Tuesday, September 16, 2014

Study: Tornado season starts earlier

A group of scientists from Montana State University issued a report Tuesday that says the tornado season is starting a week earlier than in the past across a part of the Midwest known as Tornado Alley.

The report looked at tornado statistics from 1954 to 2009 and focused primarily on Oklahoma, northeast Texas and Nebraska. Scientists said they found that the peak of tornado season in recent years has been around May 19, compared to May 26 in the early and mid 1950s.

"If we take Nebraska out (of the data), it is nearly a two-week shift earlier," said John Long, a Montana State researcher who was lead author of the study.

The scientists found a link between early tornadoes in Oklahoma and the presence of stronger El Nino conditions. You'll remember that El Nino is a condition of warmer-than-usual surface water temperatures in the eastern Pacific.

El Nino conditions tend to put a lid on hurricane development in the Atlantic and Caribbean, but they also tend to produce a lot of rain and storm activity in the winter and early spring months across a corridor stretching from California and Arizona to Texas, Oklahoma, Louisiana, Arkansas, Tennessee, Mississippi, Alabama, Georgia, and the Carolinas.

So it makes sense that El Nino years would produce early tornado outbreaks.

The Montana State researchers didn't spend a lot of time in the study looking for causes of the early tornadoes, but they said it is in line with what you'd expect from a warmer climate.

Hurricane activity: As we expected, hurricane activity in the Atlantic remains rather quiet this season. The strongest storm so far, Category-3 Hurricane Edouard, is moving across the central Atlantic Ocean this week.

It is expected to curve east of Bermuda and head back toward Europe, possibly threatening the Azores with strong winds this weekend as it turns into a post-tropical storm.

Meanwhile, Odile has weakened from a strong hurricane to a tropical storm as it pushes northward through the Gulf of California, between Baja California and the Mexican mainland. That storm is forecast to make landfall in northwest Mexico and then move northward -- in a much weakened state -- into Arizona.

Look for plenty of news coverage in coming days about flash flooding in Arizona and New Mexico. Parts of those states could get very heavy rain later this week.

Thursday, September 11, 2014

Yes, that's snow falling up north

Was it really only a week ago when it felt like summer wouldn't end?

Now the Charlotte area is looking at high temperatures only in the 70s for much of next week, and some residents in the northern-most United States awakened to snow on the ground Friday.

Up to 8 inches of snow accumulated in the Black Hills of South Dakota, and the National Weather Service in Sioux City said it was the earliest accumulating snow in the region since 1888. Snow also accumulated the past two days in Canada's Alberta province and in Montana.

Low temperatures are expected to reach the upper 20s Friday morning in parts of Minnesota and the Dakotas, and Great Lakes locations like Cleveland and Detroit will see the mid and upper 40s.

Here in the Carolinas, the heart of the cold air won't arrive. The cold front will stall along the coast, and while cooler air will be sweeping into the eastern United States, the truly chilly conditions will never get into the Southeast.

Meanwhile, it's still tropical weather season in the Atlantic and Caribbean. And there are two areas of interest.

A tropical depression developed Thursday about 700 miles west of the Azores. This system could turn into a tropical storm by early Friday and a hurricane soon after.

However, computer models indicate that the system, which would be be named Edouard if it reaches tropical storm status will curve into the open Atlantic and never threaten the mainland United State.

The other system is crossing the southern part of Florida and will emerge into the Gulf of Mexico sometime this weekend. It will not have enough time to strengthen much, but it will bring heavy rain to parts of Louisiana and south Texas.

Tuesday, September 9, 2014

Cool, wet weekend; then maybe taste of fall next week

Those of you who have been griping about hot weather can celebrate.  It looks as if a real change to cool conditions is on the way, although it might make the weekend rather unpleasant.

The first real shot of chilly air is expected to push out of Canada and into the northern edge of the United States over the next few days. There will even be a bit of snow in the northern Rockies, and scattered frost over parts of Montana and the Dakotas.

That autumn-like air mass will push eastward, bringing much cooler air to the Great Lakes over the weekend and then the Northeast early next week.

The edge of that cool air will move through the Carolinas on Friday, but there are some real questions over whether the cold front will have enough of a push to reach the Deep South.  That means the front could stall over Georgia and South Carolina, setting the stage for a cool, cloudy, wet weekend.

In September and October, it's not uncommon for these late-summer and early-autumn cool air masses to get hung up near or just south of the Charlotte area. When that happens, small low pressure systems develop on the stalled front and move eastward, bringing a mix of drizzle, light rain and even moderate rain showers.

It's a version of the cold air wedge, and it could be in our future this weekend.

By early next week, computer models indicate that the front finally will push south, allowing skies to clear in the Charlotte region. If that happens, we could be in for a real taste of autumn, with daytime highs in the mid 70s and morning lows in the low and mid 50s.

A sure bet: Speaking of cold air wedges ... Tuesday was another example of how you could make a lot of money betting against the computer models when it comes to wedge patterns in the Carolinas.

The models almost always are too optimistic in predicting when the wedge will weaken and allow the clouds to break and sunshine to return. On Tuesday, the models showed sunshine returning by midday Tuesday to Charlotte, with temperatures climbing into the mid 80s.  Naturally, the clouds hung tough all day.

That happens nearly every time in these wedge patterns.

Assuming the wedge breaks down Wednesday, we'll see a brief return to summer-like weather, with highs reaching the mid 80s.  Temperatures could hit the upper 80s Thursday, but then the cold front will arrive Friday and bring it all to an end.

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.