48 hours of weather changes ... some of them not good

It's cloudy, damp and drizzly out there, but some major changes in the weather are on the way for the Charlotte region over the next 48 hours.

We're in one of those situations where a cold air wedge will be eroded, putting us into a sector of warm air -- just in time for a strong cold front to arrive.  The timing on all of this is iffy, but the bottom line is the Carolinas could be looking down the barrel of some severe weather late Tuesday and early Wednesday.

You'll be hearing about all this on the news today and tonight, as the severe weather started Monday morning in the lower Mississippi Valley. The Storm Prediction Center has placed parts of Arkansas, Louisiana, Tennessee, Missouri and Kentucky in a "moderate" risk of severe thunderstorms and tornadoes today.

By 10 a.m., I'd already seen one report of a fatality from a possible tornado in Arkansas.

Let's go over the timeline of what is coming between now and Wednesday morning ...

TODAY ... We're locked in a cold air wedge, with temperatures in Charlotte in the lower 60s and drizzle falling.  We're familiar with these conditions, as they've been common-place with our overall weather pattern during the summer and autumn.

High pressure in the Atlantic is pumping cool, moist air into the Carolinas. The cool air, which is heavier than warm air, sinks toward the surface and becomes blocked by the North Carolina mountains. We get low clouds and light rain in the Piedmont and Foothills.

Often, these wedges erode from the south and southeast, as wind circulation in the atmosphere swings out of the south. At 10 a.m. Monday, the wedge was being pushed inland. Charleston was near 80 degrees, as were areas of the Outer Banks.

(Update at 1:45 p.m. ... The wedge is eroding steadily. It's now 80 degrees in parts of Richmond County and near Camden, about 60 miles southeast of Charlotte)

During the day, according to National Weather Service forecasters and the computer models, the warmer air will push north and west.  By early afternoon, we could see Columbia in the low 80s while Charlotte remains in the low to mid 60s.  We've seen that scenario frequently.

It doesn't look as if places like Statesville and Hickory ever will escape the cold air wedge today, but Charlotte -- and especially Rock Hill, Lancaster and Monroe -- should break into the warmer air by mid to late afternoon.

Rainfall should be light during the day.

TUESDAY DAYTIME ... It looks as if the day will begin with partly cloudy skies and mild weather. Overnight temperatures probably won't drop at all, so we'll start the day in the low to mid 60s. Charlotte could hit 80 degrees Tuesday, but by afternoon, clouds will increase as a strong cold front approaches from the west.

Showers and thunderstorm chances will ramp up quickly during the afternoon.

TUESDAY EVENING TO WEDNESDAY MORNING ... This is where the severe weather chances will top out. The Storm Prediction Center says the Charlotte region has a chance of seeing damaging wind gusts and a few tornadoes. Right now, it looks as if the highest threat will be after dark, which is never good.

Our severe weather chances are not as high as in the lower Mississippi Valley today, but you'll almost certainly be hearing a lot of talk tomorrow about the possibility of bad weather.

Flash flooding potential looks to be moderate in the mountains and foothills Tuesday and Tuesday night, but the Charlotte area might escape that problem, assuming the storms are moving quickly enough.

Some clouds, but eclipse should be visible

It won't be ideal viewing conditions, but the weather probably won't ruin our chance to see the lunar eclipse shortly before daybreak Wednesday.

A bigger problem could be the location of the eclipse in the sky.

The eclipse will begin around 5:15 a.m., when the moon begins moving into the earth's shadow. Over the next 100 minutes, the shadow will grow until total eclipse is reached about 6:55 a.m.

Fortunately, since we're in early October, sunrise in Charlotte isn't until 7:24 a.m. So while the sky definitely will be brightening, we will still be able to see the moon at that time. And of course, the early (partial) portion of the eclipse will be visible.

Unfortunately, the moon will be setting in the Carolinas shortly after it reaches full eclipse. By 6:55 a.m., the moon will be about 10 to 15 degrees above the horizon. Translated:  If there's a tree or building between you and the western sky, where the moon is setting, you won't see the total eclipse. You'll need to find a relatively clear view of the western horizon.

The weather could be another issue.

If the eclipse had been this morning, we would've been in trouble. Several weak disturbances are crossing the Carolinas today, spreading showers across the mountains. The systems have been losing their punch as they reach the Piedmont, but during the morning hours, they created a lot of clouds in the western sky.

There might be some clouds in the western sky again Wednesday morning, but the last of the weak disturbances will be moving away by that time. So I think there'll be enough clear sky to get a look at the eclipse.

The next lunar eclipse is next April 4, but it will be visible mostly in the Pacific. The next time we'll get a chance to see one is Sept. 28, 2015.

The next total solar eclipse in the United States is Aug. 21, 2017.

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.

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.

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.

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.

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.