turn, will push the track of thunderstorms from Kentucky-West Virginia-Virginia-Maryland farther south, into the Carolinas. We could see another 90-degree day Saturday, but there'll be more clouds and higher thunderstorm chances than Thursday and Friday.

The cooler weather will be apparent Sunday, with more clouds than sun and highs around 82 degrees in Charlotte.

Those cooler conditions will arrive just in time for the first day of school for most of North Carolina's public school students.

And in the tropics ... The National Hurricane Center is following an area of disturbed weather east of the Lesser Antilles. That area could become a tropical depression by Friday, and it's forecast to curve northwest.  That track will take the system near Hispaniola and Puerto Rico, and that means the mountains of those two islands could suppress the storm's development.

Once it clears those islands, it's expected to strengthen again over the Bahamas by late in the weekend or early next week.

I've seen talk about a possible impact on the U.S. Gulf or Southeast coasts, but that's extremely premature. The system could disintegrate over the Dominican Republic and Haiti, or it could recurve away from the U.S. coast.  It's far too early to worry about anything threatening the U.S. mainland.

Otherwise, it's quiet in the tropics as we move into what is typically the busiest time of the year for hurricanes. But that's what forecasters expected this year -- a quieter season.

Monday, August 18, 2014

Plenty of question marks in this week's forecast

At first, it seemed so easy.

A strong high pressure system would build over the Carolinas, and we'd experience a week of hot weather -- perhaps our hottest week of the summer.

The heat would extend through the week and possibly into the early part of next week, with only a few chances of thunderstorms. The greatest chance of storms would come Monday afternoon and evening.

Scratch that idea.

As it turns out, Monday's thunderstorms affected the mountains during the morning, then split apart and developed in the afternoon over the South Carolina Midlands and up in Virginia. The Charlotte region could escape without a drop of rain.

And as for the rest of the week?

Well, it figures to be warm, but not at the kind of levels -- mid and upper 90s -- that we first expected. Instead, it appears as if the Carolinas might wind up being right along the path of several clusters of showers and thunderstorms being shunted from the Great Lakes southeastward.

High pressure that has dominated the western United States has shifted a bit to the east, and the computer models indicate that the Carolinas will be on the eastern edge of the high. Often, clusters of storms -- known to meteorologists as mesoscale convective system (MCS) -- form on the edge of the high pressure systems and are steered around that edge.  It appears as if the Carolinas could be on that edge.

That means these clusters of storms could move into the Carolinas at times during the week. For meteorologists, that's a headache.  It makes forecasts of more than 36 or 48 hours a bit risky, and that could be the case this week.

And later in the week, there are growing signs that another cold air wedge could push into the Carolinas. Those wedges, formed when cool and moist air is pumped from the Atlantic Ocean into the Piedmont by high pressure systems over the Northeast, have made frequent appearances this summer in our region.

If that happens, forget about the 90s this weekend.  We could be looking at thick overcast and temperatures in the mid and upper 70s.

Thursday, August 14, 2014

Summer is about to deliver some heat

I hope you haven't caught yourself thinking that maybe we're done with the heat this summer.

The computer models are pointing toward a warmup over the next few days, and that could be followed by some even warmer temperatures by the end of next week and into the start of the kids' school year Aug. 25.

We're not talking about 100-degree weather, but temperatures in the mid 90s will feel hot, after the kind of weather we've experienced since mid-July.

Carolinas' temperatures -- and, in fact, readings across the eastern two-thirds of the country -- have been well below average for the last four or five weeks. In Charlotte, we're nearly 3 degrees below the monthly average temperature so far.

It's been wet, too. While the rainfall numbers at Charlotte Douglas International Airport haven't been noteworthy, there have been several heavy rain events across the region recently. Beachgoers know what I mean. Rain has fallen three straight weekends on the Carolinas coast.

I spent last week at Sunset Beach, and rain fell all seven days I was there.

It only makes sense that things will change, and now that seems to be taking place. Our pattern for the past month has been wet and cool, but the computers are hinting at a change -- warm, with only scattered daily thunderstorm activity.

The Global model was producing forecasts this week that point to 100-degree weather in the Carolinas around the Aug. 23-26 period, but with all the rainfall we've had since mid-July, it doesn't seem likely that we'll get that hot. Some of the heat will be expended drying out the ground, so we'd probably see mid 90s instead.

We'll also be watching the Atlantic, because the tropics have been quiet so far this season.

That was the prediction, with an intensifying El Nino in the Pacific basin expected to limit the development of tropical storms and hurricanes in the Atlantic and Caribbean. But we've had only two named storms so far this season, and that's the smallest number at mid-August since 2009.

Once again, it makes sense to expect some development in the Atlantic next week.

And what about autumn? The government's Climate Prediction Center seems to be pointing toward a warm autumn for the Carolinas.

The forecast for August through October calls for average temperatures, but the September-November and October-December forecasts show a strong chance of above-average temperatures -- and above-average precipitation.

In other words, expect warm and wet weather for September, October and November.

And that ties in with a couple of autumn forecasts I've seen in recent days.

Tuesday, July 22, 2014

Dreary weather pattern preparing to change

I feel sorry for anyone who's tried to take vacation days since last weekend -- assuming those vacation plans involved anything outdoors.

Charlotte-area weather has been rather unpleasant. It's been wet in many places, the humidity has been high, and sunshine has been scarce. Temperatures have been cool, but I realize some people are pleased with that development.

That cool high pressure system that we talked about 10 days ago set up shop over the Northeast, and that provided the area with the below-average temperatures last weekend. Then an upper-level low pressure system moved into the Florida Panhandle area and became stationary for a few days.

The Charlotte region was on the boundary between the influence of high pressure to the north and low pressure over the Gulf coast. Along that boundary, showers and thunderstorms developed. The Florida low pumped enough tropical moisture into the area that heavy rain fell. At my home in Matthews, we've recorded as much rain in the past week that we normally get for all of June and July.

Now all that is ready to change, for a few days, at least.

By Tuesday night, the Florida low will backtrack to the west, and the prevailing east-southeast flow in the Carolinas will switch around to the southwest and west.  That will help dry things out.

The results should be obvious Wednesday, with more of a typical summer pattern -- highs in the upper 80s, humid conditions, and afternoon thunderstorms. But "typical" won't last long.

Another cold front is forecast to barrel into the area Thursday, and drier conditions will follow Friday and Saturday.

One key player in the weather pattern has been a large area of stifling hot high pressure over the Southwest. That strong high has been nearly stationary, and it has helped set up a blocking pattern over the United States.

Much of the Great Lakes has been rather cool this month. Energy use in parts of Indiana, Michigan and Illinois is 25 to 30 percent below seasonal averages.

While Charlotte has seen some cool weather in recent days, we're only about 1 degree below average for the month. The number of cooling days -- a measurement of how the weather affects air conditioning use -- is down about 5 percent for the month in Charlotte.

It looks as if the cold front that moves through Charlotte later Thursday will dissipate after reaching the coast. Then warm and humid conditions with afternoon thunderstorms will return for next week.

Paul Pastelok, a long-range forecaster for Accu-Weather, thinks August could mark a return to more typical summer weather. He said a Bermuda high pressure system likely will establish itself off the Atlantic coast and dominate Eastern U.S. weather.  That Bermuda high, a fixture of summer weather in the Southeast, has been missing in recent days.

Sunday, July 13, 2014

Polar vortex this week ... in July?


Monday morning update: Well, common sense has taken over. The latest computer models show high temperatures for the middle and end of the week, after the cold front passage, in the mid 80s. This is certainly cooler than average, but it's also not anything in the "remarkable" category.

It'll be a break from the recent 90s, but it will still feel like summer. After all, this is July and we're in the Carolinas.

Earlier post: There has been a lot of conversation in weather circles about a rather unusual meteorological event that is likely to take place this week in the eastern United States.

Some are calling it the return of last winter's "polar vortex" -- a deep low pressure system over eastern Canada that drags cool air into the eastern part of the United States. Back during the winter, especially in January, when Charlotte averaged nearly 5 degrees below seasonal norms, the polar vortex was blamed for the extremely cold weather that settled into the East.

It was responsible for temperatures that plummeted far below zero in the Great Lakes and Northeast. The Carolinas weren't immune either.  My birthday, Jan. 7, featured a morning low of 6 degrees that ruptured a lot of water pipes.

If you look at the weather map, this week's forecast conditions bear some resemblance to last winter. Once again, a deep low pressure system will move across Canada and take up residence in the eastern part of the country. The Washington Post's weather crew, the Capital Weather Gang, examines the situation in this article.

The National Weather Service office in Greer, S.C., began discussing the situation late last week, when it appeared as if the Eastern Canadian low would drive a strong cold front through the Carolinas and off the coast.  In that situation, Charlotte could experience high temperatures at mid and late week in the upper 70s and lower 80s.

But now the computer models suggest the cold front won't make much progress south of the Charlotte region and eventually will stall just to the south. That seems more logical, given the time of year and our location in the South.

Still, it appears as if we're looking for unusually cool weather this week for the middle of July. And to the north, farther away from the stalled cold front, this week's temperatures will be unusually chilly. Some of the Great Lakes cities like Cleveland, Detroit and Chicago might struggle to get into the low 70s at midweek.

It's not really a "polar vortex," because the source of the system will be Alaska, not the polar regions. But this week apparently will give Charlotte-area residents a definite break from the type of mid-July heat we're accustomed to.