Thursday, April 10, 2014

Are we safe from frost? What about Easter weather?

The two questions I've been hearing a lot in recent days concern frost and the advance outlook for Easter weekend.

As you well know, there are dangers in giving definitive answers in either case.  The date of the last frost is an average, with wide variations. And predicting the weather for Easter, which is 10 days away, taxes the limits of meteorology.

But let's talk about it.

The average date of the last frost in Charlotte is April 2, according to numbers I found, although I also discovered a listing that said "somewhere between April 1 and 10." By either of those averages, we are safe.

But you'll be taking a chance, as you know, by planting anything tender vegetation now.  It's a small chance, but we've had freezing temperatures as late as April 25 in recent years (31 degrees on April 25, 2005). And it doesn't take freezing temperatures at Charlotte Douglas International Airport for frost to develop. If it's in the mid 30s at the airport, there easily could be frost nearby.

Looking at the last several years, here are the last dates of chilly temperatures:

2013 ... April 20 (39 degrees)

2012 ... April 24 (39 degrees); also April 13 (34 degrees)

2011 ... May 5 (36 degrees)

2010 ... April 29 (38 degrees)

Computer models show some chilly air infiltrating the Carolinas next week after the current warm spell is broken. If skies are clear at night, we easily could see some mid and upper 30s in the region. However, there are signs that the period from Wednesday through Good Friday, the three-day period of the coolest weather, could be cloudy. That would keep overnight readings warmer than they otherwise might be.

About Easter ...

Several long-range forecasts show the same thing next week -- cloudy and rather cool temperatures from Wednesday through Saturday, the day before Easter.  Predicted highs are in the mid and upper 60s, and there could be some rain around Good Friday.

But the good news is that most of those forecasts show clearing skies and much warmer temperatures for Easter Sunday, with highs around 80 degrees.

Monday, April 7, 2014

The amazing power of the cold air wedge

We talked for several days about the revved-up weather that we were expecting today. It was to be a one-two punch of heavy rain in the morning and then severe storms in the afternoon and evening.

The first part developed pretty much as expected.  But the severe storms apparently will be a no-show for the Charlotte region.

And it's all because of the amazing power of the cold air wedge.

A quick review ... the cold air wedge is the name given a condition in which cool air becomes trapped in the Piedmont and foothills of the Carolinas and Virginia.  Typically, an onshore wind brings the cool air into the Carolinas. Since cold air is heavier than warm air, it sinks -- and becomes trapped against the mountains.

Sometimes we get what's called an in-situational cold air wedge.  The air is relatively cool and quite dry. Then precipitation from a low pressure system arrives. As it falls into the dry air, it cools temperatures even more.

Often in these situations, a warm air mass is lurking somewhere to the south or southeast. Occasionally, a warm front plows into the cold air wedge and erodes it.  Usually, the cold air wedge holds on. When that happens, Charlotte is stuck in the soup, with chilly, damp conditions.

Weather computer models frequently err in predicting the erosion of the wedge. They tend to forecast the wedge will break down, but that often doesn't happen. Today is the latest case in point. The warm air that several of the models predicted would reach the I-85 corridor by Monday afternoon hasn't even pushed west of I-95.

The cold air wedge is a real pain for meteorologists, whose forecasts are busted when the warmer air never arrives.  Charlotte was supposed to have reached the middle 60s by late Monday afternoon. Barring something unexpected, temperatures will remain stuck in the lower 50s.

At 3 p.m. Monday, it was in the upper 70s along the coast and about 40 miles inland. Temperatures were 30 degrees colder along the I-85 corridor. And to the west of the mountains, temperatures were in the low and mid 60s, on the other side of the trapped air.

Sunday, April 6, 2014

Monday could be a wild, wacky weather day

Rainy days and Mondays are not a big hit with most people, especially when they're one and the same.

But Monday could be a very interesting day for weather geeks, especially if you live in the southern portion of the Charlotte region.

A big storm system that covers hundreds of miles and much of the South will affect the Carolinas on Monday, bringing plenty of rain and a chance of severe weather in some places.

If you live to the northwest of Interstate 85, chances are Monday will be a chilly, wet day -- and not a whole lot more. Places like Hickory and Statesville probably will stay in the lower 50s for much of the day, with a steady, soaking rain falling.

To the southeast of I-85 ... that's another story.

First, for the basics.  The center of low pressure will move northeastward Monday, crossing Tennessee and into Kentucky. A cold front that pushed south of Charlotte on Friday evening is moving back to the north as a warm front. Forecasters say any severe weather that develops Monday will be in the warmer, more unstable air.

The question is how far north that front will get. Cool high pressure to our north and falling rain have created a cold air wedge over the Carolinas, and severe weather won't develop in that cool pocket. But the northward-moving warm front on Monday will trim back the cold air pocket. Computer-generated forecasts show the warm front pushing as far north as I-85.

Typically in these situations, the cold air wedge is very difficult to dislodge. If Charlotte, Monroe, Rock Hill and Lancaster get into the warmer air, it probably won't happen until mid or late afternoon.

So here are some things to look for Monday:

1. A lot of rain across the entire area. The National Weather Service is predicting about 1.6 inches in Charlotte, Concord, Monroe, Rock Hill and Salisbury. The forecast is closer to 1.8 or 1.9 inches in Gastonia, Lincolnton, Hickory, Statesville and Shelby. Heavier amounts are possible, however.

2. Most of South Carolina will get into the warm, unstable air.

3. As the warm front moves into North Carolina, it will push inland toward the foothills. Areas east of U.S. 1 are likely to get into the warm, unstable air. How much of the area between U.S. 1 and I-85 gets into the warmer air? That's the question mark.

4. Winds in the atmosphere -- south of the warm front, at least -- will be set up to create rotating thunderstorms.

5. There will be remarkable contrasts in temperatures Monday. Don't be surprised to see some afternoon temperatures in the foothills in the upper 40s, while it's 75 degrees in Columbia or Florence, S.C.  And especially in the early afternoon, don't be surprised to see readings around 70 degrees near Wadesboro or Pageland, S.C., while it's 15 to 20 degrees colder in Gastonia or Lincolnton.

6. If fog develops, it could be a sign that you're near the warm front. Warmer air will pile into the area from upper levels of the atmosphere, squashing the cooler air toward the surface. That's when fog develops. If it's foggy in your area, and the ceiling suddenly lifts (and the temperature climbs), it's an almost certain sign that you're south of the warm front.

Friday, April 4, 2014

Monday could be a stormy and very wet day

We've been spared the typical springtime weather woes of heavy rain events and severe thunderstorms, largely because of that persistent block of cold air to our north that pushed its way into the Carolinas frequently in February and March.

But things are shaping up for a potentially wild day on Monday.

Our string of 80-degree days will come to an end when a cold front pushes across the region later Friday night. Behind the front on Saturday, we'll have a very nice day, with partly sunny skies and temperatures somewhere around 70 degrees.

But then things go downhill.

Low pressure is expected to form in the lower Mississippi Valley on Sunday and push northeast. The track of the system is important, because the center of the low is predicted to push across Louisiana and Mississippi through Tennessee and then Kentucky.

Clouds will increase in the Carolinas on Sunday, and it probably will be a chilly day, with temperatures not getting much above the lower 60s. And rain from the low pressure system is expected to arrive by Sunday evening.

Andrew Kimball of the National Weather Service's office in Greer, S.C., said computer models indicate "copious amounts" of moisture will be spread northward from the Gulf of Mexico into the Carolinas.

How much is "copious"?  Some of the computer-generated forecasts show up to 3 inches of rain falling from the system.  That would be enough to cause some flooding problems in areas where the heaviest rain falls.

But that's not all.  Remember the cold front that passes through our area tonight. It will stall somewhere to the south of us this weekend, then be dragged northward by the low pressure system pushing up through Tennessee and Kentucky. All the ingredients will be there for severe weather sometime Monday.

Areas to the south of that front will be at risk of severe thunderstorms with damaging winds and hail. And tornadoes will be possible, too.

It's nearly a sure thing that much of South Carolina will be in the warm sector south of the front. Kimball said computer models predict the front will move far enough north to put the I-77 / I-85 area in the warm sector, too. And there even is a possibility of the front pushing up to the foothills.

Rain, some of it heavy, is a very strong possibility from Sunday evening through late Monday. And severe weather will be in the mix, too.

We'll watch how this develops over the next few days.

Wednesday, April 2, 2014

Snowfall totals, and more Grandfather Mountain

I saw a list of North Carolina snowfall totals for the 2013-14 season, while I was looking around on various weather bulletin boards the other day. I don't recall exactly where I saw it, but I think it was at the American Wx page (www.americanwex.com).

Anyways, I was struck at the lack of uniformity in snowfall in various parts of the state. Some reporting stations within a few miles of each other had very different totals.

I think these totals came from CoCoRaHS observers, so they might not be the same numbers you get from the official National Weather Service reporting stations.

By the way ... I wrote a story online last week about the recruiting drive for more CoCoRaHS observers. Sometime in the next few days, I'll devote one day of this blog to some of the interviews I conducted with those observers. They are really neat people -- true weather geeks.

But back to the snow ...

In our part of the state, most of the snow fell Feb. 10-13. We had some light snow on the night of Monday, Feb. 10, then about an inch on grassy surfaces on Tuesday, Feb. 11. The major snow fell on Feb. 12 and 13.

Anyways, here are some of the numbers I culled:

Mount Mitchell ... 35.5 inches

Boone ... 33.8

Winston-Salem ... 16.3

Greensboro ... 15.3

New Bern ... 14 (kind of strange for a coastal area to be among the state leaders, but that's the way it works sometimes)

Rockingham ... 10.3

Salisbury ... 10.1

Concord ... 9.6

Asheville ... 9.4

Charlotte ... 9.3

Hickory ... 8.7

Greenville ... 7.2

Raleigh ... 5.8 (that number seems low)

Wilmington ... 0.6

Snow-lovers are never satisfied, but it seems as if they had a good year.  It always kind of intrigues me how people in the Carolinas cheer for snow, while their counterparts in the North would be happy to have snow-less winters.

More on Grandfather Mountain ,,, Yesterday, I wrote about the iconic Grandfather Mountain sign being crushed by wind gusts Sunday. The sign had stood for more than 50 years in Linville, but the impact of rough weather over those five decades finally claimed the sign.

Today, I heard from Sherry Fletcher, who says she and a group of people are lobbying officials to replace the sign -- with something resembling the original Grandfather Mountain sign. She says they have a Facebook page with 600 members. Here's a link, if you're interested -- https://www.facebook.com/groups/498965223547384/

And I have a correction to make. Yesterday, I wrote that the 13 inches of snow in February at Grandfather Mountain set a record for the month. I should have known better, because that total is far too low for a record.

Anyways, Kellen Short of Grandfather Mountain sent me a note today, reminding me that the February total was the most for this season.  He says they believe the February record is 36.81 inches of snow, in 1971.  And the record for any one month is 64.05 inches in March 1960.  That, of course, is the month when it snowed every Wednesday over much of the state.

Tuesday, April 1, 2014

Sunday's wind claims an iconic victim

Those gusty winds that left tree limbs cluttered across your yards and knocked out power to some Carolinas residents on Sunday also did a number to one of North Carolina's well-known tourist attractions.

The large wooden sign that advertised Grandfather Mountain for the past half-century was flattened by wind gusts early Sunday in Linville. Officials at Grandfather Mountain say the sign, at U.S. 221 and N.C. 105, had been designed by architect Charles Hartman, the same person who designed the famous Mile High Swinging Bridge.

"The sign was an icon in North Carolina's travel industry," said Harris Prevost, vice president of Grandfather Mountain Stewardship Foundation. "It was pure Americana -- 1950s, all the way. We're sorry to see this piece of history lost forever."

Grandfather Mountain officials say the sign was painted in bright yellow and green when it was built in the late 1950s, and then repainted in tan and brown in 2006. (The photo of the damaged sign above was shot by Kellen Short of the Grandfather Mountain Stewardship Foundation.)

The weather station at the Mile High Swinging Bridge recorded winds of up to 92.5 mph early Sunday. That is a lot stronger than elsewhere in North Carolina, but Grandfather Mountain is noted for having some extreme winds.

Wind speeds recorded atop the mountain came into question from some scientists, especially after the anemometer measured a 200 mph gust in 2006. Critics said the measuring device was mounted atop a building, allowing wind to funnel up the side of the building to the top -- producing an inaccurate measurement.

Grandfather Mountain officials responded by positioning the anemometer atop the Swinging Bridge, free of any interference.

Record Snow ... By the way, Grandfather Mountain set a record in February for the snowiest month ever up there.  More than 13 inches fell during the month, including 10 inches on Feb. 13. That was the same storm that brought about 8 inches to Charlotte.

Sometime over the next few days, I'll publish a list of snowfall totals across the Carolinas for the winter of 2013-14.

But Mount Mitchell led the way with about 35 inches, a few inches more than Grandfather Mountain.
This is the iconic Grandfather Mountain sign that was felled by Sunday's strong winds.

Thursday, March 27, 2014

30 years ago Friday ... tornadoes devastated Carolinas

Friday marks the 30th anniversary of one of the deadliest weather events in Carolinas history -- an outbreak of tornadoes that stretched from the western edge of South Carolina to the northeast coast of North Carolina.

Over a six-hour period, a series of 22 twisters smashed through 25 counties -- eight in South Carolina, 17 in North Carolina. Among the twisters were seven F4 storms, the second-strongest rating of tornadoes on the Fujita scale.

By the time the last of the tornadoes moved ashore from Albemarle Sound into Chowan and Perquimans counties, 57 people were killed and a staggering 1,248 injured.

None of the tornadoes hit Mecklenburg County, although large hail associated with one twister was reported in Matthews and southeast Charlotte. Only two counties in the Charlotte region -- Union (N.C.) and Lancaster (S.C.) -- were hit. But the storms were nearby, and anyone who drove on Interstate 77 from Charlotte to Columbia or to Myrtle Beach through the Bennettsville areas saw the damage for several years.

The tornadoes were bred from a powerful low pressure system that dropped barometric pressure to 28.95 inches in Charlotte. The low pressure system rode along a stationary front draped across central North Carolina. While Charlotte had temperatures in the 70s, it was 25 degrees colder in Greensboro.

In advance of the storms, the Severe Local Storms unit, a predecessor of the Storm Prediction Center in operation today, forecast a "high risk" of severe weather on March 28, 1984, for Alabama, Georgia and the Carolinas.

It was the first time a "high risk" ever had been issued.

Alabama and Georgia largely were spared of the weather.

But about 4:30 p.m. that day, an F1 tornado descended into the town of Due West, S.C., in Abbeville County. That storm injured 24 people. For the rest of the evening, National Weather Service offices across the Carolinas scrambled to keep up with these staggeringly strong storms.

Some notable facts:

-- Sixteen people died in an F4 tornado near Greenville, N.C. That storm narrowly missed a direct hit on the East Carolina University campus.

-- A tornado that hit near Bennettsville, S.C., was 2 miles wide.

-- Another twister was on the ground for 45 miles, from Bennettsville, S.C., northeast to Parkton in North Carolina.

-- The F4 tornado that crossed I-77 in Fairfield County cleared out an area of trees, about 300 feet wide, on both sides of the road. Motorists could see that damage for several years.

-- The twister that hit a shopping center in Bennettsville destroyed a shopping center and produced fatalities. Beach-bound motorists could see that damage for more than a year.

Here is a list of the 22 tornadoes and their damage:

4:30 p.m. ... F1 in Due West, S.C. (Abbeville County). 24 injuries.

4:40 p.m. ... F2 hits north of Laurens, S.C. (Laurens County). It destroys 19 mobile homes, with 19 injuries.

5:20 p.m. ... F2 hits near Newberry, S.C. (Newberry County). It is on the ground for 23 miles and destroys 80 businesses in Newberry, causing $11 million damage. One death, 38 injuries.

5:40 p.m. ... F3 hits east of Newberry. it destroys 254 homes and 86 businesses, causing $14.2 million damage. 10 injuries.

6 p.m. ... F4 hits Winnsboro, S.C. (Fairfield County). This storm crosses I-77, killing a trucker. In all, five died and 110 are injured.

6:10 p.m. ... F1 touches down briefly in Fairview (Union County), the closest storm to Charlotte. There are no injuries.

6:20 p.m. ... F4 causes massive damage to forests near Kershaw, S.C. (Lancaster County). There are 31 injuries.

6:40 p.m. ... An F2 hits north of McBee, S.C. (Chesterfield County), wiping out part of the tree cover in the Sandhills National Wildlife Refuge. There are no human casualties.

6:45 p.m. ... F4 hits near Cash, S.C. (Chesterfield County), destroying 36 farm buildings. 24 injuries.

7:10 p.m. ... Another F4 rips into the Northwood Shopping Center in Bennettsville, with a path 2 miles wide. The storm rumbles 17 miles, across Marlboro (S.C.) and Scotland (N.C.) counties. There are seven deaths and 100 injuries.

7:20 p.m. ... A devastating F4 follows a path parallel to the storm above, pushing 45 miles across Marlboro County and into North Carolina across Scotland, Robeson and Cumberland counties. The town of Red Springs is devastated, as is the South Carolina town of McColl. The toll: seven deaths, 395 injuries.

7:45 p.m. ... An F3 storm in Bladen, Cumberland and Sampson counties kills 12 and injuries 101. Six deaths are in Clinton.

8:10 p.m. ... F2 in Nash County, with no injuries.

8:15 p.m. ... F4 makes a direct hit on Mount Olive College and causes more than $25 million damage in Sampson, Duplin and Wayne counties. The toll: three dead, 70 injures.

8:30 p.m. ... F3 injures 81 persons in Wayne and Lenoir counties.

8:45 p.m. ... The deadliest storm, and F4, leaves 16 dead and 153 injures in Wayne, Lenoir, Greene and Pitt counties. More than 300 homes are destroyed in Greenville, and the storm brushes the ECU campus.

8:55 p.m. ... F3 kills six and injures 19 in Bertie County. Five deaths are in one family, living in a mobile home.

9:10 p.m. ... F2 in Bertie and Ahoskie counties. Seven injuries.

9:17 p.m. ... F1 with no injuries in Hertford County.

9:35 p.m. ... This F2 was separated from the main area of storms, down in Horry County west of Myrtle Beach. It injured eight.

9:37 p.m. ... F3 hits Gates County, killing two and injuring 10. This storm actually crossed into Chesapeake, Va.

10:15 p.m. ... The last tornado. It started as a waterspout and then came ashore as an F1 in Chowan and Perquimans counties. One person died and one was injured.