Severe weather threat area for Saturday from the Storm Prediction Center (NOAA)

A deadly weekend tornado outbreak is becoming more likely this evening. Conditions are coming together for potentially violent long track tornadoes across much of Mississippi and Alabama on Saturday. Tennessee, Arkansas and Louisiana are also threatened.

It is quite possible conditions may reach the threshold for a rare High Risk outlook from the Storm Prediction Center (NOAA) in Norman.

Several of the tornado watches tomorrow will be PDS watches. (Particularly Dangerous Situation).

Significant Tornado Parameter forecast from a NOAA NWP Model. This is for 4PM CDT Saturday. Courtesy Earl Barker.

As I mentioned in my previous post last night, the parameters for an outbreak of strong and long track tornadoes are quite high. The numbers have actually increased some. One of these parameters that forecasters look at is the significant tornado algorithm.

This index looks at instability and wind shear along with low level moisture to indicate areas where the highest threat is. Based on this index, a high risk may be needed for NW Alabama and nearby areas on Saturday.

There are already severe thunderstorms with possible tornadoes developing in Mississippi.

The greatest threat for tornadoes will be during the day and early evening tomorrow. It is very possible that more tornadic storms could develop across Arkansas and Louisiana before sunrise.

Don’t get in the “fraidy” hole yet, but you might want to vacuum the carpet in it…

Severe Storm Forecast from the Storm Prediction Center (NOAA/NWS)

It may sound crass and I do not mean it to be that way, but there are likely to be deaths from tornadoes in the next 48 hours.

If only we could only say exactly where!

What we can say is that conditions are coming together to make the development of a few strong tornadoes and they will likely be in Mississippi and Alabama on Saturday. Here in Alabama there is special concern because nearly 100,000 people will be at a major stock car race in Talladega. Here in Huntsville is a major art festival Panoply.

The odds of a tornado touching down at any one spot are minuscule, but the odds of a tornado in the area are rather high. So all we can do is to warn people to be alert and to have a NOAA Alert Weather Radio.

One other thing. If you live in a mobile home, make arrangements to go somewhere else during a tornado watch on Saturday. Believe me when i say that several will be issued. Your odds of being killed or injured from a tornado are many times higher in a mobile home. Leave the windows closed (Opening them can increase damage) and consider a walk in closet or a bathroom for safety.

You might wonder just how we know tornadoes are possible?

Tornadoes require two basic ingredients. Wind shear and instability.

A tornado can develop with a lot of one parameter and a little of another. The big outbreaks happen when you have a LOT of both.

CAPE is a measure of instability. Above 1000 is very unstable. from UIUC.

This weekend looks to have a lot of  both.

Instability can be measured in different ways but one preferred way is to use numerical weather prediction models to estimate the CAPE.

CAPE stand for Convective Available Potential Energy. Remember potential energy from high school physics? Let me just simplify it and say that numbers over 1000 joules/kg are bad.

Wind shear can also be measured (and is) in different ways. The direction of the wind shear that a storm sees as it moves along is most important and meteorologists look at what is called the storm relative helicity as an indicator. This gets even more complicated (can you say calculus?), but the basics are this- over 200 is bad.

Helicity is one measure of wind shear. It's one of the two ingredients for tornadoes.

Here are some actual NWP charts for those parameters on Saturday. I will let you check out the numbers.

There are a lot of meteorologists at NOAA and at TV stations (like me) who will be working together for very long hours to give as much warning as possible.

Take them seriously this weekend, even if you never have before.

Mother nature may be in a rotten mood.

Keflavik Radar from Iceland Met Office. No plume from the ash currently being detected!

The weather radar at the Keflivik Airport is not seeing a plume from the ash cloud this evening. The last report from the UK Met. Office is a plume height of 16,000 feet. This is much lower than over much of the last 72 hours.

There is also good news on the flight restrictions. The lower levels are looking much better. It looks possible that flights could operate from Paris tomorrow, and even some domestic UK flights might be possible.

Restricted flight zones due to ash from Iceland. Image from UK Met Office/NATS

Ash cloud approaching 30,000 feet over Iceland. Courtesy Iceland Met Office.

The UK has now grounded aircraft through 1AM GMT Sunday. The ash cloud has gotten worse and there is a new plume headed toward Europe as the image above indicates. Meteorologists from the Iceland Met Office flew o Friday near the volcano to check the height of the ash cloud and reported it is nearly 30,000 feet (10,000 meters).

The upper level winds at this level will steer the ash toward NW and Central Europe. The conditions may very well worsen over the weekend.

Why?

Look at the winds forecasted for Sunday at 34,000 feet from the UK Met Office numerical weather prediction model:

Winds at flight level 34,000 feet from UKMet Model. Image courtesy UK Met Office and 21st Weather Squadron USAF

A “Eureka Alert from SCIENCE late Friday has some interesting and alarming news:

Public release date: 16-Apr-2010
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Contact: Jay Miller
miller@iodp.tamu.edu
979-845-5740
Texas A&M University

Icelandic volcanoes can be unpredictable and dangerous, say Texas A&M prof

If history is any indication, the erupting volcano in Iceland and its immense ash plume could intensify, says a Texas A&M University researcher who has explored Icelandic volcanoes for the past 25 years.

Jay Miller, a research scientist in the Integrated Ocean Drilling Program who has made numerous trips to the region and studied there under a Fulbright grant, says the ash produced from Icelandic volcanoes can be a real killer, which is why hundreds of flights from Europe have been cancelled for fear of engine trouble.

“What happens is that the magma from the volcano is around 1,200 degrees and it hits the water there, which is near freezing,” he explains. “What is produced is a fine ash that actually has small pieces of glass in it, and it can very easily clog up a jet engine. If you were to inhale that ash, it would literally tear up your lungs.”

Miller says most volcanoes in Iceland erupt only about every five years on average and are relatively mild, but history is repeating itself. Extremely large eruptions occurred there in 934 A.D. and again in 1783 that covered Europe with ash much like today.

“Ben Franklin was ambassador to France in 1783 and he personally witnessed the large ash clouds over Europe, and he later wrote that it was a year in which there was no summer,” Miller adds. “The big question now is, what happens next? It’s very possible this eruption could last for quite some time, but no one knows for sure. Volcanoes in that part of the world are very hard to predict.”

—–

Here below is the latest ash coverage forecast from the UK Met Office:

Ash cloud from UK Met Office

More soon,

Dan

Ash cloud from Iceland Met Office and UK Met Office.

The Iceland volcano that has shut down the air traffic over much of Europe sent ash clouds high again today and the news is not good. The upper level winds are likely to continue to blow the ash toward the UK and Northern Europe.

Most of the ash is in a layer from 20,000 to 35,000 feet. Since most aircraft fly around 35,000 feet across the Atlantic, it is impacting almost all of the transatlantic flights. The ash is hard to see on weather satellites but the thicker portion of the plume is visible.

The UK Met Office has been using LIDAR to measure the intensity and location of the cloud over the UK. LIDAR is like radar but uses laser light instead of radio waves.

Forecasting the ash can be broken down into three problems.

1.  Where is it now?

2. Where is it going?

3. Is there more coming up?

Unfortunately, there IS more coming up.

The ash cloud reached 24,000 feet today. The pic above shows where it is now, and the image below shows where it is likely to go. This forecast map is for the winds at around 30,000 feet for Saturday. You can see the streamlines pointing straight toward Western Europe.

Upper level winds forecast for 11am Saturday, London time. The ash will likely spread out and cover much of NW Europe.

If the volcano calms down a bit the ash will clear in about 24-36 hours.

Update:  Here is a pic of the dusty sky over North Wales on Friday evening from a friend. Most of the time he shoots wedding not clouds. Just the opposite of me! If you ever need a wedding photographed Alan Williams in Wales, you know now who to call!

Stay tuned, and for those of you stuck in Paris or London – why are you complaining!!