Dan’s Wild Wild Science Journal

I enjoy the stories but the day to day forecast is worthless.

I always enjoy reading the stories in the Farmers Almanac. It’s been around for a LONG time and they have good basic astronomical info in it. Although you can get much more precise info from free programs like Stellarium.

About this time every year they release their forecast for the upcoming winter. TV stations everywhere gobble it up and do news stories on what the coming winter will be like.

Great free publicity!

Just to be clear here, the day to day forecasts are made up. They will not have any accuracy over that of a pure guess.

Some real science: An average of all moderate to strong La Nina's shows a milder than normal winter for much of the U.S. and Eastern Canada.

If you want to know what the winter will be like, the only think I can tell you is that with a moderate to strong La Nina brewing, the Southeast will likely have a drier and slightly milder than  normal winter. The odds of this are about 65%. That means there is a 35% chance it will be colder than normal here!

Other parts of the country will vary. See the graphics.

This kind of long range forecast is only possible because the La Nina pattern of colder than normal water in the Equatorial Pacific will cause a fairly predictable shift in the storm track over North America. The affects will actually be felt world wide.

Temperature anomalies for January during La Nina events. Images from NOAA. Click for full size image.

However, not every La Nina winter is the same. Each one is slightly different. Sometimes the La Nina pattern will hardly show up at all in some areas. Sometimes the expected warm areas are super warm.

The temperature anomalies in January for La Nina years shows that it’s quite warm in the Southeast U.S. most of the time but not always. The La Nina winters of 1971 and 1976 were slightly below normal over the Eastern U.S.

A scientific forecast would be for a good chance of having a mild winter in the Southeast. For those of you in Western Canada, a colder than normal winter seems like a good bet. Sometimes it is a super cold winter as well.

Just what you folks in Edmonton wanted to hear, isn’t it!

Later,
Dan

NASA Modis image of tropical disturbance off of Florida. Pressures are dropping and upper level winds are favourable for development.

There are strong signs that the area of disturbed weather in the Gulf is beginning to get organized today. Pressures are dropping and there seems to be a circulation already present. I suspect the the folks at the NHC in Miami will begin advisories on it later today.

Tropical Cyclone heat potential is based on the depth of the warm water, not just the surface sea water temp.

If it makes it to tropical storm strength it will be named Danielle.

While it is a bit early to talk about the track, the GFDL model is indicating that a landfall somewhere around Louisiana or Mississippi is possible late Friday night. Keep in mind, that the steering currents are very weak and this could change dramatically.

HOW STRONG COULD IT GET?

Could this system reach hurricane status? Yes, but it would be tough to get that strong by landfall. The Gulf is very warm but the tropical cyclone heat potential is not overly impressive. Still it is near the Gulf loop current and that may be helpful.

A good tropical storm may actually be quite helpful to farmers in the southeast who are suffering through an intense heatwave and drought. It’s 37.5C here in Huntsville as I type this.

That’s 100°F on the old scale.

More soon…

Dan

Colder than normal water is already appearing in the Equatorial Pacific (NOAA)

One of the reasons for the forecasts of a an active hurricane season is the predictions that La Nina would develop this summer. Remember that La Nina is an ocean circulation phase that brings unusually cold water to the surface of the Tropical Pacific.

These are the temperature probabilities for a normal/above/below normal autumn (September through Novermber). Click for full resolution image.

Well, it has started and most of the ocean atmosphere models are predicting a moderate to strong event.

This has more impact than just the number of hurricanes. NOAA revised their 2010 hurricane prediction down somewhat today but they are still predicting a 70% chance of 4-6 major hurricanes (Earlier typo said 406- that would be exceptionally bad ). La Nina is a big factor in that.

The colder tropical waters cause a shift in the jet stream. This makes it possible to make a decent prediction of the fall and winter ahead. Here in the Southeastern USA we tend to have a dry fall with normal to above normal  temps. The winter tends to be drier than  normal and sometimes a bit on the mild side.

What about where you live?
The chart at the right shows the probabilities for temperatures during a La Nina event. The image is for the period from September through November.

Take a look at the Northeast USA and Eastern Canada. The chart shows that during a La Nina year the odds are VERY low that the autumn will be below normal. The odds are higher that it will be near normal and the odds are higher still that it will be a warm autumn.

This does not mean that it will not be colder than normal. It just means that in the past this happened rarely.

You can see more of these graphics for your part of the world at the IRI website here. Precipitation maps are also available.

In my last post I gave some of the reasons I thought we would see a very active hurricane season. Here is what the NOAA folks think. They released their forecast for the 2010 season today.

As I expected it looks like it will be a mean year. Possibly one of the all time most active years. Here are NOAA’s numbers:

An 85% chance of an above normal season.

A 70% probability for each of the following ranges of activity this season:

• 14-23 Named Storms,
• 8-14 Hurricanes
• 3-7 Major Hurricanes
• An ACE range of 155%-270% of the median.

From NOAA/TPC

The ACE stands for Accumulated Cyclone Energy Index (Developed by NOAA).  It’s a measure of the total amount of energy from all the storms in a particular season. (In the same basin) NOAA’s official definition: The ACE index is a wind energy index, defined as the sum of the squares of the maximum sustained surface wind speed (knots) measured every six hours for all named systems while they are at least tropical storm strength.

An average year brings about 6 hurricanes and 10 tropical storms. So this is a forecast of a possible hyperactive season.

Could we still see a normal season?

Yes!

El Nino may linger and wind shear may not be as weak in the tropical Atlantic as forecasted. The odds are heavily against those things happening though.

For more on the reasons why see my previous post.

Church in Dekalb County Alabama after the EF3 tornado Saturday. Pic taken by Katie Johnson.

The last several posts have been about the high risk of tornadoes over the Southeastern United States on Saturday.

Library in Albertville, AL. Image from Teresa Reno.

You probably have already heard of the tornado that hit Yazoo City in Mississippi . It left 10 dead and horrible damage.

Later Saturday night, the tornadoes dropped again from new thunderstorms. These were much closer to home. We were on the air many hours as the storms moved across North Alabama into NW Georgia.

There were three EF 3 tornadoes across North Alabama. Storm survey teams from the national Weather Service in Huntsville estimated the winds were at around 140 mph.

The twister that hit Albertville was at one point over  1 km wide!

Image courtesy Teresa Reno in Albertville.

The Albertville Tornado was on the ground for nearly 30 km. It caused major damage in Albertville, and in the Dekalb County town of Geraldine.

I know a lot of people have had their lives turned upside down by these storms. There were 30+ injuries, but thankfully no deaths!

I cannot begin to tell you how happy that makes those of us who forecast them. I include those of us on TV and the meteorologists who work for NOAA.