Friday, June 21, 2013

Another 'supermoon' this weekend

We'll experience another of the so-called "supermoon" events this weekend, marking a time when the moon's closest proximity to the earth nearly coincides with the moment when the moon reaches "full" status.

Astronomers actually call this a perigee full moon.  Perigee is the term used for the point each month when the moon is closest to the earth.

The distance at perigee differs a bit from month to month, and the two celestial bodies will be closer than normal this time.

When the moon becomes full, at 7:32 a.m. Sunday in the eastern United States (well after daylight), it will be 221,824 miles from the earth.

What all this means, in effect, is the full moon up there in the sky Saturday and Sunday nights will be closer to the earth than usual. We're not talking about a lot of mileage. It's about 25 to 50 miles closer than many other months.

Of course, tides are a bit higher than normal at full moon, and that will happen this weekend.

Somehow, the term "supermoon" has become the popular term for the perigee full moon.

The biggest of these events comes Nov. 14, 2016, when the earth and moon will be 240 miles closer than they will be this weekend.

Thursday, June 20, 2013

Alaska -- the tropical paradise

Some of you weather geeks might know this already, but Alaska is experiencing some amazingly warm weather this week.

High pressure that typically establishes itself over central Canada, and at lower latitudes, has been parked over the Yukon and eastern Alaska for several days. The result has been some true summer weather up there.

Some meteorologists think the Alaskan heat eventually will have an impact on weather in parts of the lower 48 states.  More about that later.

First, here are some numbers from the land of the midnight sun:

Fairbanks has reached 86 degrees or higher for five straight days. It was 88 there Sunday. They've reached 90 degrees a number of times, but an extended streak like this is unusual.

Anchorage got to 81 degrees Tuesday, for its first 80-degree day in four years. Snow fell there a month ago.

Nome hit 86 degrees Wednesday, tying a record for the date. The average high on the west coast of Alaska is 56 at this time of year. Just 13 days ago, Nome had a high of 38 and snow fell.

Barrow, at the northern end of the world, got to 50 degrees Wednesday. The average is 42. The forecast for Thursday is upper 50s, possibly 60.  This is a place that stays well below zero for weeks at a time in the winter.

Juneau, down on the southeast part of the state, had 78 Wednesday.

The little town of Talkeetna, about 80 miles north of Anchorage, recorded 96 degrees Tuesday.

The high pressure system shifted a bit east Thursday, and temperatures are expected to be a few degrees cooler. But the National Weather Service in Fairbanks said Thursday morning that computer models indicate a return to the heat next week.

And I saw a story on Accu-Weather's website in which meteorologist Alex Sosnowski predicted  that the hot air eventually will be pushed southeast, tempered a bit, and affect Canada and the northern part of the United States.

Here's hoping Alaskans remember this heat next January, when it's 40 below zero in Fairbanks.

Wednesday, June 19, 2013

Derecho or not, last week's storms were nasty

A long-lived outbreak of violent thunderstorms that left millions of people without power last June in the mid-Atlantic introduced the term "derecho" to many people in the United States.

Then came another round of damaging storms last week -- affecting the Charlotte region, along with other parts of the Southeast and mid-Atlantic -- and the "derecho" word is back again.

I've seen some debate in recent days over whether the line of severe thunderstorms that roared across the region last Thursday was actually a derecho.  I don't think there's an official definition for the word, so the debate will continue.

But if we assume a derecho is an hours-long event in which a line or cluster of thunderstorms pushes for hundreds of miles, then our outbreak last week fits the description.

About 200,000 customers in North Carolina lost power in the storms. Some residents of Stanly County didn't get electricity back until Sunday, nearly three full days after hundreds of trees were blown onto roads, homes and power lines.

I got a taste of it.  Our home in Matthews was without power for about 20 hours -- long enough to spoil the food in the refrigerator.

Those storms were a reminder of how many people become fixated on meteorological terminology, rather than dealing with reality.

In hurricane season, some people worry about the location of landfall and the top sustained winds of a system.  They don't concern themselves about the dangers presented by a hurricane or tropical storm after it moves inland.  I've written many times about the problems presented by a dying storm -- the flash flooding, the tornadoes.

It's the same thing with thunderstorms.  Many people worry about tornadoes, dismissing severe thunderstorms as a weak cousin.  But as I've written before, those severe storms can carry winds of up to 100 mph and are capable of causing extensive damage.

Anyways, I pass along links to a couple of things worth looking at.

The Washington Post's Capital Weather Gang is a nice website, although it (understandably) focuses on the mid-Atlantic.  Kathryn Prociv wrote an interesting piece, comparing the 2012 derecho with last week's event.
In that article, she reaches the conclusion that the 2013 event was bigger but not as strong.

And I add a link from NOAA's Storm Prediction Center, showing the progress and damage reports from last week's storms.

It'll give you a healthy respect for the power of severe thunderstorms.

Monday, June 17, 2013

Imagine that -- no drought!

I've heard from a number of you about all the rain we've had recently in the Charlotte region, and while nearly everyone says we "need the rain," I also frequently hear that "enough is enough."

But the rain is good news, in at least one way. For the first time in three years, none of North Carolina has "dry" or "drought" conditions, according to the U.S. Drought Monitor.

Charlotte's official measuring station at Charlotte Douglas International Airport shows more than 5.6 inches of rain has fallen so far in June. That's well more than twice the average for June 17, and conditions indicate quite a bit of additional rain is possible this week.

Some locations in the region have been hit with much more. There are a number of automated stations showing rainfall of 8 inches or more this month.  A couple inches of rain fell early Monday in parts of Burke and McDowell counties, for example.

Some of this month's rain was courtesy of Tropical Storm Andrea, of course, but there also have been a couple of stalled fronts and slow-moving low pressure systems responsible for downpours.

The central and western part of North Carolina escaped the "dry" classification earlier this year, and now Tropical Storm Andrea's rain has lifted the eastern third of the state from that classification.

Scientists say this is the first time since the week of April 20, 2010, that not an inch of the Tar Heel State is experiencing either "dry" or "drought" conditions. There have been times during that period when the Charlotte area was classified as experiencing drought, but rainfall has been quite plentiful locally for several months.

All this can change in a hurry, of course.

Evaporation can take place quickly in summer.  A strong high pressure system over the Southeast can create searing heat, which dries the ground in a hurry and tends to cut off the development of afternoon and evening thunderstorms -- thereby reinforcing the dry conditions. That happened near the end of June last summer.

"North Carolina's rainfall becomes more difficult to forecast -- as well as less reliable -- in the summer months," said Michael Moneypenny, a meteorologist at the National Weather Service's office in Raleigh. "Weather systems are typically weaker, and the bulk of our rainfall comes from scattered shower and thunderstorm activity that pops up during the heat of the day."

For now, however, we can enjoy life without concerns about whether it's OK to water our lawns or wash our cars.

Wednesday, June 12, 2013

Wild weather night ahead to our north

All the pieces are falling in place for a night of very violent weather to our north, across parts of the Midwest, Great Lakes and Ohio Valley.

Remember the word "derecho."  Those of you who follow weather closely are already familiar with the term.

Many forecasters believe a derecho will form Wednesday evening and surge across Illinois, Indiana and Ohio, leaving a long trail of wind damage.

At mid-afternoon Wednesday, the Storm Prediction Center in Norman, Okla., said it was preparing to issue a tornado watch for parts of Iowa and Illinois. A low pressure system is expected to slide southeast from the Dakotas, moving into the Great Lakes.

Meteorologists say a few tornadoes could form initially, but they expect the storm complex to morph into a line of powerful thunderstorms later in the evening. A derecho is a term used for a long-lived line of damaging thunderstorms. There are numerous recorded accounts of a derecho lasting for hundreds of miles, covering several states.

Derecho thunderstorm winds typically are in the range of 60 to 80 mph, about the same as a weak tornado and plenty strong enough to leave millions of people without power. Sometimes those winds reach 100 mph.

Meteorologist Bernie Rayno of Accu-Weather said Wednesday morning that he expects the worst damage to be in a corridor between Interstates 70 and 80. The Storm Prediction Center has taken the unusual step of placing that area at "high" risk of severe weather later today. That "high risk" category is used only a few times each year.

People who live in or near Chicago, Indianapolis, Louisville, Cincinnati and Columbus will be most at risk. But wind and hail damage, along with flooding rain, also is possible in places like Detroit, Cleveland and Pittsburgh.

The next question is what happens Thursday.

Earlier this week, it appeared as if another outbreak of widespread severe weather would develop in the Carolinas -- as part of a much larger system stretching from New York City down to South Carolina on Thursday. But some of the more recent computer models have indicated the Carolinas could be in the middle of a weather sandwich, with severe storms to the north (Middle Atlantic) and south (Gulf coast) and the Charlotte region catching a break.

We'll watch that development over the next 12 to 18 hours.

Tuesday, June 11, 2013

90s will come ... count on it

I've come to the realization that I'm the only person who likes it when 90-degree weather arrives.

So I don't expect to hear anyone complaining that it's June 11, and we haven't reached 90 in Charlotte yet this summer. But I have heard several people who are happy about it.

Either way, don't make a big deal of it.  The 90s are coming (probably Wednesday), and there's nothing terribly unusual about our lack of 90-degree weather to this point.

Charlotte has averaged 45.7 days of 90 degrees or hotter, over the last 30 years.  Almost a year ago, I wrote that some people in the region were surprised that we'd had only one 90-degree day at that point. I also wrote that things could change in a hurry.

And they did. We had a cool down in the latter part of June, but temperatures soared at the end of the month. We had three straight 104-degree days in Charlotte, and by the time summer came to an end, we'd reached the 90-degree mark 49 days.

When it's 90, the roads are still open and get where you want to go.

When it's 30, either snow or sleet can be falling, and even a short trip to the grocery store -- for bread and milk, naturally -- is a life-threatening experience.

So I prefer the 90s.

And whether you like them or not, here are a few facts about 90-degree weather in Charlotte:

-- The most 90-degree days in a year was in 1954, when we had 88. That was one of the hottest summers in U.S. history, by the way. Second-most was just three years ago, when we had 87.

-- The least 90-degree days was in 1967, with 8. There were only 9 in 2003.

-- The earliest 90-degree day in Charlotte was in 1945, when we reached that mark on March 17. The latest first 90-degree days was July 8, 2003.

-- The last time we went until June 11 without a 90-degree days was in 2009 (June 20 was the first day that year). Before that, it was 2003.

-- The longest streak of 90-degree days was 33, in 1993.  Second, with 32, was in 2007.

Thursday, June 6, 2013

Andrea ... a problematic forecast

Forecasting the strength, track and location of heaviest precipitation with Tropical Storm Andrea isn't easy.

The ramifications are huge for the Charlotte region.  Someone along Andrea's track stands to get 3 or 4 inches of rain, and if that falls in the immediate Charlotte area, we'll be looking at some real flooding problems from late tonight until midday Friday.

One thing to watch is the transformation of Andrea from a tropical to an extratropical system.

As a tropical storm, Andrea's heaviest rain is close to the center. In tropical weather systems, the worst conditions typically are in the eastern quadrant.

But as these storms lose their tropical characteristics, the rain shield tends to expand -- especially on the west side of the storm's center.

The question is when Andrea will become extratropical.  If that happens fairly early, before the storm's center moves into South Carolina, the heavy rain bands will spread into the Charlotte region. In fact, the foothills and mountains will get in on the action.

(Incidentally, separate low pressure systems could bring heavy rain to the mountains Friday night, long after Andrea has zoomed up the East Coast.)

We'll keep an eye on this during the evening and early Friday.

Wednesday, June 5, 2013

A tropical storm ... and heavy rain for the Carolinas

We didn't have to wait long for the first named storm of the tropical season.

Tropical Storm Andrea formed Wednesday afternoon in the Gulf of Mexico, with the center of the storm about 300 miles west of Tampa.

Before all is said and done, Andrea likely will have an impact -- though probably indirect -- on the Charlotte region.  The storm's effects on our area is expected to be in the form of drenching thunderstorms, possibly enough to cause flash flooding.

The National Hurricane Center's likely track for Andrea carries the center of the storm northward along the coastal plain of the Carolinas, about 50 miles inland.  That path is close enough to bring heavy rain to the eastern edge of the Charlotte region -- say, Richmond and Anson counties in North Carolina, and Chesterfield County in South Carolina.

But don't be fooled. As the system races northward Thursday and Friday and changes from tropical to extratropical, its rain shield will expand.  Showers and thunderstorms likely will surge northward (as they're doing tonight) across the Carolinas Piedmont.

In short, look for a very wet period from Thursday through Friday afternoon or evening, until Andrea pushes northeast of the region.

We'll likely see some flash flood warnings issued on a local basis.

As of now, the National Weather Service office locally doesn't expect to issue any widespread flood watches, but if Andrea should track a bit farther inland, all that could change.

In short, the next 24 to 48 hours will bear watching.  Andrea won't be a big wind-producer, but it's likely to cause some flooding problems.

Samaras tribute:  I understand that the Discovery Channel will air a tribute tonight to veteran scientist and tornado chaser Tim Samaras, who was killed -- along with son Paul and another veteran scientist, Carl Young -- by a huge Oklahoma tornado last week.

I've seen comments from people who thought Samaras was a glory-seeking tornado-chaser.  Nothing could be farther from the truth.  He was a true scientist who had produced some valuable studies on severe weather.  His death is a huge loss to the world of meteorology and science, in general.

Tonight's tribute is at 9 p.m., from what I understand.

Tropical system could bring flood threat

This is a quick post, as I'm trying to handle a few other stories early this afternoon.  I'll try to post something more in-depth later in the day.

But the bottom line is that we'll have to watch for a possible significant heavy rain threat Thursday and Friday across the Charlotte region. The culprit will be a tropical system forming near Florida, but there are other players involved.

A moist pattern already is established across the area.  We saw that with the 4-inch rainfall late Sunday and early Monday in parts of the Charlotte region.

By Thursday, it looks as if moisture will be streaming northward from the tropical low.  The question is exactly where the heaviest precipitation will fall, and that depends on the track and strength of the low.

A strong and well-organized tropical low will bring heavy rain near the storm's center.

A less-organized system -- which is what's expected -- will spread the heavy rain over a wider area.

Most of the computer models predict the system will go up the Carolinas coast, which would mean widespread heavy rain in the eastern half of the state.  But some pockets of flood-producing thunderstorms would develop in the Piedmont.

Further complicating the picture is a cold front that is forecast to cross the mountains by Friday. That would add lift in the atmosphere and possibly bring strong storms to the mountains and foothills.

One of the models, the NAM, predicts rain of 4 to 6 inches Thursday and Friday in the Charlotte region. The NAM forecasts the tropical low will take an inland route across the Carolinas.

Justin Lane, a meteorologist at the National Weather Service's office in Greer, S.C., says the NAM has a history of predicting tropical systems will veer too far inland.

But one or two other models are trending more inland with the storm's track.

Stay tuned.