Dan’s Wild Wild Weather Journal

Well, we finally broke the heat wave. Many areas had some heavy rains over the last 48 hours as well, so that should make the farmers happy.

I have a tree in the yard that’s about 3 years old. It was almost dead from lack of water. After a good heavy rain Thursday night, it had perked back up nicely! I had been kicking myself for not noticing it, but the rains came just in time!

The damage may be done for many of the farmers in these parts. Several counties in the area are now classified as in severe drought now.

It might seem easy to classify a drought - just look at rainfall and perhaps temperatures, right?

It’s not that simple though.

Do you classify drought conditions based on rainfall for the past 30 days, or 60. What abut 90-180 days? Even rainfall over 6 months ago can impact crops. Some crops need more rain than others and some crops can handle a dry spell better than others.

You see it’s not really that easy!

There are several different drought classification methods in place. Each with their attributes and deficiencies.

One of the older ones is the Palmer Index. There are actually several different versions of it, but the main index is a long term index. The Palmer index will not change much for our area, in spite of getting 1-2 inches of rain late last week.

Below is the Palmer Index for July 2006:

There is a newer more experimental index that has been developed by the USDA and NOAA. This index reacts a bit more quickly to drought busting rains.

The link at the bottom of the image will take you the drought monitor web site where you can read more about how the chart is made.

One final note. The temperature is vitally important in a drought. In the winter, the air and ground are cold, and there is little evaporation from the soil. Just the opposite in the warm season. Evaporation rates are very high and plants are green. The high rate of photosynthesis and transpiration also uses up the soil water quickly.

This means that an inch of rain in January, will keep the soil wet much longer than even 2-3 inches of rain in early August.

It looks like we will go back to a fairly dry pattern next week (But not as hot!). The warm weather, and green plants will suck that moisture out of the ground quickly, and the soil will be bone dry again in just a few days!

The news media seems to love these long range hurricane forecasts. Dr. William Gray started forecasting the number of tropical storms and hurricanes in the Atlantic Basin over 20 years ago. NOAA in Washington has begun to make an annual prediction as well.

There is some good in these predictions. They get lots of attention, and hopefully get coastal residents thinking about what they would do if they were faced with an impending category 5, on their door step. That’s where the good ends in my opinion.

NOAA today and Dr. Gray last week revised down the number of storms expected this year. That did not surprise us in the weather office. JP, Spencer and I have all thought that it would be extremely unusual to have another record breaking year in the tropics. That said, we did, and still do expect an above average season. You will not see any forecasts like that from the WHNT weather center. Frankly, it is just not possible yet to make a prediction of how many storms will develop several months ahead of time.

A forecast of an above normal, or well above normal season, is not beyond current science, and most meteorologists I know will agree that an above normal year is still likely.

There are a bunch of factors that go into these forecasts. Some are obvious, like the sea surface temperature anomalies. If the water in the tropical Atlantic is well above normal then that would favor a more active season.

Another factor that is not so obvious, is the wind direction in the stratosphere above 75,000 feet. These winds tend to switch directions from West to East every few years. This is called the QBO or (get ready for it) the Quasi Biennial Oscillation. When the winds are strong from the East we tend to see considerably fewer tropical storms in the Atlantic and Gulf. This is likely because of the high wind shear in the Stratosphere. A Westerly QBO tends to bring an active hurricane season.

There are other factors as well, but suffice it to say- take these hurricane forecasts with a grain of salt. If you hear that we are expecting an active season- that is a forecast that will probably verify.

If you hear that we are going to have 9 hurricanes and 14 tropical storms, three of which will hit land-then do what I do-laugh.

Later,
Dan

We have a new weather satellite going up later this month. Goes N will be launched (hopefully) on 24 June. This is the first of a new series of geostationary weather satellites.

GOES N will eventually become GOES 13 and replace GOES 12 which has done a great job for the last several years.

GOES images are the ones you see on TV every night during my weathercast. (and every one else’s for that matter!)
They are one of the most visible symbols of advanced science technology that people come into contact with on a daily basis (I’d be willing to bet I will get an argument on that assertion though!)

This new GOES will have significant improvements over the current one. We will also likely get the images faster and the pointing accuracy is greatly improved.

In case you do not know. GOES stands for Geostationary Operational Environmental Satellite. These satellites are placed at an altitude of 35,786 km. If they break, there is no rescue from the space shuttle since it can go no higher than around 500km in altitude.

Why so high?? Because at this altitude, a satellite will circle the earth in 1,436 minutes. It so happens that the earth takes just that many minutes to rotate on its axis. Thus, the satellite hovers over the same spot on earth, above the equator all the time.

If you do the math you will find out that 1,436 minutes is 23 hours and 56 minutes.
You thought the earth turned once every 24 hours exactly, didn’t you.

WRONG!

So why does the sunset not change by 4 minutes each day. It should since we are on a 24 hour clock and the earth turns once in 23hr. and 56 mins. I suspect you know. If not…I’ll let you look that one up yourself!

Later,
Dan

27 May, 2005

I showed some of our first echo id data on air at 10pm Thursday.(See the last blog)
Using ARMOR and it’s dual polarimetric capability, a computer program can be run to analyze the radar echoes using different variables like differential reflectivity and specific differential phase etc. (I have a link at the end that will explain these)

This program can then estimate whether the echo is rain..sleet hail etc. Truly the future of weather radar technology and I just bet I am the first person to ever show it on tv! (Something I care about and no one else!)

Missed it? Here it is (It will make sense when you look at it!)
HYDRO ID

A great web site on how dual polarimetric radar works is at this NSSL web site.

Our next goal is to be able to have this data in real time during severe storms.

Later,
Dan